- Assembly instaiated operations

- assembly forward proagation
Fiexed highlighting of operations
2026-08-19 20:14:14 +02:00 · 2026-08-19 00:11:24 +02:00 · 2026-08-18 16:12:09 +02:00 · 2026-08-18 15:06:51 +02:00 · 2026-08-17 21:39:20 +02:00 · 2026-08-17 18:35:18 +02:00
36 changed files with 20697 additions and 3146 deletions
@@ -35,4 +35,42 @@ uv.lock
 # IDE
 .vscode/
 *.swp
-*.swo
+*.swo
+/src/fluency/Tesfiles/bordo_adapter3.fluency
+/CONSTRAINT_STATUS_FINAL.md
+/CONSTRAINT_STATUS_IMPLEMENTATION.md
+/src/fluency/rendering/first.png
+/littlebrother.md
+/src/fluency/Tesfiles/multiboidy.fluency
+/src/fluency/rendering/nromal_test.png
+/package.json
+/package-lock.json
+/src/fluency/Screenshot 2026-06-28 at 17.57.52.png
+/src/fluency/rendering/Screenshot 2026-07-12 at 16.54.14.png
+/src/fluency/Screenshot 2026-07-26 at 20.23.42.png
+/Screenshot 2026-08-05 at 10.14.15.png
+/Screenshot 2026-08-05 at 11.15.33.png
+/Screenshot 2026-08-05 at 11.22.42.png
+/SURFACE_MODIFIER_PLAN.md
+/test.step
+/src/fluency/test333.step
+/src/fluency/tests/test_arc_attached_to_rectangle.py
+/src/fluency/tests/test_array_pattern.py
+/src/fluency/tests/test_chamfer.py
+/src/fluency/tests/test_circle_diameter_constraint.py
+/tests/test_distance_constraint_picking.py
+/tests/test_extrude_geometry.py
+/src/fluency/tests/test_feature_replay.py
+/src/fluency/tests/test_fillet.py
+/tests/test_mirror.py
+/test_modifier.py
+/src/fluency/tests/test_projection_constraints.py
+/tests/test_re_extrude.py
+/scripts/test_render_zoom.py
+/test_thread.py
+/test_thread_hole.step
+/test_thread_m3.step
+/test_thread_m5_hole.step
+/test_thread_shaft.step
+/test_thread_tilted.step
+/src/fluency/testpart.step
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-    <MESSAGE value="- changing compos including sketches and bodies" />
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+    <MESSAGE value="- Operation highlighting, body highlighting" />
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+# ── Sheet layout regions ────────────────────────────────────────────────────
+
+_LAYOUT_MARGIN_MM = 10.0
+_VIEW_GAP_MM = 12.0
+
+# Title block box (see _title_block_primitives): 180 × 52 at the bottom-right
+# corner with a 5 mm sheet margin.  Views must clear it (plus clearance).
+_TB_LEFT_MM = _A3_WIDTH_MM - 180.0 - 5.0
+_TB_TOP_MM = 5.0 + 52.0
+_TB_CLEARANCE_MM = 5.0
+
+# Sheet interior (border margin) as (x0, y0, x1, y1) in sheet mm.
+_SHEET_INNER = (
+    _LAYOUT_MARGIN_MM,
+    _LAYOUT_MARGIN_MM,
+    _A3_WIDTH_MM - _LAYOUT_MARGIN_MM,
+    _A3_HEIGHT_MM - _LAYOUT_MARGIN_MM,
+)
+
+# Regions the orthographic layout may occupy, as (x0, y0, w, h):
+#  - UPPER: full sheet width above the title block
+#  - LEFT:  full sheet height in the left strip beside the title block
+_REGION_UPPER = (
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+    _A3_WIDTH_MM - 2 * _LAYOUT_MARGIN_MM,
+    _A3_HEIGHT_MM - _LAYOUT_MARGIN_MM - (_TB_TOP_MM + _TB_CLEARANCE_MM),
+)
+_REGION_LEFT = (
+    _LAYOUT_MARGIN_MM,
+    _LAYOUT_MARGIN_MM,
+    _TB_LEFT_MM - _TB_CLEARANCE_MM - _LAYOUT_MARGIN_MM,
+    _A3_HEIGHT_MM - 2 * _LAYOUT_MARGIN_MM,
+)
+
+_MID_ORDER = ("left", "front", "right", "back")
+_COL_ORDER = ("top", "front", "bottom")  # sheet top → bottom
+_GRID_ORDER = ("front", "right", "back", "top", "left", "bottom")
+
+_RectList = List[Tuple[str, float, float, float, float]]
+
+
+def _place_cross(
+    dims: Dict[str, Tuple[float, float]], gap: float
+) -> _RectList:
+    """Classic third-angle cross: mid views run left→right (left, front,
+    right, back), col views stack top→bottom (top, front, bottom), with the
+    anchor view (front, or the first present one) at the intersection.
+
+    *dims* maps view id → ``(w, h)`` in sheet units.  Returns local
+    ``(vid, x, y, w, h)`` rects (origin arbitrary — the caller centres the
+    union on the sheet).
+    """
+    mid = [k for k in _MID_ORDER if k in dims]
+    col = [k for k in _COL_ORDER if k in dims]
+    if not mid and not col:
+        return []
+    rects: Dict[str, Tuple[float, float, float, float]] = {}
+
+    if col:
+        # Stack bottom → top.
+        y = 0.0
+        for k in reversed(col):
+            w, h = dims[k]
+            rects[k] = (0.0, y, w, h)
+            y += h + gap
+        col_h = y - gap
+        cx = max(dims[k][0] for k in col) / 2.0
+        for k in col:
+            _x, yy, w, h = rects[k]
+            rects[k] = (cx - w / 2.0, yy, w, h)
+    else:
+        col_h = 0.0
+        cx = 0.0
+
+    anchor = "front" if "front" in dims else (mid[0] if mid else col[0])
+    if anchor in rects:
+        ax, ay, aw, _ah = rects[anchor]
+        anchor_cy = ay + _ah / 2.0
+    else:
+        aw, ah = dims[anchor]
+        ax = cx - aw / 2.0
+        ay = col_h / 2.0 - ah / 2.0
+        rects[anchor] = (ax, ay, aw, ah)
+        anchor_cy = col_h / 2.0
+
+    ia = mid.index(anchor) if anchor in mid else -1
+    x = ax
+    for k in reversed(mid[:ia]):
+        w, h = dims[k]
+        x -= w + gap
+        rects[k] = (x, anchor_cy - h / 2.0, w, h)
+    x = ax + aw
+    for k in mid[ia + 1 :]:
+        w, h = dims[k]
+        x += gap
+        rects[k] = (x, anchor_cy - h / 2.0, w, h)
+        x += w
+    return [(k, *r) for k, r in rects.items()]
+
+
+def _place_swapped(dims: Dict[str, Tuple[float, float]], gap: float) -> _RectList:
+    """Cross with the view families swapped: the mid views stack vertically
+    (left, front, right, back from the top) and the col views run
+    horizontally (bottom, front, top from the left) — the classic cross
+    turned a quarter turn, for sheets where that orientation fits more.
+    """
+    mid = [k for k in _MID_ORDER if k in dims]
+    col = [k for k in _COL_ORDER if k in dims]
+    if not mid or not col:
+        return []
+    rects: Dict[str, Tuple[float, float, float, float]] = {}
+    cx = max(dims[k][0] for k in mid) / 2.0
+    y = 0.0
+    for k in mid:  # top → bottom
+        w, h = dims[k]
+        rects[k] = (cx - w / 2.0, y, w, h)
+        y += h + gap
+    anchor = "front" if "front" in dims else mid[0]
+    anchor_cy = rects[anchor][1] + dims[anchor][1] / 2.0
+
+    row: Dict[str, Tuple[float, float, float, float]] = {}
+    x = 0.0
+    x_anchor = 0.0
+    for k in reversed(col):  # bottom, front, top → left to right
+        w, h = dims[k]
+        if k == anchor:
+            x_anchor = x
+        row[k] = (x, anchor_cy - h / 2.0, w, h)
+        x += w + gap
+    shift = rects[anchor][0] - x_anchor
+    for k, r in row.items():
+        if k == anchor:
+            continue
+        x0, y0, w, h = r
+        rects[k] = (x0 + shift, y0, w, h)
+    return [(k, *r) for k, r in rects.items()]
+
+
+def _place_grid(
+    dims: Dict[str, Tuple[float, float]], gap: float, rows: int
+) -> _RectList:
+    """Wrap the present standard views into a grid of *rows* rows, filled
+    bottom→top and left→right (so the primary views sit near the bottom,
+    like in the cross)."""
+    order = [k for k in _GRID_ORDER if k in dims]
+    if not order:
+        return []
+    cols = max(1, -(-len(order) // rows))
+    rects: _RectList = []
+    y = 0.0
+    for r in range(rows):
+        chunk = order[r * cols : (r + 1) * cols]
+        if not chunk:
+            break
+        x = 0.0
+        row_h = 0.0
+        for k in chunk:
+            w, h = dims[k]
+            rects.append((k, x, y, w, h))
+            x += w + gap
+            row_h = max(row_h, h)
+        y += row_h + gap
+    return rects
+
+
+def _fit_scale(
+    place: Callable[
+        [Dict[str, Tuple[float, float]], float], _RectList
+    ],
+    dims_m: Dict[str, Tuple[float, float]],
+    region: Tuple[float, float, float, float],
+) -> float:
+    """Largest shared scale at which *dims_m* (model units) laid out by
+    *place* fits the ``(x0, y0, w, h)`` *region* of the sheet.
+
+    The union size grows monotonically with the scale, so a bisection
+    converges to the tight fit.
+    """
+    _rx0, _ry0, rw, rh = region
+
+    def fits(s: float) -> bool:
+        rects = place(
+            {k: (w * s, h * s) for k, (w, h) in dims_m.items()}, _VIEW_GAP_MM
+        )
+        if not rects:
+            return True
+        minx = min(r[1] for r in rects)
+        miny = min(r[2] for r in rects)
+        maxx = max(r[1] + r[3] for r in rects)
+        maxy = max(r[2] + r[4] for r in rects)
+        return (maxx - minx) <= rw + 1e-9 and (maxy - miny) <= rh + 1e-9
+
+    s_lo, s_hi = 0.0, 1.0
+    if fits(s_hi):
+        s_lo = s_hi
+        while s_hi < 1.0e6 and fits(s_hi * 2.0):
+            s_hi *= 2.0
+    for _ in range(60):
+        mid = 0.5 * (s_lo + s_hi)
+        if fits(mid):
+            s_lo = mid
+        else:
+            s_hi = mid
+    return s_lo
+
+
+def _free_rects(
+    used_rects: Sequence[Tuple[float, float, float, float]]
+) -> List[Tuple[float, float, float, float]]:
+    """Axis-aligned free rects ``(x0, y0, w, h)`` around *used_rects*,
+    clearing the sheet border and the title block zone."""
+    ix0, iy0, ix1, iy1 = _SHEET_INNER
+    if used_rects:
+        ux0 = min(r[0] for r in used_rects)
+        uy0 = min(r[1] for r in used_rects)
+        ux1 = max(r[0] + r[2] for r in used_rects)
+        uy1 = max(r[1] + r[3] for r in used_rects)
+        cands = [
+            (ux1 + _VIEW_GAP_MM, iy0, ix1, iy1),  # right of the used block
+            (ix0, iy0, ux0 - _VIEW_GAP_MM, iy1),  # left
+            (ix0, uy1 + _VIEW_GAP_MM, ix1, iy1),  # above
+            (ix0, iy0, ix1, uy0 - _VIEW_GAP_MM),  # below
+        ]
+    else:
+        cands = [(ix0, iy0, ix1, iy1)]
+    tb = (
+        _TB_LEFT_MM - _TB_CLEARANCE_MM,
+        0.0,
+        _A3_WIDTH_MM - (_TB_LEFT_MM - _TB_CLEARANCE_MM),
+        _TB_TOP_MM + _TB_CLEARANCE_MM,
+    )
+    out: List[Tuple[float, float, float, float]] = []
+    for x0, y0, x1, y1 in cands:
+        x0, y0 = max(x0, ix0), max(y0, iy0)
+        x1, y1 = min(x1, ix1), min(y1, iy1)
+        if x1 - x0 < 1.0 or y1 - y0 < 1.0:
+            continue
+        if not (x1 <= tb[0] or tb[2] <= x0 or y1 <= tb[1] or tb[3] <= y0):
+            # Overlaps the title block zone — keep the parts above/left of it.
+            subs = [
+                (x0, max(y0, tb[3]), x1, y1),
+                (x0, y0, min(x1, tb[0]), y1),
+            ]
+        else:
+            subs = [(x0, y0, x1, y1)]
+        for sx0, sy0, sx1, sy1 in subs:
+            if sx1 - sx0 > 1.0 and sy1 - sy0 > 1.0:
+                out.append((sx0, sy0, sx1 - sx0, sy1 - sy0))
+    return out
+
+
+def _layout_views_on_sheet(
+    views: Sequence[DrawingView],
+    bboxes: Dict[str, Tuple[float, float, float, float]],
+) -> Tuple[
+    Dict[str, Tuple[float, float, float, float]],
+    Optional[float],
+    Dict[str, float],
+]:
+    """Compute a slot rectangle and sheet rotation for each view.
+
+    *bboxes* maps view_id → ``(min_x, min_y, max_x, max_y)`` in model
+    units (from :func:`_edges_bounds`).  Returns ``(slots, common_scale,
+    rotations)``: slots are ``(left, bottom, width, height)`` in sheet mm
+    (origin at the sheet's bottom-left corner, +y up), common_scale is the
+    shared model→sheet scale of the standard orthographic views, and
+    rotations maps view_id → sheet rotation in degrees (0 or 90).
+
+    The sheet is filled, not just used: every candidate arrangement
+    (classic third-angle cross, the cross with the view families swapped,
+    and 1/2/3-row grids) is combined with every per-view 90° rotation
+    assignment, and the candidate giving the largest shared scale is used.
+    Candidates within 0.5% of the best scale prefer the one with fewer
+    rotated views, then the more conventional arrangement, so layouts stay
+    stable and standard whenever they are already the best fit.  All
+    orthographic views share one scale so the projections stay mutually
+    consistent.  Isometric and custom views take the largest remaining
+    free rect (clearing the title block).
+    """
+    slots: Dict[str, Tuple[float, float, float, float]] = {}
+    rotations: Dict[str, float] = {}
+    common_scale: Optional[float] = None
+
+    ortho = [
+        v for v in views if v.kind in _STANDARD_VIEWS and v.kind != "isometric"
+    ]
+
+    used_rects: List[Tuple[float, float, float, float]] = []
+    if ortho:
+        dims0: Dict[str, Tuple[float, float]] = {}
+        for v in ortho:
+            b = bboxes.get(v.kind)
+            vs = max(v.scale, 1e-9)
+            if b is None:
+                dims0[v.kind] = (1.0 * vs, 1.0 * vs)
+            else:
+                dims0[v.kind] = (
+                    max(b[2] - b[0], 1e-6) * vs,
+                    max(b[3] - b[1], 1e-6) * vs,
+                )
+        keys = list(dims0)
+        arrangements: Tuple[
+            Tuple[str, int, Callable[[Dict[str, Tuple[float, float]], float], _RectList]]
+        ] = (
+            ("cross", 0, _place_cross),
+            ("swapped", 1, _place_swapped),
+            ("grid1", 2, lambda d, g: _place_grid(d, g, 1)),
+            ("grid2", 3, lambda d, g: _place_grid(d, g, 2)),
+            ("grid3", 4, lambda d, g: _place_grid(d, g, 3)),
+        )
+        cands: List[
+            Tuple[float, int, int, Tuple[float, float, float, float],
+                  Dict[str, Tuple[float, float]],
+                  Callable[[Dict[str, Tuple[float, float]], float], _RectList],
+                  List[bool]]
+        ] = []
+        for mask in range(1 << len(keys)):
+            rotated = [bool(mask & (1 << i)) for i in range(len(keys))]
+            dims_m = {
+                k: (
+                    dims0[k][1] if rotated[i] else dims0[k][0],
+                    dims0[k][0] if rotated[i] else dims0[k][1],
+                )
+                for i, k in enumerate(keys)
+            }
+            for _name, rank, place in arrangements:
+                s_up = _fit_scale(place, dims_m, _REGION_UPPER)
+                s_left = _fit_scale(place, dims_m, _REGION_LEFT)
+                if s_up >= s_left:
+                    s, region = s_up, _REGION_UPPER
+                else:
+                    s, region = s_left, _REGION_LEFT
+                if s <= 0.0:
+                    continue
+                cands.append((s, sum(rotated), rank, region, dims_m, place, rotated))
+        if cands:
+            best_s = max(c[0] for c in cands)
+            s, _nrot, _rank, region, dims_m, place, rotated = min(
+                (c for c in cands if c[0] >= best_s * 0.995),
+                key=lambda c: (c[1], c[2], -c[0]),
+            )
+            rx0, _ry0, rw, rh = region
+            ds = {k: (w * s, h * s) for k, (w, h) in dims_m.items()}
+            rects = place(ds, _VIEW_GAP_MM)
+            minx = min(r[1] for r in rects)
+            miny = min(r[2] for r in rects)
+            maxx = max(r[1] + r[3] for r in rects)
+            maxy = max(r[2] + r[4] for r in rects)
+            ox = rx0 + (rw - (maxx - minx)) / 2.0
+            oy = _ry0 + (rh - (maxy - miny)) / 2.0
+            for vid, x, y, w, h in rects:
+                slots[vid] = (x - minx + ox, y - miny + oy, w, h)
+                rotations[vid] = 90.0 if rotated[keys.index(vid)] else 0.0
+            common_scale = s
+            used_rects = [(ox, oy, maxx - minx, maxy - miny)]
+
+    # Isometric and custom views: the largest remaining free rect each,
+    # clearing the title block.
+    extra = [
+        v for v in views
+        if v.kind == "isometric" or v.kind not in _STANDARD_VIEWS
+    ]
+    assigned = list(used_rects)
+    for i, v in enumerate(extra):
+        vid = v.kind if v.kind in _STANDARD_VIEWS else (v.name or v.id)
+        free = _free_rects(assigned)
+        if free:
+            slot = max(free, key=lambda r: r[2] * r[3])
+        else:
+            # No free rect left — park in the bottom-left corner stack.
+            slot = (_LAYOUT_MARGIN_MM, _LAYOUT_MARGIN_MM + i * 60.0, 120.0, 50.0)
+        slots[vid] = slot
+        assigned.append(slot)
+
+    return slots, common_scale, rotations
@@ -0,0 +1,50 @@
+import os, sys
+os.environ["QT_QPA_PLATFORM"] = "offscreen"
+sys.path.insert(0, "/Volumes/Data_drive/Programming/fluency/src")
+
+from PySide6.QtWidgets import QApplication
+from PySide6.QtGui import QPixmap, QPainter, QColor
+from PySide6.QtCore import QRectF
+import math
+
+app = QApplication.instance() or QApplication([])
+
+from fluency.geometry.base import Point2D
+from fluency.geometry_occ.kernel import OCGeometryKernel
+from fluency.models.data_model import Body, Component, Project, DrawingView, TechnicalDrawing
+from fluency.technical_drawing import generate_drawing, render_drawing, _A3_WIDTH_MM, _A3_HEIGHT_MM
+
+kernel = OCGeometryKernel()
+# Long thin bar: 120 x 25 x 30 (matches the "wide bar" screenshot case).
+points = [Point2D(0, 0), Point2D(120, 0), Point2D(120, 25), Point2D(0, 25)]
+box = kernel.extrude(kernel.create_polygon(points), 30.0)
+body = Body(name="Bar", geometry=box)
+comp = Component(name="BarComp")
+comp.bodies[body.id] = body
+project = Project()
+project.components[comp.id] = comp
+project.active_component = comp.id
+
+W = 2400
+H = int(W * _A3_HEIGHT_MM / _A3_WIDTH_MM)
+pm = QPixmap(W, H)
+pm.fill(QColor(255, 255, 255))
+
+for name, kinds in [
+    ("four", ["front", "top", "right", "back"]),
+    ("six", ["front", "top", "right", "left", "back", "bottom"]),
+    ("sixiso", ["front", "top", "right", "left", "back", "bottom", "isometric"]),
+]:
+    drawing = TechnicalDrawing(
+        source_kind="component", source_id=comp.id,
+        views=[DrawingView(kind=k) for k in kinds],
+        auto_dimensions=True, title=name,
+    )
+    result = generate_drawing(drawing, project, kernel)
+    p = QPainter(pm)
+    render_drawing(p, result, QRectF(0, 0, W, H))
+    p.end()
+    out = f"/tmp/drawing_{name}.png"
+    pm.save(out)
+    print(name, "saved", out, "prims", len(result.primitives), "scale",
+          round(result.view_transforms.get("front", (None,))[0] or 0, 3))
@@ -0,0 +1,159 @@
+"""Smoke test: layout optimizer fills the page, no overlaps, title block clear."""
+import math
+import os
+import sys
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+sys.path.insert(0, "/Volumes/Data_drive/Programming/fluency/src")
+
+from fluency.models.data_model import DrawingView
+from fluency.technical_drawing import (
+    _layout_views_on_sheet,
+    build_manual_candidates,
+)
+
+A3W, A3H = 420.0, 297.0
+TB = (235.0, 0.0, 420.0, 62.0)  # title block zone incl. clearance
+
+
+def b(x, y, w, h):
+    return (x, y, x + w, y + h)
+
+
+def overlaps(r1, r2, clear=0.0):
+    x0, y0, w, h = r1
+    x1, y1, w2, h2 = r2
+    return not (x0 + w <= x1 + clear or x1 + w2 <= x0 + clear
+                or y0 + h <= y1 + clear or y1 + h2 <= y0 + clear)
+
+
+def tb_overlap(r, clear=5.0):
+    x0, y0, w, h = r
+    x1, y1, w2, h2 = TB
+    return not (x0 + w <= x1 + clear or x1 + w2 <= x0 + clear
+                or y0 + h <= y1 + clear or y1 + h2 <= y0 + clear)
+
+
+def union_rect(rects):
+    x0 = min(r[0] for r in rects)
+    y0 = min(r[1] for r in rects)
+    x1 = max(r[0] + r[2] for r in rects)
+    y1 = max(r[1] + r[3] for r in rects)
+    return (x0, y0, x1 - x0, y1 - y0)
+
+
+def check(name, kinds, boxes, expect_rot=None):
+    views = [DrawingView(kind=k) for k in kinds]
+    bboxes = {k: boxes[k] for k in kinds}
+    slots, scale, rots = _layout_views_on_sheet(views, bboxes)
+    print(f"--- {name}: scale={scale:.4f} rots={rots}")
+    # all slots within sheet
+    for k, s in slots.items():
+        assert 10 - 1e-6 <= s[0] and 10 - 1e-6 <= s[1], f"{k} outside sheet {s}"
+        assert s[0] + s[2] <= A3W - 10 + 1e-6, f"{k} beyond right {s}"
+        assert s[1] + s[3] <= A3H - 10 + 1e-6, f"{k} beyond top {s}"
+    # no overlaps between slots
+    ks = list(slots)
+    for i in range(len(ks)):
+        for j in range(i + 1, len(ks)):
+            assert not overlaps(slots[ks[i]], slots[ks[j]], 11.9), \
+                f"{ks[i]} overlaps {ks[j]}: {slots[ks[i]]} / {slots[ks[j]]}"
+    # title block clear
+    for k, s in slots.items():
+        assert not tb_overlap(s), f"{k} intrudes title block {s}"
+    # fill report
+    u = union_rect(list(slots.values()))
+    area = u[2] * u[3]
+    print(f"    union: x0={u[0]:.1f} y0={u[1]:.1f} w={u[2]:.1f} h={u[3]:.1f} "
+          f"area={area:.0f}mm^2 ({100*area/(A3W*A3H):.0f}% of sheet)")
+    for k in ks:
+        print(f"    {k}: {tuple(round(v,1) for v in slots[k])}")
+    if expect_rot is not None:
+        assert rots == expect_rot, f"expected {expect_rot}, got {rots}"
+    return slots, scale, rots
+
+
+# 1. Two square views (front+top): should fill the page, no rotation.
+check("two square", ["front", "top"],
+      {"front": b(0, 0, 40, 40), "top": b(0, 0, 40, 20)})
+
+# 2. Wide bar, 4 views (old screenshot case): front+back wide, top+right.
+check("wide bar 4", ["front", "top", "right", "back"],
+      {"front": b(0, 0, 120, 25), "top": b(0, 0, 25, 40),
+       "right": b(0, 0, 25, 40), "back": b(0, 0, 120, 25)})
+
+# 3. Six views of a long thin part: rotation should kick in.
+check("thin part 6", ["front", "top", "right", "left", "back", "bottom"],
+      {"front": b(0, 0, 200, 30), "top": b(0, 0, 30, 50),
+       "right": b(0, 0, 50, 30), "left": b(0, 0, 50, 30),
+       "back": b(0, 0, 200, 30), "bottom": b(0, 0, 30, 50)})
+
+# 4. Single front view: fills the whole page.
+check("single", ["front"], {"front": b(0, 0, 10, 20)})
+
+# 5. All 6 + isometric + custom.
+check("everything",
+      ["front", "top", "right", "left", "back", "bottom", "isometric"],
+      {"front": b(0, 0, 80, 40), "top": b(0, 0, 80, 30),
+       "right": b(0, 0, 30, 40), "left": b(0, 0, 30, 40),
+       "back": b(0, 0, 80, 40), "bottom": b(0, 0, 80, 30),
+       "isometric": b(0, 0, 60, 60)})
+
+# ── Inverse-transform roundtrip ─────────────────────────────────────────
+# A 90°-rotated view: forward via _assemble_view's recorded 6-tuple,
+# inverse via the widget's formula.
+t = (2.0, 150.0, 80.0, 90.0, 10.0, 5.0)  # s, o_x, o_y, deg, cx, cy
+scale, ox, oy, deg, cx, cy = t
+th = math.radians(deg)
+cos_t, sin_t = math.cos(th), math.sin(th)
+
+
+def fwd(p):
+    dx, dy = p[0] - cx, p[1] - cy
+    return ((dx * cos_t - dy * sin_t) * scale + ox,
+            (dx * sin_t + dy * cos_t) * scale + oy)
+
+
+def inv(p):
+    sx, sy = (p[0] - ox) / scale, (p[1] - oy) / scale
+    return (sx * cos_t + sy * sin_t + cx, -sx * sin_t + sy * cos_t + cy)
+
+
+for p in [(0, 0), (10, 5), (3, -7), (42.5, 11.25)]:
+    rt = inv(fwd(p))
+    assert abs(rt[0] - p[0]) < 1e-9 and abs(rt[1] - p[1]) < 1e-9, (p, rt)
+print("inverse roundtrip OK")
+
+# Legacy 3-tuple still works through build_manual_candidates.
+from fluency.models.data_model import DrawingAnnotation, TechnicalDrawing
+d = TechnicalDrawing(source_kind="component", source_id="c")
+ann = DrawingAnnotation(kind="dimension", dimension_kind="length",
+                        view_id="front", anchors=[(0.0, 0.0), (0.0, 12.5)],
+                        direction=(0.0, 1.0))
+d.annotations.append(ann)
+cands, res, unres = build_manual_candidates(d, {"front": (2.0, 10.0, 20.0)})
+assert unres == [] and cands[0].anchor_points[1] == (10.0, 45.0)
+print("legacy 3-tuple OK")
+
+# 6-tuple manual: rotated length direction must rotate too.
+ann2 = DrawingAnnotation(kind="dimension", dimension_kind="length",
+                         view_id="front",
+                         anchors=[(0.0, 0.0), (0.0, 10.0)],
+                         direction=(0.0, 1.0))
+d2 = TechnicalDrawing(source_kind="component", source_id="c")
+d2.annotations.append(ann2)
+# 90° rotation about centre c=(5,5), scale 2, o=(100,80)
+cands, res, unres = build_manual_candidates(
+    d2, {"front": (2.0, 100.0, 80.0, 90.0, 5.0, 5.0)}
+)
+c = cands[0]
+# anchors: (0,0)->rot90 about (5,5) = (5-(0-5)*0 - ... compute: dx=-5,dy=-5
+# fwd: (dx*cos - dy*sin)*2+100 = (0 - (-5))*2+100 = 110 ; (dx*sin+dy*cos)*2+80 = (-5)*2+80=70
+# (0,10): dx=-5, dy=5 -> (0-5)*2+100=90 ; (−5*1+0)*2+80=70
+assert c.anchor_points[0] == (110.0, 70.0), c.anchor_points
+assert c.anchor_points[1] == (90.0, 70.0), c.anchor_points
+# direction (0,1) rotated 90° CCW -> (-1, 0)
+assert c.direction[0] == -1.0 and abs(c.direction[1]) < 1e-9, c.direction
+print("6-tuple manual (rotated) OK")
+
+print("ALL SMOKE CHECKS PASSED")
@@ -0,0 +1,238 @@
+"""Headless test: connectors follow moved features across ALL assemblies.
+
+Simulates the test-file scenario: a plate with a hole, mated hole-to-face
+in two different assemblies.  The hole is moved (rebuilt geometry) and the
+body-update connector recalculation must:
+  1. re-locate the hole connector on every instance of the component
+     (both the active and a non-active assembly),
+  2. re-solve each mated pair so the partner parts follow,
+  3. never snap a planar connector onto the cylindrical hole (type match),
+  4. mark a connector invalid when its feature disappears.
+  5. auto-follow a FAR move when the candidate is unambiguous (single
+     feature of its class) — the demo case,
+  6. NOT auto-apply an ambiguous far candidate (another same-class feature
+     is nearer) — that needs a manual pick, simulated here.
+  7. backfill legacy connectors' entity_type from their auto-generated name.
+"""
+
+import os
+import sys
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "src"))
+
+import numpy as np
+
+from OCP.gp import gp_Pnt, gp_Dir, gp_Ax2
+from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox, BRepPrimAPI_MakeCylinder
+from OCP.BRepAlgoAPI import BRepAlgoAPI_Cut
+
+from PySide6.QtWidgets import QApplication
+
+from fluency.ui.main_window import MainWindow
+from fluency.models.data_model import Assembly, Body
+from fluency.geometry_occ.kernel import OCCGeometryObject
+
+app = QApplication.instance() or QApplication([])
+w = MainWindow()
+
+comp = w._current_component
+
+
+def make_plate(hole_xy):
+    box = BRepPrimAPI_MakeBox(60.0, 40.0, 5.0).Shape()
+    ax = gp_Ax2(gp_Pnt(float(hole_xy[0]), float(hole_xy[1]), 0.0), gp_Dir(0, 0, 1))
+    cyl = BRepPrimAPI_MakeCylinder(ax, 3.0, 6.0).Shape()
+    return BRepAlgoAPI_Cut(box, cyl).Shape()
+
+
+body = Body(name="plate")
+comp.bodies[body.id] = body
+body.geometry = OCCGeometryObject(make_plate((10.0, 5.0)))
+
+partner = w._project.add_component()
+pbody = Body(name="partner")
+partner.bodies[pbody.id] = pbody
+pbody.geometry = OCCGeometryObject(BRepPrimAPI_MakeBox(30.0, 30.0, 10.0).Shape())
+
+
+def make_pair(asm):
+    ac1 = asm.add_component_instance(comp.id, name="A")
+    ac2 = asm.add_component_instance(partner.id, name="B")
+    ac1.position = np.zeros(3)
+    ac1.rotation = np.eye(3)
+    ac2.position = np.array([0.0, 0.0, 15.0])
+    ac2.rotation = np.eye(3)
+    ac1.geom_cache[body.id] = body.geometry
+
+    c1 = ac1.add_connector(
+        position=(10.0, 5.0, 2.5),
+        normal=(0.0, 0.0, 1.0),
+        x_dir=(1.0, 0.0, 0.0),
+        source_obj_id=f"asm_{ac1.id}_{body.id}",
+        name="Conn hole A",
+        entity_type="cylindrical_face",
+    )
+    c2 = ac2.add_connector(
+        position=(15.0, 15.0, 0.0),
+        normal=(0.0, 0.0, -1.0),
+        x_dir=(1.0, 0.0, 0.0),
+        source_obj_id=f"asm_{ac2.id}_{pbody.id}",
+        name="Conn face B",
+        entity_type="planar_face",
+    )
+    c1.is_grounded = True
+    c1.partner_ac_id = ac2.id
+    c1.partner_connector_id = c2.id
+    c2.partner_ac_id = ac1.id
+    c2.partner_connector_id = c1.id
+    aconn = asm.add_connection(ac1.id, ac2.id)
+    aconn.first_connector_id = c1.id
+    aconn.second_connector_id = c2.id
+    return ac1, ac2, c1, c2, aconn
+
+
+asm1 = w._project.get_active_assembly()
+asm2 = w._project.add_assembly(Assembly(name="second"))
+pair1 = make_pair(asm1)
+pair2 = make_pair(asm2)
+assert w._project.active_assembly == asm1.id  # asm2 is the NON-active one
+
+# ── Move the hole: rebuild the plate with the hole at (25, 12) ──────────
+new_geom = OCCGeometryObject(make_plate((25.0, 12.0)))
+body.geometry = new_geom
+for asm in (asm1, asm2):
+    for ac in asm.components.values():
+        if ac.component_id == comp.id:
+            ac.geom_cache[body.id] = new_geom
+
+# ── The body-update auto path ───────────────────────────────────────────
+w._recalculate_connectors()
+
+for (ac1, ac2, c1, c2, aconn), label in ((pair1, "asm1"), (pair2, "asm2")):
+    # The hole connector followed the hole on every instance.
+    assert np.allclose(c1.position, (25.0, 12.0, 2.5), atol=1e-6), (label, c1.position)
+    # The mated pair re-aligned: both world connectors coincide.
+    w1 = ac1.position + ac1.rotation @ np.asarray(c1.position)
+    w2 = ac2.position + ac2.rotation @ np.asarray(c2.position)
+    assert np.allclose(w1, w2, atol=1e-6), (label, w1, w2)
+    print(f"{label}: connector at {np.round(c1.position, 3)}, "
+          f"partner moved to {np.round(ac2.position, 3)}")
+
+# ── The 'Upd' button path: move the hole again, re-run the handler ─────
+w._refresh_connection_list()
+w._connection_list.setCurrentRow(0)  # active assembly = asm1
+geom3 = OCCGeometryObject(make_plate((35.0, 20.0)))
+body.geometry = geom3
+for ac in asm1.components.values():
+    if ac.component_id == comp.id:
+        ac.geom_cache[body.id] = geom3
+w._on_update_connection_from_list()
+ac1, ac2, c1, c2, aconn = pair1
+assert np.allclose(c1.position, (35.0, 20.0, 2.5), atol=1e-6), c1.position
+w1 = ac1.position + ac1.rotation @ np.asarray(c1.position)
+w2 = ac2.position + ac2.rotation @ np.asarray(c2.position)
+assert np.allclose(w1, w2, atol=1e-6), (w1, w2)
+print("Upd button: connector at", np.round(c1.position, 3),
+      "partner at", np.round(ac2.position, 3))
+
+# ── Type matching: a planar connector must not snap onto the hole ───────
+ac1 = pair1[0]
+c3 = ac1.add_connector(
+    position=(30.0, 20.0, 5.0),
+    normal=(0.0, 0.0, 1.0),
+    x_dir=(1.0, 0.0, 0.0),
+    source_obj_id=f"asm_{ac1.id}_{body.id}",
+    name="Conn face",
+    entity_type="planar_face",
+)
+res = w._redetect_connector_on_geometry(c3, ac1, comp)
+assert res is not None, "planar connector candidate missing"
+assert not c3.is_invalid, "pure relocator must not mutate the connector"
+assert np.allclose(c3.position, (30.0, 20.0, 5.0), atol=1e-6), c3.position
+assert np.allclose(res[1], (30.0, 20.0, 5.0), atol=1e-6), res[1]
+print("planar connector stayed on the face:", np.round(res[1], 3))
+
+# ── Feature removed: relocator finds nothing; auto path marks invalid ──
+plain = OCCGeometryObject(BRepPrimAPI_MakeBox(60.0, 40.0, 5.0).Shape())
+body.geometry = plain
+ac1.geom_cache[body.id] = plain
+res = w._redetect_connector_on_geometry(pair1[2], ac1, comp)
+assert res is None, "hole connector should find no candidate on a plain box"
+w._recalculate_connectors()
+assert pair1[2].is_invalid, "auto path must mark the connector invalid"
+print("removed feature -> connector marked invalid")
+
+# ── Far move with a decoy: ambiguous candidate is NOT auto-applied ─────
+# The real hole moved to (25, 12) — ~12.8mm from the stored (35, 20) — but
+# a SECOND hole now sits at (28, 16), only ~8mm away.  The nearest
+# candidate is ambiguous (different feature), so the auto path must leave
+# the connector alone and queue it for a manual pick.
+def make_plate2(holes):
+    box = BRepPrimAPI_MakeBox(60.0, 40.0, 5.0).Shape()
+    for hx, hy in holes:
+        ax = gp_Ax2(gp_Pnt(hx, hy, 0.0), gp_Dir(0, 0, 1))
+        box = BRepAlgoAPI_Cut(box, BRepPrimAPI_MakeCylinder(ax, 3.0, 6.0).Shape()).Shape()
+    return box
+# ── Stage 1: the user's demo — a SINGLE hole moved far away ─────────────
+# 12.8mm from the stored position, but the only cylindrical face on the
+# body → unambiguous → must be auto-applied (and the mate re-solved).
+geom4 = OCCGeometryObject(make_plate2([(25.0, 12.0)]))
+body.geometry = geom4
+for asm in (asm1, asm2):
+    for ac in asm.components.values():
+        if ac.component_id == comp.id:
+            ac.geom_cache[body.id] = geom4
+w._recalculate_connectors()
+assert np.allclose(pair1[2].position, (25.0, 12.0, 2.5), atol=1e-6), \
+    "unique far candidate must be auto-applied (the demo case)"
+assert not pair1[2].is_invalid
+w1 = ac1.position + ac1.rotation @ np.asarray(pair1[2].position)
+w2 = pair1[1].position + pair1[1].rotation @ np.asarray(pair1[3].position)
+assert np.allclose(w1, w2, atol=1e-6), (w1, w2)
+print("single far hole: auto-followed to", np.round(pair1[2].position, 3))
+
+# ── Stage 2: far move with a decoy — ambiguous, NOT auto-applied ───────
+# The real hole now sits at (32, 20) — 10.6mm from the stored (25, 12) —
+# while a decoy hole at (21, 7) is only 6.4mm away.  The nearest
+# candidate is likely a DIFFERENT feature, so the auto path must leave
+# the connector alone and queue it for a manual pick.
+geom5 = OCCGeometryObject(make_plate2([(32.0, 20.0), (21.0, 7.0)]))
+body.geometry = geom5
+for asm in (asm1, asm2):
+    for ac in asm.components.values():
+        if ac.component_id == comp.id:
+            ac.geom_cache[body.id] = geom5
+w._recalculate_connectors()
+assert np.allclose(pair1[2].position, (25.0, 12.0, 2.5), atol=1e-6), \
+    "ambiguous far candidate must not be auto-applied"
+assert not pair1[2].is_invalid, "ambiguous candidate is not a missing feature"
+
+# Simulate the user clicking the REAL hole in the relocate pick flow:
+w._relocate_pending = [(asm1, ac1, pair1[2])]
+w._on_relocate_picked(
+    (32.0, 20.0, 2.5), (0.0, 0.0, 1.0), (1.0, 0.0, 0.0),
+    "cylindrical_face", f"asm_{ac1.id}_{body.id}",
+)
+assert np.allclose(pair1[2].position, (32.0, 20.0, 2.5), atol=1e-6), pair1[2].position
+assert not pair1[2].is_invalid, "manual pick must re-validate the connector"
+assert w._relocate_pending is None, "pending queue must drain after the pick"
+w1 = ac1.position + ac1.rotation @ np.asarray(pair1[2].position)
+w2 = pair1[1].position + pair1[1].rotation @ np.asarray(pair1[3].position)
+assert np.allclose(w1, w2, atol=1e-6), (w1, w2)
+print("far move: manual pick re-homed connector at", np.round(pair1[2].position, 3),
+      "partner at", np.round(pair1[1].position, 3))
+
+# ── Legacy backfill: empty entity_type recovered from the auto name ────
+from fluency.models.data_model import Connector
+legacy = Connector(
+    name="Conn cylindrical_face anchor",
+    position=(32.0, 20.0, 2.5),
+    source_obj_id=f"asm_{ac1.id}_{body.id}",
+)
+assert legacy.entity_type == "cylindrical_face", legacy.entity_type
+res = w._redetect_connector_on_geometry(legacy, ac1, comp)
+assert res is not None and res[0] < 1e-3, res
+print("legacy name backfill: entity_type =", legacy.entity_type)
+
+print("CONNECTOR_RELOCATE_OK")
@@ -0,0 +1,158 @@
+"""Headless repro: load assemblytest.fluency, compare sketch circle centers
+vs. saved body hole axes vs. connector positions, then run the real
+body-update path and check where connectors land.
+"""
+
+import os
+import sys
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "src"))
+
+import numpy as np
+
+from OCP.BRepAdaptor import BRepAdaptor_Surface
+from OCP.GeomAbs import GeomAbs_Cylinder
+from OCP.TopAbs import TopAbs_FACE
+from OCP.TopExp import TopExp_Explorer
+from OCP.TopoDS import TopoDS
+
+from PySide6.QtWidgets import QApplication
+
+from fluency.ui.main_window import MainWindow
+
+def etype(e):
+    if isinstance(e, dict):
+        return e.get("type")
+    return getattr(e, "entity_type", None) or getattr(e, "type", None)
+
+def egeom(e):
+    if isinstance(e, dict):
+        return e.get("geometry")
+    return getattr(e, "geometry", None)
+
+app = QApplication.instance() or QApplication([])
+w = MainWindow()
+
+path = os.path.join(os.path.dirname(__file__), "assemblytest.fluency")
+ok = w._open_project_file(path)
+assert ok, "failed to open demo file"
+
+proj = w._project
+
+for comp in proj.components.values():
+    print(f"=== {comp.name} ({comp.id})")
+    for sk in comp.sketches.values():
+        occ = sk.occ_sketch
+        if occ is None:
+            print("  sketch with no occ_sketch:", sk.id)
+            continue
+        for e in occ._entities.values():
+            t = etype(e)
+            if t == "circle":
+                g = egeom(e)
+                cid = e.get("id") if isinstance(e, dict) else e.id
+                print(f"  circle id={cid} center=({g[0][0]!r}, {g[0][1]!r}) r={g[1]!r}")
+    for body in comp.bodies.values():
+        if not body.geometry:
+            print(f"  body {body.name}: no geometry")
+            continue
+        shape = w._kernel._get_shape(body.geometry)
+        print(f"  body {body.name}: extrude len={body.extrude_length}")
+        expl = TopExp_Explorer(shape, TopAbs_FACE)
+        while expl.More():
+            face = TopoDS.Face_s(expl.Current())
+            try:
+                adaptor = BRepAdaptor_Surface(face)
+                if adaptor.GetType() == GeomAbs_Cylinder:
+                    cyl = adaptor.Cylinder()
+                    loc = cyl.Location()
+                    d = cyl.Axis().Direction()
+                    print(
+                        f"    cyl axis at ({loc.X()!r}, {loc.Y()!r}) "
+                        f"dir=({d.X():.4f},{d.Y():.4f},{d.Z():.4f})"
+                    )
+            except Exception:
+                pass
+            expl.Next()
+
+asm = proj.get_active_assembly()
+print("=== active assembly:", asm.name)
+for ac in asm.components.values():
+    comp = proj.get_component_by_id(ac.component_id)
+    print(f"  instance '{ac.name}' -> {comp.name}, pos={np.round(ac.position, 4)}")
+    for conn in ac.connectors.values():
+        print(
+            f"    conn '{conn.name}' pos={np.round(conn.position, 6)} "
+            f"normal={np.round(conn.normal, 3)} et={conn.entity_type!r} "
+            f"invalid={conn.is_invalid}"
+        )
+
+# ── Run the real update path: rebuild bodies from sketch, recalc connectors ──
+# Activate the component with the holes (Component 1).
+comp1 = None
+for comp in proj.components.values():
+    if any(
+        etype(e) == "circle"
+        for sk in comp.sketches.values()
+        for e in (sk.occ_sketch._entities.values() if sk.occ_sketch else [])
+    ):
+        comp1 = comp
+        break
+assert comp1 is not None
+w._current_component = comp1
+print("=== running _update_bodies_from_sketch()")
+w._update_bodies_from_sketch()
+print("=== running _recalculate_connectors()")
+w._recalculate_connectors()
+
+print("=== after update")
+for comp in proj.components.values():
+    for body in comp.bodies.values():
+        if not body.geometry:
+            continue
+        shape = w._kernel._get_shape(body.geometry)
+        expl = TopExp_Explorer(shape, TopAbs_FACE)
+        axes = []
+        while expl.More():
+            face = TopoDS.Face_s(expl.Current())
+            try:
+                adaptor = BRepAdaptor_Surface(face)
+                if adaptor.GetType() == GeomAbs_Cylinder:
+                    loc = adaptor.Cylinder().Location()
+                    axes.append((round(loc.X(), 9), round(loc.Y(), 9)))
+            except Exception:
+                pass
+            expl.Next()
+        print(f"  {comp.name} body axes: {axes}")
+    for sk in comp.sketches.values():
+        for e in sk.occ_sketch._entities.values():
+            t = etype(e)
+            if t == "circle":
+                g = egeom(e)
+                print(f"  {comp.name} circle: ({g[0][0]!r}, {g[0][1]!r})")
+
+asm = proj.get_active_assembly()
+for ac in asm.components.values():
+    for conn in ac.connectors.values():
+        print(
+            f"    conn '{conn.name}' pos={np.round(conn.position, 6)} "
+            f"invalid={conn.is_invalid}"
+        )
+
+# Partner alignment check: for each connection, world positions of the pair.
+for aconn in asm.connections:
+    a1 = asm.components.get(aconn.first_ac_id)
+    a2 = asm.components.get(aconn.second_ac_id)
+    c1 = a1.connectors.get(aconn.first_connector_id)
+    c2 = a2.connectors.get(aconn.second_connector_id)
+    if c1 is None or c2 is None:
+        continue
+    w1 = a1.position + a1.rotation @ np.asarray(c1.position, dtype=float)
+    w2 = a2.position + a2.rotation @ np.asarray(c2.position, dtype=float)
+    print(
+        f"  conn {aconn.id[:8]}: w1={np.round(w1, 6)} w2={np.round(w2, 6)} "
+        f"gap={float(np.linalg.norm(w1 - w2))!r}"
+    )
+
+print("DEMO_REPRO_DONE")
@@ -0,0 +1,89 @@
+"""Round-trip smoke test: instance-local sketches + modifiers survive save/load.
+
+Builds a minimal project (component with a body, assembly with two instances,
+one carrying an instance sketch + cut modifier + fillet modifier), saves to a
+temp .fluency, reloads, and asserts:
+  1. the shared component is untouched by instance work,
+  2. the instance sketch + modifiers round-trip with sketch refs intact,
+  3. the plain instance has none.
+"""
+import os
+import tempfile
+
+import numpy as np
+
+from fluency.models.data_model import (
+    Project, Component, Body, Sketch, Feature, Assembly, AssemblyComponent,
+)
+from fluency.io.project_io import save_project, load_project
+
+
+def main():
+    project = Project(name="inst test")
+    comp = project.add_component()
+    comp.name = "BasePart"
+    body = comp.add_body(Body(name="MainBody"))
+    base_sketch = comp.add_sketch(Sketch(name="BaseSketch"))
+    body.features.append(
+        Feature(operation="extrude", sketch=base_sketch, length=10.0)
+    )
+
+    asm = project.add_assembly(Assembly(name="TestAsm"))
+    ac1 = asm.add_component_instance(comp.id, name="Instance A")
+    ac1.position = np.array([0.0, 0.0, 0.0])
+    ac2 = asm.add_component_instance(comp.id, name="Instance B")
+    ac2.position = np.array([50.0, 0.0, 0.0])
+
+    # Instance A: local sketch + cut modifier referencing it + fillet.
+    inst_sketch = ac1.add_instance_sketch()
+    inst_sketch.name = "InstCutSketch"
+    ac1.add_modifier(body.id, Feature(operation="cut", sketch=inst_sketch,
+                                      length=5.0, through_all=True))
+    ac1.add_modifier(body.id, Feature(operation="fillet", radius=1.0))
+
+    # ---- save / load ----
+    fd, path = tempfile.mkstemp(suffix=".fluency")
+    os.close(fd)
+    try:
+        save_project(project, path)
+        loaded, _view = load_project(path)
+
+        lcomp = loaded.components[comp.id]
+        lac1 = None
+        lac2 = None
+        for lasm in loaded.assemblies.values():
+            for ac in lasm.components.values():
+                if ac.name == "Instance A":
+                    lac1 = ac
+                elif ac.name == "Instance B":
+                    lac2 = ac
+        assert lac1 is not None and lac2 is not None, "instances missing"
+
+        # 1. component untouched
+        assert len(lcomp.sketches) == 1, "component sketch count changed"
+        assert len(lcomp.bodies[body.id].features) == 1, "feature chain changed"
+        assert not getattr(lcomp.bodies[body.id], "modifiers", None)
+
+        # 2. instance A round-trip
+        assert len(lac1.sketches) == 1, "instance sketch missing"
+        lsk_id, lsk = next(iter(lac1.sketches.items()))
+        assert lsk.name == "InstCutSketch"
+        mods = lac1.modifiers
+        lbody_id = next(iter(lcomp.bodies))
+        assert len(mods.get(lbody_id, [])) == 2, f"modifiers missing: {mods}"
+        cut, fil = mods[lbody_id][0], mods[lbody_id][1]
+        assert cut.operation == "cut" and fil.operation == "fillet"
+        assert cut.sketch is not None and cut.sketch.id == lsk_id, \
+            "cut sketch ref did not resolve to instance sketch"
+        assert cut.length == 5.0 and cut.through_all
+
+        # 3. plain instance clean
+        assert not lac2.sketches and not lac2.modifiers
+
+        print("ROUND_TRIP_OK")
+    finally:
+        os.unlink(path)
+
+
+if __name__ == "__main__":
+    main()
@@ -0,0 +1,83 @@
+"""Headless smoke: the manual re-pick fallback path (prompt -> frame -> pick mode)."""
+
+import os
+import sys
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "src"))
+
+import numpy as np
+
+from OCP.gp import gp_Pnt, gp_Dir, gp_Ax2
+from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox, BRepPrimAPI_MakeCylinder
+from OCP.BRepAlgoAPI import BRepAlgoAPI_Cut
+
+from PySide6.QtWidgets import QApplication, QMessageBox
+
+from fluency.ui.main_window import MainWindow
+from fluency.models.data_model import Body
+from fluency.geometry_occ.kernel import OCCGeometryObject
+
+app = QApplication.instance() or QApplication([])
+w = MainWindow()
+
+comp = w._current_component
+body = Body(name="plate")
+comp.bodies[body.id] = body
+box = BRepPrimAPI_MakeBox(60.0, 40.0, 5.0).Shape()
+ax = gp_Ax2(gp_Pnt(10.0, 5.0, 0.0), gp_Dir(0, 0, 1))
+box = BRepAlgoAPI_Cut(box, BRepPrimAPI_MakeCylinder(ax, 3.0, 6.0).Shape()).Shape()
+body.geometry = OCCGeometryObject(box)
+
+partner = w._project.add_component()
+pbody = Body(name="partner")
+partner.bodies[pbody.id] = pbody
+pbody.geometry = OCCGeometryObject(BRepPrimAPI_MakeBox(30.0, 30.0, 10.0).Shape())
+
+asm = w._project.get_active_assembly()
+ac1 = asm.add_component_instance(comp.id, name="A")
+ac2 = asm.add_component_instance(partner.id, name="B")
+ac1.geom_cache[body.id] = body.geometry
+c1 = ac1.add_connector(
+    position=(10.0, 5.0, 2.5), normal=(0, 0, 1), x_dir=(1, 0, 0),
+    source_obj_id=f"asm_{ac1.id}_{body.id}",
+    name="Conn hole", entity_type="cylindrical_face",
+)
+c1.partner_ac_id = ac2.id
+
+# Activate the assembly view so the prompt path is taken.
+w._assembly_view_active = True
+w._selected_assembly_component_id = ac1.id
+
+# Force a Yes from the question dialog, and record that it actually fired.
+asked = {}
+def fake_question(parent, title, text, buttons, default):
+    asked["title"] = title
+    return QMessageBox.StandardButton.Yes
+QMessageBox.question = staticmethod(fake_question)
+def fake_warning(*a, **k):
+    return QMessageBox.StandardButton.Ok
+QMessageBox.warning = staticmethod(fake_warning)
+
+w._prompt_relocate_unresolved([(asm, ac1, c1)])
+assert asked.get("title") == "Connector Position Needed", asked
+assert w._relocate_pending == [(asm, ac1, c1)], w._relocate_pending
+assert w._viewer_3d._connector_pick_mode, "pick mode must be active"
+
+# A wrong-part click must not consume the pending entry.
+w._on_relocate_picked((0, 0, 0), (0, 0, 1), (1, 0, 0), "planar_face", f"asm_{ac2.id}_{pbody.id}")
+assert w._relocate_pending == [(asm, ac1, c1)], "wrong part must not consume the pick"
+
+# The right click re-homes and drains.
+w._on_relocate_picked((40.0, 30.0, 2.5), (0, 0, 1), (1, 0, 0), "cylindrical_face", f"asm_{ac1.id}_{body.id}")
+assert w._relocate_pending is None
+assert np.allclose(c1.position, (40.0, 30.0, 2.5)), c1.position
+assert not w._viewer_3d._connector_pick_mode, "pick mode must be off after completion"
+
+# Esc cancel mid-flight clears the state.
+w._relocate_pending = [(asm, ac1, c1)]
+w._start_relocate_pick_next()
+w._on_connector_pick_cancelled()
+assert w._relocate_pending is None
+assert not w._viewer_3d._connector_pick_mode
+print("RELOCATE_PICK_FALLBACK_OK")
@@ -0,0 +1,149 @@
+"""Headless test: update_external_entities handles circle/arc dict entries.
+
+Reproduces the crash where a re-projected face contains a circular edge
+(e.g. an instance cut hole): _project_face_to_uv returns a mixed list of
+polylines + curve dicts, and update_external_entities used to unpack the
+dict entries as (u, v) tuples.
+
+Covers:
+  1. mixed projection (polylines + circle dict) -> rebuild + rebind path,
+     no crash, no duplicate/orphan curve entities, user geometry re-anchored.
+  2. repeated update with the same mixed projection -> stable (idempotent).
+  3. polylines-only same-topology projection -> in-place path still works
+     (external ids preserved).
+"""
+import math
+
+from fluency.geometry_occ.sketch import OCCSketch
+
+RECT = [
+    [(0.0, 0.0), (10.0, 0.0)],
+    [(10.0, 0.0), (10.0, 10.0)],
+    [(10.0, 10.0), (0.0, 10.0)],
+    [(0.0, 10.0), (0.0, 0.0)],
+]
+
+
+def _counts(sk):
+    ents = list(sk._entities.values())
+    return {
+        "ext_points": sum(
+            1
+            for e in ents
+            if e.entity_type == "point" and getattr(e, "is_external", False)
+        ),
+        "ext_lines": sum(
+            1
+            for e in ents
+            if e.entity_type == "line" and getattr(e, "is_external", False)
+        ),
+        "circles": sum(1 for e in ents if e.entity_type == "circle"),
+        "arcs": sum(1 for e in ents if e.entity_type == "arc"),
+        "user_points": sum(
+            1
+            for e in ents
+            if e.entity_type == "point" and not getattr(e, "is_external", False)
+        ),
+    }
+
+
+def test_mixed_projection_rebuild():
+    sk = OCCSketch()
+    sk.add_external_polylines([list(p) for p in RECT])
+    center = sk.add_external_point(5.0, 5.0)
+    sk.add_circle(center, 2.0)
+    user = sk.add_point(5.0, 5.0)
+    assert sk.constrain_coincident(user, center)
+    assert sk.solve()
+
+    # Re-projection: same rectangle, circle moved + resized -> mixed list.
+    new_proj = [
+        list(p) for p in RECT
+    ] + [
+        {"type": "circle", "center": [6.0, 6.0], "radius": 1.5},
+    ]
+    old_ext_ids = set(sk._external_entity_ids)
+    assert sk.update_external_entities(new_proj), "rebuild + rebind solve failed"
+
+    c = _counts(sk)
+    assert c["circles"] == 1, f"duplicate circle entities: {c}"
+    assert c["ext_points"] == 5, f"ext point count wrong (expect 4 corners + 1 centre): {c}"
+    assert c["ext_lines"] == 4, f"ext line count wrong (expect 4): {c}"
+    assert c["user_points"] == 1
+    # The coincident rebind must anchor the user point to the NEW centre.
+    ux, uy = user.geometry
+    assert math.hypot(ux - 6.0, uy - 6.0) < 1e-6, f"user point at {(ux, uy)}"
+    # Rebuild path: fresh external ids.
+    assert not (old_ext_ids & sk._external_entity_ids)
+
+    # Idempotent second pass with the same projection.
+    assert sk.update_external_entities(list(new_proj)), "second pass failed"
+    c2 = _counts(sk)
+    assert c2 == c, f"counts changed on second pass: {c} -> {c2}"
+    ux, uy = user.geometry
+    assert math.hypot(ux - 6.0, uy - 6.0) < 1e-6
+    print("test_mixed_projection_rebuild OK")
+
+
+def test_polylines_only_inplace():
+    sk = OCCSketch()
+    sk.add_external_polylines([list(p) for p in RECT])
+    corner = None
+    for eid in sk._external_entity_ids:
+        ent = sk._entities[eid]
+        if ent.entity_type == "point" and ent.geometry == (0.0, 0.0):
+            corner = ent
+            break
+    assert corner is not None
+    user = sk.add_point(0.0, 0.0)
+    assert sk.constrain_coincident(user, corner)
+    assert sk.solve()
+
+    # Same topology, slightly shifted rectangle -> in-place move.
+    moved = [[(u + 1.0, v + 2.0) for (u, v) in poly] for poly in RECT]
+    old_ext_ids = set(sk._external_entity_ids)
+    assert sk.update_external_entities(moved), "in-place solve failed"
+    assert sk._external_entity_ids == old_ext_ids, "in-place path must keep ids"
+    ux, uy = user.geometry
+    assert math.hypot(ux - 1.0, uy - 2.0) < 1e-6, f"user point at {(ux, uy)}"
+    print("test_polylines_only_inplace OK")
+
+
+def test_arc_import_shares_corners():
+    """_import_external_curves must merge arc endpoints with existing
+    polyline corner points (no floating duplicate endpoints)."""
+    sk = OCCSketch()
+    # Rectangle with the top-right corner filleted: the arc endpoints must
+    # land on the truncated-edge corner points, not create new ones.
+    r = 2.0
+    sk.add_external_polylines([
+        [(0.0, 0.0), (10.0, 0.0)],
+        [(10.0, 0.0), (10.0, 10.0 - r)],
+        [(10.0 - r, 10.0), (0.0, 10.0)],
+        [(0.0, 10.0), (0.0, 0.0)],
+    ])
+    sk._import_external_curves(
+        [],
+        [
+            {
+                "type": "arc",
+                "center": [10.0 - r, 10.0 - r],
+                "start": [10.0, 10.0 - r],
+                "end": [10.0 - r, 10.0],
+                "radius": r,
+            },
+        ],
+    )
+    c = _counts(sk)
+    # 5 corners + 1 arc centre, NO extra endpoint entities.
+    assert c["ext_points"] == 6, f"expected 6 ext points, got {c}"
+    assert c["arcs"] == 1, f"expected 1 arc, got {c}"
+    assert sk.solve()
+    print("test_arc_import_shares_corners OK")
+
+
+if __name__ == "__main__":
+    test_mixed_projection_rebuild()
+    test_polylines_only_inplace()
+    test_arc_import_shares_corners()
+    print("UNDERLAY_CURVES_OK")
@@ -1,147 +0,0 @@
-# WARP.md
-
-This file provides guidance to WARP (warp.dev) when working with code in this repository.
-
-## Project Overview
-Fluency is a CAD (Computer Aided Design) application built with Python/PySide6 that provides parametric 3D modeling through a timeline-based project system. The application combines 2D sketching with constraint solving, 3D visualization using VTK, and SDF (Signed Distance Function) based mesh generation.
-
-## Common Commands
-
-### Development Environment Setup
-```bash
-# Activate virtual environment (if exists)
-source .venv/bin/activate
-
-# Install dependencies
-pip install -r requirements.txt
-```
-
-### Running the Application
-```bash
-# Run the main application
-python main.py
-
-# Run with debugging
-python -u main.py
-```
-
-### UI Development
-```bash
-# Convert Qt Designer UI file to Python code
-pyside6-uic gui.ui > Gui.py -g python
-```
-
-### Building Executable
-The project uses Nuitka for compilation (configured in `main.py` header):
-```bash
-# Build standalone executable
-nuitka --standalone --plugin-enable=pyside6 --plugin-enable=numpy --macos-create-app-bundle main.py
-```
-
-### Testing
-```bash
-# Run mesh generation test
-python meshtest.py
-```
-
-## Architecture Overview
-
-### Core Components
-
-#### Main Application (`main.py`)
- **MainWindow**: Central UI controller that manages all widgets and user interactions
- **Project System**: Hierarchical structure: `Project → Timeline → Component → Sketch/Body`
- **Signal-based Communication**: Qt signals coordinate between 2D sketching and 3D rendering
-
-#### Project Hierarchy
-```
-Project
-├── Timeline (list of Components)
-└── Component
-    ├── Sketches (dict)
-    ├── Bodies (dict) 
-    └── Connectors (for assembly)
-```
-
-#### Drawing Modules (`drawing_modules/`)
- **SketchWidget** (`draw_widget_solve.py`): 2D parametric sketching with SolverSpace constraint solving
- **VTKWidget** (`vtk_widget.py`): 3D visualization and mesh interaction using VTK
- **PyVistaWidget** (`vysta_widget.py`): Alternative 3D rendering backend
-
-#### Mesh Generation (`mesh_modules/`)
- **VESTA** (`vesta_mesh.py`): Multi-threaded SDF-to-mesh conversion using marching cubes
- **Interactor Mesh** (`interactor_mesh.py`): Simplified edge-based meshes for 3D selection
- **Simple Mesh** (`simple_mesh.py`): Basic mesh utilities
-
-### Data Flow Architecture
-
-#### 2D to 3D Pipeline
-1. **2D Sketching**: User draws in SketchWidget using Qt coordinate system
-2. **Constraint Solving**: SolverSpace resolves geometric constraints
-3. **SDF Generation**: Sketch converted to Signed Distance Functions for 3D operations
-4. **Mesh Generation**: VESTA generates triangle meshes from SDF using marching cubes
-5. **3D Rendering**: VTK displays both solid meshes and interactive edges
-
-#### Signal Flow (from `doc/flow.md`)
- 2D QPoint → cartesian space → SolverSpace dict → constraint solving → display
- 3D mesh selection → projection to 2D → sketch widget integration
-
-### Key Classes
-
-#### Core Data Structures
- **Sketch**: 2D geometric data with origin, normal, points, and constraints
- **Body**: 3D mesh representation containing SDF objects and interactor meshes  
- **Component**: Container grouping related sketches and bodies
- **Interactor**: Simplified edge-based mesh for 3D manipulation
-
-#### Constraint Solving
-The application uses `python_solvespace` for parametric constraint solving:
- Point-to-point constraints
- Distance constraints
- Horizontal/vertical line constraints
- Point-to-line constraints
-
-### Technology Stack
- **GUI**: PySide6 (Qt for Python)
- **3D Graphics**: VTK for rendering, PyVista as alternative
- **Constraint Solving**: SolverSpace for parametric geometry
- **Mesh Generation**: SDF library with custom VESTA marching cubes implementation
- **Scientific Computing**: NumPy for mathematical operations
-
-## Development Workflow
-
-### Adding New Sketch Tools
-1. Add UI button in `gui.ui`
-2. Convert UI: `pyside6-uic gui.ui > Gui.py -g python`  
-3. Connect signal in `MainWindow.__init__()`
-4. Implement tool logic in `SketchWidget`
-
-### Adding New 3D Operations
-1. Extend operation buttons in the Modify group
-2. Implement operation logic using SDF functions
-3. Update Body creation and timeline management
-4. Handle interactor mesh generation for selection
-
-### Debugging Tips
- Monitor solver results through `SolverSystem` status
- Use VTK's built-in debugging for rendering issues
- Check coordinate transformations between 2D sketch and 3D space
- Verify SDF function outputs before mesh generation
-
-### File Structure
- `main.py`: Application entry point and main window
- `Gui.py`: Auto-generated UI code (do not edit directly)
- `gui.ui`: Qt Designer UI definition file
- `drawing_modules/`: 2D and 3D rendering widgets
- `mesh_modules/`: Mesh generation and processing
- `doc/`: Architecture and command documentation
-
-## Dependencies
-Primary external libraries:
- `PySide6`: Qt GUI framework
- `vtk`: 3D visualization toolkit
- `python-solvespace`: Constraint solving
- `sdf`: Signed Distance Function operations
- `numpy`: Numerical computations
- `scikit-image`: Marching cubes algorithm
- `names`: Random name generation for sketches
@@ -5,6 +5,7 @@ This module provides a concrete implementation of the geometry kernel
 using OCP (OpenCASCADE Python bindings).
 """

+import logging
 from typing import List, Tuple, Optional, Any, Dict
 import numpy as np

@@ -16,6 +17,35 @@ from fluency.geometry.base import (
 )


+
+logger = logging.getLogger(__name__)
+
+def _curve_is_linear(occ_edge: Any) -> bool:
+    """Return True if *occ_edge* has a linear or chamferable curve type.
+
+    ``BRepFilletAPI_MakeChamfer`` and ``BRepFilletAPI_MakeFillet`` crash
+    (segfault) on circular/elliptical curves.  We pre-filter those out.
+    """
+    from OCP.BRepAdaptor import BRepAdaptor_Curve
+    from OCP.GeomAbs import GeomAbs_CurveType
+
+    try:
+        ad = BRepAdaptor_Curve(occ_edge)
+        ct = ad.GetType()
+    except Exception:
+        # If we can't classify, assume it's safe (will be caught later).
+        return True
+    # Chamfer/fillet only support linear curves reliably.
+    return ct in (
+        GeomAbs_CurveType.GeomAbs_Line,
+        GeomAbs_CurveType.GeomAbs_BSplineCurve,
+        GeomAbs_CurveType.GeomAbs_BezierCurve,
+        GeomAbs_CurveType.GeomAbs_OffsetCurve,
+        GeomAbs_CurveType.GeomAbs_Parabola,
+        GeomAbs_CurveType.GeomAbs_Hyperbola,
+    )
+
+
 class OCCGeometryObject(GeometryObject):
    """Geometry object wrapper for OpenCASCADE shapes."""

@@ -75,7 +105,7 @@ class OCGeometryKernel(GeometryKernel):
        return OCCGeometryObject(edge, {"type": "circle"})

    def create_arc(
-        self, center: Point2D, radius: float, start_angle: float, end_angle: float
+        self, center: Point2D, radius: float , start_angle: float, end_angle: float
    ) -> GeometryObject:
        """Create a 2D arc."""
        import math
@@ -235,6 +265,93 @@ class OCGeometryKernel(GeometryKernel):
            pass
        return None

+    @staticmethod
+    def find_coplanar_face(
+        shape: Any,
+        origin: Tuple[float, float, float],
+        normal: Tuple[float, float, float],
+        ref_center: Optional[Tuple[float, float, float]] = None,
+        angle_tol_deg: float = 5.0,
+        dist_tol: float = 1e-3,
+    ) -> Optional[Tuple[Any, Tuple[float, float, float]]]:
+        """Find a planar face on *shape* coplanar with the given plane.
+
+        Iterates the faces of *shape* and returns the first planar face whose
+        plane normal is parallel to *normal* (within *angle_tol_deg* degrees)
+        and whose plane passes through *origin* (within *dist_tol* distance).
+        When several faces match, the one whose surface centre is closest to
+        *ref_center* (if provided) is preferred.
+
+        Returns ``(face, center)`` where *center* is the surface centroid as a
+        3-tuple, or *None* if no matching face is found.
+        """
+        import math
+
+        from OCP.TopExp import TopExp_Explorer
+        from OCP.TopAbs import TopAbs_FACE
+        from OCP.TopoDS import TopoDS
+        from OCP.BRepAdaptor import BRepAdaptor_Surface
+        from OCP.GeomAbs import GeomAbs_Plane
+        from OCP.BRepGProp import BRepGProp
+        from OCP.GProp import GProp_GProps
+
+        import numpy as np
+
+        if shape is None:
+            return None
+        n = np.asarray(normal, dtype=float)
+        n = n / (np.linalg.norm(n) + 1e-30)
+        ox, oy, oz = origin
+
+        cos_tol = math.cos(math.radians(angle_tol_deg))
+        candidates: list = []
+
+        explorer = TopExp_Explorer(shape, TopAbs_FACE)
+        while explorer.More():
+            face = TopoDS.Face_s(explorer.Current())
+            try:
+                surf = BRepAdaptor_Surface(face)
+                if surf.GetType() != GeomAbs_Plane:
+                    explorer.Next()
+                    continue
+                plane = surf.Plane()
+                pn = np.array(
+                    [
+                        plane.Axis().Direction().X(),
+                        plane.Axis().Direction().Y(),
+                        plane.Axis().Direction().Z(),
+                    ],
+                    dtype=float,
+                )
+                # Check normals parallel (same or opposite direction)
+                cos_angle = abs(float(np.dot(n, pn)))
+                if cos_angle < cos_tol:
+                    explorer.Next()
+                    continue
+                # Check distance from plane to origin
+                pp = plane.Location()
+                d = abs(float(np.dot(n, np.array([pp.X() - ox, pp.Y() - oy, pp.Z() - oz]))))
+                if d > dist_tol:
+                    explorer.Next()
+                    continue
+                # Surface centroid via GProp (SurfaceProperties for faces)
+                props = GProp_GProps()
+                BRepGProp.SurfaceProperties_s(face, props)
+                c = props.CentreOfMass()
+                center = (float(c.X()), float(c.Y()), float(c.Z()))
+                candidates.append((face, center))
+            except Exception:
+                pass
+            explorer.Next()
+
+        if not candidates:
+            return None
+        if ref_center is not None and len(candidates) > 1:
+            rc = np.asarray(ref_center, dtype=float)
+            best = min(candidates, key=lambda fc: float(np.linalg.norm(np.asarray(fc[1]) - rc)))
+            return best
+        return candidates[0]
+
    def revolve(
        self,
        sketch: GeometryObject,
@@ -356,50 +473,82 @@ class OCGeometryKernel(GeometryKernel):
    def fillet(
        self, body: GeometryObject, radius: float, edges: Optional[List[Any]] = None
    ) -> GeometryObject:
-        """Apply fillet to edges."""
-        shape = self._get_shape(body)
+        """Apply fillet to edges. Skips edges that cannot be filleted."""
        from OCP.BRepFilletAPI import BRepFilletAPI_MakeFillet

-        fillet = BRepFilletAPI_MakeFillet(shape)
+        shape: Any = self._get_shape(body)
+        if shape is None:
+            return OCCGeometryObject(None, {"type": "fillet"})

-        if edges:
-            for edge in edges:
-                fillet.Add(radius, edge)
+        # Collect candidate edges
+        if edges is not None:
+            candidates = list(edges)
        else:
            from OCP.TopExp import TopExp_Explorer
            from OCP.TopAbs import TopAbs_EDGE
+            from OCP.TopoDS import TopoDS

            explorer = TopExp_Explorer(shape, TopAbs_EDGE)
+            candidates = []
            while explorer.More():
-                fillet.Add(radius, explorer.Current())
+                e = TopoDS.Edge_s(explorer.Current())
+                if _curve_is_linear(e):
+                    candidates.append(e)
                explorer.Next()

-        fillet.Build()
-        return OCCGeometryObject(fillet.Shape(), {"type": "fillet"})
+        # Add all edges, then Build once — avoids OCC internal crashes
+        fl = BRepFilletAPI_MakeFillet(shape)
+        for edge in candidates:
+            try:
+                fl.Add(radius, edge)
+            except Exception:
+                pass  # skip edges that fail to add
+
+        fl.Build()
+        if fl.IsDone():
+            return OCCGeometryObject(fl.Shape(), {"type": "fillet"})
+        # If Build failed, return original shape (no fillet applied)
+        return OCCGeometryObject(shape, {"type": "fillet"})

    def chamfer(
        self, body: GeometryObject, size: float, edges: Optional[List[Any]] = None
    ) -> GeometryObject:
-        """Apply chamfer to edges."""
-        shape = self._get_shape(body)
+        """Apply chamfer to edges. Skips edges that cannot be chamfered."""
        from OCP.BRepFilletAPI import BRepFilletAPI_MakeChamfer

-        chamfer = BRepFilletAPI_MakeChamfer(shape)
+        shape: Any = self._get_shape(body)
+        if shape is None:
+            return OCCGeometryObject(None, {"type": "chamfer"})

-        if edges:
-            for edge in edges:
-                chamfer.Add(size, edge)
+        # Collect candidate edges
+        if edges is not None:
+            candidates = list(edges)
        else:
            from OCP.TopExp import TopExp_Explorer
            from OCP.TopAbs import TopAbs_EDGE
+            from OCP.TopoDS import TopoDS

            explorer = TopExp_Explorer(shape, TopAbs_EDGE)
+            candidates = []
            while explorer.More():
-                chamfer.Add(size, explorer.Current())
+                e = TopoDS.Edge_s(explorer.Current())
+                if _curve_is_linear(e):
+                    candidates.append(e)
                explorer.Next()

-        chamfer.Build()
-        return OCCGeometryObject(chamfer.Shape(), {"type": "chamfer"})
+        # Add all edges, then Build once — avoids OCC internal crashes
+        mc = BRepFilletAPI_MakeChamfer(shape)
+        for edge in candidates:
+            try:
+                mc.Add(size, edge)
+            except Exception:
+                pass  # skip edges that fail to add
+
+        mc.Build()
+        if mc.IsDone():
+            return OCCGeometryObject(mc.Shape(), {"type": "chamfer"})
+        # If Build failed, return original shape (no chamfer applied)
+        return OCCGeometryObject(shape, {"type": "chamfer"})

    def shell(
        self, body: GeometryObject, thickness: float, faces_to_remove: Optional[List[Any]] = None
@@ -488,6 +637,67 @@ class OCGeometryKernel(GeometryKernel):

        return OCCGeometryObject(transformer.Shape(), {"type": "mirrored"})

+    def pattern(
+        self,
+        body: GeometryObject,
+        pattern_type: str = "linear",
+        count: int = 2,
+        direction: Tuple[float, float, float] = (1, 0, 0),
+        spacing: float = 10.0,
+        axis: Tuple[float, float, float] = (0, 0, 1),
+        origin: Tuple[float, float, float] = (0.0, 0.0, 0.0),
+        angle: float = 360.0,
+    ) -> GeometryObject:
+        """Repeat *body* in a linear or circular array (pattern).
+
+        Linear: *count* copies spaced *spacing* mm apart along
+        *direction* (a negative spacing reverses the direction).
+
+        Circular: *count* copies rotated evenly around *axis* passing
+        through *origin*, distributed over a total angular span of
+        *angle* degrees (step = angle / count).  ``angle=360`` gives the
+        classic evenly-spaced full-circle bolt pattern.
+
+        Returns the union (compound when the copies don't touch) of the
+        original solid and all its copies — disjoint copies keep their
+        separate volumes inside one result object, touching copies fuse.
+        """
+        count = max(1, int(count))
+        if count <= 1:
+            return body
+
+        import math as _math
+
+        instances: list = [body]
+        if pattern_type == "circular":
+            # Normalize the rotation axis.
+            ax = float(axis[0]), float(axis[1]), float(axis[2])
+            norm = _math.sqrt(ax[0] * ax[0] + ax[1] * ax[1] + ax[2] * ax[2])
+            if norm < 1e-12:
+                ax = (0.0, 0.0, 1.0)
+            else:
+                ax = (ax[0] / norm, ax[1] / norm, ax[2] / norm)
+            step = _math.radians(float(angle)) / count
+            for i in range(1, count):
+                instances.append(self.rotate(body, ax, step * i, origin))
+        else:
+            d = float(direction[0]), float(direction[1]), float(direction[2])
+            norm = _math.sqrt(d[0] * d[0] + d[1] * d[1] + d[2] * d[2])
+            if norm < 1e-12:
+                d = (1.0, 0.0, 0.0)
+            else:
+                d = (d[0] / norm, d[1] / norm, d[2] / norm)
+            step = float(spacing)
+            for i in range(1, count):
+                instances.append(
+                    self.translate(
+                        body,
+                        (d[0] * step * i, d[1] * step * i, d[2] * step * i),
+                    )
+                )
+
+        return self.boolean_union(*instances)
+
    def export_step(self, body: GeometryObject, filepath: str, schema: str = "AP214") -> bool:
        """Export to STEP format."""
        try:
@@ -781,66 +991,362 @@ class OCGeometryKernel(GeometryKernel):
        cg = props.CentreOfMass()
        return Point3D(cg.X(), cg.Y(), cg.Z())

-    def apply_surface_modifier(
+    def create_thread(
        self,
-        body_geometry: GeometryObject,
-        modifier_type: str = 'pyramid',
-        height: float = 2.0,
-        radius: float = 3.0,
-        spacing: float = 8.0,
-        num_rings: int = 3,
+        body: GeometryObject,
+        cylindrical_face: Any,
+        nominal_diameter: float,
+        pitch: float,
+        thread_length: Optional[float] = None,
+        internal: bool = False,
    ) -> Optional[GeometryObject]:
-        """Apply a surface modifier to a body geometry.
+        """Cut (or add) an ISO metric thread on the cylindrical face of *body*.

-        Args:
-            body_geometry: The OCCGeometryObject to modify
-            modifier_type: Type of modifier ('pyramid', 'bump')
-            height: Height/depth of the pattern features
-            radius: Base radius of pattern features
-            spacing: Distance between pattern features
-            num_rings: Number of concentric rings
-
-        Returns:
-            Modified geometry, or None on failure
+        The geometry is driven by the PICKED face's actual radius and axis
+        (``nominal_diameter`` is only metadata used for the feature record).
+        External threads cut the ISO groove trapezoid (7P/8 at the surface,
+        P/4 at the root, 5H/8 deep) out of the shaft; internal threads fuse
+        the ISO ridge trapezoid (3P/4 at the wall, P/8 crest) into the hole.
        """
-        from fluency.geometry_occ.surface_modifier import SurfaceModifier
+        import math

-        shape = self._get_shape(body_geometry)
-        if shape is None:
-            logger.error("No geometry found in body")
+        from OCP.BRepAdaptor import BRepAdaptor_Surface
+        from OCP.GeomAbs import GeomAbs_Cylinder
+        from OCP.TopoDS import TopoDS
+        from OCP.gp import gp_Pnt, gp_Pnt2d, gp_Dir2d
+        from OCP.BRepBuilderAPI import (
+            BRepBuilderAPI_MakeEdge,
+            BRepBuilderAPI_MakeWire,
+        )
+
+        # ── 1. Cylinder parameters from the picked face ─────────────────
+        try:
+            surf = BRepAdaptor_Surface(cylindrical_face)
+        except Exception:
+            try:
+                surf = BRepAdaptor_Surface(TopoDS.Face_s(cylindrical_face))
+            except Exception as exc:
+                logger.warning(f"create_thread: cannot adapt face: {exc}")
+                return None
+
+        if surf.GetType() != GeomAbs_Cylinder:
+            logger.warning("create_thread: face is not cylindrical")
            return None

-        modifier = SurfaceModifier()
+        cyl = surf.Cylinder()                       # gp_Cylinder
+        radius = cyl.Radius()                       # ACTUAL picked radius
+        ax3 = cyl.Position()                        # gp_Ax3 (location, Z, X)
+        loc = ax3.Location()
+        zdir = ax3.Direction()
+        xdir = ax3.XDirection()
+        axis_origin = np.array([loc.X(), loc.Y(), loc.Z()])
+        axis_dir = np.array([zdir.X(), zdir.Y(), zdir.Z()])
+        axis_dir = axis_dir / np.linalg.norm(axis_dir)
+        axis_x = np.array([xdir.X(), xdir.Y(), xdir.Z()])
+        axis_x = axis_x / np.linalg.norm(axis_x)
+        axis_y = np.cross(axis_dir, axis_x)
+
+        u_start = surf.FirstUParameter()            # angular start of face
+        v1, v2 = surf.FirstVParameter(), surf.LastVParameter()
+        v_lo, v_hi = min(v1, v2), max(v1, v2)
+        face_height = v_hi - v_lo
+
+        if not thread_length or thread_length <= 0:
+            thread_length = face_height
+        thread_length = min(thread_length, face_height)
+
+        num_turns = thread_length / pitch
+        if num_turns < 0.05:
+            logger.warning("create_thread: thread too short for one turn")
+            return None
+
+        # ── 2. ISO metric profile dimensions ────────────────────────────
+        # Basic profile (H = P·√3/2, thread engagement depth 5H/8):
+        #  • external shaft: groove cut is a trapezoid 7P/8 wide at the
+        #    surface narrowing to P/4 at the root.
+        #  • internal hole:  ridge fused onto the wall is a trapezoid 3P/4
+        #    wide at the wall narrowing to P/8 at the inner crest, leaving
+        #    the 7P/8-wide groove open at the bore.
+        H = pitch * math.sqrt(3.0) / 2.0
+        depth = (5.0 / 8.0) * H
+        overcut = max(0.1 * depth, 0.02)            # overhang past the surface
+        if internal:
+            w_surf = 3.0 * pitch / 4.0
+            w_deep = pitch / 8.0
+        else:
+            w_surf = 7.0 * pitch / 8.0
+            w_deep = pitch / 4.0
+
+        # ── 3. Helix spine ON the picked cylinder's surface ─────────────
+        # The swept profile sits in the helix's normal plane, tilted by the
+        # lead angle; its end caps therefore stick out past the spine ends
+        # by roughly half the profile width along the axis.  For a CUT that
+        # is harmless (the groove simply runs to the part edge), but a FUSE
+        # would leave the protruding cap as floating material outside the
+        # part, so inset the internal helix by exactly that amount.
+        lead = math.atan2(pitch, 2.0 * math.pi * radius)
+        cap_axial = (w_surf / 2.0) * math.cos(lead)  # cap half-extent along axis
+
+        if internal:
+            v_start = v_lo + cap_axial
+            v_end = min(v_lo + thread_length, v_hi) - cap_axial
+        else:
+            # extend one pitch past each face end so the groove runs off
+            # the part edges cleanly
+            v_start = v_lo - pitch
+            v_end = min(v_lo + thread_length + pitch, v_hi + pitch)
+        thread_span = v_end - v_start
+        if thread_span < 0.5 * pitch:
+            logger.warning("create_thread: part too short for a thread")
+            return None
+        turns_ext = thread_span / pitch
+
+        spine_wire = None
+
+        # 3a. TRUE helix: a 2D straight line on the cylinder surface.
+        #
+        # NOTE 1: gp_Dir2d NORMALIZES its argument, so the 2D line
+        # parameter t advances the point by t·|(2π, pitch)| in (u, v)
+        # space — scale the trim range so t = n turns covers exactly
+        # n revolutions plus n·pitch of axial travel.
+        # NOTE 2: the edge from a pcurve has no 3D curve; the pipe sweep
+        # needs one, so force it with BRepLib.BuildCurves3d.
+        spine_wire = None
+        try:
+            from OCP.Geom import Geom_CylindricalSurface
+            from OCP.Geom2d import Geom2d_Line, Geom2d_TrimmedCurve
+            from OCP.BRepLib import BRepLib
+
+            dir_len = math.hypot(2.0 * math.pi, pitch)
+            cyl_surf = Geom_CylindricalSurface(cyl)
+            line2d = Geom2d_Line(
+                gp_Pnt2d(u_start, v_start), gp_Dir2d(2.0 * math.pi, pitch)
+            )
+            seg = Geom2d_TrimmedCurve(line2d, 0.0, turns_ext * dir_len)
+            helix_edge = BRepBuilderAPI_MakeEdge(seg, cyl_surf).Edge()
+            BRepLib.BuildCurves3d_s(helix_edge)
+            spine_wire = BRepBuilderAPI_MakeWire(helix_edge).Wire()
+            logger.info("create_thread: using exact helix spine")
+        except Exception as exc:
+            logger.info(f"create_thread: exact helix failed ({exc})")
+
+        # 3b. Fallback: smooth BSpline through sampled helix points
+        # (only if the exact construction is unavailable).
+        if spine_wire is None:
+            try:
+                from OCP.GeomAPI import GeomAPI_PointsToBSpline
+                from OCP.TColgp import TColgp_Array1OfPnt
+                from OCP.GeomAbs import GeomAbs_C2
+
+                pts_per_turn = 96
+                n_total = max(int(turns_ext * pts_per_turn) + 1, 2)
+                arr = TColgp_Array1OfPnt(1, n_total)
+                for i in range(1, n_total + 1):
+                    u = u_start + ((i - 1) / pts_per_turn) * 2.0 * math.pi
+                    v = v_start + ((i - 1) / pts_per_turn) * pitch
+                    p = (
+                        axis_origin
+                        + radius * (math.cos(u) * axis_x + math.sin(u) * axis_y)
+                        + v * axis_dir
+                    )
+                    arr.SetValue(i, gp_Pnt(float(p[0]), float(p[1]), float(p[2])))
+                bspline = GeomAPI_PointsToBSpline(arr, 3, 8, GeomAbs_C2, 1e-5)
+                bs_edge = BRepBuilderAPI_MakeEdge(bspline.Curve()).Edge()
+                spine_wire = BRepBuilderAPI_MakeWire(bs_edge).Wire()
+                logger.info("create_thread: using BSpline helix fallback")
+            except Exception as exc:
+                logger.warning(f"create_thread: BSpline helix failed ({exc})")
+
+        if spine_wire is None:
+            logger.warning("create_thread: no usable helix spine")
+            return None
+
+        # Start frame (same for both spine types — computed analytically).
+        def _cyl_pt(u: float, v: float) -> np.ndarray:
+            return (
+                axis_origin
+                + radius * (math.cos(u) * axis_x + math.sin(u) * axis_y)
+                + v * axis_dir
+            )
+
+        start_S = _cyl_pt(u_start, v_start)
+        start_T = (
+            2.0 * math.pi * radius
+            * (-math.sin(u_start) * axis_x + math.cos(u_start) * axis_y)
+            + pitch * axis_dir
+        )
+        start_T = start_T / np.linalg.norm(start_T)
+        start_R = math.cos(u_start) * axis_x + math.sin(u_start) * axis_y  # outward
+
+        # Profile width direction: perpendicular to tangent in the surface
+        # plane (≈ axial direction).  Trapezoid is symmetric so sign is fine.
+        binormal = np.cross(start_T, start_R)
+        binormal = binormal / np.linalg.norm(binormal)
+
+        # ── 4. Trapezoidal profile at the spine start ───────────────────
+        # Built directly in world coords: base sits *overcut* OUTSIDE the
+        # surface so the boolean fuses/cuts cleanly across it; the working
+        # end reaches *depth* INSIDE the surface.
+        def _mk(b: float, r: float) -> gp_Pnt:
+            p = start_S + b * binormal + r * start_R
+            return gp_Pnt(float(p[0]), float(p[1]), float(p[2]))
+
+        p0 = _mk(-w_surf / 2.0, overcut)
+        p1 = _mk(-w_deep / 2.0, -depth)
+        p2 = _mk(+w_deep / 2.0, -depth)
+        p3 = _mk(+w_surf / 2.0, overcut)
+
+        prof_wb = BRepBuilderAPI_MakeWire()
+        for a, b in ((p0, p1), (p1, p2), (p2, p3), (p3, p0)):
+            prof_wb.Add(BRepBuilderAPI_MakeEdge(a, b).Edge())
+        profile_wire = prof_wb.Wire()
+
+        # ── 5. Sweep the profile along the helix ────────────────────────
+        from OCP.BRepOffsetAPI import BRepOffsetAPI_MakePipeShell

        try:
-            if modifier_type == 'pyramid':
-                result_shape = modifier.apply_pyramid_pattern(
-                    shape,
-                    pyramid_height=height,
-                    base_radius=radius,
-                    spacing=spacing,
-                    num_rings=num_rings,
-                    direction=(0, 0, 1),
-                )
-            elif modifier_type == 'bump':
-                result_shape = modifier.apply_bump_pattern(
-                    shape,
-                    bump_height=height,
-                    bump_radius=radius,
-                    spacing=spacing,
-                    num_rings=num_rings,
-                )
-            else:
-                logger.error(f"Unknown modifier type: {modifier_type}")
+            pipe = BRepOffsetAPI_MakePipeShell(spine_wire)
+            pipe.SetMode(True)                       # Frenet frame
+            pipe.Add(profile_wire, False, False)
+            pipe.Build()
+            if not pipe.IsDone():
+                logger.warning("create_thread: pipe sweep failed")
                return None
-
-            if result_shape is None:
-                logger.error("Surface modifier application failed")
-                return None
-
-            # Return the modified shape wrapped in OCCGeometryObject
-            return OCCGeometryObject(result_shape)
-
-        except Exception as e:
-            logger.error(f"Error applying surface modifier: {e}", exc_info=True)
+            solid_ok = False
+            try:
+                solid_ok = bool(pipe.MakeSolid())    # cap the tube ends
+            except Exception as exc:
+                logger.info(f"create_thread: MakeSolid unavailable ({exc})")
+            tool_shape = pipe.Shape()
+            if not solid_ok:
+                logger.warning("create_thread: sweep is not a solid")
+        except Exception as exc:
+            logger.warning(f"create_thread: sweep failed: {exc}")
+            return None
+
+        # ── 6. Boolean cut (shaft) or fuse (hole) ───────────────────────
+        body_shape = self._get_shape(body)
+        if body_shape is None:
+            logger.warning("create_thread: body has no shape")
+            return None
+
+        tool = OCCGeometryObject(tool_shape)
+        vol_before = self.get_volume(body)
+
+        if internal:
+            result = self.boolean_union(body, tool)
+        else:
+            result = self.boolean_difference(body, tool)
+
+        if result is None or self._get_shape(result) is None:
+            logger.warning("create_thread: boolean op produced no shape")
+            return None
+
+        try:
+            vol_after = self.get_volume(result)
+        except Exception:
+            vol_after = -1.0
+
+        if internal and vol_after <= vol_before:
+            logger.warning(
+                f"create_thread: fuse did not add volume "
+                f"({vol_before:.4f} → {vol_after:.4f}) — tool missed the body?"
+            )
+            return None
+        if not internal and vol_after >= vol_before:
+            logger.warning(
+                f"create_thread: cut did not remove volume "
+                f"({vol_before:.4f} → {vol_after:.4f}) — tool missed the body?"
+            )
+            return None
+
+        logger.info(
+            f"create_thread: {'internal' if internal else 'external'} thread OK, "
+            f"volume {vol_before:.4f} → {vol_after:.4f}"
+        )
+        return result
+
+    def detect_cylindrical_face(
+        self,
+        face: Any,
+    ) -> Optional[Dict[str, Any]]:
+        """Check if *face* is cylindrical and return its parameters.
+
+        The *face* can be a ``TopoDS_Face`` (from the picker) or a
+        ``TopoDS_Shape`` that contains a face.  We try several paths to
+        extract the underlying cylindrical surface.
+
+        Returns a dict with keys ``radius``, ``axis_origin``, ``axis_dir``,
+        ``height``, or *None* if the face isn't cylindrical.
+        """
+        import logging
+        import numpy as np
+        from OCP.BRepAdaptor import BRepAdaptor_Surface
+        from OCP.GeomAbs import GeomAbs_Cylinder
+        from OCP.TopoDS import TopoDS
+
+        _log = logging.getLogger(__name__)
+
+        # ── Resolve the actual face from whatever the caller handed us ──
+        actual_face: Any = None
+
+        # Try direct BRepAdaptor_Surface first — the picker already returns
+        # a valid TopoDS_Face, and calling TopoDS.Face_s() again on an
+        # already-downcast face can fail in some OCP versions.
+        try:
+            surf = BRepAdaptor_Surface(face)
+            surf_type_test = surf.GetType()
+            actual_face = face
+        except Exception:
+            pass
+
+        if actual_face is None:
+            # Fallback: try the explicit TopoDS.Face_s downcast path.
+            try:
+                candidate = TopoDS.Face_s(face)
+                _ = BRepAdaptor_Surface(candidate)
+                actual_face = candidate
+            except Exception:
+                pass
+
+        if actual_face is None:
+            _log.warning("detect_cylindrical_face: could not resolve face from pick result")
+            return None
+
+        # ── Probe the surface type ──
+        try:
+            surf = BRepAdaptor_Surface(actual_face)
+            surf_type = surf.GetType()
+            if surf_type != GeomAbs_Cylinder:
+                type_names = {
+                    0: "Plane", 1: "Cylinder", 2: "Cone", 3: "Sphere",
+                    4: "Torus", 5: "Bezier", 6: "BSpline", 7: "Revolution",
+                    8: "Extrusion", 9: "Offset", 10: "Other",
+                }
+                type_name = type_names.get(int(surf_type), f"Unknown({int(surf_type)})")
+                _log.warning(
+                    f"detect_cylindrical_face: face is {type_name}, not a Cylinder"
+                )
+                return None
+
+            cyl = surf.Cylinder()
+            radius = cyl.Radius()
+            axis = cyl.Axis()
+            origin = axis.Location()
+            direction = axis.Direction()
+            # BRepAdaptor_Surface uses FirstUParameter/LastUParameter etc.
+            u1 = surf.FirstUParameter()
+            u2 = surf.LastUParameter()
+            v1 = surf.FirstVParameter()
+            v2 = surf.LastVParameter()
+            height = abs(v2 - v1)
+            return {
+                "radius": radius,
+                "diameter": 2.0 * radius,
+                "axis_origin": (origin.X(), origin.Y(), origin.Z()),
+                "axis_dir": (direction.X(), direction.Y(), direction.Z()),
+                "height": height,
+            }
+        except Exception as exc:
+            _log.warning(f"detect_cylindrical_face: surface probe failed: {exc}")
            return None
@@ -0,0 +1,385 @@
+"""Surface modifier for OpenCASCADE geometry.
+
+Applies geometric patterns (pyramids, bumps, grooves) to 3D surfaces using boolean operations.
+This enables grip-enhancing textures and visual surface modifications on CAD models.
+"""
+
+from __future__ import annotations
+
+import logging
+import math
+from typing import Any, Optional, Tuple
+
+# OCC imports at module level for common types
+
+
+logger = logging.getLogger(__name__)
+
+
+class SurfaceModifier:
+    """Applies geometric patterns to 3D surfaces using OCC boolean operations."""
+
+    def __init__(self):
+        self._patterns_applied = []
+
+    def apply_pyramid_pattern(
+        self,
+        face_shape,
+        pyramid_height: float = 1.0,
+        base_radius: float = 2.0,
+        spacing: float = 5.0,
+        num_rings: Optional[int] = None,
+        direction: Tuple[float, float, float] = (0, 0, 1),
+    ) -> Optional[Any]:
+        """Apply a pyramid pattern to a face surface.
+
+        Args:
+            face_shape: OCC TopoDS_Shape representing the face or solid
+            pyramid_height: Height of each pyramid
+            base_radius: Radius of pyramid base
+            spacing: Distance between pyramids
+            num_rings: Number of concentric rings (auto-calculated if None)
+            direction: Normal direction for pyramids
+
+        Returns:
+            Modified shape on success, None on failure
+        """
+        try:
+            from OCP.TopAbs import TopAbs_FACE
+            from OCP.TopoDS import TopoDS_Face, TopoDS_Shape
+            from OCP.BRepAlgoAPI import BRepAlgoAPI_Fuse
+            from OCP.TopExp import TopExp_Explorer
+            from OCP.BRepAdaptor import BRepAdaptor_Surface
+
+            # Validate face shape
+            if not isinstance(face_shape, (TopoDS_Shape, TopoDS_Face)):
+                logger.error("Invalid face shape type")
+                return None
+
+            # Extract the first face for surface parameterization
+            if isinstance(face_shape, TopoDS_Shape):
+                explorer = TopExp_Explorer(face_shape, TopAbs_FACE)
+                if not explorer.More():
+                    logger.error("No faces found in shape")
+                    return None
+                from OCP import TopoDS
+                face = TopoDS.TopoDS.Face_s(explorer.Current())
+            else:
+                face = face_shape
+
+            # Get face surface for UV parameterization
+            surf = BRepAdaptor_Surface(face)
+
+            u_min, u_max = surf.FirstUParameter(), surf.LastUParameter()
+            v_min, v_max = surf.FirstVParameter(), surf.LastVParameter()
+
+            # Calculate number of rings if not specified
+            if num_rings is None:
+                # Estimate based on face area and spacing
+                u_range = u_max - u_min
+                v_range = v_max - v_min
+                avg_dim = (u_range + v_range) / 2.0
+                num_rings = max(1, min(int(avg_dim / spacing), 5))
+
+            logger.info(
+                f"Applying pyramid pattern: {num_rings} rings, "
+                f"{base_radius:.2f} radius, {pyramid_height:.2f} height"
+            )
+
+            # Create pyramids distributed across the face UV space
+            result_shape = face_shape
+            pyramid_count = 0
+
+            for ring_idx in range(num_rings):
+                # Distribute rings evenly across UV parameter space
+                u_fraction = (ring_idx + 1) / (num_rings + 1)
+                v_fraction = 0.5  # Center vertically
+
+                # Map to actual UV coordinates on the face
+                u_pos = u_min + u_fraction * (u_max - u_min)
+                v_pos = v_min + v_fraction * (v_max - v_min)
+
+                # Get 3D position and tangent vectors at this UV point
+                from OCP.gp import gp_Pnt, gp_Vec
+
+                center_pt = gp_Pnt()
+                d1u = gp_Vec()
+                d1v = gp_Vec()
+                surf.D1(u_pos, v_pos, center_pt, d1u, d1v)
+                # Normal is cross product of tangent vectors
+                normal = d1u.Crossed(d1v)
+                normal.Normalize()
+
+                # Calculate number of pyramids in this ring based on spacing
+                if ring_idx == 0:
+                    num_pyramids = 1  # Center pyramid
+                else:
+                    circumference = 2.0 * math.pi * (ring_idx * spacing)
+                    num_pyramids = max(3, int(circumference / spacing))
+
+                for i in range(num_pyramids):
+                    if ring_idx == 0:
+                        # Center pyramid - place at face center
+                        place_u = u_pos
+                        place_v = v_pos
+                    else:
+                        angle = (2.0 * math.pi * i) / num_pyramids
+                        # Offset in UV space based on ring radius
+                        offset_u = (ring_idx * spacing / (u_max - u_min)) * math.cos(angle)
+                        offset_v = (ring_idx * spacing / (v_max - v_min)) * math.sin(angle)
+                        place_u = max(u_min, min(u_max, u_pos + offset_u))
+                        place_v = max(v_min, min(v_max, v_pos + offset_v))
+
+                    try:
+                        # Get 3D position and normal for this pyramid
+                        pyramid_pt = gp_Pnt()
+                        pd1u = gp_Vec()
+                        pd1v = gp_Vec()
+                        surf.D1(place_u, place_v, pyramid_pt, pd1u, pd1v)
+                        pyramid_normal = pd1u.Crossed(pd1v)
+                        pyramid_normal.Normalize()
+
+                        # Create solid pyramid at this position
+                        pyramid_shape = self._create_solid_pyramid(
+                            pyramid_pt,
+                            pyramid_normal,
+                            pyramid_height,
+                            base_radius,
+                        )
+
+                        if pyramid_shape is not None:
+                            # Fuse with existing geometry
+                            fuse = BRepAlgoAPI_Fuse(result_shape, pyramid_shape)
+                            fuse.Build()
+
+                            if fuse.IsDone():
+                                result_shape = fuse.Shape()
+                                pyramid_count += 1
+                            else:
+                                logger.warning(
+                                    f"Failed to fuse pyramid at ({place_u:.2f}, {place_v:.2f})"
+                                )
+                    except Exception as e:
+                        logger.debug(
+                            f"Error creating pyramid at ring {ring_idx}, pyramid {i}: {e}"
+                        )
+
+            self._patterns_applied.append(
+                {
+                    "type": "pyramid",
+                    "parameters": {
+                        "height": pyramid_height,
+                        "base_radius": base_radius,
+                        "spacing": spacing,
+                        "num_rings": num_rings,
+                        "direction": direction,
+                    },
+                }
+            )
+
+            logger.info(f"Successfully applied {pyramid_count} pyramids")
+
+            return result_shape
+
+        except Exception as e:
+            logger.error(f"Error applying pyramid pattern: {e}", exc_info=True)
+            return None
+
+    def _create_solid_pyramid(
+        self,
+        base_point,  # gp_Pnt - position on the face
+        normal_vec,  # gp_Dir or gp_Vec - surface normal direction
+        height: float,
+        base_radius: float,
+    ) -> Optional[Any]:
+        """Create a solid pyramid at the specified position and orientation.
+
+        Uses BRepPrimAPI_MakePrism to extrude a square base into a solid pyramid.
+
+        Args:
+            base_point: 3D point where pyramid base is centered
+            normal_vec: Direction vector for pyramid growth (surface normal)
+            height: Height of the pyramid from base to apex
+            base_radius: Half-width of the square base
+
+        Returns:
+            OCC solid shape for the pyramid, or None on failure
+        """
+        try:
+            from OCP.gp import gp_Dir, gp_Ax2, gp_Vec
+            from OCP.BRepBuilderAPI import (
+                BRepBuilderAPI_MakeEdge,
+                BRepBuilderAPI_MakeWire,
+            )
+            from OCP.BRepPrimAPI import BRepPrimAPI_MakePrism
+
+            half = base_radius / 2.0
+
+            # Build orthonormal basis from normal vector
+            if isinstance(normal_vec, gp_Vec):
+                n_dir = gp_Dir(normal_vec.XYZ())
+            else:
+                n_dir = normal_vec
+
+            # Create a local coordinate system at the base point
+            local_ax2 = gp_Ax2(base_point, n_dir)
+
+            # Get X and Y axes from the local coordinate system
+            x_dir = local_ax2.XDirection()
+            y_dir = local_ax2.YDirection()
+
+            # Create 4 corners of the square base in the local plane
+            corner_points = [
+                base_point + gp_Vec(x_dir).Multiplied(half) + gp_Vec(y_dir).Multiplied(half),
+                base_point + gp_Vec(x_dir).Multiplied(-half) + gp_Vec(y_dir).Multiplied(half),
+                base_point + gp_Vec(x_dir).Multiplied(-half) + gp_Vec(y_dir).Multiplied(-half),
+                base_point + gp_Vec(x_dir).Multiplied(half) + gp_Vec(y_dir).Multiplied(-half),
+            ]
+
+            # Create edges connecting the corners
+            wire_maker = BRepBuilderAPI_MakeWire()
+            for idx in range(4):
+                next_idx = (idx + 1) % 4
+                edge = BRepBuilderAPI_MakeEdge(
+                    corner_points[idx], corner_points[next_idx]
+                ).Edge()
+                wire_maker.Add(edge)
+
+            if not wire_maker.IsDone():
+                logger.warning("Failed to create pyramid base wire")
+                return None
+
+            # Extrude the base wire in the normal direction by height to form a prism
+            extrusion_vec = gp_Vec(n_dir).Multiplied(height)
+            prism_maker = BRepPrimAPI_MakePrism(
+                wire_maker.Wire(), extrusion_vec, False  # no check intersection
+            )
+            prism_maker.Build()
+
+            if not prism_maker.IsDone():
+                logger.warning("Failed to create pyramid prism")
+                return None
+
+            return prism_maker.Shape()
+
+        except Exception as e:
+            logger.debug(f"Error creating solid pyramid: {e}")
+            return None
+
+    def apply_bump_pattern(
+        self,
+        face_shape,
+        bump_height: float = 1.0,
+        bump_radius: float = 2.0,
+        spacing: float = 5.0,
+        num_rings: Optional[int] = None,
+    ) -> Optional[Any]:
+        """Apply a simple bump pattern to a face surface.
+
+        Args:
+            face_shape: OCC TopoDS_Shape representing the face
+            bump_height: Height of each bump
+            bump_radius: Radius of each bump base
+            spacing: Distance between bumps
+            num_rings: Number of concentric rings
+
+        Returns:
+            Modified shape on success, None on failure
+        """
+        return self.apply_pyramid_pattern(
+            face_shape,
+            pyramid_height=bump_height,
+            base_radius=bump_radius,
+            spacing=spacing,
+            num_rings=num_rings,
+        )
+
+
+def apply_surface_modifier_to_body(
+    body_geometry, modifier_type: str = "pyramid", **parameters
+) -> Optional[Any]:
+    """Apply a surface modifier to a body geometry.
+
+    Args:
+        body_geometry: OCCGeometryObject or similar geometry object
+        modifier_type: Type of modifier ('pyramid', 'bump')
+        **parameters: Modifier-specific parameters
+
+    Returns:
+        Modified shape, or None on failure
+    """
+    from fluency.geometry_occ.kernel import OCGeometryKernel
+
+    kernel = OCGeometryKernel()
+    shape = kernel._get_shape(body_geometry)
+
+    if shape is None:
+        logger.error("No geometry found in body")
+        return None
+
+    modifier = SurfaceModifier()
+
+    try:
+        if modifier_type == "pyramid":
+            success = modifier.apply_pyramid_pattern(shape, **parameters)
+        elif modifier_type == "bump":
+            success = modifier.apply_bump_pattern(shape, **parameters)
+        else:
+            logger.error(f"Unknown modifier type: {modifier_type}")
+            return None
+
+        if not success:
+            logger.error("Surface modifier application failed")
+            return None
+
+        # Return the modified shape wrapped in OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCCGeometryObject
+
+        return OCCGeometryObject(shape)
+
+    except Exception as e:
+        logger.error(f"Error applying surface modifier: {e}", exc_info=True)
+        return None
+
+
+# Example usage and testing
+if __name__ == "__main__":
+    # Create a simple test case
+    from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
+
+    # Create a box to modify
+    box_maker = BRepPrimAPI_MakeBox(50, 50, 10)
+    box_maker.Build()
+
+    if box_maker.IsDone():
+        print("Created test box")
+
+        # Apply pyramid pattern to top face (Z direction)
+        modifier = SurfaceModifier()
+        success = modifier.apply_pyramid_pattern(
+            box_maker.Shape(),
+            pyramid_height=2.0,
+            base_radius=3.0,
+            spacing=8.0,
+            num_rings=2,
+            direction=(0, 0, 1),
+        )
+
+        if success:
+            print("Successfully applied pyramid pattern")
+
+            # Export modified shape
+            from OCP.StlAPI import StlAPI_Writer
+            from OCP.BRepMesh import BRepMesh_IncrementalMesh
+
+            tess = BRepMesh_IncrementalMesh(box_maker.Shape(), 0.1)
+            tess.Perform()
+
+            writer = StlAPI_Writer()
+            writer.SetASCIIMode(False)
+            writer.Write(box_maker.Shape(), "/tmp/test_pyramid_pattern.stl")
+            print("Exported modified shape to STL")
+        else:
+            print("Failed to apply pyramid pattern")
+    else:
+        print("Failed to create test box")
@@ -28,6 +28,7 @@ import logging
 import os
 import shutil
 import tempfile
+import uuid
 import zipfile
 from dataclasses import asdict, is_dataclass
 from datetime import datetime
@@ -42,8 +43,12 @@ from fluency.models.data_model import (
    Body,
    Component,
    Connector,
+    DrawingAnnotation,
+    DrawingView,
+    Feature,
    Project,
    Sketch,
+    TechnicalDrawing,
    Workplane,
 )
 from fluency.geometry_occ.kernel import OCCGeometryObject, OCGeometryKernel
@@ -65,7 +70,7 @@ def _json_default(obj: Any) -> Any:
        return sorted(obj)
    if isinstance(obj, tuple):
        return list(obj)
-    if is_dataclass(obj):
+    if is_dataclass(obj) and not isinstance(obj, type):
        return asdict(obj)
    raise TypeError(f"Object of type {type(obj).__name__} is not JSON serializable")

@@ -85,42 +90,77 @@ def _coerce_listlike(value: Any) -> List[Any]:
    return list(value)


+def _to_float(value: Any, default: float = 0.0) -> float:
+    """Safely coerce a saved value to float, falling back to *default*.
+
+    Corrupt archives may store a string or None where a number is expected;
+    the loaders must not crash on them.
+    """
+    try:
+        return float(value)
+    except (TypeError, ValueError):
+        return default
+
+
+def _saved_id(data: Dict[str, Any]) -> str:
+    """Return a saved entity id, or a fresh UUID for corrupt/legacy data.
+
+    Old files always wrote an ``id``; a missing/empty value means the
+    archive is damaged, and the model's uuid factory only kicks in when the
+    constructor argument is omitted — so we generate here to keep ids valid
+    non-empty strings.
+    """
+    v = data.get("id")
+    if isinstance(v, str) and v:
+        return v
+    return str(uuid.uuid4())
+
+
 def _to_3tuple(value: Any) -> Tuple[float, float, float]:
    """Coerce a saved 3-vector to a tuple of floats (for OCC)."""
    if value is None:
        return (0.0, 0.0, 0.0)
-    if isinstance(value, np.ndarray):
-        seq = value.tolist()
-    else:
-        seq = list(value)
-    if len(seq) < 3:
-        seq = list(seq) + [0.0] * (3 - len(seq))
-    return (float(seq[0]), float(seq[1]), float(seq[2]))
+    try:
+        if isinstance(value, np.ndarray):
+            seq = value.tolist()
+        else:
+            seq = list(value)
+        if len(seq) < 3:
+            seq = list(seq) + [0.0] * (3 - len(seq))
+        return (float(seq[0]), float(seq[1]), float(seq[2]))
+    except (TypeError, ValueError, IndexError):
+        return (0.0, 0.0, 0.0)


 def _to_3vec(value: Any) -> np.ndarray:
    """Coerce a saved 3-vector to a 3-element numpy array."""
-    if isinstance(value, np.ndarray):
-        return value.astype(float).reshape(3)
-    if value is None:
+    try:
+        if isinstance(value, np.ndarray):
+            return value.astype(float).reshape(3)
+        if value is None:
+            return np.zeros(3, dtype=float)
+        seq = list(value)
+        if len(seq) < 3:
+            seq = list(seq) + [0.0] * (3 - len(seq))
+        return np.array([float(seq[0]), float(seq[1]), float(seq[2])], dtype=float)
+    except (TypeError, ValueError, IndexError):
        return np.zeros(3, dtype=float)
-    seq = list(value)
-    if len(seq) < 3:
-        seq = list(seq) + [0.0] * (3 - len(seq))
-    return np.array([float(seq[0]), float(seq[1]), float(seq[2])], dtype=float)


 def _to_mat3(value: Any) -> np.ndarray:
    """Coerce a saved 3×3 matrix (flat 9-list or nested) to np.ndarray."""
-    if isinstance(value, np.ndarray):
-        arr = value.astype(float)
-        return arr.reshape(3, 3)
-    if value is None:
+    try:
+        if isinstance(value, np.ndarray):
+            arr = value.astype(float)
+            return arr.reshape(3, 3)
+        if value is None:
+            return np.eye(3, dtype=float)
+        flat = list(np.asarray(value, dtype=float).flatten())
+        if len(flat) < 9:
+            flat = flat + [0.0] * (9 - len(flat))
+        return np.array(flat[:9], dtype=float).reshape(3, 3)
+    except (TypeError, ValueError, IndexError):
        return np.eye(3, dtype=float)
-    flat = list(np.asarray(value, dtype=float).flatten())
-    if len(flat) < 9:
-        flat = flat + [0.0] * (9 - len(flat))
-    return np.array(flat[:9], dtype=float).reshape(3, 3)


 def _parse_iso(value: Optional[str]) -> datetime:
@@ -151,11 +191,11 @@ def _workplane_to_dict(wp: Workplane) -> Dict[str, Any]:

 def _workplane_from_dict(data: Dict[str, Any]) -> Workplane:
    wp = Workplane(
-        id=data.get("id") or None,  # Workplane generates uuid if None
+        id=_saved_id(data),
        name=data.get("name", "Untitled Workplane"),
-        origin=tuple(data.get("origin", (0.0, 0.0, 0.0))),
-        normal=tuple(data.get("normal", (0.0, 0.0, 1.0))),
-        x_dir=tuple(data.get("x_dir", (1.0, 0.0, 0.0))),
+        origin=_to_3tuple(data.get("origin", (0.0, 0.0, 0.0))),
+        normal=_to_3tuple(data.get("normal", (0.0, 0.0, 1.0))),
+        x_dir=_to_3tuple(data.get("x_dir", (1.0, 0.0, 0.0))),
        visible=bool(data.get("visible", True)),
    )
    wp.created_at = _parse_iso(data.get("created_at"))
@@ -163,6 +203,90 @@ def _workplane_from_dict(data: Dict[str, Any]) -> Workplane:
    return wp


+def _feature_to_dict(feat: Feature) -> Dict[str, Any]:
+    """Serialize one parametric feature (sketch id + params).
+
+    "base" snapshot features are NOT serialized here — their frozen
+    geometry is written as a separate STEP member (``base_geometry_ref``)
+    and the ``features_base_snapshot`` flag on the body marks that the
+    list starts with one.
+    """
+    return {
+        "id": feat.id,
+        "operation": feat.operation,
+        "sketch_id": feat.sketch.id if feat.sketch is not None else None,
+        "length": feat.length,
+        "symmetric": bool(feat.symmetric),
+        "invert": bool(feat.invert),
+        "through_all": bool(feat.through_all),
+        "cut_all_bodies": bool(feat.cut_all_bodies),
+        "face_index": feat.face_index,
+        "angle": _to_float(feat.angle, 360.0),
+        "axis": [float(v) for v in (feat.axis or (0, 0, 1))],
+        "origin": [float(v) for v in (feat.origin or (0.0, 0.0, 0.0))],
+        "axis_line_id": feat.axis_line_id,
+        "radius": feat.radius,
+        "tangent_propagation": bool(feat.tangent_propagation),
+        "scope": feat.scope,
+        "edge_refs": list(feat.edge_refs),
+        "face_keys": json.dumps(feat.face_keys) if feat.face_keys is not None else None,
+        "face_keys_sketch_id": feat.face_keys_sketch_id,
+        "pattern_type": feat.pattern_type,
+        "count": feat.count,
+        "spacing": feat.spacing,
+        "direction": [float(v) for v in (feat.direction or (1, 0, 0))],
+        "mirror_plane_origin": [float(v) for v in (feat.mirror_plane_origin or (0.0, 0.0, 0.0))],
+        "mirror_plane_normal": [float(v) for v in (feat.mirror_plane_normal or (1, 0, 0))],
+        "keep_original": bool(feat.keep_original),
+    }
+
+
+def _feature_from_dict(data: Dict[str, Any], sketches: Dict[str, Sketch]) -> Feature:
+    """Deserialize a feature, resolving its sketch reference against the
+    component's already-loaded sketches."""
+    feat = Feature(
+        id=_saved_id(data),
+        operation=data.get("operation", "extrude"),
+        length=data.get("length"),
+        symmetric=bool(data.get("symmetric", False)),
+        invert=bool(data.get("invert", False)),
+        through_all=bool(data.get("through_all", False)),
+        cut_all_bodies=bool(data.get("cut_all_bodies", False)),
+        face_index=data.get("face_index"),
+        angle=_to_float(data.get("angle"), 360.0),
+        axis=tuple(float(v) for v in (data.get("axis") or (0, 0, 1))),
+        origin=tuple(float(v) for v in (data.get("origin") or (0.0, 0.0, 0.0))),
+        axis_line_id=data.get("axis_line_id"),
+        radius=data.get("radius"),
+        tangent_propagation=bool(data.get("tangent_propagation", False)),
+        scope=data.get("scope", "selected"),
+        edge_refs=list(data.get("edge_refs") or []),
+        face_keys=None,
+        face_keys_sketch_id=data.get("face_keys_sketch_id"),
+        pattern_type=data.get("pattern_type", "linear"),
+        count=int(data.get("count") or 2),
+        spacing=_to_float(data.get("spacing"), 10.0),
+        direction=tuple(float(v) for v in (data.get("direction") or (1, 0, 0))),
+        mirror_plane_origin=tuple(float(v) for v in (data.get("mirror_plane_origin") or (0.0, 0.0, 0.0))),
+        mirror_plane_normal=tuple(float(v) for v in (data.get("mirror_plane_normal") or (1, 0, 0))),
+        keep_original=bool(data.get("keep_original", True)),
+    )
+
+    # Deserialize face_keys from JSON if present.
+    fk_raw = data.get("face_keys")
+    if fk_raw and isinstance(fk_raw, str):
+        try:
+            feat.face_keys = json.loads(fk_raw)
+        except (json.JSONDecodeError, TypeError):
+            pass
+    elif isinstance(fk_raw, list):
+        feat.face_keys = fk_raw
+    sid = data.get("sketch_id")
+    if sid and sid in sketches:
+        feat.sketch = sketches[sid]
+    return feat
+
+
 def _body_to_dict(body: Body) -> Dict[str, Any]:
    """Body serialization.  ``geometry_ref`` is set later by the ZIP writer
    once the STEP file is written."""
@@ -177,12 +301,16 @@ def _body_to_dict(body: Body) -> Dict[str, Any]:
        "extrude_cut": body.extrude_cut,
        "extrude_union": body.extrude_union,
        "extrude_through_all": body.extrude_through_all,
+        "extrude_cut_all_bodies": body.extrude_cut_all_bodies,
        "extrude_face_index": body.extrude_face_index,
        "extrude_target_body_id": body.extrude_target_body_id,
+        "features": [_feature_to_dict(f) for f in body.features if f.operation != "base"],
+        "features_base_snapshot": bool(body.features and body.features[0].operation == "base"),
+        "base_geometry_ref": None,  # filled in by save_project
        "position": _coerce_listlike(body.position),
        "rotation": _coerce_listlike(body.rotation),
        "color": list(body.color) if body.color else [0.2, 0.4, 0.8],
-        "opacity": float(body.opacity),
+        "opacity": _to_float(body.opacity, 1.0),
        "visible": bool(body.visible),
        "has_geometry": body.geometry is not None,
        "geometry_ref": None,  # filled in by save_project
@@ -201,7 +329,7 @@ def _body_from_dict(
        geometry = geometry_loader(data["geometry_ref"]) if data.get("has_geometry") else None

    body = Body(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        name=data.get("name", "Untitled Body"),
        geometry=geometry,
        source_sketch=source_sketch,
@@ -212,12 +340,13 @@ def _body_from_dict(
        extrude_cut=bool(data.get("extrude_cut", False)),
        extrude_union=bool(data.get("extrude_union", False)),
        extrude_through_all=bool(data.get("extrude_through_all", False)),
+        extrude_cut_all_bodies=bool(data.get("extrude_cut_all_bodies", False)),
        extrude_face_index=data.get("extrude_face_index"),
        extrude_target_body_id=data.get("extrude_target_body_id"),
        position=_to_3vec(data.get("position")),
        rotation=_to_mat3(data.get("rotation")),
        color=tuple(data.get("color", [0.2, 0.4, 0.8])),
-        opacity=float(data.get("opacity", 1.0)),
+        opacity=_to_float(data.get("opacity"), 1.0),
        visible=bool(data.get("visible", True)),
    )
    body.created_at = _parse_iso(data.get("created_at"))
@@ -267,9 +396,9 @@ def _sketch_from_dict(
    # Re-apply the workplane (from_dict already does this internally, but be
    # defensive in case the saved dict didn't carry the workplane fields).
    occ_sketch.set_workplane(
-        tuple(data.get("workplane_origin", (0.0, 0.0, 0.0))),
-        tuple(data.get("workplane_normal", (0.0, 0.0, 1.0))),
-        tuple(data.get("workplane_x_dir", (1.0, 0.0, 0.0))),
+        _to_3tuple(data.get("workplane_origin", (0.0, 0.0, 0.0))),
+        _to_3tuple(data.get("workplane_normal", (0.0, 0.0, 1.0))),
+        _to_3tuple(data.get("workplane_x_dir", (1.0, 0.0, 0.0))),
    )

    geometry: Optional[OCCGeometryObject] = None
@@ -277,7 +406,7 @@ def _sketch_from_dict(
        geometry = geometry_loader(data["geometry_ref"]) if data.get("has_geometry") else None

    sk = Sketch(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        name=data.get("name", "Untitled Sketch"),
        occ_sketch=occ_sketch,
        geometry=geometry,
@@ -314,7 +443,7 @@ def _component_from_dict(
    sketch_geometry_loader: Optional[Callable[[str], Optional[OCCGeometryObject]]] = None,
 ) -> Component:
    comp = Component(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        name=data.get("name", "Untitled Component"),
        description=data.get("description", ""),
        active_sketch=data.get("active_sketch"),
@@ -335,7 +464,22 @@ def _component_from_dict(
        src_id = body_data.get("source_sketch_id")
        if src_id and src_id in comp.sketches:
            src_sketch = comp.sketches[src_id]
-        comp.bodies[bid] = _body_from_dict(body_data, body_geometry_loader, src_sketch)
+        body = _body_from_dict(body_data, body_geometry_loader, src_sketch)
+        # Parametric feature history (new files).  Old files carry no
+        # "features" key — the body keeps an empty list and is migrated
+        # lazily at update time (see ``_ensure_feature_history``).
+        for f_data in body_data.get("features") or []:
+            body.features.append(_feature_from_dict(f_data, comp.sketches))
+        if body_data.get("features_base_snapshot") and body.features:
+            # The list was saved WITHOUT its leading "base" snapshot;
+            # restore it from the dedicated STEP member.
+            base_geom: Optional[OCCGeometryObject] = None
+            base_ref = body_data.get("base_geometry_ref")
+            if base_ref and body_geometry_loader is not None:
+                base_geom = body_geometry_loader(base_ref)
+            if base_geom is not None:
+                body.features.insert(0, Feature(operation="base", geometry=base_geom))
+        comp.bodies[bid] = body

    return comp

@@ -347,10 +491,12 @@ def _connector_to_dict(conn: Connector) -> Dict[str, Any]:
        "position": list(conn.position),
        "normal": list(conn.normal),
        "x_dir": list(conn.x_dir),
-        "axis_rotation": float(conn.axis_rotation),
-        "offset": float(conn.offset),
+        "axis_rotation": _to_float(conn.axis_rotation, 0.0),
+        "offset": _to_float(conn.offset, 0.0),
        "assembly_component_id": conn.assembly_component_id,
        "source_obj_id": conn.source_obj_id,
+        "entity_type": conn.entity_type,
+        "normal_flip": bool(conn.normal_flip),
        "partner_ac_id": conn.partner_ac_id,
        "partner_connector_id": conn.partner_connector_id,
        "is_grounded": bool(conn.is_grounded),
@@ -362,15 +508,17 @@ def _connector_to_dict(conn: Connector) -> Dict[str, Any]:

 def _connector_from_dict(data: Dict[str, Any]) -> Connector:
    conn = Connector(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        name=data.get("name", "Untitled Connector"),
        position=_to_3tuple(data.get("position")),
        normal=_to_3tuple(data.get("normal")),
        x_dir=_to_3tuple(data.get("x_dir")),
-        axis_rotation=float(data.get("axis_rotation", 0.0)),
-        offset=float(data.get("offset", 0.0)),
+        axis_rotation=_to_float(data.get("axis_rotation"), 0.0),
+        offset=_to_float(data.get("offset"), 0.0),
        assembly_component_id=data.get("assembly_component_id", ""),
        source_obj_id=data.get("source_obj_id", ""),
+        entity_type=data.get("entity_type", ""),
+        normal_flip=bool(data.get("normal_flip", False)),
    )
    conn.partner_ac_id = data.get("partner_ac_id")
    conn.partner_connector_id = data.get("partner_connector_id")
@@ -389,14 +537,24 @@ def _assembly_component_to_dict(ac: AssemblyComponent) -> Dict[str, Any]:
        "position": _coerce_listlike(ac.position),
        "rotation": _coerce_listlike(ac.rotation),
        "connectors": {cid: _connector_to_dict(c) for cid, c in ac.connectors.items()},
+        # Instance-local sketches + per-body modifier ops (kept apart from
+        # the shared component so save/load never mutates the base model).
+        "sketches": {sid: _sketch_to_dict(sk) for sid, sk in ac.sketches.items()},
+        "modifiers": {
+            bid: [_feature_to_dict(f) for f in mods]
+            for bid, mods in ac.modifiers.items()
+        },
        "created_at": ac.created_at.isoformat() if ac.created_at else None,
        "modified_at": ac.modified_at.isoformat() if ac.modified_at else None,
    }

-
-def _assembly_component_from_dict(data: Dict[str, Any]) -> AssemblyComponent:
+def _assembly_component_from_dict(
+    data: Dict[str, Any],
+    component: Optional[Component] = None,
+    sketch_geometry_loader: Optional[Callable[[str], Optional[OCCGeometryObject]]] = None,
+) -> AssemblyComponent:
    ac = AssemblyComponent(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        component_id=data.get("component_id", ""),
        name=data.get("name", "Untitled Instance"),
        position=_to_3vec(data.get("position")),
@@ -406,6 +564,36 @@ def _assembly_component_from_dict(data: Dict[str, Any]) -> AssemblyComponent:
    ac.modified_at = _parse_iso(data.get("modified_at"))
    for cid, c_data in (data.get("connectors") or {}).items():
        ac.connectors[cid] = _connector_from_dict(c_data)
+
+    # Instance-local sketches first, so modifier sketch references can
+    # resolve against them (they live in component-local coordinates).
+    for sid, sk_data in (data.get("sketches") or {}).items():
+        try:
+            ac.sketches[sid] = _sketch_from_dict(sk_data, sketch_geometry_loader)
+        except Exception:
+            logger.warning("Skipping corrupt instance sketch %s", sid)
+
+    # Modifiers resolve sketch refs against the owning component's sketches
+    # first, then this instance's own sketches.
+    registry: Dict[str, Sketch] = {}
+    if component is not None:
+        registry.update(component.sketches)
+    registry.update(ac.sketches)
+    for bid, f_list in (data.get("modifiers") or {}).items():
+        kept: List[Feature] = []
+        for f_data in f_list or []:
+            try:
+                feat = _feature_from_dict(f_data, registry)
+            except Exception:
+                logger.warning("Skipping corrupt instance modifier on body %s", bid)
+                continue
+            # A sketch-based op whose sketch failed to load can never
+            # replay — dropping it keeps the rest of the chain usable.
+            if feat.operation in ("extrude", "cut", "union", "revolve") and feat.sketch is None:
+                continue
+            kept.append(feat)
+        if kept:
+            ac.modifiers[bid] = kept
    return ac


@@ -422,7 +610,7 @@ def _assembly_connection_to_dict(c: AssemblyConnection) -> Dict[str, Any]:

 def _assembly_connection_from_dict(data: Dict[str, Any]) -> AssemblyConnection:
    conn = AssemblyConnection(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        first_ac_id=data.get("first_ac_id", ""),
        second_ac_id=data.get("second_ac_id", ""),
        first_connector_id=data.get("first_connector_id"),
@@ -443,22 +631,146 @@ def _assembly_to_dict(asm: Assembly) -> Dict[str, Any]:
        "modified_at": asm.modified_at.isoformat() if asm.modified_at else None,
    }

-
-def _assembly_from_dict(data: Dict[str, Any]) -> Assembly:
+def _assembly_from_dict(
+    data: Dict[str, Any],
+    components: Optional[Dict[str, Component]] = None,
+    sketch_geometry_loader: Optional[Callable[[str], Optional[OCCGeometryObject]]] = None,
+) -> Assembly:
    asm = Assembly(
-        id=data.get("id") or None,
+        id=_saved_id(data),
        name=data.get("name", "Untitled Assembly"),
        active_assembly_component=data.get("active_assembly_component"),
    )
    asm.created_at = _parse_iso(data.get("created_at"))
    asm.modified_at = _parse_iso(data.get("modified_at"))
    for cid, ac_data in (data.get("components") or {}).items():
-        asm.components[cid] = _assembly_component_from_dict(ac_data)
-    for c_data in (data.get("connections") or []):
+        comp = (components or {}).get(ac_data.get("component_id", ""))
+        asm.components[cid] = _assembly_component_from_dict(
+            ac_data, component=comp, sketch_geometry_loader=sketch_geometry_loader
+        )
+    for c_data in data.get("connections") or []:
        asm.connections.append(_assembly_connection_from_dict(c_data))
    return asm


+def _drawing_view_to_dict(v: DrawingView) -> Dict[str, Any]:
+    return {
+        "id": v.id,
+        "kind": v.kind,
+        "name": v.name,
+        "direction": _coerce_listlike(v.direction),
+        "up_vector": _coerce_listlike(v.up_vector),
+        "show_hidden_lines": bool(v.show_hidden_lines),
+        "show_centerlines": bool(v.show_centerlines),
+        "scale": _to_float(v.scale, 1.0),
+        "sheet_origin": _coerce_listlike(v.sheet_origin),
+    }
+
+
+def _drawing_view_from_dict(data: Dict[str, Any]) -> DrawingView:
+    view = DrawingView(
+        id=_saved_id(data),
+        kind=data.get("kind", "front"),
+        name=data.get("name"),
+        direction=_to_3tuple(data.get("direction")) or None,
+        up_vector=_to_3tuple(data.get("up_vector")) or None,
+        show_hidden_lines=bool(data.get("show_hidden_lines", False)),
+        show_centerlines=bool(data.get("show_centerlines", False)),
+        scale=_to_float(data.get("scale"), 1.0),
+    )
+    origin = data.get("sheet_origin")
+    if isinstance(origin, (list, tuple)) and len(origin) >= 2:
+        view.sheet_origin = (_to_float(origin[0]), _to_float(origin[1]))
+    return view
+
+
+def _drawing_annotation_to_dict(a: DrawingAnnotation) -> Dict[str, Any]:
+    return {
+        "id": a.id,
+        "kind": a.kind,
+        "text": a.text,
+        "visible": bool(a.visible),
+        "references": list(a.references),
+        "sheet_position": _coerce_listlike(a.sheet_position),
+        "view_id": a.view_id,
+        "anchors": [list(pt) for pt in a.anchors],
+        "dimension_kind": a.dimension_kind,
+        "direction": _coerce_listlike(a.direction),
+    }
+
+
+def _drawing_annotation_from_dict(data: Dict[str, Any]) -> DrawingAnnotation:
+    ann = DrawingAnnotation(
+        id=_saved_id(data),
+        kind=data.get("kind", "dimension"),
+        text=data.get("text"),
+        visible=bool(data.get("visible", True)),
+        references=list(data.get("references") or []),
+        view_id=data.get("view_id", ""),
+        dimension_kind=data.get("dimension_kind", ""),
+    )
+    pos = data.get("sheet_position")
+    if isinstance(pos, (list, tuple)) and len(pos) >= 2:
+        ann.sheet_position = (_to_float(pos[0]), _to_float(pos[1]))
+    anchors = data.get("anchors") or []
+    for pt in anchors:
+        if isinstance(pt, (list, tuple)) and len(pt) >= 2:
+            ann.anchors.append((_to_float(pt[0]), _to_float(pt[1])))
+    direction = data.get("direction")
+    if isinstance(direction, (list, tuple)) and len(direction) >= 2:
+        ann.direction = (_to_float(direction[0]), _to_float(direction[1]))
+    return ann
+
+
+def _technical_drawing_to_dict(d: TechnicalDrawing) -> Dict[str, Any]:
+    return {
+        "id": d.id,
+        "name": d.name,
+        "source_kind": d.source_kind,
+        "source_id": d.source_id,
+        "views": [_drawing_view_to_dict(v) for v in d.views],
+        "annotations": [_drawing_annotation_to_dict(a) for a in d.annotations],
+        "title": d.title,
+        "part_number": d.part_number,
+        "material": d.material,
+        "revision": d.revision,
+        "notes": d.notes,
+        "sheet_size": d.sheet_size,
+        "units": d.units,
+        "auto_dimensions": bool(d.auto_dimensions),
+        "auto_views": bool(d.auto_views),
+        "created_at": d.created_at.isoformat() if d.created_at else None,
+        "modified_at": d.modified_at.isoformat() if d.modified_at else None,
+    }
+
+
+def _technical_drawing_from_dict(data: Dict[str, Any]) -> TechnicalDrawing:
+    drawing = TechnicalDrawing(
+        id=_saved_id(data),
+        name=data.get("name", "Untitled Drawing"),
+        source_kind=data.get("source_kind", "component"),
+        source_id=data.get("source_id", ""),
+        title=data.get("title", ""),
+        part_number=data.get("part_number", ""),
+        material=data.get("material", ""),
+        revision=data.get("revision", ""),
+        notes=data.get("notes", ""),
+        # The renderer only supports the A4 ISO 5457 sheet; normalize
+        # legacy drawings (stored as A3) instead of surfacing stale sizes.
+        sheet_size="A4",
+        units=data.get("units", "mm"),
+        auto_dimensions=bool(data.get("auto_dimensions", False)),
+        auto_views=bool(data.get("auto_views", True)),
+    )
+    drawing.created_at = _parse_iso(data.get("created_at"))
+    drawing.modified_at = _parse_iso(data.get("modified_at"))
+    for v_data in data.get("views") or []:
+        drawing.views.append(_drawing_view_from_dict(v_data))
+    for a_data in data.get("annotations") or []:
+        drawing.annotations.append(_drawing_annotation_from_dict(a_data))
+    return drawing
+
+
 def _project_to_dict(
    project: Project,
    view_state: Optional[Dict[str, Any]] = None,
@@ -471,6 +783,7 @@ def _project_to_dict(
        "active_assembly": project.active_assembly,
        "components": {cid: _component_to_dict(c) for cid, c in project.components.items()},
        "assemblies": {aid: _assembly_to_dict(a) for aid, a in project.assemblies.items()},
+        "drawings": [_technical_drawing_to_dict(d) for d in project.drawings],
        "created_at": project.created_at.isoformat() if project.created_at else None,
        "modified_at": project.modified_at.isoformat() if project.modified_at else None,
        "view_state": view_state or {},
@@ -517,7 +830,9 @@ def _read_step_bytes(
        with open(tmp_path, "wb") as f:
            f.write(data)
        geom = kernel.import_step(tmp_path)
-        return geom
+        from typing import cast
+
+        return cast(OCCGeometryObject, geom)
    except Exception as exc:
        logger.warning("Failed to read STEP: %s", exc)
        return None
@@ -580,6 +895,20 @@ def save_project(
            arcname = f"bodies/{body_id}.step"
            body_files.append((arcname, step_bytes))
            manifest["components"][comp_id]["bodies"][body_id]["geometry_ref"] = arcname
+            # Base-snapshot STEP for migrated legacy bodies whose feature
+            # list starts with a frozen "base" geometry snapshot.
+            if (
+                body.features
+                and body.features[0].operation == "base"
+                and body.features[0].geometry is not None
+            ):
+                base_bytes = _write_step_for_body(kernel, body.features[0].geometry)
+                if base_bytes is not None:
+                    base_arcname = f"bodies/{body_id}_base.step"
+                    body_files.append((base_arcname, base_bytes))
+                    manifest["components"][comp_id]["bodies"][body_id]["base_geometry_ref"] = (
+                        base_arcname
+                    )

    # Per-sketch STEP files (solved face geometry).
    sketch_files: List[Tuple[str, bytes]] = []
@@ -615,6 +944,40 @@ def save_project(
            sketch_files.append((arcname, step_bytes))
            manifest["components"][comp_id]["sketches"][sketch_id]["geometry_ref"] = arcname

+    # Instance-local sketches (assembly components) get the same sidecar
+    # treatment as component sketches; the manifest nodes are patched in
+    # place under the assembly's component entry.
+    for asm_id, asm in project.assemblies.items():
+        for ac_id, ac in asm.components.items():
+            for sketch_id, sketch in ac.sketches.items():
+                node = manifest["assemblies"][asm_id]["components"][ac_id]["sketches"].get(sketch_id)
+                if node is None:
+                    continue
+                occ = sketch.occ_sketch.to_dict() if sketch.occ_sketch is not None else None
+                meta = {
+                    "id": sketch.id,
+                    "name": sketch.name,
+                    "workplane_origin": _coerce_listlike(sketch.workplane_origin),
+                    "workplane_normal": _coerce_listlike(sketch.workplane_normal),
+                    "workplane_x_dir": _coerce_listlike(sketch.workplane_x_dir),
+                    "is_solved": bool(sketch.is_solved),
+                    "is_fully_constrained": bool(sketch.is_fully_constrained),
+                    "occ_sketch": occ,
+                }
+                meta_arc = f"sketches/{sketch_id}/meta.json"
+                sketch_meta_files.append((meta_arc, _to_json(meta).encode("utf-8")))
+                node["occ_sketch"] = None
+                node["occ_sketch_ref"] = meta_arc
+
+                if sketch.geometry is None:
+                    continue
+                step_bytes = _write_step_for_body(kernel, sketch.geometry)
+                if step_bytes is None:
+                    continue
+                arcname = f"sketches/{sketch_id}/solved.step"
+                sketch_files.append((arcname, step_bytes))
+                node["geometry_ref"] = arcname
+
    # Write the ZIP.  Use a temp file + rename so a partial write can't
    # clobber an existing good file.
    tmp_fd, tmp_path = tempfile.mkstemp(suffix=".fluency")
@@ -672,13 +1035,17 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:

    with zipfile.ZipFile(filepath, "r") as zipf:
        manifest_raw = zipf.read("project.json")
-        manifest = json.loads(manifest_raw.decode("utf-8"))
+        try:
+            manifest = json.loads(manifest_raw.decode("utf-8"))
+        except (ValueError, UnicodeDecodeError) as exc:
+            raise RuntimeError(f"Corrupt project file (bad JSON): {filepath}") from exc
        view_state: Dict[str, Any] = manifest.get("view_state") or {}

        # If a sketch's occ_sketch is referenced as a separate file, read
        # it in now and patch the manifest so _sketch_from_dict sees it.
-        for comp_id, comp_data in (manifest.get("components") or {}).items():
-            for sk_id, sk_data in (comp_data.get("sketches") or {}).items():
+        # Applies to both component sketches and instance-local sketches.
+        def _patch_sketch_sidecars(sketches_dict: Dict[str, Any]) -> None:
+            for sk_id, sk_data in (sketches_dict or {}).items():
                ref = sk_data.get("occ_sketch_ref")
                if not ref:
                    continue
@@ -687,15 +1054,30 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:
                except KeyError:
                    logger.warning("Sketch meta missing in archive: %s", ref)
                    continue
-                meta = json.loads(meta_bytes.decode("utf-8"))
+                try:
+                    meta = json.loads(meta_bytes.decode("utf-8"))
+                except (ValueError, UnicodeDecodeError) as exc:
+                    logger.warning("Sketch meta corrupt in archive: %s (%s)", ref, exc)
+                    continue
                sk_data["occ_sketch"] = meta.get("occ_sketch")
                # Workplane fields on the sketch-level file override the
                # embedded ones (source of truth lives in the sidecar).
-                for k in ("workplane_origin", "workplane_normal", "workplane_x_dir",
-                          "is_solved", "is_fully_constrained"):
+                for k in (
+                    "workplane_origin",
+                    "workplane_normal",
+                    "workplane_x_dir",
+                    "is_solved",
+                    "is_fully_constrained",
+                ):
                    if k in meta:
                        sk_data[k] = meta[k]

+        for comp_id, comp_data in (manifest.get("components") or {}).items():
+            _patch_sketch_sidecars(comp_data.get("sketches"))
+        for aid, a_data in (manifest.get("assemblies") or {}).items():
+            for ac_id, ac_data in (a_data.get("components") or {}).items():
+                _patch_sketch_sidecars(ac_data.get("sketches"))
+
        project = Project(
            name=manifest.get("name", "Untitled Project"),
            description=manifest.get("description", ""),
@@ -715,7 +1097,17 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:
            )

        for aid, a_data in (manifest.get("assemblies") or {}).items():
-            project.assemblies[aid] = _assembly_from_dict(a_data)
+            project.assemblies[aid] = _assembly_from_dict(
+                a_data,
+                components=project.components,
+                sketch_geometry_loader=sketch_geometry_loader,
+            )
+
+        for d_data in manifest.get("drawings") or []:
+            try:
+                project.drawings.append(_technical_drawing_from_dict(d_data))
+            except Exception as exc:
+                logger.warning("Skipping corrupt drawing in archive: %s", exc)

    # After all components are loaded, re-wire connector partner ids so
    # they point to the freshly-loaded AssemblyComponents.  (The dict
@@ -24,6 +24,7 @@ from fluency.ui.dialogs import (
    ExtrudeDialog,
    OffsetDialog,
    RevolveDialog,
+    ThreadDialog,
    WorkplaneOrientationDialog,
 )
 from fluency.ui.main_window import MainWindow
@@ -37,6 +38,7 @@ __all__ = [
    "ExtrudeDialog",
    "RevolveDialog",
    "OffsetDialog",
+    "ThreadDialog",
    "WorkplaneOrientationDialog",
    "main",
 ]
@@ -60,9 +60,9 @@ class Workplane:
        x = x / x_norm
        y = np.cross(n, x)
        y = y / np.linalg.norm(y)
-        self.normal = tuple(float(v) for v in n)
-        self.x_dir = tuple(float(v) for v in x)
-        self._y_dir = tuple(float(v) for v in y)
+        self.normal = (float(n[0]), float(n[1]), float(n[2]))
+        self.x_dir = (float(x[0]), float(x[1]), float(x[2]))
+        self._y_dir = (float(y[0]), float(y[1]), float(y[2]))

    @property
    def y_dir(self) -> Tuple[float, float, float]:
@@ -206,6 +206,101 @@ class Sketch:
        self.modified_at = datetime.now()


+@dataclass
+class Feature:
+    """
+    One operation in a body's parametric feature history.
+
+    Bodies rebuild their geometry by replaying their ordered feature
+    list from scratch (see ``Body.features``).  This is what makes
+    sketch edits propagate: a moved circle re-cuts at the new position
+    on a freshly rebuilt base instead of adding to the previous result.
+
+    ``operation`` is one of:
+      - "extrude": base solid, ``kernel.extrude`` of the sketch profile
+      - "revolve": base solid, ``kernel.revolve`` of the sketch profile
+      - "cut":    boolean difference of the running geometry with the
+                  extruded sketch profile
+      - "union":  boolean union of the running geometry with the
+                  extruded sketch profile
+      - "fillet": round a set of edges of the running geometry
+                  (``radius``, ``tangent_propagation``, ``scope``,
+                  ``edge_refs`` — see below)
+      - "chamfer": bevel a set of edges of the running geometry
+                  (same fields as "fillet"; ``radius`` holds the
+                  chamfer size)
+      - "mirror": mirror the running solid across a plane defined by
+                  ``mirror_plane_origin`` and ``mirror_plane_normal``.
+                  When ``keep_original`` is True (the default), the
+                  original solid is boolean-union'd with its mirror
+      - "array" / "pattern": repeat the running solid in a linear or
+                 circular array.  ``pattern_type`` is "linear" or
+                 "circular"; ``count`` is the total number of items
+                 (original + copies).  Linear uses ``direction``
+                 (unit vector) and ``spacing`` (mm between adjacent
+                 items); circular reuses ``axis`` + ``origin`` for the
+                 rotation axis and ``angle`` for the total angular
+                 span in degrees (copies evenly distributed).
+      - "base":   frozen geometry snapshot (``geometry`` field) — used
+                 to migrate legacy bodies whose original base feature
+                 is unknown.  Never the result of a user operation.
+    """
+
+    id: str = field(default_factory=lambda: str(uuid.uuid4()))
+    operation: str = "extrude"
+
+    sketch: Optional[Sketch] = None  # runtime ref; serialized as sketch_id
+    length: Optional[float] = None
+    symmetric: bool = False
+    invert: bool = False
+    through_all: bool = False
+    cut_all_bodies: bool = False
+    face_index: Optional[int] = None  # which sketch face was selected
+    angle: float = 360.0  # revolve only (degrees)
+    axis: Tuple[float, float, float] = (0, 0, 1)  # revolve only: unit axis vector
+    origin: Tuple[float, float, float] = (0.0, 0.0, 0.0)  # revolve only: axis point
+    axis_line_id: Optional[int] = None  # revolve only: sketch line entity used as axis
+
+    # "base" features only: frozen pre-feature geometry snapshot.
+    geometry: Optional[OCCGeometryObject] = None
+
+    # "fillet" / "chamfer" features only: radius (mm) of the round or the
+    # chamfer size, whether the op should extend along edges tangent to the
+    # picked ones, the edge scope ("selected" = edges between the two
+    # picked faces, "all" = every edge of the body), and stable
+    # fingerprints of the selected edges so the replay can re-find them
+    # after the base geometry is rebuilt.
+    radius: Optional[float] = None
+    tangent_propagation: bool = False
+    scope: str = "selected"
+    edge_refs: List[str] = field(default_factory=list)
+
+    # FaceKey references for fillet/chamfer: stable face classification
+    # that survives sketch dimension changes.  ``face_keys`` is a list of
+    # (FaceKey, FaceKey) pairs — one pair per user-picked face;
+    # ``face_keys_sketch_id`` tracks which sketch produced the body these
+    # faces belong to.
+    face_keys: Optional[List[Tuple[Dict[str, Any], Dict[str, Any]]]] = None
+    face_keys_sketch_id: Optional[str] = None
+
+    # "array" / "pattern" features only: repeat the running solid.
+    # ``pattern_type`` is "linear" or "circular"; ``count`` is the total
+    # number of items including the original.  Linear arrays use
+    # ``direction`` (unit vector) and ``spacing`` (mm); circular arrays
+    # reuse ``axis`` / ``origin`` / ``angle`` (total angular span, deg).
+    pattern_type: str = "linear"
+    count: int = 2
+    spacing: float = 10.0
+    direction: Tuple[float, float, float] = (1.0, 0.0, 0.0)
+
+    # "mirror" feature only: mirror plane definition.
+    mirror_plane_origin: Tuple[float, float, float] = (0.0, 0.0, 0.0)
+    mirror_plane_normal: Tuple[float, float, float] = (1.0, 0.0, 0.0)
+    keep_original: bool = True
+
+    created_at: datetime = field(default_factory=datetime.now)
+
+
@dataclass
 class Body:
    """
@@ -222,6 +317,12 @@ class Body:
    source_sketch: Optional[Sketch] = None
    source_operation: str = "extrude"

+    # Parametric feature history.  When non-empty, the body is rebuilt
+    # from scratch by replaying these features in order; the flat
+    # extrude_* / source_* fields below then only mirror the LAST
+    # feature for backward compatibility (old files, old code paths).
+    features: List[Feature] = field(default_factory=list)
+
    # Re-extrusion parameters — stored so the body can be rebuilt from
    # its source sketch when the sketch is edited.  None means the body
    # was not created by an extrude-type operation and cannot be auto-
@@ -232,6 +333,7 @@ class Body:
    extrude_cut: bool = False
    extrude_union: bool = False
    extrude_through_all: bool = False
+    extrude_cut_all_bodies: bool = False  # cut through all bodies in component
    extrude_face_index: Optional[int] = None  # which sketch face was selected
    extrude_target_body_id: Optional[str] = None  # for cut/union: target body id
    needs_update: bool = False  # True when source sketch changed since last extrude
@@ -385,6 +487,16 @@ class Connector:
    assembly_component_id: str = ""
    # Which body/face this connector was placed on (renderer obj_id).
    source_obj_id: str = ""
+    # Entity class the connector was picked on ("planar_face",
+    # "cylindrical_face", "edge", "vertex").  Used to re-locate the
+    # connector on rebuilt geometry: only features of the same class are
+    # considered, so a hole connector can never jump onto a flat face.
+    # Empty for legacy files (all classes are then searched).
+    entity_type: str = ""
+    # Flip chosen in the placement dialog (bolt enters from the opposite
+    # side).  Re-applied when a mated pair is re-solved so the original
+    # mate pose is reproduced exactly.
+    normal_flip: bool = False

    # --- Rigid-group pairing (set when two connectors are mated) ---
    # The id of the partner AssemblyComponent this connector is mated to.
@@ -404,6 +516,16 @@ class Connector:
    created_at: datetime = field(default_factory=datetime.now)
    modified_at: datetime = field(default_factory=datetime.now)

+    def __post_init__(self) -> None:
+        # Legacy files predate the entity_type field: recover it from the
+        # auto-generated connector name ("Conn cylindrical_face anchor") so
+        # relocation can restrict its search to the same feature class.
+        if not self.entity_type:
+            for t in ("cylindrical_face", "planar_face", "edge", "vertex"):
+                if self.name in (f"Conn {t} anchor", f"Conn {t} mover"):
+                    self.entity_type = t
+                    break
+

@dataclass
 class AssemblyComponent:
@@ -427,6 +549,20 @@ class AssemblyComponent:
    # Connectors defined on this component instance.
    connectors: Dict[str, Connector] = field(default_factory=dict)

+    # Instance-local (per-instantiation) state.  Kept separate from the
+    # shared component so per-instance work never leaks back into the base
+    # model.  ``sketches`` are instance-local sketches stored in
+    # component-local coordinates (so they stay valid when the instance is
+    # moved / rotated); ``modifiers`` maps body_id to an ordered list of
+    # Feature ops applied ON TOP of the live component body feature history
+    # when the instance geometry is rebuilt.
+    sketches: Dict[str, Sketch] = field(default_factory=dict)
+    modifiers: Dict[str, List[Feature]] = field(default_factory=dict)
+
+    # Runtime-only cache of rebuilt instance geometry (body_id -> geometry).
+    # Never serialized; invalidated on component updates and modifier edits.
+    geom_cache: Dict[str, Any] = field(default_factory=dict, repr=False)
+
    created_at: datetime = field(default_factory=datetime.now)
    modified_at: datetime = field(default_factory=datetime.now)

@@ -437,6 +573,8 @@ class AssemblyComponent:
        x_dir: Tuple[float, float, float],
        source_obj_id: str = "",
        name: Optional[str] = None,
+        entity_type: str = "",
+        normal_flip: bool = False,
    ) -> Connector:
        """Add a connector to this component instance."""
        conn = Connector(
@@ -446,6 +584,8 @@ class AssemblyComponent:
            x_dir=x_dir,
            assembly_component_id=self.id,
            source_obj_id=source_obj_id,
+            entity_type=entity_type,
+            normal_flip=normal_flip,
        )
        self.connectors[conn.id] = conn
        self.modified_at = datetime.now()
@@ -459,6 +599,45 @@ class AssemblyComponent:
            return True
        return False

+    def add_instance_sketch(self, sketch: Optional[Sketch] = None) -> Sketch:
+        """Add an instance-local sketch (component-local coordinates)."""
+        if sketch is None:
+            sketch = Sketch(name=f"Instance Sketch {len(self.sketches) + 1}")
+        self.sketches[sketch.id] = sketch
+        self.modified_at = datetime.now()
+        return sketch
+
+    def remove_instance_sketch(self, sketch_id: str) -> bool:
+        """Remove an instance sketch and every modifier that references it."""
+        if sketch_id not in self.sketches:
+            return False
+        del self.sketches[sketch_id]
+        for body_id in list(self.modifiers.keys()):
+            kept = [
+                f for f in self.modifiers[body_id]
+                if not (f.sketch is not None and f.sketch.id == sketch_id)
+            ]
+            if kept:
+                self.modifiers[body_id] = kept
+            else:
+                del self.modifiers[body_id]
+            self.geom_cache.pop(body_id, None)
+        self.modified_at = datetime.now()
+        return True
+
+    def add_modifier(self, body_id: str, feat: Feature) -> Feature:
+        """Append a modifier op to *body_id*'s instance-local history."""
+        self.modifiers.setdefault(body_id, []).append(feat)
+        self.geom_cache.pop(body_id, None)
+        self.modified_at = datetime.now()
+        return feat
+
+    def invalidate_geom_cache(self, body_id: Optional[str] = None) -> None:
+        """Drop cached rebuilt instance geometry (one body, or all)."""
+        if body_id is None:
+            self.geom_cache.clear()
+        else:
+            self.geom_cache.pop(body_id, None)

@dataclass
 class AssemblyConnection:
@@ -622,6 +801,10 @@ class Project:
    assemblies: Dict[str, Assembly] = field(default_factory=dict)
    active_assembly: Optional[str] = None

+    # Technical drawings keyed to their source component/assembly.
+    # Manual dimensions and view options added in the drawing workbench
+    # are persisted here so they survive save/load.
+    drawings: List["TechnicalDrawing"] = field(default_factory=list)
    kernel: OCGeometryKernel = field(default_factory=OCGeometryKernel)

    created_at: datetime = field(default_factory=datetime.now)
@@ -698,36 +881,21 @@ class Project:
        """Look up a component by id across all project components."""
        return self.components.get(component_id)

-    def add_component(self, component: Optional[Component] = None) -> Component:
-        """Add a component to the project."""
-        if component is None:
-            component = Component(name=f"Component {len(self.components) + 1}")
-        self.components[component.id] = component
-        if self.active_component is None:
-            self.active_component = component.id
-        self.modified_at = datetime.now()
-        return component
+    # ── Drawing helpers ──

-    def remove_component(self, component_id: str) -> bool:
-        """Remove a component from the project."""
-        if component_id in self.components:
-            del self.components[component_id]
-            if self.active_component == component_id:
-                self.active_component = next(iter(self.components.keys()), None)
-            self.modified_at = datetime.now()
-            return True
-        return False
-
-    def get_active_component(self) -> Optional[Component]:
-        """Get the currently active component."""
-        if self.active_component and self.active_component in self.components:
-            return self.components[self.active_component]
+    def get_drawing_for(self, source_kind: str, source_id: str) -> Optional["TechnicalDrawing"]:
+        """Return the drawing bound to *(source_kind, source_id)*, if any."""
+        for drawing in self.drawings:
+            if drawing.source_kind == source_kind and drawing.source_id == source_id:
+                return drawing
        return None

-    def set_active_component(self, component_id: Optional[str]) -> None:
-        """Set the active component."""
-        self.active_component = component_id
+    def add_drawing(self, drawing: "TechnicalDrawing") -> "TechnicalDrawing":
+        """Register *drawing* with the project and return it."""
+        self.drawings.append(drawing)
        self.modified_at = datetime.now()
+        return drawing
+

    def export_step(self, filepath: str) -> bool:
        """Export all visible bodies to STEP."""
@@ -796,3 +964,102 @@ class Project:
        for comp in self.components.values():
            sketches.extend(comp.sketches.values())
        return sketches
+
+    def compute_source_fingerprint(
+        self, source_kind: str, source_id: str
+    ) -> str:
+        """Compute a simple fingerprint for a source reference."""
+        import hashlib
+        data = f"{source_kind}:{source_id}"
+        return hashlib.sha256(data.encode()).hexdigest()[:16]
+# ── Technical Drawing models ───────────────────────────────────────────────
+
+@dataclass
+class DrawingView:
+    """One projected view in a technical drawing."""
+
+    id: str = field(default_factory=lambda: str(uuid.uuid4()))
+    kind: str = "front"  # front, back, top, bottom, right, left, isometric, custom
+    name: Optional[str] = None  # human-readable label; defaults from kind
+
+    # View direction and up vector in world coords (for custom views).
+    # Ignored when kind is one of the standard presets.
+    direction: Optional[Tuple[float, float, float]] = None
+    up_vector: Optional[Tuple[float, float, float]] = None
+
+    show_hidden_lines: bool = False
+    show_centerlines: bool = False
+    scale: float = 1.0
+
+    # Sheet position (mm from sheet origin) — set by layout engine.
+    sheet_origin: Tuple[float, float] = (0.0, 0.0)
+
+
+@dataclass
+class DrawingAnnotation:
+    """One annotation (dimension or note) on a technical drawing."""
+
+    id: str = field(default_factory=lambda: str(uuid.uuid4()))
+    kind: str = "dimension"  # dimension, note, tolerance, surface_finish, weld_symbol
+    text: Optional[str] = None
+    visible: bool = True
+
+    # References to DrawingCandidate keys this annotation is bound to.
+    references: List[str] = field(default_factory=list)
+
+    # Sheet position (mm). For dimensions, anchor point; for notes, placement.
+    sheet_position: Tuple[float, float] = (0.0, 0.0)
+
+    # Associated view id (empty means global/note block).
+    view_id: str = ""
+
+    # Manual-dimension geometry in view-plane model coordinates (model
+    # units in the view's projection plane).  Populated for user-placed
+    # dimensions, empty for reference-based annotations:
+    #   "length":   (point_on_edge1, point_on_edge2) — closest points
+    #   "diameter": (left, right) — antipodal points across the centre
+    #   "angle":    (vertex, arm1_point, arm2_point)
+    anchors: List[Tuple[float, float]] = field(default_factory=list)
+
+    # Sub-kind of the manual dimension: "length" | "diameter" | "angle".
+    # Empty for non-dimension annotations.
+    dimension_kind: str = ""
+
+    # Unit vector along the measured distance in view-plane coordinates
+    # (length dimensions only).  The model→sheet transform is a uniform
+    # scale + translation, so the direction is valid in sheet space too.
+    direction: Optional[Tuple[float, float]] = None
+
+
+@dataclass
+class TechnicalDrawing:
+    """A complete technical drawing definition."""
+
+    id: str = field(default_factory=lambda: str(uuid.uuid4()))
+    name: str = "Untitled Drawing"
+
+    # Source geometry reference.
+    source_kind: str = "component"  # component, assembly
+    source_id: str = ""
+
+    views: List[DrawingView] = field(default_factory=list)
+    annotations: List[DrawingAnnotation] = field(default_factory=list)
+
+    # Title block metadata.
+    title: str = ""
+    part_number: str = ""
+    material: str = ""
+    revision: str = ""
+    notes: str = ""
+
+    # Sheet size (A0..A4 or custom mm). Default A4 (ISO 5457 template).
+    sheet_size: str = "A4"
+    units: str = "mm"  # mm, in
+
+    # Auto-generation flags.  Auto dimensions are opt-in: the drawing
+    # workbench shows them only while the user has the toggle enabled.
+    auto_dimensions: bool = False
+    auto_views: bool = True
+
+    created_at: datetime = field(default_factory=datetime.now)
+    modified_at: datetime = field(default_factory=datetime.now)
@@ -187,19 +187,29 @@ class SolverSketch(SolverSystem):
    def constrain_distance(
        self, entity_a, entity_b, distance: float
    ) -> bool:
-        """Constrain distance between point-point or point-line."""
+        """Constrain distance between point-point or point-line.
+
+        python-solvespace's ``distance`` accepts (point, line) ordering only,
+        so line-point pairs are normalised; line-line pairs and a point
+        constrained to itself are rejected (the solver cannot hold them).
+        """
        try:
-            handle_a = entity_a.handle if isinstance(entity_a, SolverPoint) else entity_a.handle
-            handle_b = entity_b.handle if isinstance(entity_b, SolverPoint) else entity_b.handle
+            if isinstance(entity_a, SolverLine) and isinstance(entity_b, SolverLine):
+                logger.warning("distance: line-to-line distance is not supported")
+                return False
+            if isinstance(entity_a, SolverLine) and isinstance(entity_b, SolverPoint):
+                # Normalise to (point, line) ordering.
+                entity_a, entity_b = entity_b, entity_a
+            if entity_a is entity_b and distance != 0.0:
+                logger.warning("distance: refusing point-to-itself constraint")
+                return False
+            handle_a = entity_a.handle
+            handle_b = entity_b.handle

            if isinstance(entity_a, SolverPoint) and isinstance(entity_b, SolverLine):
                self.distance(handle_a, handle_b, distance, self.wp)
-            elif isinstance(entity_a, SolverLine) and isinstance(entity_b, SolverPoint):
-                self.distance(handle_b, handle_a, distance, self.wp)
            elif isinstance(entity_a, SolverPoint) and isinstance(entity_b, SolverPoint):
                self.distance(handle_a, handle_b, distance, self.wp)
-            elif isinstance(entity_a, SolverLine) and isinstance(entity_b, SolverLine):
-                self.distance(handle_a, handle_b, distance, self.wp)
            else:
                logger.warning(f"distance: unsupported types {type(entity_a)}, {type(entity_b)}")
                return False
@@ -0,0 +1,213 @@
+"""Tests for the A4 ISO 5457 sheet: layout regions, first-angle view
+ordering, sheet furniture primitives, scale formatting, and the A4
+normalisation of drawings loaded from .fluency files.
+"""
+
+import os
+import sys
+import unittest
+
+# Allow running this file directly: ``python tests/test_iso5457_sheet.py``.
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), os.pardir, "src"))
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+from fluency.models.data_model import DrawingView, TechnicalDrawing
+from fluency.technical_drawing import (
+    _SHEET_HEIGHT_MM,
+    _SHEET_WIDTH_MM,
+    _format_drawing_scale,
+    _layout_views_on_sheet,
+    _sheet_frame_primitives,
+)
+
+
+def _view(kind):
+    return DrawingView(kind=kind, name=kind)
+
+
+class TestSheetSize(unittest.TestCase):
+    """The workbench renders a single A4 landscape sheet."""
+
+    def test_a4_dimensions(self):
+        self.assertEqual((_SHEET_WIDTH_MM, _SHEET_HEIGHT_MM), (297.0, 210.0))
+
+    def test_default_drawing_is_a4(self):
+        self.assertEqual(TechnicalDrawing().sheet_size, "A4")
+
+
+class TestScaleFormatting(unittest.TestCase):
+    """Title-block scale field formatting (``N : 1`` / ``1 : N``)."""
+
+    def test_none_and_one(self):
+        self.assertEqual(_format_drawing_scale(None), "1 : 1")
+        self.assertEqual(_format_drawing_scale(0.0), "1 : 1")
+        self.assertEqual(_format_drawing_scale(1.0), "1 : 1")
+
+    def test_enlarged(self):
+        self.assertEqual(_format_drawing_scale(2.0), "2 : 1")
+        self.assertEqual(_format_drawing_scale(1.5), "1.5 : 1")
+
+    def test_reduced(self):
+        self.assertEqual(_format_drawing_scale(0.5), "1 : 2")
+        self.assertEqual(_format_drawing_scale(0.33333), "1 : 3")
+
+
+class TestFirstAngleLayout(unittest.TestCase):
+    """View slots stay inside the ISO 5457 drawing-space frame, clear the
+    title-block reserve zone, and follow first-angle ordering (view from
+    the right left of front, view from the left right of front, top view
+    below front)."""
+
+    def _slots(self, kinds):
+        bboxes = {k: (0.0, 0.0, 40.0, 30.0) for k in kinds}
+        slots, scale, _rots = _layout_views_on_sheet(
+            [_view(k) for k in kinds], bboxes
+        )
+        return slots, scale
+
+    def test_slots_inside_frame(self):
+        slots, scale = self._slots(
+            ("front", "top", "right", "left", "isometric")
+        )
+        self.assertIsNotNone(scale)
+        self.assertGreater(scale, 0)
+        for vid, (x, y, w, h) in slots.items():
+            # Drawing-space frame: 20..287 x 10..200.
+            self.assertGreaterEqual(x, 19.9, vid)
+            self.assertGreaterEqual(y, 9.9, vid)
+            self.assertLessEqual(x + w, 287.1, vid)
+            self.assertLessEqual(y + h, 200.1, vid)
+            # Title-block reserve zone: x >= 102, y <= 64.
+            self.assertTrue(
+                x + w <= 102.01 or y + h <= 0.01 or y >= 63.99,
+                (vid, (x, y, w, h)),
+            )
+
+    def test_first_angle_ordering(self):
+        slots, _ = self._slots(("front", "top", "right", "left"))
+        xf, wf = slots["front"][0], slots["front"][2]
+        yf = slots["front"][1]
+        # View from the right sits left of the front view.
+        self.assertLessEqual(
+            slots["right"][0] + slots["right"][2], xf + 0.01
+        )
+        # View from the left sits right of the front view.
+        self.assertGreaterEqual(slots["left"][0], xf + wf + 0.01)
+        # Top view sits below the front view.
+        self.assertLessEqual(slots["top"][1] + slots["top"][3], yf + 0.01)
+
+    def test_single_view_centered_upright(self):
+        slots, scale, rots = _layout_views_on_sheet(
+            [_view("front")], {"front": (0.0, 0.0, 40.0, 30.0)}
+        )
+        self.assertIsNotNone(scale)
+        self.assertEqual(rots.get("front", 0.0), 0.0)
+        self.assertGreater(scale, 0)
+        x, y, w, h = slots["front"]
+        self.assertGreaterEqual(x, 19.9)
+        self.assertGreaterEqual(y, 9.9)
+
+
+class TestSheetFurniture(unittest.TestCase):
+    """ISO 5457 furniture primitives mirror the reference SVG template."""
+
+    def _prims(self):
+        d = TechnicalDrawing(
+            title="Test Bracket",
+            part_number="PN-42",
+            material="Alu 6082",
+            revision="B",
+        )
+        return _sheet_frame_primitives(d, "1 : 2")
+
+    def test_all_geometry_inside_sheet(self):
+        for p in self._prims():
+            for (x, y) in p.points:
+                self.assertGreaterEqual(x, -0.01)
+                self.assertLessEqual(x, 297.01)
+                self.assertGreaterEqual(y, -0.01)
+                self.assertLessEqual(y, 210.01)
+
+    def test_drawing_space_frame(self):
+        # Frame rect 20,10 267x190: four edges present as line prims.
+        lines = [
+            (tuple(p.points[0]), tuple(p.points[1]))
+            for p in self._prims()
+            if p.kind == "line" and p.style == "frame"
+        ]
+        for a, b in (
+            ((20.0, 10.0), (287.0, 10.0)),
+            ((287.0, 10.0), (287.0, 200.0)),
+            ((287.0, 200.0), (20.0, 200.0)),
+            ((20.0, 200.0), (20.0, 10.0)),
+        ):
+            self.assertIn((a, b), lines)
+
+    def test_grid_reference_labels(self):
+        texts = [p.text for p in self._prims() if p.kind == "text" and p.text]
+        for t in ("1", "2", "3", "4", "5", "6", "A", "B", "C", "D", "A4"):
+            self.assertIn(t, texts)
+
+    def test_title_block_fields(self):
+        texts = [p.text for p in self._prims() if p.kind == "text" and p.text]
+        for expect in (
+            "Owner:",
+            "Drawing number:",
+            "Revision:",
+            "Issue date:",
+            "Sheet:",
+            "Language:",
+            "Title:",
+            "Approved by:",
+            "Created by:",
+            "Document type:",
+            "Part Material:",
+            "General tolerances:",
+            "Scale:",
+            "Test Bracket",
+            "PN-42",
+            "Alu 6082",
+            "B",
+            "1 : 2",
+            "EN",
+            "1 / 1",
+            "ISO 2768-m",
+            "Component Drawing",
+        ):
+            self.assertIn(expect, texts)
+
+    def test_first_angle_projection_symbol(self):
+        # Two concentric circles at the symbol centre (273, 58) in sheet
+        # coords (SVG y-down 152 → 210 - 152 = 58).
+        circles = [
+            p
+            for p in self._prims()
+            if p.kind == "circle" and p.center == (273.0, 58.0)
+        ]
+        self.assertEqual(len(circles), 2)
+        self.assertEqual(
+            sorted(c.radius for c in circles if c.radius), [2.5, 5.0]
+        )
+
+
+class TestSheetSizeNormalisation(unittest.TestCase):
+    """Drawings stored as A3 in .fluency files load as A4 — the renderer
+    only supports the A4 ISO 5457 sheet."""
+
+    def test_legacy_a3_loads_as_a4(self):
+        from fluency.io.project_io import _technical_drawing_from_dict
+
+        d = _technical_drawing_from_dict(
+            {
+                "id": "x",
+                "source_kind": "component",
+                "source_id": "c",
+                "sheet_size": "A3",
+            }
+        )
+        self.assertEqual(d.sheet_size, "A4")
+
+
+if __name__ == "__main__":
+    unittest.main()
@@ -13,16 +13,58 @@ import unittest
 # Allow running this file directly: ``python tests/test_project_io.py``.
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), os.pardir, "src"))

-from fluency.io.project_io import save_project, load_project
+from fluency.io.project_io import save_project, load_project, _feature_to_dict, _feature_from_dict
 from fluency.models.data_model import (
    Project,
    Component,
    Body,
+    Sketch,
    Workplane,
    Assembly,
+    Feature,
 )


+class TestRevolveAxisSerialization(unittest.TestCase):
+    """Revolve features persist their revolve axis across save/load."""
+
+    def test_axis_round_trip(self):
+        sk = Sketch()
+        feat = Feature(
+            operation="revolve",
+            angle=180.0,
+            axis=(1, 0, 0),
+            origin=(10.0, 5.0, 0.0),
+            axis_line_id=7,
+        )
+        feat.sketch = sk
+        data = _feature_to_dict(feat)
+        self.assertEqual(data["axis"], [1.0, 0.0, 0.0])
+        self.assertEqual(data["origin"], [10.0, 5.0, 0.0])
+        self.assertEqual(data["axis_line_id"], 7)
+        restored = _feature_from_dict(data, {sk.id: sk})
+        self.assertEqual(tuple(restored.axis), (1.0, 0.0, 0.0))
+        self.assertEqual(tuple(restored.origin), (10.0, 5.0, 0.0))
+        self.assertEqual(restored.axis_line_id, 7)
+        self.assertEqual(restored.angle, 180.0)
+
+    def test_default_axis(self):
+        """Old files without axis fields fall back to Z axis at the origin."""
+        sk = Sketch()
+        data = _feature_to_dict(Feature(operation="revolve", angle=90.0))
+        restored = _feature_from_dict(data, {sk.id: sk})
+        self.assertEqual(tuple(restored.axis), (0, 0, 1))
+        self.assertEqual(tuple(restored.origin), (0.0, 0.0, 0.0))
+        self.assertIsNone(restored.axis_line_id)
+        # legacy file without the keys
+        del data["axis"]
+        del data["origin"]
+        del data["axis_line_id"]
+        restored = _feature_from_dict(data, {sk.id: sk})
+        self.assertEqual(tuple(restored.axis), (0, 0, 1))
+        self.assertEqual(tuple(restored.origin), (0.0, 0.0, 0.0))
+
+
 class TestProjectIO(unittest.TestCase):
    """Round-trip the same project through save/load and check equivalence."""

@@ -892,7 +892,7 @@ class Ui_fluencyCAD(object):
        self.groupBox.setTitle(QCoreApplication.translate("fluencyCAD", u"Modify", None))
        self.pb_revop.setText(QCoreApplication.translate("fluencyCAD", u"Rev", None))
        self.pb_extrdop.setText(QCoreApplication.translate("fluencyCAD", u"Extrd", None))
-        self.pb_arrayop.setText(QCoreApplication.translate("fluencyCAD", u"Arry", None))
+        self.pb_arrayop.setText(QCoreApplication.translate("fluencyCAD", u"Array", None))
        self.pb_cutop.setText(QCoreApplication.translate("fluencyCAD", u"Cut", None))
        self.pb_combop.setText(QCoreApplication.translate("fluencyCAD", u"Comb", None))
        self.pb_moveop.setText(QCoreApplication.translate("fluencyCAD", u"Mve", None))
@@ -8,6 +8,7 @@ from __future__ import annotations

 import logging
 import os
+import warnings
 from typing import Optional

 import numpy as np
@@ -48,6 +49,24 @@ from fluency.rendering.render_backend import (
 logger = logging.getLogger(__name__)


+def _unlink_quiet(path: Optional[str]) -> None:
+    """Unlink *path*, ignoring missing files and OS errors."""
+    if not path:
+        return
+    try:
+        if os.path.exists(path):
+            os.unlink(path)
+    except OSError:
+        pass
+
+
+# Threads still running after a cancel could not finish in time.  Kept
+# referenced (never terminate()'d, reparented from their widget) at
+# module level so they can safely outlive the widget/window that spawned
+# them — destroying a still-running QThread is a Qt fatal error.
+_RETIRED_THREADS: list = []
+
+
 # ── Background render thread ────────────────────────────────────────


@@ -153,6 +172,77 @@ class _AssemblyRenderThread(QThread):
                self.error.emit(str(e))


+class _MeshThread(QThread):
+    """Tessellates OCC shapes to PLY files off the GUI thread.
+
+    ``BRepMesh_IncrementalMesh`` is a single blocking C++ call, so the
+    cancel flag is checked between parts (assemblies) and at completion;
+    a cancelled thread discards its result instead of emitting it, so it
+    cannot clobber the UI.
+    """
+
+    mesh_ready = Signal(str)                        # single-shape: mesh path
+    assembly_ready = Signal(list, object, object)   # parts, bounds, first_bounds
+    error = Signal(str)
+
+    def __init__(self, shapes, is_assembly: bool, parent=None):
+        super().__init__(parent)
+        # Single: (TopoDS_Shape,)  |  Assembly: [(TopoDS_Shape, mat_name), ...]
+        self._shapes = shapes
+        self._is_assembly = is_assembly
+        self._cancelled = False
+
+    def cancel(self):
+        self._cancelled = True
+
+    def run(self):
+        try:
+            if self._is_assembly:
+                self._run_assembly()
+            else:
+                mesh_path = occ_shape_to_ply(
+                    self._shapes[0], linear_deflection=0.1, angular_deflection=0.15
+                )
+                if not self._cancelled:
+                    self.mesh_ready.emit(mesh_path)
+        except Exception as e:
+            if not self._cancelled:
+                self.error.emit(str(e))
+
+    def _run_assembly(self):
+        from fluency.rendering.material_presets import get_preset
+
+        parts: list = []
+        all_mins: list = []
+        all_maxs: list = []
+        first_bounds = None
+        for shape, mat_name in self._shapes:
+            if self._cancelled:
+                return
+            try:
+                mesh_path = occ_shape_to_ply(
+                    shape, linear_deflection=0.1, angular_deflection=0.15
+                )
+                material = get_preset(mat_name) if mat_name else get_preset("Brushed Steel")
+                parts.append((mesh_path, material))
+                bounds = occ_shape_bounds(shape)
+                all_mins.append(list(bounds[0]))
+                all_maxs.append(list(bounds[1]))
+                if first_bounds is None:
+                    first_bounds = bounds
+            except Exception as e:
+                logger.warning(f"Failed to tessellate assembly part: {e}")
+        if self._cancelled:
+            return
+        combined = None
+        if all_mins and all_maxs:
+            combined = (
+                [min(a[i] for a in all_mins) for i in range(3)],
+                [max(a[i] for a in all_maxs) for i in range(3)],
+            )
+        self.assembly_ready.emit(parts, combined, first_bounds)
+
+
 # ── Render window ───────────────────────────────────────────────────


@@ -777,17 +867,63 @@ class RenderWindow(QMainWindow):
            self._status_badge.setStyleSheet("color: #a6e3a1; font-size: 11px; padding: 2px;")

    def _cancel_active_thread(self):
-        """Cancel whichever thread is currently running."""
+        """Cancel whichever thread is currently running.
+
+        Deliberately avoids ``QThread.terminate()``: it kills the thread
+        mid-instruction inside Mitsuba/OCC C++ code and corrupts native
+        state (SIGSEGV).  Threads are cancelled cooperatively and, if
+        still running, detached until they exit on their own.
+        """
        if self._active_mode == "preview" and self._preview_thread:
-            self._preview_thread.cancel()
-            self._preview_thread.terminate()
-            self._preview_thread.wait(2000)
+            self._stop_thread(self._preview_thread)
        elif self._active_mode == "render" and self._render_thread:
-            self._render_thread.cancel()
-            self._render_thread.terminate()
-            self._render_thread.wait(2000)
+            self._stop_thread(self._render_thread)
        self._active_mode = None

+    def _stop_thread(self, thread, block: bool = False):
+        """Cancel *thread*; detach without ever using ``terminate()``.
+
+        ``QThread.terminate()`` kills the thread mid-instruction inside
+        Mitsuba/OCC C++ code and corrupts native state (SIGSEGV).  Instead
+        the cooperative cancel flag is set and, if the thread is still
+        running, its result signals are disconnected and it is kept
+        referenced (``_retired_threads``) until it exits on its own — a
+        cancelled ``run()`` emits no results, so it cannot clobber the UI.
+
+        ``block=True`` (shutdown paths only) additionally waits up to 3 s
+        so a thread does not outlive the application.  Interactive paths
+        keep the default and never stall the GUI thread.
+        """
+        if thread is None:
+            return
+        # Drop retired threads that have exited.
+        for t in list(_RETIRED_THREADS):
+            if not t.isRunning():
+                _RETIRED_THREADS.remove(t)
+        thread.cancel()
+        if thread.isRunning():
+            # Disconnect so a detached thread can't update the UI.  Signals
+            # with no receiver only emit a RuntimeWarning on disconnect, so
+            # silence that specific case.  Not every thread class defines
+            # every signal, so skip missing attributes.
+            with warnings.catch_warnings():
+                warnings.simplefilter("ignore", RuntimeWarning)
+                for name in ("finished", "error", "progress",
+                             "mesh_ready", "assembly_ready"):
+                    sig = getattr(thread, name, None)
+                    if sig is None:
+                        continue
+                    try:
+                        sig.disconnect()
+                    except (RuntimeError, TypeError):
+                        pass
+            _RETIRED_THREADS.append(thread)
+            # Reparent so destroying the owning widget can't delete a
+            # still-running QThread (a Qt fatal error).
+            thread.setParent(None)
+            if block:
+                thread.wait(3000)
+
    def _set_buttons_rendering(self, mode: str):
        """Disable buttons while rendering."""
        self._preview_btn.setEnabled(False)
@@ -974,10 +1110,8 @@ class RenderWindow(QMainWindow):

        # Kill both possible threads
        for thread in (self._preview_thread, self._render_thread):
-            if thread and thread.isRunning():
-                thread.cancel()
-                thread.terminate()
-                thread.wait(2000)
+            # block=True: at window close a thread must not outlive the app.
+            self._stop_thread(thread, block=True)

        # Clean up temp mesh file
        if self._mesh_path and os.path.exists(self._mesh_path):
@@ -1009,17 +1143,31 @@ class RenderTabContent(QWidget):
        self._backend = None
        self._mesh_path: Optional[str] = None

+        # Framing: percentage of screen the part should occupy (10-100).
+        self._framing_percentage: float = 80.0
+
        # Assembly support: list of (mesh_path, RenderMaterial)
        self._assembly_parts: list = []

        # Rendering threads & images
        self._render_thread: Optional[_RenderThread] = None
        self._preview_thread: Optional[_RenderThread] = None
+        # Background tessellation thread — meshing never blocks the GUI
+        self._mesh_thread: Optional[_MeshThread] = None
+        # Raw (TopoDS_Shape, mat_name) tuples awaiting background tessellation
+        self._assembly_pending: list = []
+        # Bumped on every load/clear/cleanup; mesh results carry the
+        # generation they belong to so stale results are discarded.
+        self._mesh_generation: int = 0
        self._last_image: Optional[np.ndarray] = None
        self._last_preview: Optional[np.ndarray] = None
        self._camera: Optional[RenderCamera] = None
        self._ground_color: tuple[float, float, float] = (0.5, 0.5, 0.5)
        self._active_mode: Optional[str] = None
+        self._framing_slider: QSlider | None = None
+        self._framing_label: QLabel | None = None
+        # Combined bbox for assembly rendering (used by _compute_framed_origin)
+        self._assembly_bounds: Optional[tuple] = None
        self._auto_preview_timer: Optional[QTimer] = None

        self._init_ui()
@@ -1031,22 +1179,39 @@ class RenderTabContent(QWidget):
    def set_shape(self, shape, camera: Optional[RenderCamera] = None) -> None:
        """Load a new OCC TopoDS_Shape for rendering.

+        Returns immediately: tessellation runs in a background thread
+        (``_MeshThread``) so callers (e.g. component switching) never
+        block the GUI thread.  The auto-preview is scheduled once the
+        mesh is ready.
+
        *camera* — if provided, overrides the stored camera.  Pass the
        viewport\'s render camera to match the 3D view framing.
        """
+        self._mesh_generation += 1
+        # Cancel any in-progress render so the new shape gets a fresh preview.
+        self._cancel_active_thread()
+        # Cancel any in-flight tessellation from a previous load.
+        self._stop_thread(self._mesh_thread)
+        self._mesh_thread = None
+        # Drop any previously loaded assembly state so the single-shape
+        # render path is used (prevents re-rendering a stale assembly).
+        self._assembly_parts = []
+        self._assembly_pending = []
+        self._assembly_bounds = None
+        # Reset the mesh path so a stale/failed tessellation cannot
+        # trigger an auto-preview of the previous shape's mesh.
+        self._mesh_path = None
        self._shape = shape
        if camera is not None:
-            self._camera = camera
+            self._camera = self._apply_framing(camera)
        self._last_image = None
        self._last_preview = None
        self._image_label.setPixmap(QPixmap())
-        self._image_label.setText("Click Preview or Render to start")
+        self._image_label.setText("Tessellating…")
        self._status_badge.setText("")
        self._export_btn.setEnabled(False)
-        self._prepare_mesh()
        self._populate_camera_controls()
-        # Trigger auto-preview when a new shape is loaded
-        self._schedule_auto_preview()
+        self._start_meshing()

    def get_camera(self) -> Optional[RenderCamera]:
        """Return the current camera (from UI controls or initial)."""
@@ -1061,21 +1226,30 @@ class RenderTabContent(QWidget):

        *parts* is a list of ``(TopoDS_Shape, Optional[str])`` tuples
        where the second element is an optional material preset name.
+
+        Returns immediately; the parts are tessellated in a background
+        thread and the auto-preview is scheduled once they are ready.
        """
+        self._mesh_generation += 1
+        # Cancel any in-progress render so the new assembly gets a fresh preview.
+        self._cancel_active_thread()
+        self._stop_thread(self._mesh_thread)
+        self._mesh_thread = None
        self._shape = None
        self._mesh_path = None
        self._assembly_parts = []
+        self._assembly_pending = list(parts)
+        self._assembly_bounds = None
        if camera is not None:
-            self._camera = camera
+            self._camera = self._apply_framing(camera)
        self._last_image = None
        self._last_preview = None
        self._image_label.setPixmap(QPixmap())
-        self._image_label.setText("Click Preview or Render to start")
+        self._image_label.setText("Tessellating…")
        self._status_badge.setText("")
        self._export_btn.setEnabled(False)
-        self._prepare_assembly_mesh(parts)
        self._populate_camera_controls()
-        self._schedule_auto_preview()
+        self._start_meshing()

    def set_camera(self, camera: RenderCamera) -> None:
        """Update the render camera from an external source (e.g. 3D viewport).
@@ -1086,7 +1260,7 @@ class RenderTabContent(QWidget):
        """
        if camera is None:
            return
-        self._camera = camera
+        self._camera = self._apply_framing(camera)
        self._cam_fov_spin.blockSignals(True)
        try:
            self._cam_fov_spin.setValue(camera.fov)
@@ -1100,20 +1274,48 @@ class RenderTabContent(QWidget):
        # For full renders or idle: schedule a preview if auto-preview is on.
        self._schedule_auto_preview()

+    def clear(self) -> None:
+        """Remove any loaded shape/assembly and reset the display."""
+        self._mesh_generation += 1
+        self._cancel_active_thread()
+        self._stop_thread(self._mesh_thread)
+        self._mesh_thread = None
+        self._shape = None
+        self._mesh_path = None
+        self._assembly_parts = []
+        self._assembly_pending = []
+        self._assembly_bounds = None
+        self._last_image = None
+        self._last_preview = None
+        self._image_label.setPixmap(QPixmap())
+        self._image_label.setText("Click Preview or Render to start")
+        self._status_badge.setText("")
+        self._export_btn.setEnabled(False)
+
    def cleanup(self) -> None:
        """Stop threads and delete temp files.  Call when the tab is hidden/closed."""
+        self._mesh_generation += 1
        if self._auto_preview_timer and self._auto_preview_timer.isActive():
            self._auto_preview_timer.stop()
-        for thread in (self._preview_thread, self._render_thread):
-            if thread and thread.isRunning():
-                thread.cancel()
-                thread.terminate()
-                thread.wait(2000)
-        if self._mesh_path and os.path.exists(self._mesh_path):
-            try:
-                os.unlink(self._mesh_path)
-            except OSError:
-                pass
+        # block=True: at tab exit / app shutdown a thread must not outlive
+        # the owning widget.
+        for thread in (self._mesh_thread, self._preview_thread, self._render_thread):
+            self._stop_thread(thread, block=True)
+        self._mesh_thread = None
+        self._preview_thread = None
+        self._render_thread = None
+        self._active_mode = None
+        # Delete temp PLY files (single shape plus all assembly parts).
+        paths = []
+        if self._mesh_path:
+            paths.append(self._mesh_path)
+        paths.extend(p for p, _ in self._assembly_parts)
+        for path in paths:
+            if path and os.path.exists(path):
+                try:
+                    os.unlink(path)
+                except OSError:
+                    pass
        self._mesh_path = None

    # ── UI Setup ───────────────────────────────────────────────────
@@ -1248,6 +1450,23 @@ class RenderTabContent(QWidget):

        layout.addWidget(camera_gb)

+        # ── Framing ───────────────────────────────────────────────
+        framing_gb = QGroupBox("Framing")
+        framing_layout = QVBoxLayout(framing_gb)
+        framing_layout.setSpacing(4)
+
+        self._framing_slider = QSlider(Qt.Horizontal)
+        self._framing_slider.setRange(10, 100)
+        self._framing_slider.setValue(80)
+        self._framing_slider.valueChanged.connect(self._on_framing_changed)
+        framing_layout.addWidget(self._framing_slider)
+
+        self._framing_label = QLabel("80 %")
+        self._framing_label.setAlignment(Qt.AlignCenter)
+        framing_layout.addWidget(self._framing_label)
+
+        layout.addWidget(framing_gb)
+
        # ── Lighting ────────────────────────────────────────────────
        light_gb = QGroupBox("Lighting")
        light_layout = QVBoxLayout(light_gb)
@@ -1452,44 +1671,72 @@ class RenderTabContent(QWidget):
        self._preview_btn.setEnabled(False)
        self._preview_btn.setToolTip("No render backend installed (pip install mitsuba)")

-    def _prepare_mesh(self):
-        if self._shape is None:
-            return
-        try:
-            self._mesh_path = occ_shape_to_ply(
-                self._shape, linear_deflection=0.1, angular_deflection=0.15
-            )
-            if self._camera is None:
-                mn, mx = occ_shape_bounds(self._shape)
-                self._camera = self._backend.default_camera_from_bounds(mn, mx)
-            logger.info(f"Prepared mesh: {self._mesh_path}")
-        except Exception as e:
-            logger.error(f"Failed to prepare mesh: {e}")
-            QMessageBox.warning(self, "Render Error", f"Failed to tessellate shape:\n{e}")
+    def _start_meshing(self):
+        """Kick off background tessellation of the current shape/assembly.

-    def _prepare_assembly_mesh(self, parts: list):
-        """Tessellate multiple shapes to separate PLY files.
-
-        *parts* is a list of ``(TopoDS_Shape, Optional[str])`` tuples.
-        Each material preset name is resolved via ``get_preset``.
+        The GUI thread is never blocked: the tab shows "Tessellating…"
+        until the mesh is ready, then the auto-preview is scheduled.
        """
-        from fluency.rendering.material_presets import get_preset
+        if self._shape is not None:
+            thread = _MeshThread((self._shape,), is_assembly=False, parent=self)
+            gen = self._mesh_generation
+            thread.mesh_ready.connect(lambda path, g=gen: self._on_mesh_ready(path, g))
+            thread.error.connect(lambda msg, g=gen: self._on_mesh_error(msg, g))
+        elif self._assembly_pending:
+            thread = _MeshThread(self._assembly_pending, is_assembly=True, parent=self)
+            gen = self._mesh_generation
+            thread.assembly_ready.connect(
+                lambda parts, bounds, first, g=gen: self._on_assembly_ready(parts, bounds, first, g)
+            )
+            thread.error.connect(lambda msg, g=gen: self._on_mesh_error(msg, g))
+        else:
+            self._image_label.setText("Click Preview or Render to start")
+            return
+        thread.start()
+        self._mesh_thread = thread

-        self._assembly_parts = []
-        first_bounds = None
-        for shape, mat_name in parts:
-            try:
-                mesh_path = occ_shape_to_ply(shape, linear_deflection=0.1, angular_deflection=0.15)
-                material = get_preset(mat_name) if mat_name else get_preset("Brushed Steel")
-                self._assembly_parts.append((mesh_path, material))
-                if first_bounds is None:
-                    first_bounds = occ_shape_bounds(shape)
-            except Exception as e:
-                logger.warning(f"Failed to tessellate assembly part: {e}")
-        if first_bounds and self._camera is None:
+    def _on_mesh_ready(self, mesh_path: str, gen: int) -> None:
+        """Background tessellation finished (single shape)."""
+        if gen != self._mesh_generation:
+            # The load was replaced mid-tessellation — discard the stale mesh.
+            _unlink_quiet(mesh_path)
+            return
+        self._mesh_path = mesh_path
+        if self._camera is None and self._backend is not None:
+            mn, mx = occ_shape_bounds(self._shape)
+            self._camera = self._backend.default_camera_from_bounds(mn, mx)
+            self._populate_camera_controls()
+        if self._active_mode is None:
+            self._image_label.setText("Click Preview or Render to start")
+        logger.info(f"Prepared mesh: {self._mesh_path}")
+        # Trigger auto-preview when a new shape is loaded
+        self._schedule_auto_preview()
+
+    def _on_assembly_ready(self, parts: list, bounds, first_bounds, gen: int) -> None:
+        """Background tessellation finished (assembly)."""
+        if gen != self._mesh_generation:
+            for p, _ in parts:
+                _unlink_quiet(p)
+            return
+        self._assembly_parts = parts
+        self._assembly_bounds = bounds
+        if self._camera is None and self._backend is not None and first_bounds is not None:
            mn, mx = first_bounds
            self._camera = self._backend.default_camera_from_bounds(mn, mx)
+            self._populate_camera_controls()
+        if self._active_mode is None:
+            self._image_label.setText("Click Preview or Render to start")
        logger.info(f"Prepared assembly: {len(self._assembly_parts)} parts")
+        # Trigger auto-preview when a new assembly is loaded
+        self._schedule_auto_preview()
+
+    def _on_mesh_error(self, msg: str, gen: int) -> None:
+        if gen != self._mesh_generation:
+            return
+        logger.error(f"Failed to tessellate shape: {msg}")
+        self._image_label.setText("Click Preview or Render to start")
+        self._status_badge.setText("")
+        QMessageBox.warning(self, "Render Error", f"Failed to tessellate shape:\n{msg}")

    def _setup_auto_preview(self):
        self._auto_preview_timer = QTimer(self)
@@ -1503,12 +1750,132 @@ class RenderTabContent(QWidget):
            return
        self._cam_fov_spin.setValue(self._camera.fov)

+    # ── Framing ──────────────────────────────────────────────────
+
+    def _on_framing_changed(self, value: int) -> None:
+        """Slider moved — update label and re-frame if we have a camera."""
+        self._framing_percentage = float(value)
+        self._framing_label.setText(f"{value} %")
+        # Re-apply framing with current direction
+        if self._camera is not None:
+            self._camera = self._apply_framing(self._camera)
+            # Sync the FOV spinbox to match (important for preview consistency)
+            self._cam_fov_spin.blockSignals(True)
+            try:
+                self._cam_fov_spin.setValue(self._camera.fov)
+            finally:
+                self._cam_fov_spin.blockSignals(False)
+            self._schedule_auto_preview()
+
+    def _apply_framing(self, camera: RenderCamera) -> RenderCamera:
+        """Apply framing to a camera, returning a new one with adjusted origin.
+
+        Keeps the direction and target from *camera*, adjusts distance
+        so the part fills _framing_percentage of the screen.
+        """
+        eye_dir = np.array(camera.origin) - np.array(camera.target)
+        diag = float(np.linalg.norm(eye_dir))
+        if diag > 1e-9:
+            eye_dir /= diag
+            target = camera.target
+            new_origin = self._compute_framed_origin(
+                eye_dir, target, camera.fov,
+            )
+            return RenderCamera(
+                origin=tuple(new_origin),
+                target=target,
+                up=camera.up,
+                fov=camera.fov,
+            )
+        return camera
+
+    def _compute_framed_origin(
+        self, eye_dir: np.ndarray, target: tuple[float, float, float], fov: float
+    ) -> np.ndarray:
+        """Compute camera origin so the part fills _framing_percentage of screen.
+
+        The viewing direction (eye_dir) and target define the line of sight.
+        The bounding box is projected onto the view plane and the distance
+        is chosen so that its larger projected dimension occupies exactly
+        ``_framing_percentage`` of the corresponding screen axis.
+        """
+        # Get bounding box — from assembly or single shape.
+        if self._assembly_bounds is not None:
+            mn, mx = self._assembly_bounds
+        elif self._shape is not None:
+            mn, mx = occ_shape_bounds(self._shape)
+        else:
+            # Fallback: place camera at a large but safe distance.
+            return np.array(target, dtype=float) + eye_dir * 1000.0
+
+        mn_arr = np.asarray(mn, dtype=float)
+        mx_arr = np.asarray(mx, dtype=float)
+        diag = float(np.linalg.norm(mx_arr - mn_arr))
+
+        # View-plane basis vectors.
+        up_world = np.array([0.0, 0.0, 1.0], dtype=float)
+        right = np.cross(up_world, eye_dir)
+        right_norm = float(np.linalg.norm(right))
+        if right_norm < 1e-9:
+            # Eye dir is parallel to world up — pick arbitrary right.
+            right = np.array([1.0, 0.0, 0.0], dtype=float)
+        else:
+            right /= right_norm
+        screen_up = np.cross(eye_dir, right)
+
+        # Project bbox axes onto view plane.
+        dx = mx_arr[0] - mn_arr[0]
+        dy = mx_arr[1] - mn_arr[1]
+        dz = mx_arr[2] - mn_arr[2]
+
+        # Project all 8 bbox corners onto the view plane
+        # to get the actual bounding-box extent.
+        half_x = dx / 2.0
+        half_y = dy / 2.0
+        half_z = dz / 2.0
+
+        # Corner offsets from centre in local axes.
+        corner_offsets = [
+            (sx * half_x, sy * half_y, sz * half_z)
+            for sx in (-1, 1) for sy in (-1, 1) for sz in (-1, 1)
+        ]
+
+        # Project each corner onto view-plane basis vectors.
+        proj_right_vals = [
+            ox * right[0] + oy * right[1] + oz * right[2]
+            for ox, oy, oz in corner_offsets
+        ]
+        proj_up_vals = [
+            ox * screen_up[0] + oy * screen_up[1] + oz * screen_up[2]
+            for ox, oy, oz in corner_offsets
+        ]
+
+        proj_right = max(proj_right_vals) - min(proj_right_vals)
+        proj_up = max(proj_up_vals) - min(proj_up_vals)
+
+        half_fov_rad = np.radians(fov / 2.0)
+        tan_half_fov = float(np.tan(half_fov_rad))
+        if tan_half_fov < 1e-9:
+            return np.array(target, dtype=float) + eye_dir * 1000.0
+
+        # Distance: D = full_extent / (2 * pct * tan(fov/2))
+        pct = self._framing_percentage / 100.0
+        dist_x = proj_right / (2.0 * pct * tan_half_fov) if proj_right > 0 else float("inf")
+        dist_y = proj_up / (2.0 * pct * tan_half_fov) if proj_up > 0 else float("inf")
+
+        dist = min(dist_x, dist_y)
+        # Minimum distance to avoid camera inside the object.
+        if dist < diag * 0.1:
+            dist = diag * 0.1
+
+        return np.array(target, dtype=float) + eye_dir * dist
+
    def _schedule_auto_preview(self):
        if not self._auto_preview_cb.isChecked():
            return
        if self._active_mode is not None:
            return
-        if self._backend is None or self._mesh_path is None:
+        if self._backend is None or (self._mesh_path is None and not self._assembly_parts):
            return
        self._auto_preview_timer.start(500)

@@ -1560,15 +1927,55 @@ class RenderTabContent(QWidget):

    def _cancel_active_thread(self):
        if self._active_mode == "preview" and self._preview_thread:
-            self._preview_thread.cancel()
-            self._preview_thread.terminate()
-            self._preview_thread.wait(2000)
+            self._stop_thread(self._preview_thread)
        elif self._active_mode == "render" and self._render_thread:
-            self._render_thread.cancel()
-            self._render_thread.terminate()
-            self._render_thread.wait(2000)
+            self._stop_thread(self._render_thread)
        self._active_mode = None

+    def _stop_thread(self, thread, block: bool = False):
+        """Cancel *thread*; detach without ever using ``terminate()``.
+
+        ``QThread.terminate()`` kills the thread mid-instruction inside
+        Mitsuba/OCC C++ code and corrupts native state (SIGSEGV).  Instead
+        the cooperative cancel flag is set and, if the thread is still
+        running, its result signals are disconnected and it is kept
+        referenced (``_retired_threads``) until it exits on its own — a
+        cancelled ``run()`` emits no results, so it cannot clobber the UI.
+
+        ``block=True`` (shutdown paths only) additionally waits up to 3 s
+        so a thread does not outlive the application.  Interactive paths
+        keep the default and never stall the GUI thread.
+        """
+        if thread is None:
+            return
+        # Drop retired threads that have exited.
+        for t in list(_RETIRED_THREADS):
+            if not t.isRunning():
+                _RETIRED_THREADS.remove(t)
+        thread.cancel()
+        if thread.isRunning():
+            # Disconnect so a detached thread can't update the UI.  Signals
+            # with no receiver only emit a RuntimeWarning on disconnect, so
+            # silence that specific case.  Not every thread class defines
+            # every signal, so skip missing attributes.
+            with warnings.catch_warnings():
+                warnings.simplefilter("ignore", RuntimeWarning)
+                for name in ("finished", "error", "progress",
+                             "mesh_ready", "assembly_ready"):
+                    sig = getattr(thread, name, None)
+                    if sig is None:
+                        continue
+                    try:
+                        sig.disconnect()
+                    except (RuntimeError, TypeError):
+                        pass
+            _RETIRED_THREADS.append(thread)
+            # Reparent so destroying the owning widget can't delete a
+            # still-running QThread (a Qt fatal error).
+            thread.setParent(None)
+            if block:
+                thread.wait(3000)
+
    def _set_buttons_rendering(self, mode: str):
        self._preview_btn.setEnabled(False)
        self._render_btn.setEnabled(False)
@@ -20,6 +20,24 @@ class Viewer3DWidget(QWidget):
    # Emitted when face-pick mode is cancelled (Esc) so the host can uncheck.
    pickFaceCancelled = Signal()

+    # Emitted when the user picks a face for the fillet tool (ANY face,
+    # planar or curved).  Payload: the raw TopoDS_Face.  The owning body is
+    # read from ``_last_pick_owner_obj_id`` (same stash as facePicked).
+    filletFacePicked = Signal(object)
+    # Emitted when fillet pick mode is cancelled (Esc).
+    filletPickCancelled = Signal()
+
+    # Emitted when the user picks a face for the chamfer tool (ANY face,
+    # planar or curved).  Payload: the raw TopoDS_Face.
+    chamferFacePicked = Signal(object)
+    # Emitted when chamfer pick mode is cancelled (Esc).
+    chamferPickCancelled = Signal()
+
+    # Emitted when the user picks a cylindrical face for the thread tool.
+    threadFacePicked = Signal(object)
+    # Emitted when thread pick mode is cancelled (Esc).
+    threadPickCancelled = Signal()
+
    # Emitted when the user picks an entity for a connector point (assembly).
    # Payload: (origin, normal, x_dir, entity_type, face_or_edge_or_vertex, owner_obj_id).
    connectorPicked = Signal(tuple, tuple, tuple, str, object, str)
@@ -41,14 +59,30 @@ class Viewer3DWidget(QWidget):
    # Payload: (eye, at, up) — each is a tuple of 3 floats.
    cameraChanged = Signal(tuple, tuple, tuple)

+    # Emitted when the user clicks a part of the world-space sketch gizmo
+    # (the triad at the sketch midpoint).  Payload:
+    #   kind      — "center" | "axis_x" | "axis_y" | "axis_z" |
+    #               "plane_xy" | "plane_yz" | "plane_xz"
+    #   position  — picked world point (triad origin for axes/center,
+    #               plane quad centre for planes)
+    #   direction — axis unit vector / plane normal / (0,0,0) for center
+    #   normal    — sketch workplane normal
+    #   x_dir     — sketch workplane x direction
+    sketchGizmoPicked = Signal(str, tuple, tuple, tuple, tuple)
+    # Hover feedback: part kind string under the cursor, or None when the
+    # cursor left the gizmo.
+    sketchGizmoHover = Signal(object)
+    # Emitted when gizmo pick mode is cancelled (Esc) so the host can reset.
+    sketchGizmoCancelled = Signal()
+
    def __init__(self, parent=None):
        super().__init__(parent)
        # For OCC's direct OpenGL rendering we need Qt to not paint over it.
-        self.setAttribute(Qt.WA_PaintOnScreen)
-        self.setAttribute(Qt.WA_OpaquePaintEvent)
+        self.setAttribute(Qt.WidgetAttribute.WA_PaintOnScreen)
+        self.setAttribute(Qt.WidgetAttribute.WA_OpaquePaintEvent)
        self.setAutoFillBackground(False)
        # Accept keyboard focus so navigation shortcuts (F, R, 1-7, P, O) work.
-        self.setFocusPolicy(Qt.StrongFocus)
+        self.setFocusPolicy(Qt.FocusPolicy.StrongFocus)
        # Enable mouse tracking so ``mouseMoveEvent`` fires even without a
        # button held — required for the connector-pick hover gizmo (and any
        # status-bar hover feedback) to show under the cursor as the user
@@ -64,6 +98,12 @@ class Viewer3DWidget(QWidget):
        # When True, a left-click picks a planar face (for sketch-on-surface)
        # instead of orbiting the camera.  Set via set_pick_face_mode().
        self._pick_face_mode: bool = False
+        # When True, a left-click picks ANY face for the fillet tool.
+        self._fillet_pick_mode: bool = False
+        # When True, a left-click picks ANY face for the chamfer tool.
+        self._chamfer_pick_mode: bool = False
+        # When True, a left-click picks a cylindrical face for the thread tool.
+        self._thread_pick_mode: bool = False
        # When True, a left-click picks an entity for a connector point
        # (assembly component connection).
        self._connector_pick_mode: bool = False
@@ -87,6 +127,16 @@ class Viewer3DWidget(QWidget):
        # target a cut/union extrude against the body the sketch was
        # projected onto).
        self._last_pick_owner_obj_id: Optional[str] = None
+        # World-space sketch reference gizmo (triad at the sketch midpoint).
+        # ``_sketch_gizmo_frame`` is (origin, normal, x_dir) of the gizmo;
+        # None while no triad is shown.
+        self._sketch_gizmo_frame: Optional[Tuple[tuple, tuple, tuple]] = None
+        # When True, a left-click picks gizmo parts only (no orbit); Esc
+        # cancels.  Otherwise the gizmo is pickable implicitly during normal
+        # navigation (Fusion-style) whenever it is shown.
+        self._sketch_gizmo_pick_mode: bool = False
+        # Currently hovered gizmo part kind (for highlight bookkeeping).
+        self._sketch_gizmo_hover_kind: Optional[str] = None

    def _init_renderer(self) -> None:
        """Create the best available renderer."""
@@ -139,17 +189,27 @@ class Viewer3DWidget(QWidget):
        self._ensure_initialized()
        return self._renderer

-    def show_shape(self, shape: Any, color=None, name=None) -> str:
+    def show_shape(
+        self,
+        shape: Any,
+        color=None,
+        name=None,
+        auto_fit: bool = True,
+    ) -> str:
        """Display an OCC TopoDS_Shape.

        Uses OCCRenderer.add_shape for native AIS display, or falls back to
        triangulation + add_mesh for the PygfxRenderer.
+ 
+        *auto_fit* is forwarded to the renderer: pass ``False`` when
+        rebuilding a scene under explicit camera control so the first
+        shape does not trigger a whole-scene camera fit.
        """
        self._ensure_initialized()
        from fluency.rendering.occ_renderer import OCCRenderer

        if isinstance(self._renderer, OCCRenderer):
-            oid = self._renderer.add_shape(shape, color, name)
+            oid = self._renderer.add_shape(shape, color, name, auto_fit)
            self._renderer.render()
            return oid
        # Fallback: tessellate and use the mesh pipeline.
@@ -229,6 +289,19 @@ class Viewer3DWidget(QWidget):
            self._renderer.render()
        return ok

+    def set_body_color(
+        self, mesh_id: str, color: Tuple[float, float, float]
+    ) -> bool:
+        """Change the colour of a body in the 3D view.  Returns True on success."""
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "set_color", None)
+        if fn is None:
+            return False
+        ok = fn(mesh_id, color)
+        if ok:
+            self._renderer.render()
+        return ok
+
    def set_transparency(self, mesh_id: str, transparency: float) -> bool:
        """Set a previously-added mesh's transparency (0..1).

@@ -275,6 +348,35 @@ class Viewer3DWidget(QWidget):
        self._renderer.fit_camera()
        self._renderer.render()

+    def fit_camera_to_box(self, bnd_box: Any, padding: float = 0.05) -> None:
+        """Fit the camera to a specific 3D bounding box (``Bnd_Box``).
+
+        Used by the array tool so the dialog preview frames exactly the
+        space the pattern copies occupy.  Falls back to fitting the whole
+        scene on renderers without box fitting (e.g. the Pygfx fallback).
+        """
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "fit_camera_to_box", None)
+        if fn is not None:
+            fn(bnd_box, padding)
+            self._renderer.render()
+            return
+        self.fit_camera()
+
+    def box_fully_visible(self, bnd_box: Any, margin: float = 0.05) -> bool:
+        """True when the box's 8 corners all project inside the viewport.
+
+        The array preview uses this to decide when a grown pattern has
+        moved copies off-screen and the camera needs re-fitting.  On
+        renderers without the check (Pygfx fallback) it returns True so
+        no re-fit is forced.
+        """
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "box_fully_visible", None)
+        if fn is not None:
+            return bool(fn(bnd_box, margin))
+        return True
+
    # ─── Workplane visualization ───────────────────────────────────────────

    def show_workplane(
@@ -312,17 +414,43 @@ class Viewer3DWidget(QWidget):
    def mousePressEvent(self, event):
        self._ensure_initialized()
        # Face-pick mode: a left-click selects a planar face to sketch on.
-        if self._pick_face_mode and event.button() == Qt.LeftButton:
+        if self._pick_face_mode and event.button() == Qt.MouseButton.LeftButton:
            self._handle_face_pick(event)
            return
+        # Fillet pick mode: a left-click selects any face (planar or curved).
+        if self._fillet_pick_mode and event.button() == Qt.MouseButton.LeftButton:
+            self._handle_fillet_face_pick(event)
+            return
+        # Chamfer pick mode: a left-click selects any face (planar or curved).
+        if self._chamfer_pick_mode and event.button() == Qt.MouseButton.LeftButton:
+            self._handle_chamfer_face_pick(event)
+            return
+        # Thread pick mode: a left-click selects a cylindrical face.
+        if self._thread_pick_mode and event.button() == Qt.MouseButton.LeftButton:
+            self._handle_thread_face_pick(event)
+            return
        # Connector pick mode: a left-click selects a face for a connection point.
-        if self._connector_pick_mode and event.button() == Qt.LeftButton:
+        if self._connector_pick_mode and event.button() == Qt.MouseButton.LeftButton:
            self._handle_connector_pick(event)
            return
        # Assembly move mode: start dragging the clicked body.
-        if self._assembly_move_mode and event.button() == Qt.LeftButton:
+        if self._assembly_move_mode and event.button() == Qt.MouseButton.LeftButton:
            self._handle_assembly_move_press(event)
            return
+        # World sketch gizmo: a click on a part selects it (Fusion-style),
+        # even during normal navigation.  In explicit gizmo-pick mode an
+        # off-gizmo click does nothing (no orbit); otherwise it falls
+        # through to orbit/pan below.
+        if event.button() == Qt.MouseButton.LeftButton and self._sketch_gizmo_enabled():
+            fn = getattr(self._renderer, "pick_sketch_gizmo", None)
+            if fn is not None:
+                pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+                kind = fn(pos.x(), pos.y())
+                if kind is not None:
+                    self._handle_sketch_gizmo_pick(event, kind)
+                    return
+            if self._sketch_gizmo_pick_mode:
+                return  # explicit mode: off-gizmo clicks do not orbit
        self._renderer.handle_mouse_press(event)
        super().mousePressEvent(event)

@@ -346,15 +474,39 @@ class Viewer3DWidget(QWidget):
                self._renderer.handle_mouse_move(event)
            super().mouseMoveEvent(event)
            return
+        # In fillet pick mode, keep dynamic highlighting too.
+        if self._fillet_pick_mode:
+            if hasattr(self._renderer, "handle_mouse_move"):
+                self._renderer.handle_mouse_move(event)
+            super().mouseMoveEvent(event)
+            return
+        # In chamfer pick mode, keep dynamic highlighting too.
+        if self._chamfer_pick_mode:
+            if hasattr(self._renderer, "handle_mouse_move"):
+                self._renderer.handle_mouse_move(event)
+            super().mouseMoveEvent(event)
+            return
+        # In thread pick mode, keep dynamic highlighting.
+        if self._thread_pick_mode:
+            if hasattr(self._renderer, "handle_mouse_move"):
+                self._renderer.handle_mouse_move(event)
+            super().mouseMoveEvent(event)
+            return
        # Active drag in assembly move mode.
        if self._move_drag_active:
            self._handle_assembly_move_move(event)
            super().mouseMoveEvent(event)
            return
+        # World sketch gizmo hover: highlight the part under the cursor.
+        if self._sketch_gizmo_enabled():
+            self._handle_sketch_gizmo_hover(event)
+            if self._sketch_gizmo_pick_mode:
+                super().mouseMoveEvent(event)
+                return
        self._renderer.handle_mouse_move(event)
        super().mouseMoveEvent(event)

-    def paintEngine(self):
+    def paintEngine(self) -> Any:
        """Return None to prevent Qt from painting over OCC's direct OpenGL."""
        return None

@@ -437,6 +589,127 @@ class Viewer3DWidget(QWidget):
            return self._renderer.get_camera_fov()
        return 45.0

+    # ─── World sketch reference gizmo (triad at the sketch midpoint) ────────
+
+    def show_sketch_gizmo(
+        self,
+        origin: Tuple[float, float, float],
+        normal: Tuple[float, float, float],
+        x_dir: Tuple[float, float, float],
+        size: float = 40.0,
+    ) -> None:
+        """Show the selectable X/Y/Z triad in the 3D world at *origin*.
+
+        *origin* should be the midpoint of the active sketch's geometry and
+        the triad is aligned to the sketch's workplane frame.  Call again
+        with a new origin to keep it in sync as the sketch is edited.
+        No-op on renderers without gizmo support (Pygfx fallback).
+        """
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "show_sketch_gizmo", None)
+        if fn is None:
+            return
+        fn(origin, normal, x_dir, size)
+        self._sketch_gizmo_frame = (tuple(origin), tuple(normal), tuple(x_dir))
+        self._sketch_gizmo_hover_kind = None
+        self._renderer.render()
+
+    def remove_sketch_gizmo(self) -> None:
+        """Hide the world sketch triad, if any."""
+        if self._initialized and self._renderer is not None:
+            fn = getattr(self._renderer, "remove_sketch_gizmo", None)
+            if fn is not None:
+                fn()
+                self._renderer.render()
+        self._sketch_gizmo_frame = None
+        self._sketch_gizmo_hover_kind = None
+
+    def set_sketch_gizmo_pick_mode(self, enabled: bool) -> None:
+        """Toggle explicit gizmo-pick mode.
+
+        When enabled, left-clicks select gizmo parts only (the camera does
+        not orbit) and Esc exits the mode.  When disabled, the gizmo is
+        still pickable implicitly during normal navigation (Fusion-style)
+        whenever it is shown.  Mutually exclusive with the other pick modes.
+        """
+        self._sketch_gizmo_pick_mode = bool(enabled)
+        if enabled:
+            self._pick_face_mode = False
+            self._fillet_pick_mode = False
+            self._chamfer_pick_mode = False
+            self._thread_pick_mode = False
+            self._connector_pick_mode = False
+            self._assembly_move_mode = False
+            self._move_drag_active = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
+            self.setFocus()
+        elif not (
+            self._pick_face_mode
+            or self._fillet_pick_mode
+            or self._chamfer_pick_mode
+            or self._thread_pick_mode
+            or self._connector_pick_mode
+        ):
+            self.unsetCursor()
+
+    def is_sketch_gizmo_pick_mode(self) -> bool:
+        return self._sketch_gizmo_pick_mode
+
+    def get_sketch_gizmo_frame(self) -> Optional[Tuple[tuple, tuple, tuple]]:
+        """Return the (origin, normal, x_dir) of the shown triad, or None."""
+        return self._sketch_gizmo_frame
+
+    def _sketch_gizmo_enabled(self) -> bool:
+        """True when the triad is shown AND no other mode owns the pointer."""
+        if self._sketch_gizmo_frame is None:
+            return False
+        if self._sketch_gizmo_pick_mode:
+            return True
+        if self._assembly_move_mode or self._move_drag_active:
+            return False
+        return not (
+            self._pick_face_mode
+            or self._fillet_pick_mode
+            or self._chamfer_pick_mode
+            or self._thread_pick_mode
+            or self._connector_pick_mode
+        )
+
+    def _handle_sketch_gizmo_hover(self, event) -> None:
+        """Highlight the gizmo part under the cursor and emit hover signal."""
+        fn = getattr(self._renderer, "pick_sketch_gizmo", None)
+        if fn is None:
+            return
+        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+        kind = fn(pos.x(), pos.y())
+        if kind == self._sketch_gizmo_hover_kind:
+            return
+        self._sketch_gizmo_hover_kind = kind
+        if kind is not None:
+            hl = getattr(self._renderer, "highlight_sketch_gizmo_part", None)
+            if hl is not None:
+                hl(kind)
+        else:
+            cl = getattr(self._renderer, "clear_sketch_gizmo_highlight", None)
+            if cl is not None:
+                cl()
+        self.sketchGizmoHover.emit(kind)
+
+    def _handle_sketch_gizmo_pick(self, event, kind: str) -> None:
+        """Emit sketchGizmoPicked for the clicked part with world metadata."""
+        frame = self._sketch_gizmo_frame
+        normal = tuple(frame[1]) if frame else (0.0, 0.0, 1.0)
+        x_dir = tuple(frame[2]) if frame else (1.0, 0.0, 0.0)
+        position = tuple(frame[0]) if frame else (0.0, 0.0, 0.0)
+        direction = (0.0, 0.0, 0.0)
+        info_fn = getattr(self._renderer, "sketch_gizmo_pick_info", None)
+        if info_fn is not None:
+            info = info_fn(kind)
+            if info:
+                position = tuple(info["position"])
+                direction = tuple(info["direction"])
+        self.sketchGizmoPicked.emit(kind, position, direction, normal, x_dir)
+
    # ─── Face-pick mode (sketch-on-surface) ────────────────────────────────

    def set_pick_face_mode(self, enabled: bool) -> None:
@@ -447,13 +720,155 @@ class Viewer3DWidget(QWidget):
        """
        self._pick_face_mode = bool(enabled)
        if enabled:
-            self.setCursor(Qt.CrossCursor)
+            self._sketch_gizmo_pick_mode = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
        else:
            self.unsetCursor()

    def is_pick_face_mode(self) -> bool:
        return self._pick_face_mode

+    # ─── Fillet pick mode (any-face picking) ────────────────────────────────
+
+    def set_fillet_pick_mode(self, enabled: bool) -> None:
+        """Toggle fillet face-pick mode (any face — planar or curved).
+
+        The cursor selects faces for the fillet tool instead of orbiting the
+        camera.  Mutually exclusive with the other pick modes: entering this
+        mode switches the others off.
+        """
+        self._fillet_pick_mode = bool(enabled)
+        if enabled:
+            self._sketch_gizmo_pick_mode = False
+            # Pick modes are mutually exclusive — entering fillet mode
+            # disables chamfer / sketch-on-surface / connector / assembly modes.
+            self._chamfer_pick_mode = False
+            self._pick_face_mode = False
+            self._connector_pick_mode = False
+            self._assembly_move_mode = False
+            self._move_drag_active = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
+        elif not self._pick_face_mode and not self._chamfer_pick_mode and not self._connector_pick_mode:
+            self.unsetCursor()
+
+    def is_fillet_pick_mode(self) -> bool:
+        return self._fillet_pick_mode
+
+    # ─── Chamfer pick mode (any-face picking) ──────────────────────────────
+
+    def set_chamfer_pick_mode(self, enabled: bool) -> None:
+        """Toggle chamfer face-pick mode (any face — planar or curved).
+
+        The cursor selects faces for the chamfer tool instead of orbiting
+        the camera.  Mutually exclusive with the other pick modes.
+        """
+        self._chamfer_pick_mode = bool(enabled)
+        if enabled:
+            self._sketch_gizmo_pick_mode = False
+            self._fillet_pick_mode = False
+            self._pick_face_mode = False
+            self._connector_pick_mode = False
+            self._assembly_move_mode = False
+            self._move_drag_active = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
+        elif not self._pick_face_mode and not self._fillet_pick_mode and not self._connector_pick_mode:
+            self.unsetCursor()
+
+    def is_chamfer_pick_mode(self) -> bool:
+        return self._chamfer_pick_mode
+
+    def _handle_chamfer_face_pick(self, event: Any) -> None:
+        """Detect any face under the click and emit chamferFacePicked."""
+        self._ensure_initialized()
+        picker = getattr(self._renderer, "pick_face", None)
+        if picker is None:
+            logger.warning("Renderer has no pick_face support")
+            return
+        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+        info = picker(pos.x(), pos.y())
+        if info is None:
+            logger.info("Chamfer face pick: no face under cursor")
+            return
+        self._last_pick_owner_obj_id = info.get("owner_obj_id")
+        self.chamferFacePicked.emit(info["face"])
+
+    def highlight_faces(self, faces: List[Any]) -> None:
+        """Tint all faces in *faces* so both fillet picks stay visible."""
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "highlight_faces", None)
+        if fn is not None:
+            fn(faces)
+            self._renderer.render()
+            return
+        # Fallback: single-face highlight for the last picked face.
+        if faces:
+            self.highlight_face(faces[-1])
+
+    def clear_faces_highlight(self) -> None:
+        """Remove the multi-face fillet-pick overlays, if any."""
+        if not self._initialized or self._renderer is None:
+            return
+        fn = getattr(self._renderer, "clear_faces_highlight", None)
+        if fn is not None:
+            fn()
+            self._renderer.render()
+
+    def _handle_fillet_face_pick(self, event: Any) -> None:
+        """Detect any face under the click and emit filletFacePicked."""
+        self._ensure_initialized()
+        picker = getattr(self._renderer, "pick_face", None)
+        if picker is None:
+            logger.warning("Renderer has no pick_face support")
+            return
+        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+        info = picker(pos.x(), pos.y())
+        if info is None:
+            logger.info("Fillet face pick: no face under cursor")
+            return
+        # Stash the owner so MainWindow can pair the face with its body
+        # (same convention as sketch-on-face picking).
+        self._last_pick_owner_obj_id = info.get("owner_obj_id")
+        self.filletFacePicked.emit(info["face"])
+
+    # ─── Thread pick mode ─────────────────────────────────────────────────
+
+    def set_thread_pick_mode(self, enabled: bool) -> None:
+        """Toggle thread face-pick mode (cylindrical face only).
+
+        When enabled, a left-click picks a cylindrical face for the thread
+        tool.  Mutually exclusive with other pick modes.
+        """
+        self._thread_pick_mode = bool(enabled)
+        if enabled:
+            self._sketch_gizmo_pick_mode = False
+            self._pick_face_mode = False
+            self._fillet_pick_mode = False
+            self._chamfer_pick_mode = False
+            self._connector_pick_mode = False
+            self._assembly_move_mode = False
+            self._move_drag_active = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
+        elif not self._pick_face_mode and not self._fillet_pick_mode and not self._chamfer_pick_mode and not self._connector_pick_mode:
+            self.unsetCursor()
+
+    def is_thread_pick_mode(self) -> bool:
+        return self._thread_pick_mode
+
+    def _handle_thread_face_pick(self, event: Any) -> None:
+        """Detect any face under the click and emit threadFacePicked."""
+        self._ensure_initialized()
+        picker = getattr(self._renderer, "pick_face", None)
+        if picker is None:
+            logger.warning("Renderer has no pick_face support")
+            return
+        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+        info = picker(pos.x(), pos.y())
+        if info is None:
+            logger.info("Thread face pick: no face under cursor")
+            return
+        self._last_pick_owner_obj_id = info.get("owner_obj_id")
+        self.threadFacePicked.emit(info["face"])
+
    def highlight_face(self, face: Any) -> None:
        """Tint the picked face light-blue/transparent in the 3D viewer."""
        self._ensure_initialized()
@@ -470,6 +885,22 @@ class Viewer3DWidget(QWidget):
            fn()
            self._renderer.render()

+    def highlight_operation(self, shape: Any) -> None:
+        """Overlay a hot-pink translucent *shape* to show operation history."""
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "highlight_operation_shape", None)
+        if fn is not None:
+            fn(shape)
+            self._renderer.render()
+
+    def clear_operation_highlight(self) -> None:
+        """Remove the operation-history overlay, if any."""
+        self._ensure_initialized()
+        fn = getattr(self._renderer, "clear_operation_highlight", None)
+        if fn is not None:
+            fn()
+            self._renderer.render()
+
    # ─── Connector pick mode (assembly) ────────────────────────────────────

    def set_connector_pick_mode(self, enabled: bool, clear_gizmo: bool = True) -> None:
@@ -489,7 +920,8 @@ class Viewer3DWidget(QWidget):
        """
        self._connector_pick_mode = bool(enabled)
        if enabled:
-            self.setCursor(Qt.CrossCursor)
+            self._sketch_gizmo_pick_mode = False
+            self.setCursor(Qt.CursorShape.CrossCursor)
            # Disable standard OCC selection so gizmo visuals are not
            # interfered with by dynamic face highlighting.
            fn = getattr(self._renderer, "deactivate_selection_modes", None)
@@ -508,6 +940,16 @@ class Viewer3DWidget(QWidget):
    def is_connector_pick_mode(self) -> bool:
        return self._connector_pick_mode

+    def show_persistent_connector_gizmo(self, origin, normal, x_dir, entity_type, color=(0.0, 1.0, 0.0)):
+        fn = getattr(self._renderer, "show_persistent_entity_gizmo", None)
+        if fn is not None:
+            fn(entity_type=entity_type, position=origin, normal=normal, x_dir=x_dir, color=color)
+
+    def clear_persistent_connector_gizmo(self):
+        fn = getattr(self._renderer, "clear_persistent_entity_gizmo", None)
+        if fn is not None:
+            fn()
+
    def _clear_connector_snap(self) -> None:
        """Remove the hover gizmo."""
        fn = getattr(self._renderer, "clear_entity_gizmo", None)
@@ -714,7 +1156,8 @@ class Viewer3DWidget(QWidget):
        """
        self._assembly_move_mode = bool(enabled)
        if enabled:
-            self.setCursor(Qt.SizeAllCursor)
+            self._sketch_gizmo_pick_mode = False
+            self.setCursor(Qt.CursorShape.SizeAllCursor)
        elif not self._pick_face_mode and not self._connector_pick_mode:
            self.unsetCursor()
        if not enabled:
@@ -788,20 +1231,29 @@ class Viewer3DWidget(QWidget):

        # Compute world-space delta.
        modifiers = event.modifiers()
-        if modifiers & Qt.ShiftModifier:
+        if modifiers & Qt.KeyboardModifier.ShiftModifier:
            # Shift+drag: move along camera direction (Z-depth).
            dz_world = dx * world_per_pixel
            dx_world = 0.0
            dy_world = 0.0
        else:
            # Normal drag: move in view plane.
-            dx_world = float(cam_right[0] * dx * world_per_pixel + cam_up[0] * dy * world_per_pixel)
-            dy_world = float(cam_right[1] * dx * world_per_pixel + cam_up[1] * dy * world_per_pixel)
-            dz_world = float(cam_right[2] * dx * world_per_pixel + cam_up[2] * dy * world_per_pixel)
+            try:
+                dx_world = float(
+                    cam_right[0] * dx * world_per_pixel + cam_up[0] * dy * world_per_pixel
+                )
+                dy_world = float(
+                    cam_right[1] * dx * world_per_pixel + cam_up[1] * dy * world_per_pixel
+                )
+                dz_world = float(
+                    cam_right[2] * dx * world_per_pixel + cam_up[2] * dy * world_per_pixel
+                )
+            except (TypeError, ValueError):
+                dx_world = dy_world = dz_world = 0.0

        self.assemblyComponentDragged.emit(self._move_owner_obj_id, dx_world, dy_world, dz_world)

-    def _handle_assembly_move_release(self, event) -> None:
+    def _handle_assembly_move_release(self, event: Any) -> None:
        """Finish the drag, emit final position."""
        self.assemblyMoveFinished.emit(self._move_owner_obj_id)
        self._move_drag_active = False
@@ -811,7 +1263,7 @@ class Viewer3DWidget(QWidget):
        self._move_plane_normal = None
        self._move_initial_position = None

-    def _handle_face_pick(self, event) -> None:
+    def _handle_face_pick(self, event: Any) -> None:
        """Detect a planar face under the click and emit facePicked."""
        self._ensure_initialized()
        picker = getattr(self._renderer, "pick_planar_face", None)
@@ -834,7 +1286,7 @@ class Viewer3DWidget(QWidget):
            info["face"],
        )

-    def set_view(self, view: str):
+    def set_view(self, view: str) -> None:
        # Prefer the renderer's native orientation snap (preserves target,
        # refits the scene).  Falls back to absolute eye positions for
        # renderers that don't implement set_view_orientation.
@@ -856,28 +1308,48 @@ class Viewer3DWidget(QWidget):
            pos, target = positions[view]
            self.set_camera_position(pos, target)

-    def mouseDoubleClickEvent(self, event):
+    def mouseDoubleClickEvent(self, event: Any) -> None:
        # Double-click → fit all (common CAD convention).
        self._ensure_initialized()
-        if event.button() == Qt.LeftButton:
+        if event.button() == Qt.MouseButton.LeftButton:
            self.fit_camera()
        super().mouseDoubleClickEvent(event)

-    def keyPressEvent(self, event):
+    def keyPressEvent(self, event: Any) -> None:
        # Esc cancels face-pick mode.
-        if self._pick_face_mode and event.key() == Qt.Key_Escape:
+        if self._pick_face_mode and event.key() == Qt.Key.Key_Escape:
            self.set_pick_face_mode(False)
            self.pickFaceCancelled.emit()
            return
+        # Esc cancels fillet pick mode.
+        if self._fillet_pick_mode and event.key() == Qt.Key.Key_Escape:
+            self.set_fillet_pick_mode(False)
+            self.filletPickCancelled.emit()
+            return
+        # Esc cancels chamfer pick mode.
+        if self._chamfer_pick_mode and event.key() == Qt.Key.Key_Escape:
+            self.set_chamfer_pick_mode(False)
+            self.chamferPickCancelled.emit()
+            return
+        # Esc cancels thread pick mode.
+        if self._thread_pick_mode and event.key() == Qt.Key.Key_Escape:
+            self.set_thread_pick_mode(False)
+            self.threadPickCancelled.emit()
+            return
        # Esc cancels connector pick mode.
-        if self._connector_pick_mode and event.key() == Qt.Key_Escape:
+        if self._connector_pick_mode and event.key() == Qt.Key.Key_Escape:
            self.set_connector_pick_mode(False)
            self.connectorPickCancelled.emit()
            return
        # Esc cancels assembly move mode.
-        if self._assembly_move_mode and event.key() == Qt.Key_Escape:
+        if self._assembly_move_mode and event.key() == Qt.Key.Key_Escape:
            self.set_assembly_move_mode(False)
            return
+        # Esc cancels explicit sketch-gizmo pick mode.
+        if self._sketch_gizmo_pick_mode and event.key() == Qt.Key.Key_Escape:
+            self.set_sketch_gizmo_pick_mode(False)
+            self.sketchGizmoCancelled.emit()
+            return
        # Navigation shortcuts (lowercase = view presets, F = fit,
        # P/O = perspective/orthographic, R = reset).
        self._ensure_initialized()
@@ -1,7 +1,6 @@
 """Tests for Fluency CAD geometry kernel."""

 import pytest
-import numpy as np

 from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
 from fluency.geometry_occ.sketch import OCCSketch
@@ -195,10 +194,14 @@ class TestOCCSketch:
        sk = OCCSketch()
        sk.set_workplane((10.0, 0.0, 5.0), normal, x_dir)
        # 20x20 square in UV
-        p0 = sk.add_point(-10, -10); p1 = sk.add_point(10, -10)
-        p2 = sk.add_point(10, 10);   p3 = sk.add_point(-10, 10)
-        sk.add_line(p0, p1); sk.add_line(p1, p2)
-        sk.add_line(p2, p3); sk.add_line(p3, p0)
+        p0 = sk.add_point(-10, -10)
+        p1 = sk.add_point(10, -10)
+        p2 = sk.add_point(10, 10)
+        p3 = sk.add_point(-10, 10)
+        sk.add_line(p0, p1)
+        sk.add_line(p1, p2)
+        sk.add_line(p2, p3)
+        sk.add_line(p3, p0)

        geom = sk.get_geometry()
        # The face must carry the plane normal for the kernel.
@@ -220,10 +223,14 @@ class TestOCCSketch:

        sk = OCCSketch()
        sk.set_workplane((0, 0, 0), (0, 0, 1), (1, 0, 0))
-        a = sk.add_point(-10, -10); b = sk.add_point(10, -10)
-        c = sk.add_point(10, 10);   d = sk.add_point(-10, 10)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(-10, -10)
+        b = sk.add_point(10, -10)
+        c = sk.add_point(10, 10)
+        d = sk.add_point(-10, 10)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
        ctr = sk.add_point(0, 0)
        sk.add_circle(ctr, 3.0)

@@ -290,10 +297,14 @@ class TestExternalEntities:
        # Underlay: a 20x20 square projected from a face (closed polyline).
        sk.add_external_polyline([(0, 0), (20, 0), (20, 20), (0, 20), (0, 0)])
        # User profile: a 5x5 square — this is what should be extruded.
-        a = sk.add_point(2, 2); b = sk.add_point(8, 2)
-        c = sk.add_point(8, 8); d = sk.add_point(2, 8)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(2, 2)
+        b = sk.add_point(8, 2)
+        c = sk.add_point(8, 8)
+        d = sk.add_point(2, 8)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
        faces = sk.detect_faces()
        # Only the user-drawn face (5x5 square) should be detected.
        assert len(faces) == 1
@@ -310,10 +321,14 @@ class TestExternalEntities:
    def test_external_entities_excluded_from_get_polygon_points(self):
        sk = OCCSketch()
        sk.add_external_polyline([(0, 0), (100, 0), (100, 100), (0, 100), (0, 0)])
-        a = sk.add_point(1, 1); b = sk.add_point(2, 1)
-        c = sk.add_point(2, 2); d = sk.add_point(1, 2)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(1, 1)
+        b = sk.add_point(2, 1)
+        c = sk.add_point(2, 2)
+        d = sk.add_point(1, 2)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
        poly = sk.get_polygon_points()
        # The user square (1..2 range) should appear, not the 0..100 underlay.
        assert all(1.0 <= p.x <= 2.0 for p in poly)
@@ -328,10 +343,14 @@ class TestExternalEntities:
        # Underlay (NOT to be extruded).
        sk.add_external_polyline([(0, 0), (10, 0), (10, 10), (0, 10), (0, 0)])
        # User profile: a 2x2 square inside the underlay.
-        a = sk.add_point(1, 1); b = sk.add_point(3, 1)
-        c = sk.add_point(3, 3); d = sk.add_point(1, 3)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(1, 1)
+        b = sk.add_point(3, 1)
+        c = sk.add_point(3, 3)
+        d = sk.add_point(1, 3)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
        geom = sk.get_geometry()
        # Volume = 2 * 2 * 4 = 16, NOT 10 * 10 * 4 = 400.
        kernel = OCGeometryKernel()
@@ -498,10 +517,9 @@ class TestExtrudeCutFix:
        and the tool is no longer needed.
        """
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCGeometryKernel
        from OCP.GProp import GProp_GProps
        from OCP.BRepGProp import BRepGProp
-        import math

        k = OCGeometryKernel()
        target_shape = BRepPrimAPI_MakeBox(100, 100, 100).Shape()
@@ -511,17 +529,18 @@ class TestExtrudeCutFix:
        # expected volume easy to compute.
        from OCP.BRepPrimAPI import BRepPrimAPI_MakePrism
        from OCP.gp import gp_Pnt, gp_Vec
+
        # 20x20 square at (0,0,0), extruded along +Z by 200.
        from OCP.BRepBuilderAPI import BRepBuilderAPI_MakePolygon
+
        mp = BRepBuilderAPI_MakePolygon()
-        for (x, y) in [(0, 0), (20, 0), (20, 20), (0, 20)]:
+        for x, y in [(0, 0), (20, 0), (20, 20), (0, 20)]:
            mp.Add(gp_Pnt(x, y, 0))
        mp.Close()
        from OCP.BRepBuilderAPI import BRepBuilderAPI_MakeFace
+
        face = BRepBuilderAPI_MakeFace(mp.Wire()).Face()
-        tool_shape = BRepPrimAPI_MakePrism(
-            face, gp_Vec(0, 0, 200)
-        ).Shape()
+        tool_shape = BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, 200)).Shape()
        tool_obj = OCCGeometryObject(tool_shape, {"type": "prism"})

        # Before cut: target is 100^3 = 1_000_000.
@@ -536,9 +555,7 @@ class TestExtrudeCutFix:
        # After cut: target is 1_000_000 - 20*20*100 = 960_000
        # (the prism only intersects the box in z=[0,100], i.e. 100 deep).
        g1 = GProp_GProps()
-        BRepGProp.VolumeProperties_s(
-            k._get_shape(target_obj_geometry), g1
-        )
+        BRepGProp.VolumeProperties_s(k._get_shape(target_obj_geometry), g1)
        assert abs(g1.Mass() - 960_000.0) < 1.0

    def test_boolean_difference_does_not_leave_separate_cavity_body(self):
@@ -551,10 +568,9 @@ class TestExtrudeCutFix:
        target, so a single body remains.
        """
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from OCP.BRepAlgoAPI import BRepAlgoAPI_Cut
        from OCP.TopExp import TopExp_Explorer
        from OCP.TopAbs import TopAbs_SOLID
-        from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCGeometryKernel

        k = OCGeometryKernel()
        target_shape = BRepPrimAPI_MakeBox(100, 100, 100).Shape()
@@ -562,6 +578,7 @@ class TestExtrudeCutFix:

        # Tool: small box at the centre, fully inside the target.
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox as BBox
+
        tool_shape = BBox(20, 20, 20).Shape()
        tool_obj = OCCGeometryObject(tool_shape, {})

@@ -595,91 +612,59 @@ class TestBodyVisibilityToggle:

    def _make_window(self):
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import MainWindow
+
        return MainWindow()

    def test_body_list_uses_checkable_items(self):
-        """Each body list item must be a checkable QListWidgetItem."""
+        """Each body list item has a data role for the toggle handler."""
        from PySide6.QtCore import Qt
+
        win = self._make_window()
        # Add a fake body to the current component so the list isn't empty.
        from fluency.models.data_model import Body
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
+
+        box = OCCGeometryObject(BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {})
        win._current_component.bodies["a"] = Body(name="A", geometry=box)
        win._refresh_lists()
        items = win._body_list.findItems("A", Qt.MatchExactly)
        assert len(items) == 1
-        # Item is checkable (so the user can toggle visibility).
-        assert items[0].flags() & Qt.ItemIsUserCheckable
        # And the body id is stored on the item for the toggle handler.
        assert items[0].data(Qt.UserRole) == "a"
-        # Default state is checked (= visible).
-        assert items[0].checkState() == Qt.Checked
+        # Default state is visible.
+        assert win._current_component.bodies["a"].visible is True

    def test_toggling_visibility_updates_body_model(self):
-        """Flipping the checkbox should set body.visible accordingly."""
+        """Toggling visibility via _on_body_visibility_changed updates the model."""
        from PySide6.QtCore import Qt
+
        win = self._make_window()
        from fluency.models.data_model import Body
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
+
+        box = OCCGeometryObject(BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {})
        win._current_component.bodies["a"] = Body(name="A", geometry=box)
        win._refresh_lists()
        item = win._body_list.findItems("A", Qt.MatchExactly)[0]

        # Toggle off.
-        item.setCheckState(Qt.Unchecked)
        win._on_body_visibility_changed(item)
        assert win._current_component.bodies["a"].visible is False

        # Toggle back on.
-        item.setCheckState(Qt.Checked)
        win._on_body_visibility_changed(item)
        assert win._current_component.bodies["a"].visible is True

-    def test_visibility_no_op_when_unchanged(self):
-        """Re-emitting the same state must not trigger a viewer call.
-
-        The set_visibility call into the viewer is cheap but not free;
-        spamming it on every selection change would be wasteful.  The
-        handler short-circuits when the new state matches the model's.
-        """
-        from PySide6.QtCore import Qt
-        win = self._make_window()
-        from fluency.models.data_model import Body
-        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
-        win._current_component.bodies["a"] = Body(name="A", geometry=box)
-        win._refresh_lists()
-        item = win._body_list.findItems("A", Qt.MatchExactly)[0]
-
-        # Force the model's visibility to False to mimic a desync.
-        win._current_component.bodies["a"].visible = False
-        # Set the checkbox to Unchecked — this matches the model, so the
-        # handler should short-circuit (not call set_visibility).
-        item.setCheckState(Qt.Unchecked)
-        # We can't directly assert "viewer was not called" without
-        # monkey-patching; instead assert that re-firing the handler
-        # doesn't raise and the state is consistent.
-        win._on_body_visibility_changed(item)
-        assert win._current_component.bodies["a"].visible is False
-

 def math_hypot(x, y):
    import math
+
    return math.hypot(x, y)


@@ -698,10 +683,13 @@ class TestConstraintTagRendering:
    def _make_widget_with_sketch(self, sk):
        """Build a Sketch2DWidget in offscreen mode and attach *sk* to it."""
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import Sketch2DWidget
+
        w = Sketch2DWidget()
        w.set_sketch(sk)
        return w
@@ -824,6 +812,7 @@ class TestConstraintTagRendering:
        class _BadRound:
            def __round__(self, ndigits=0):
                raise TypeError("cannot round")
+
        sk._entities[c.id].geometry = (_BadRound(), _BadRound())
        tags = w._compute_constraint_tags()
        assert all(t["center"] is not None for t in tags)
@@ -865,12 +854,13 @@ class TestExtrudeRedesign:

    def _make_window_with_box(self, box_side=100.0):
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import MainWindow
        from fluency.models.data_model import Sketch, Body
-        from fluency.geometry_occ.kernel import OCCGeometryObject
        from fluency.geometry_occ.sketch import OCCSketch
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox

@@ -896,7 +886,6 @@ class TestExtrudeRedesign:
        return win, sketch, sk, box_obj

    def _add_circle(self, sk, r=10.0):
-        from fluency.geometry_occ.sketch import OCCSketch
        c = sk.add_point(0, 0)
        sk.add_circle(c, r)
        sk.solve()
@@ -905,6 +894,7 @@ class TestExtrudeRedesign:
    def _geometry_volume(self, win, geom):
        from OCP.GProp import GProp_GProps
        from OCP.BRepGProp import BRepGProp
+
        sh = win._kernel._get_shape(geom)
        g = GProp_GProps()
        BRepGProp.VolumeProperties_s(sh, g)
@@ -919,37 +909,48 @@ class TestExtrudeRedesign:
        so a 5 mm cut makes a real 5 mm-deep pocket.
        """
        import math
+
        win, sketch, sk, box_obj = self._make_window_with_box(100.0)
        face_geom = self._add_circle(sk, r=10.0)
        # Plain cut, length=5, NOT inverted.  Pre-redesign this would have
        # removed nothing; post-redesign it must remove a 5 mm cylinder.
        result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=5.0, symmetric=False, invert=False,
-            cut=True, union=False, through_all=False,
+            sketch,
+            face_geom,
+            length=5.0,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=False,
        )
        assert result is not None
        assert result["target_body"] is not None
        assert result["target_body"].name == "Box1"
        vol = self._geometry_volume(win, result["result_geom"])
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 5.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 5.0
        assert abs(vol - expected) < 1.0

    def test_cut_through_all_passes_through(self):
-        """"Through All" cut fully passes through the body."""
+        """ "Through All" cut fully passes through the body."""
        import math
+
        win, sketch, sk, box_obj = self._make_window_with_box(100.0)
        face_geom = self._add_circle(sk, r=10.0)
        result = win._compute_extrude_result(
-            sketch, face_geom,
+            sketch,
+            face_geom,
            length=5.0,  # ignored when through_all
-            symmetric=False, invert=False,
-            cut=True, union=False, through_all=True,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=True,
        )
        assert result is not None
        vol = self._geometry_volume(win, result["result_geom"])
        # Full through cylinder = pi * r^2 * box_depth.
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 100.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 100.0
        assert abs(vol - expected) < 1.0

    def test_cut_auto_targets_source_body_not_existing_zero(self):
@@ -960,30 +961,23 @@ class TestExtrudeRedesign:
        """
        import math
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import MainWindow
        from fluency.models.data_model import Sketch, Body
-        from fluency.geometry_occ.kernel import OCCGeometryObject
        from fluency.geometry_occ.sketch import OCCSketch
        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox

        win = MainWindow()
        # First body in the dict: a 50-millimetre box ALSO.
-        first = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(50, 50, 50).Shape(), {}
-        )
-        win._current_component.bodies["first"] = Body(
-            name="First", geometry=first
-        )
+        first = OCCGeometryObject(BRepPrimAPI_MakeBox(50, 50, 50).Shape(), {})
+        win._current_component.bodies["first"] = Body(name="First", geometry=first)
        # Source body: a 100-millimetre box (drawn over).
-        src = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(100, 100, 100).Shape(), {}
-        )
-        win._current_component.bodies["src"] = Body(
-            name="Src", geometry=src
-        )
+        src = OCCGeometryObject(BRepPrimAPI_MakeBox(100, 100, 100).Shape(), {})
+        win._current_component.bodies["src"] = Body(name="Src", geometry=src)
        # Sketch circle on top of the SOURCE box (0,0 so normal +Z).
        sk = OCCSketch()
        sk.set_workplane((50, 50, 100), (0, 0, 1), (1, 0, 0))
@@ -999,16 +993,21 @@ class TestExtrudeRedesign:

        face_geom = sk.get_geometry()
        result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=5.0, symmetric=False, invert=False,
-            cut=True, union=False, through_all=True,
+            sketch,
+            face_geom,
+            length=5.0,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=True,
        )
        assert result is not None
        # Target is the source box, NOT the dict's first body.
        assert result["target_body"].name == "Src"
        vol = self._geometry_volume(win, result["result_geom"])
        # 100^3 - pi*100*100 (through-all full-depth cut on the 100 box).
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 100.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 100.0
        assert abs(vol - expected) < 1.0

    def test_union_default_builds_outward(self):
@@ -1019,17 +1018,23 @@ class TestExtrudeRedesign:
        rather than "subtracting" from the existing box.
        """
        import math
+
        win, sketch, sk, box_obj = self._make_window_with_box(100.0)
        face_geom = self._add_circle(sk, r=10.0)
        result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=10.0, symmetric=False, invert=False,
-            cut=False, union=True, through_all=False,
+            sketch,
+            face_geom,
+            length=10.0,
+            symmetric=False,
+            invert=False,
+            cut=False,
+            union=True,
+            through_all=False,
        )
        assert result is not None
        vol = self._geometry_volume(win, result["result_geom"])
        # 100^3 + pi*100*10 — material added on top.
-        expected = 100.0 ** 3 + math.pi * (10.0 ** 2) * 10.0
+        expected = 100.0**3 + math.pi * (10.0**2) * 10.0
        assert abs(vol - expected) < 1.0

    def test_plain_extrude_untouched_by_source_body(self):
@@ -1037,9 +1042,14 @@ class TestExtrudeRedesign:
        win, sketch, sk, box_obj = self._make_window_with_box(100.0)
        face_geom = self._add_circle(sk, r=10.0)
        result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=10.0, symmetric=False, invert=False,
-            cut=False, union=False, through_all=False,
+            sketch,
+            face_geom,
+            length=10.0,
+            symmetric=False,
+            invert=False,
+            cut=False,
+            union=False,
+            through_all=False,
        )
        assert result is not None
        # No boolean target; result is the standalone tool extrusion.
@@ -1047,7 +1057,8 @@ class TestExtrudeRedesign:
        vol = self._geometry_volume(win, result["result_geom"])
        # Standalone cylinder 10 mm tall.
        import math
-        assert abs(vol - math.pi * (10.0 ** 2) * 10.0) < 1.0
+
+        assert abs(vol - math.pi * (10.0**2) * 10.0) < 1.0

    def test_freshly_picked_sketch_is_auto_selected(self):
        """After _on_face_picked, the new sketch is the current list row.
@@ -1055,7 +1066,6 @@ class TestExtrudeRedesign:
        The user should be able to click Extrude/Cut immediately without
        first hunting for the new sketch in the left list.
        """
-        from fluency.geometry_occ.kernel import OCCGeometryObject
        win, _, sk, box_obj = self._make_window_with_box(100.0)
        # Simulate _on_face_picked by calling it through a fake face
        # shape — but the simplest behavioural check is to call the
@@ -1063,6 +1073,7 @@ class TestExtrudeRedesign:
        # set as _current_sketch, and it appears (and is selected) in
        # the list after _refresh_lists + setCurrentRow.
        from fluency.models.data_model import Sketch
+
        sketch = Sketch(name="Sketch on face 99")
        sketch._source_body_id = "b1"
        sketch.set_workplane((50, 50, 100), (0, 0, 1), (1, 0, 0))
@@ -1084,8 +1095,10 @@ class TestExtrudeRedesign:
    def test_preview_callback_invoked_on_value_change(self):
        """The live preview callback fires on spinbox/checkbox changes."""
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import ExtrudeDialog

@@ -1110,8 +1123,10 @@ class TestExtrudeRedesign:
    def test_preview_hidden_event_sends_none(self):
        """hideEvent should deliver None to the callback so the host clears."""
        import os
+
        os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
        from PySide6.QtWidgets import QApplication
+
        app = QApplication.instance() or QApplication([])
        from fluency.main import ExtrudeDialog

@@ -0,0 +1,916 @@
+"""Tests for the technical drawing workbench.
+
+Covers the manual-dimension pipeline (model-space annotations →
+sheet-space candidates → placed primitives), the 2D pick geometry
+helpers, and persistence of drawings (manual dimensions included) in
+the .fluency project file.
+"""
+
+import json
+import math
+import os
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+import pytest
+
+from fluency.models.data_model import (
+    Body,
+    Component,
+    DrawingAnnotation,
+    DrawingView,
+    Project,
+    TechnicalDrawing,
+)
+from fluency.technical_drawing import (
+    build_manual_candidates,
+    generate_drawing,
+    _layout_views_on_sheet,
+)
+from fluency.io.project_io import (
+    _technical_drawing_from_dict,
+    _technical_drawing_to_dict,
+    load_project,
+    save_project,
+)
+from fluency.ui.technical_drawing_widget import (
+    _closest_point_on_segment,
+    _closest_points_on_segments,
+    _line_intersection,
+    _point_to_segment,
+)
+
+
+# ── Fixtures ───────────────────────────────────────────────────────────────
+
+
+@pytest.fixture(scope="module")
+def qapp():
+    """Offscreen QApplication for widget-level tests."""
+    from PySide6.QtWidgets import QApplication
+
+    app = QApplication.instance() or QApplication([])
+    yield app
+
+
+def _drawing_with_views(view_kinds=("front",)):
+    drawing = TechnicalDrawing(source_kind="component", source_id="comp-1")
+    for kind in view_kinds:
+        drawing.views.append(DrawingView(kind=kind))
+    return drawing
+
+
+def _manual_annotation(
+    dimension_kind: str,
+    view_id: str,
+    anchors,
+    direction=None,
+) -> DrawingAnnotation:
+    return DrawingAnnotation(
+        kind="dimension",
+        dimension_kind=dimension_kind,
+        view_id=view_id,
+        anchors=list(anchors),
+        direction=direction,
+    )
+
+
+# ── build_manual_candidates ────────────────────────────────────────────────
+
+
+class TestBuildManualCandidates:
+    def test_length_candidate_reprojects_anchors(self):
+        drawing = _drawing_with_views()
+        ann = _manual_annotation(
+            "length", "front", ((0.0, 0.0), (0.0, 12.5)), direction=(0.0, 1.0)
+        )
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"front": (2.0, 10.0, 20.0)}
+        )
+
+        assert unresolved == []
+        assert resolved == [ann.id]
+        c = cands[0]
+        assert c.kind == "length"
+        assert c.view_id == "front"
+        assert c.key == f"manual:{ann.id}"
+        assert c.references == (ann.id,)
+        assert c.value == pytest.approx(12.5)
+        assert c.label == "12.50"
+        # sheet = model * scale + offset
+        assert c.anchor_points[0] == pytest.approx((10.0, 20.0))
+        assert c.anchor_points[1] == pytest.approx((10.0, 45.0))
+        assert c.direction == (0.0, 1.0)
+
+    def test_length_without_transform_is_unresolved(self):
+        drawing = _drawing_with_views()
+        ann = _manual_annotation("length", "front", ((0.0, 0.0), (3.0, 4.0)))
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(drawing, {})
+        assert cands == []
+        assert unresolved == [ann.id]
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"front": (1.0, 0.0, 0.0)}
+        )
+        assert unresolved == []
+        c = cands[0]
+        assert c.value == pytest.approx(5.0)
+        assert c.direction == pytest.approx((0.6, 0.8))
+
+    def test_diameter_candidate(self):
+        drawing = _drawing_with_views()
+        ann = _manual_annotation("diameter", "top", ((-5.0, 0.0), (5.0, 0.0)))
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"top": (1.0, 0.0, 0.0)}
+        )
+
+        assert unresolved == []
+        c = cands[0]
+        assert c.kind == "diameter"
+        assert c.value == pytest.approx(10.0)
+        assert c.label == "Ø10.00"
+        assert c.direction == ()
+
+    def test_angle_candidate(self):
+        drawing = _drawing_with_views()
+        ann = _manual_annotation(
+            "angle", "front", ((0.0, 0.0), (10.0, 0.0), (0.0, 10.0))
+        )
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"front": (1.0, 0.0, 0.0)}
+        )
+
+        assert unresolved == []
+        c = cands[0]
+        assert c.kind == "angle"
+        assert c.value == pytest.approx(90.0)
+        assert c.label == "90.00°"
+        assert len(c.anchor_points) == 3
+
+    def test_degenerate_angle_is_unresolved(self):
+        # Collinear arms → 180° → not a usable angle dimension.
+        drawing = _drawing_with_views()
+        ann = _manual_annotation(
+            "angle", "front", ((0.0, 0.0), (10.0, 0.0), (-10.0, 0.0))
+        )
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"front": (1.0, 0.0, 0.0)}
+        )
+
+        assert cands == []
+        assert resolved == []
+        assert unresolved == [ann.id]
+    def test_hidden_annotation_is_skipped(self):
+        drawing = _drawing_with_views()
+        ann = _manual_annotation("length", "front", ((0.0, 0.0), (1.0, 0.0)))
+        ann.visible = False
+        drawing.annotations.append(ann)
+
+        cands, resolved, unresolved = build_manual_candidates(
+            drawing, {"front": (1.0, 0.0, 0.0)}
+        )
+
+        assert cands == []
+        assert resolved == []
+        assert unresolved == []
+
+
+# ── generate_drawing: auto vs manual dimensions ───────────────────────────
+
+
+@pytest.fixture(scope="module")
+def kernel():
+    from fluency.geometry_occ.kernel import OCGeometryKernel
+
+    return OCGeometryKernel()
+
+
+@pytest.fixture(scope="module")
+def box_project(kernel):
+    """Project with one 10 x 20 x 5 box (x: 0..10, y: 0..20, z: 0..5)."""
+    from fluency.geometry.base import Point2D
+
+    points = [Point2D(0, 0), Point2D(10, 0), Point2D(10, 20), Point2D(0, 20)]
+    polygon = kernel.create_polygon(points)
+    box = kernel.extrude(polygon, 5.0)
+    body = Body(name="Box", geometry=box)
+    comp = Component(name="BoxComp")
+    comp.bodies[body.id] = body
+    project = Project()
+    project.components[comp.id] = comp
+    project.active_component = comp.id
+    return project, comp
+
+
+class TestGenerateDrawingManualDimensions:
+    def test_manual_dimension_placed_with_auto_off(self, kernel, box_project):
+        project, comp = box_project
+        drawing = TechnicalDrawing(
+            source_kind="component",
+            source_id=comp.id,
+            views=[DrawingView(kind="front")],
+            auto_dimensions=False,
+        )
+        # Distance between the two vertical edges of the box front face.
+        ann = _manual_annotation(
+            "length", "front", ((0.0, 0.0), (10.0, 0.0)), direction=(1.0, 0.0)
+        )
+        drawing.annotations.append(ann)
+
+        result = generate_drawing(drawing, project, kernel)
+
+        assert result.view_transforms, "view transforms must be published"
+        manual_keys = [
+            p.candidate_key for p in result.primitives if p.candidate_key
+        ]
+        assert f"manual:{ann.id}" in manual_keys
+        label_texts = [
+            p.text
+            for p in result.primitives
+            if p.candidate_key == f"manual:{ann.id}" and p.kind == "text"
+        ]
+        assert label_texts == ["10.00"]
+        # Auto off → no auto-placed dimensions.
+        assert not any(
+            k for k in manual_keys if not k.startswith("manual:")
+        ), "auto dimensions must stay out while auto_dimensions is off"
+        assert ann.id in result.resolved_annotation_ids
+
+    def test_auto_off_places_no_auto_dimensions(self, kernel, box_project):
+        project, comp = box_project
+        drawing = TechnicalDrawing(
+            source_kind="component",
+            source_id=comp.id,
+            views=[DrawingView(kind="front")],
+            auto_dimensions=False,
+        )
+        result = generate_drawing(drawing, project, kernel)
+        dim_keys = [p.candidate_key for p in result.primitives if p.candidate_key]
+        assert dim_keys == [], f"expected no dimensions, got {dim_keys}"
+
+    def test_auto_on_places_auto_dimensions(self, kernel, box_project):
+        project, comp = box_project
+        drawing = TechnicalDrawing(
+            source_kind="component",
+            source_id=comp.id,
+            views=[DrawingView(kind="front")],
+            auto_dimensions=True,
+        )
+        result = generate_drawing(drawing, project, kernel)
+        dim_keys = [p.candidate_key for p in result.primitives if p.candidate_key]
+        assert dim_keys, "auto dimensions expected with auto_dimensions on"
+        assert all(not k.startswith("manual:") for k in dim_keys)
+
+    def test_auto_and_manual_coexist(self, kernel, box_project):
+        project, comp = box_project
+        drawing = TechnicalDrawing(
+            source_kind="component",
+            source_id=comp.id,
+            views=[DrawingView(kind="front")],
+            auto_dimensions=True,
+        )
+        ann = _manual_annotation(
+            "length", "front", ((0.0, 0.0), (10.0, 0.0)), direction=(1.0, 0.0)
+        )
+        drawing.annotations.append(ann)
+
+        result = generate_drawing(drawing, project, kernel)
+        dim_keys = {p.candidate_key for p in result.primitives if p.candidate_key}
+        assert f"manual:{ann.id}" in dim_keys
+        assert any(k for k in dim_keys if not k.startswith("manual:"))
+    def test_diameter_manual_on_cylinder(self, kernel):
+        from OCP.BRepPrimAPI import BRepPrimAPI_MakeCylinder
+        from OCP.gp import gp_Ax2, gp_Dir, gp_Pnt
+
+        from fluency.geometry_occ.kernel import OCCGeometryObject
+
+        ax = gp_Ax2(gp_Pnt(0, 0, 0), gp_Dir(0, 0, 1))
+        cyl = OCCGeometryObject(
+            BRepPrimAPI_MakeCylinder(ax, 4.0, 8.0).Shape(),
+            {"type": "cylinder"},
+        )
+        body = Body(name="Cyl", geometry=cyl)
+        comp = Component(name="CylComp")
+        comp.bodies[body.id] = body
+        project = Project()
+        project.components[comp.id] = comp
+        project.active_component = comp.id
+
+        drawing = TechnicalDrawing(
+            source_kind="component",
+            source_id=comp.id,
+            views=[DrawingView(kind="front")],
+            auto_dimensions=False,
+        )
+        ann = _manual_annotation("diameter", "front", ((-4.0, 0.0), (4.0, 0.0)))
+        drawing.annotations.append(ann)
+
+        result = generate_drawing(drawing, project, kernel)
+        label_texts = [
+            p.text
+            for p in result.primitives
+            if p.candidate_key == f"manual:{ann.id}" and p.kind == "text"
+        ]
+        assert label_texts == ["Ø8.00"]
+
+
+# ── Circle centres: ISO center marks + centre-point dimensioning ──────────
+
+
+def _cylinder_project(kernel):
+    """One Ø8 x 8 cylinder (axis +Z) as a draw-able component.
+
+    HLR may split a circle's edge into sampled segments for some shapes,
+    so tests that need a guaranteed circle primitive build it directly
+    (see :class:`TestCircleCenterMarks` / :class:`TestCircleCenterPick`).
+    """
+    from OCP.BRepPrimAPI import BRepPrimAPI_MakeCylinder
+    from OCP.gp import gp_Ax2, gp_Dir, gp_Pnt
+
+    from fluency.geometry_occ.kernel import OCCGeometryObject
+
+    ax = gp_Ax2(gp_Pnt(0, 0, 0), gp_Dir(0, 0, 1))
+    cyl = OCCGeometryObject(
+        BRepPrimAPI_MakeCylinder(ax, 4.0, 8.0).Shape(),
+        {"type": "cylinder"},
+    )
+    body = Body(name="Cyl", geometry=cyl)
+    comp = Component(name="CylComp")
+    comp.bodies[body.id] = body
+    project = Project()
+    project.components[comp.id] = comp
+    project.active_component = comp.id
+    return project, comp
+
+
+class TestCircleCenterMarks:
+    """ISO 14128 center marks: a thin cross at each projected circle's
+    centre, crossing at the centre and extending past the circle edge."""
+
+    def test_center_marks_emitted_for_circles(self):
+        from fluency.technical_drawing import _assemble_view
+
+        # Synthetic view plane: a 20 × 16 box with a r4 circle at (10, 8).
+        edges = [
+            ((0.0, 0.0), (20.0, 0.0), "line", "visible"),
+            ((20.0, 0.0), (20.0, 16.0), "line", "visible"),
+            ((20.0, 16.0), (0.0, 16.0), "line", "visible"),
+            ((0.0, 16.0), (0.0, 0.0), "line", "visible"),
+            ((10.0, 8.0), (14.0, 8.0), "circle_full", "visible"),
+        ]
+        view = DrawingView(kind="top")
+        prims, _cands, _warns = _assemble_view(edges, [], view, (10, 10, 200, 150))
+        circles = [p for p in prims if p.kind == "circle"]
+        assert len(circles) == 1
+        c = circles[0]
+        cx, cy = c.center
+        marks = [p for p in prims if p.kind == "line" and p.style == "center"]
+        assert len(marks) == 2, "one horizontal and one vertical center mark"
+        horiz = next(p for p in marks if p.points[0][1] == p.points[1][1])
+        vert = next(p for p in marks if p.points[0][0] == p.points[1][0])
+        # The marks cross at the circle centre.
+        assert horiz.points[0][1] == cy and horiz.points[1][1] == cy
+        assert vert.points[0][0] == cx and vert.points[1][0] == cx
+        # And each extends past the circle edge.
+        half_h = abs(horiz.points[1][0] - horiz.points[0][0]) / 2.0
+        half_v = abs(vert.points[1][1] - vert.points[0][1]) / 2.0
+        assert half_h > c.radius
+        assert half_v > c.radius
+
+class TestCircleCenterAnchors:
+    """Distance picks between circle centres, and between a centre and an
+    edge, resolve to the right model-space anchor pair."""
+
+    def _w(self):
+        from fluency.ui.technical_drawing_widget import TechnicalDrawingWidget
+
+        return TechnicalDrawingWidget
+
+    def test_pick_point_kinds(self):
+        W = self._w()
+        assert W._pick_point({"kind": "point", "point": (1.0, 2.0)}) == (1.0, 2.0)
+        assert W._pick_point(
+            {"kind": "circle", "center": (3.0, 4.0), "radius": 1.0}
+        ) == (3.0, 4.0)
+        assert W._pick_point({"kind": "segment", "p1": (0, 0), "p2": (1, 1)}) is None
+
+    def test_center_to_center(self):
+        W = self._w()
+        a = {"kind": "circle", "view_id": "v", "center": (0.0, 0.0), "radius": 2.0}
+        b = {"kind": "circle", "view_id": "v", "center": (5.0, 12.0), "radius": 3.0}
+        p1, p2 = W._distance_anchors(a, b)
+        assert p1 == (0.0, 0.0)
+        assert p2 == (5.0, 12.0)
+
+    def test_center_to_edge(self):
+        W = self._w()
+        a = {"kind": "point", "view_id": "v", "point": (4.0, 6.0)}
+        b = {"kind": "segment", "view_id": "v", "p1": (0.0, 0.0), "p2": (10.0, 0.0)}
+        p1, p2 = W._distance_anchors(a, b)
+        assert p1 == (4.0, 6.0)
+        # Closest point on the edge is straight below the centre.
+        assert p2 == pytest.approx((4.0, 0.0))
+
+    def test_edge_to_edge_unchanged(self):
+        W = self._w()
+        a = {"kind": "segment", "view_id": "v", "p1": (0.0, 0.0), "p2": (10.0, 0.0)}
+        b = {"kind": "segment", "view_id": "v", "p1": (2.0, 5.0), "p2": (8.0, 5.0)}
+        p1, p2 = W._distance_anchors(a, b)
+        assert p1 == pytest.approx((2.0, 0.0))
+        assert p2 == pytest.approx((2.0, 5.0))
+
+
+# ── View layout: page fill, no overlaps, title-block clearance ───────────
+
+
+class TestViewLayout:
+    """_layout_views_on_sheet packs the views to fill the sheet, keeps
+    them apart and clear of the title block, and rotates individual
+    views when that makes the set fit more."""
+
+    A3W, A3H = 420.0, 297.0
+    # Title block box + 5 mm clearance zone (see _title_block_primitives).
+    TB = (235.0, 0.0, 420.0, 62.0)
+
+    @staticmethod
+    def _bbox(w, h):
+        return (0.0, 0.0, float(w), float(h))
+
+    def _layout(self, kinds, boxes):
+        views = [DrawingView(kind=k) for k in kinds]
+        return _layout_views_on_sheet(views, {k: boxes[k] for k in kinds})
+
+    def _assert_valid(self, slots):
+        for k, s in slots.items():
+            assert s[0] >= 10.0 - 1e-6 and s[1] >= 10.0 - 1e-6, (k, s)
+            assert s[0] + s[2] <= self.A3W - 10.0 + 1e-6, (k, s)
+            assert s[1] + s[3] <= self.A3H - 10.0 + 1e-6, (k, s)
+            x0, y0, w, h = s
+            x1, y1, w2, h2 = self.TB
+            assert x0 + w <= x1 or x1 + w2 <= x0 or y0 + h <= y1 or y1 + h2 <= y0, \
+                f"{k} intrudes title block: {s}"
+        ks = list(slots)
+        for i in range(len(ks)):
+            for j in range(i + 1, len(ks)):
+                a, b_ = slots[ks[i]], slots[ks[j]]
+                sep = (
+                    a[0] + a[2] <= b_[0] + 0.1 or b_[0] + b_[2] <= a[0] + 0.1
+                    or a[1] + a[3] <= b_[1] + 0.1 or b_[1] + b_[3] <= a[1] + 0.1
+                )
+                assert sep, f"{ks[i]} overlaps {ks[j]}: {a} / {b_}"
+
+    @staticmethod
+    def _fill(slots):
+        x0 = min(s[0] for s in slots.values())
+        y0 = min(s[1] for s in slots.values())
+        x1 = max(s[0] + s[2] for s in slots.values())
+        y1 = max(s[1] + s[3] for s in slots.values())
+        return (x1 - x0) * (y1 - y0) / (420.0 * 297.0)
+
+    def test_single_view_fills_page(self):
+        slots, scale, rots = self._layout(["front"], {"front": self._bbox(10, 20)})
+        self._assert_valid(slots)
+        # 1–2 views stay upright — no sideways single view.
+        assert rots == {"front": 0.0}
+        # The tall 10 × 20 view is scaled until it touches the full-height
+        # left strip's reduced height (0.8 × 277 mm).
+        assert scale == pytest.approx(221.6 / 20.0)
+        assert slots["front"][3] == pytest.approx(221.6)
+
+    def test_two_views_share_page(self):
+        slots, _scale, _rots = self._layout(
+            ["front", "top"],
+            {"front": self._bbox(40, 40), "top": self._bbox(40, 20)},
+        )
+        self._assert_valid(slots)
+        assert self._fill(slots) > 0.30
+
+    def test_classic_three_view_keeps_cross(self):
+        boxes = {k: self._bbox(40, 40) for k in ("front", "top", "right")}
+        slots, _scale, rots = self._layout(list(boxes), boxes)
+        self._assert_valid(slots)
+        assert set(rots.values()) == {0.0}, "classic cross must not rotate"
+        # Top sits directly above front; right directly to its right.
+        assert abs(slots["top"][0] - slots["front"][0]) < 1e-6
+        assert slots["top"][1] > slots["front"][1] + slots["front"][3]
+        assert slots["right"][0] > slots["front"][0] + slots["front"][2]
+        assert abs(slots["right"][1] - slots["front"][1]) < 1e-6
+
+    def test_thin_part_gets_rotated_views(self):
+        boxes = {
+            "front": self._bbox(200, 30),
+            "top": self._bbox(30, 50),
+            "right": self._bbox(50, 30),
+            "left": self._bbox(50, 30),
+            "back": self._bbox(200, 30),
+            "bottom": self._bbox(30, 50),
+        }
+        slots, scale, rots = self._layout(list(boxes), boxes)
+        self._assert_valid(slots)
+        assert any(r == 90.0 for r in rots.values()), "rotation must kick in"
+        # Each slot is the (possibly swapped) model size times the scale.
+        for k, s in slots.items():
+            w, h = boxes[k][2], boxes[k][3]
+            sw, sh = s[2] / scale, s[3] / scale
+            assert (
+                (sw == pytest.approx(w) and sh == pytest.approx(h))
+                or (sw == pytest.approx(h) and sh == pytest.approx(w))
+            ), (k, s, w, h)
+
+    def test_all_views_plus_isometric_fill_page(self):
+        boxes = {
+            "front": self._bbox(80, 40),
+            "top": self._bbox(80, 30),
+            "right": self._bbox(30, 40),
+            "left": self._bbox(30, 40),
+            "back": self._bbox(80, 40),
+            "bottom": self._bbox(80, 30),
+            "isometric": self._bbox(60, 60),
+        }
+        slots, _scale, _rots = self._layout(list(boxes), boxes)
+        self._assert_valid(slots)
+        assert self._fill(slots) > 0.55
+
+
+# ── Project drawing persistence ────────────────────────────────────────────
+
+
+def _drawing_with_manual_dim():
+    drawing = TechnicalDrawing(
+        source_kind="component",
+        source_id="comp-42",
+        views=[DrawingView(kind="front"), DrawingView(kind="top")],
+        auto_dimensions=True,
+        title="Persisted Drawing",
+        revision="B",
+    )
+    drawing.annotations.append(
+        _manual_annotation(
+            "length", "front", ((0.0, 0.0), (0.0, 12.5)), direction=(0.0, 1.0)
+        )
+    )
+    drawing.annotations.append(
+        _manual_annotation("diameter", "top", ((-5.0, 0.0), (5.0, 0.0)))
+    )
+    return drawing
+
+
+class TestDrawingPersistence:
+    def test_drawing_dict_roundtrip(self):
+        drawing = _drawing_with_manual_dim()
+        data = _technical_drawing_to_dict(drawing)
+        restored = _technical_drawing_from_dict(json.loads(json.dumps(data)))
+
+        assert restored.id == drawing.id
+        assert restored.source_kind == "component"
+        assert restored.source_id == "comp-42"
+        assert restored.auto_dimensions is True
+        assert [v.kind for v in restored.views] == ["front", "top"]
+        assert len(restored.annotations) == 2
+
+        a = restored.annotations[0]
+        assert a.dimension_kind == "length"
+        assert a.view_id == "front"
+        assert a.anchors == [(0.0, 0.0), (0.0, 12.5)]
+        assert a.direction == (0.0, 1.0)
+
+        b = restored.annotations[1]
+        assert b.dimension_kind == "diameter"
+        assert b.anchors == [(-5.0, 0.0), (5.0, 0.0)]
+
+    def test_project_drawings_lookup(self):
+        project = Project()
+        drawing = _drawing_with_manual_dim()
+        project.add_drawing(drawing)
+
+        assert project.get_drawing_for("component", "comp-42") is drawing
+        assert project.get_drawing_for("assembly", "comp-42") is None
+        assert project.get_drawing_for("component", "other") is None
+
+    def test_project_save_load_roundtrip(self, tmp_path):
+        project = Project(name="Drawing Project")
+        drawing = _drawing_with_manual_dim()
+        project.add_drawing(drawing)
+
+        path = save_project(project, str(tmp_path / "proj.fluency"))
+        loaded, _view_state = load_project(path)
+
+        assert len(loaded.drawings) == 1
+        restored = loaded.drawings[0]
+        assert restored.source_id == "comp-42"
+        assert restored.auto_dimensions is True
+        assert restored.title == "Persisted Drawing"
+        assert len(restored.annotations) == 2
+
+        a = restored.annotations[0]
+        assert a.dimension_kind == "length"
+        assert a.view_id == "front"
+        assert a.anchors == [(0.0, 0.0), (0.0, 12.5)]
+        assert a.direction == (0.0, 1.0)
+        assert a.id == drawing.annotations[0].id
+
+        # The restored drawing must still build the same candidates.
+        cands, resolved, unresolved = build_manual_candidates(
+            restored, {"front": (1.0, 0.0, 0.0), "top": (1.0, 0.0, 0.0)}
+        )
+        assert unresolved == []
+        labels = sorted(c.label for c in cands)
+        assert labels == ["12.50", "Ø10.00"]
+
+    def test_load_ignores_corrupt_drawing_entry(self, tmp_path):
+        import zipfile
+
+        project = Project(name="Mixed")
+        project.add_drawing(_drawing_with_manual_dim())
+        path = save_project(project, str(tmp_path / "proj.fluency"))
+
+        with zipfile.ZipFile(path, "r") as zf:
+            names = zf.namelist()
+            contents = {n: zf.read(n) for n in names}
+        manifest = json.loads(contents["project.json"])
+        manifest["drawings"].append({"id": "broken", "views": "not-a-list"})
+        contents["project.json"] = json.dumps(manifest).encode("utf-8")
+
+        with zipfile.ZipFile(path, "w") as zf:
+            for name in names:
+                zf.writestr(name, contents[name])
+
+        loaded, _ = load_project(path)
+        # Corrupt entry skipped, valid one kept.
+        assert len(loaded.drawings) == 1
+        assert loaded.drawings[0].source_id == "comp-42"
+
+    def test_auto_dimensions_default_off(self):
+        assert TechnicalDrawing().auto_dimensions is False
+
+
+# ── Pick geometry helpers ──────────────────────────────────────────────────
+
+
+class TestPickGeometry:
+    def test_point_to_segment_inside(self):
+        q, d = _point_to_segment((5.0, 3.0), (0.0, 0.0), (10.0, 0.0))
+        assert q == pytest.approx((5.0, 0.0))
+        assert d == pytest.approx(3.0)
+
+    def test_point_to_segment_clamps_at_endpoint(self):
+        q, d = _point_to_segment((-2.0, 1.0), (0.0, 0.0), (10.0, 0.0))
+        assert q == pytest.approx((0.0, 0.0))
+        assert d == pytest.approx(math.hypot(2.0, 1.0))
+
+    def test_crossing_segments(self):
+        q1, q2, d = _closest_points_on_segments(
+            (0.0, 0.0), (10.0, 0.0), (4.0, -2.0), (4.0, 8.0)
+        )
+        assert q1 == pytest.approx((4.0, 0.0))
+        assert q2 == pytest.approx((4.0, 0.0))
+        assert d == pytest.approx(0.0, abs=1e-9)
+
+    def test_parallel_overlapping_segments(self):
+        # The classic "distance between two parallel edges" pick:
+        # result must be the true perpendicular distance.
+        q1, q2, d = _closest_points_on_segments(
+            (0.0, 0.0), (10.0, 0.0), (2.0, 5.0), (8.0, 5.0)
+        )
+        assert d == pytest.approx(5.0)
+        assert q1[1] == pytest.approx(0.0)
+        assert q2[1] == pytest.approx(5.0)
+        assert q1[0] == pytest.approx(q2[0])
+
+    def test_parallel_disjoint_segments(self):
+        q1, q2, d = _closest_points_on_segments(
+            (0.0, 0.0), (2.0, 0.0), (5.0, 3.0), (7.0, 3.0)
+        )
+        assert d == pytest.approx(math.hypot(3.0, 3.0))
+
+    def test_line_intersection(self):
+        pt = _line_intersection(
+            (0.0, 0.0), (10.0, 0.0), (4.0, -2.0), (4.0, 8.0)
+        )
+        assert pt == pytest.approx((4.0, 0.0))
+
+    def test_line_intersection_parallel_is_none(self):
+        assert _line_intersection(
+            (0.0, 0.0), (10.0, 0.0), (2.0, 5.0), (8.0, 5.0)
+        ) is None
+
+    def test_closest_point_on_segment(self):
+        q = _closest_point_on_segment((4.0, 9.0), (0.0, 0.0), (10.0, 0.0))
+        assert q == pytest.approx((4.0, 0.0))
+
+
+# ── Widget: dimension tool plumbing (offscreen) ────────────────────────────
+
+
+class TestDrawingWidgetTools:
+    def _widget(self, qapp):
+        from fluency.ui.technical_drawing_widget import TechnicalDrawingWidget
+
+        return TechnicalDrawingWidget()
+
+    def test_widget_starts_without_pick_mode(self, qapp):
+        w = self._widget(qapp)
+        assert w._canvas._pick_mode == ""
+        assert not w._auto_dim_check.isChecked()
+        assert not any(b.isChecked() for b in w._tool_buttons.values())
+
+    def test_tool_toggle_enters_pick_mode(self, qapp):
+        w = self._widget(qapp)
+        btn = w._tool_buttons["distance"]
+        btn.setChecked(True)
+        assert w._canvas._pick_mode == "distance"
+        assert "Distance" in w._status_label.text()
+        assert "edge" in w._status_label.text()
+
+        # Switching tools re-targets the canvas and unchecks the old tool.
+        w._tool_buttons["diameter"].setChecked(True)
+        assert btn.isChecked() is False
+        assert w._canvas._pick_mode == "diameter"
+
+        # Escape path: cancels the tool, clears all buttons and mode.
+        w._cancel_pick()
+        assert w._canvas._pick_mode == ""
+        for other in w._tool_buttons.values():
+            assert not other.isChecked()
+
+    def test_add_manual_dimension_appends_and_emits(self, qapp):
+        w = self._widget(qapp)
+        w.set_drawing(
+            TechnicalDrawing(source_kind="component", source_id="c1")
+        )
+        changes = []
+        w.drawing_changed.connect(lambda: changes.append(1))
+
+        w._add_manual_dimension(
+            "length",
+            anchors=((0.0, 0.0), (10.0, 0.0)),
+            view_id="front",
+            direction=(1.0, 0.0),
+        )
+
+        anns = w._drawing.annotations
+        assert len(anns) == 1
+        assert anns[0].dimension_kind == "length"
+        assert anns[0].view_id == "front"
+        assert anns[0].anchors == [(0.0, 0.0), (10.0, 0.0)]
+        assert changes == [1]
+
+    def test_clear_removes_manual_dimensions_only(self, qapp):
+        w = self._widget(qapp)
+        drawing = TechnicalDrawing(source_kind="component", source_id="c1")
+        drawing.annotations.append(
+            DrawingAnnotation(kind="note", text="keep me")
+        )
+        drawing.annotations.append(
+            _manual_annotation(
+                "length", "front", ((0.0, 0.0), (5.0, 0.0))
+            )
+        )
+        w.set_drawing(drawing)
+
+        w._on_clear_clicked()
+
+        assert len(drawing.annotations) == 1
+        assert drawing.annotations[0].kind == "note"
+
+    def test_adopt_stored_project_drawing(self, qapp, kernel):
+        w = self._widget(qapp)
+        project = Project()
+        comp = Component(name="ExistingComp")
+        project.components[comp.id] = comp
+        stored = TechnicalDrawing(
+            source_kind="component", source_id=comp.id
+        )
+        stored.annotations.append(
+            _manual_annotation(
+                "diameter", "front", ((-4.0, 0.0), (4.0, 0.0))
+            )
+        )
+        project.add_drawing(stored)
+        w.set_project(project, kernel)
+
+        w.set_active_component(comp)
+
+        # The stored drawing is re-adopted (not replaced).
+        assert w._drawing is stored
+        assert len(w._drawing.annotations) == 1
+
+    def test_new_source_creates_and_registers_drawing(self, qapp, kernel):
+        w = self._widget(qapp)
+        project = Project()
+        comp = Component(name="NewComp")
+        project.components[comp.id] = comp
+        w.set_project(project, kernel)
+
+        w.set_active_component(comp)
+
+        assert w._drawing is not None
+        assert w._drawing.source_kind == "component"
+        assert w._drawing.source_id == comp.id
+        assert len(project.drawings) == 1
+        assert project.drawings[0] is w._drawing
+
+
+class TestCircleCenterPick:
+    """Clicking a circle's centre mark while a distance tool is active
+    picks a point feature at the circle centre (model coords + radius).
+
+    HLR only projects a true circle for some hole shapes (a plain
+    cylinder discretises into segments), so the render result is built
+    directly with one guaranteed circle primitive.
+    """
+
+    def _canvas_with_circle(self, qapp):
+        from PySide6.QtCore import QPointF
+
+        from fluency.technical_drawing import (
+            DrawingPrimitive,
+            DrawingRenderResult,
+        )
+        from fluency.ui.technical_drawing_widget import DrawingCanvas
+
+        # One r4 circle at model (20, 15), drawn at 10× scale at the
+        # sheet centre: model (20,15) → sheet (200, 150).
+        circle = DrawingPrimitive(
+            kind="circle",
+            points=(),
+            style="visible",
+            center=(200.0, 150.0),
+            radius=40.0,
+            view_id="top",
+        )
+        result = DrawingRenderResult(
+            primitives=(circle,),
+            candidates=(),
+            resolved_annotation_ids=(),
+            unresolved_annotation_ids=(),
+            source_fingerprint="",
+            warnings=(),
+            view_transforms={"top": (10.0, 0.0, 0.0)},
+        )
+        canvas = DrawingCanvas()
+        canvas.resize(840, 600)
+        canvas.set_render_result(result)
+        canvas.set_pick_mode("distance")
+        return canvas, QPointF
+
+    def test_pick_center_mark_returns_point(self, qapp):
+        canvas, QPointF = self._canvas_with_circle(qapp)
+        # Sheet → device position of the circle centre.
+        rect = canvas._sheet_rect()
+        scale = rect.width() / 420.0
+        pos = QPointF(rect.x() + 200.0 * scale, rect.y() + (297.0 - 150.0) * scale)
+
+        hit = canvas._pick_feature(pos)
+        assert hit is not None, "clicking the centre mark must hit something"
+        assert hit["kind"] == "point"
+        assert hit["view_id"] == "top"
+        assert hit["radius"] == pytest.approx(4.0, abs=1e-6)
+        # The picked model point is the inverse-transformed sheet centre:
+        # (200, 150) at 10× scale → (20, 15).
+        assert hit["point"] == pytest.approx((20.0, 15.0), abs=1e-9)
+
+    def test_distance_tool_accepts_center_then_edge(self, qapp, kernel):
+        from fluency.ui.technical_drawing_widget import TechnicalDrawingWidget
+
+        w = TechnicalDrawingWidget()
+        project, comp = _cylinder_project(kernel)
+        w.set_project(project, kernel)
+        w.set_active_component(comp)
+        assert w._drawing is not None
+
+        # First pick: a circle centre at model (10, 12) — the dict a
+        # centre-mark click produces (see test above).
+        w._first_pick = {
+            "kind": "point",
+            "view_id": "top",
+            "point": (10.0, 12.0),
+            "radius": 4.0,
+        }
+        # Second pick: a horizontal edge 6 mm above the centre.
+        second = {
+            "kind": "segment",
+            "view_id": "top",
+            "p1": (0.0, 18.0),
+            "p2": (20.0, 18.0),
+        }
+        w._on_edge_pick(second, "distance")
+        assert w._drawing.annotations, "a manual dimension must be appended"
+        ann = w._drawing.annotations[-1]
+        assert ann.dimension_kind == "length"
+        assert ann.view_id == "top"
+        # First anchor is the picked centre; the second is the closest
+        # point on the edge, straight above it.
+        assert ann.anchors[0] == pytest.approx((10.0, 12.0), abs=1e-9)
+        assert ann.anchors[1] == pytest.approx((10.0, 18.0), abs=1e-6)
+
Author	SHA1	Message	Date
bklronin	9abeb6266a	- Assembly instaiated operations - assembly forward proagation	2026-08-19 20:14:14 +02:00
bklronin	6b6f7de5ab	Fiexed highlighting of operations	2026-08-19 00:11:24 +02:00
bklronin	b184ade967	- added iso sheet for tech draw	2026-08-18 16:12:09 +02:00
bklronin	67b73c13b8	- tech drawing and render improv	2026-08-18 15:06:51 +02:00
bklronin	813ddc3596	- tech draw draft v2	2026-08-17 21:39:20 +02:00
bklronin	37e5335446	- tech draw draft v2	2026-08-17 18:35:18 +02:00
bklronin	108ad2d5b5	- tech draw draft v2	2026-08-16 22:01:36 +02:00
bklronin	1eee203ba8	- tech draw draft	2026-08-16 15:54:41 +02:00
bklronin	a00129603c	- Operation highlighting, body highlighting	2026-08-08 13:49:59 +02:00
bklronin	3d63f033f2	- Operation highlighting, body highlighting	2026-08-08 13:46:12 +02:00
bklronin	b29bc11b42	- Operation highlighting, body highlighting	2026-08-08 11:15:49 +02:00
bklronin	79ad85594e	- arc improvements, fillets, operations, bodys	2026-08-07 19:55:15 +02:00
bklronin	655df71cd8	- arc improvements, fillets, operations, bodys	2026-08-07 15:44:53 +02:00
bklronin	7072dcee08	- arc improvements, fillets, operations, bodys	2026-08-05 18:53:48 +02:00
bklronin	1e9b0cab1c	- arc improvements, fillets, operations, bodys	2026-08-05 16:47:25 +02:00
bklronin	a7e7a9f2c3	- arc improvements, fillets, operations, bodys	2026-08-05 09:44:17 +02:00
bklronin	48042659fc	- arc improvements, fillets, operations, bodys	2026-08-02 22:04:57 +02:00
bklronin	baa2fd5d47	- added "measurement lines"	2026-08-02 20:58:43 +02:00
bklronin	0daa6152ee	- added "measurement lines"	2026-07-26 21:39:47 +02:00