- Assembly instaiated operations

- assembly forward proagation

.gitignore

@@ -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

.idea/workspace.xml

@@ -4,21 +4,16 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- arc improvements, fillets, operations, bodys">
+    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="Fiexed highlighting of operations">
       <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/gui.ui" beforeDir="false" afterPath="$PROJECT_DIR$/gui.ui" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/gui_ui.py" beforeDir="false" afterPath="$PROJECT_DIR$/gui_ui.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/geometry_occ/kernel.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/geometry_occ/kernel.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/geometry_occ/sketch.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/geometry_occ/sketch.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/io/project_io.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/io/project_io.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/main.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/main.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/models/data_model.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/models/data_model.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/tests/test_project_io.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/tests/test_project_io.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/ui/dialogs.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/dialogs.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/ui/gui_ui.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/gui_ui.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/ui/main_window.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/main_window.py" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/fluency/ui/render_window.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/render_window.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/ui/sketch_widget.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/sketch_widget.py" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/fluency/ui/technical_drawing_widget.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/technical_drawing_widget.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/ui/viewer_widget.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/viewer_widget.py" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
@@ -80,6 +75,7 @@
     &quot;Python.side_fluency.executor&quot;: &quot;Run&quot;,
     &quot;Python.simple_mesh.executor&quot;: &quot;Run&quot;,
     &quot;Python.sketch.executor&quot;: &quot;Run&quot;,
+    &quot;Python.technical_drawing_widget.executor&quot;: &quot;Run&quot;,
     &quot;Python.vtk_widget.executor&quot;: &quot;Run&quot;,
     &quot;Python.vulkan.executor&quot;: &quot;Run&quot;,
     &quot;RunOnceActivity.OpenProjectViewOnStart&quot;: &quot;true&quot;,
@@ -89,7 +85,7 @@
     &quot;RunOnceActivity.typescript.service.memoryLimit.init&quot;: &quot;true&quot;,
     &quot;codeWithMe.voiceChat.enabledByDefault&quot;: &quot;false&quot;,
     &quot;git-widget-placeholder&quot;: &quot;feature/occ-migration&quot;,
-    &quot;last_opened_file_path&quot;: &quot;/Volumes/Data_drive/Programming/fluency&quot;,
+    &quot;last_opened_file_path&quot;: &quot;/Volumes/Data_drive/Programming/fluency/src/fluency&quot;,
     &quot;node.js.detected.package.eslint&quot;: &quot;true&quot;,
     &quot;node.js.selected.package.eslint&quot;: &quot;(autodetect)&quot;,
     &quot;node.js.selected.package.tslint&quot;: &quot;(autodetect)&quot;,
@@ -104,11 +100,11 @@
   </component>
   <component name="RecentsManager">
     <key name="CopyFile.RECENT_KEYS">
-      <recent name="$PROJECT_DIR$" />
       <recent name="$PROJECT_DIR$/src/fluency" />
+      <recent name="$PROJECT_DIR$" />
+      <recent name="$PROJECT_DIR$/src/fluency/Tesfiles" />
       <recent name="$PROJECT_DIR$/src/fluency/rendering" />
       <recent name="$PROJECT_DIR$/drawing_modules" />
-      <recent name="$PROJECT_DIR$/modules" />
     </key>
     <key name="MoveFile.RECENT_KEYS">
       <recent name="$PROJECT_DIR$" />
@@ -130,54 +126,6 @@
       <option name="presentableId" value="Default" />
       <updated>1703867682707</updated>
     </task>
-    <task id="LOCAL-00001" summary="init">
-      <option name="closed" value="true" />
-      <created>1703951701948</created>
-      <option name="number" value="00001" />
-      <option name="presentableId" value="LOCAL-00001" />
-      <option name="project" value="LOCAL" />
-      <updated>1703951701948</updated>
-    </task>
-    <task id="LOCAL-00002" summary="- Basic oop sketch widget implement">
-      <option name="closed" value="true" />
-      <created>1729958532384</created>
-      <option name="number" value="00002" />
-      <option name="presentableId" value="LOCAL-00002" />
-      <option name="project" value="LOCAL" />
-      <updated>1729958532384</updated>
-    </task>
-    <task id="LOCAL-00003" summary="- Sketch projection partly works again :)">
-      <option name="closed" value="true" />
-      <created>1735563255455</created>
-      <option name="number" value="00003" />
-      <option name="presentableId" value="LOCAL-00003" />
-      <option name="project" value="LOCAL" />
-      <updated>1735563255455</updated>
-    </task>
-    <task id="LOCAL-00004" summary="- Sketch projection partly works again :)">
-      <option name="closed" value="true" />
-      <created>1735585968733</created>
-      <option name="number" value="00004" />
-      <option name="presentableId" value="LOCAL-00004" />
-      <option name="project" value="LOCAL" />
-      <updated>1735585968733</updated>
-    </task>
-    <task id="LOCAL-00005" summary="- Added new componnt controls">
-      <option name="closed" value="true" />
-      <created>1735601610504</created>
-      <option name="number" value="00005" />
-      <option name="presentableId" value="LOCAL-00005" />
-      <option name="project" value="LOCAL" />
-      <updated>1735601610504</updated>
-    </task>
-    <task id="LOCAL-00006" summary="- Added new componnt controls">
-      <option name="closed" value="true" />
-      <created>1735601786207</created>
-      <option name="number" value="00006" />
-      <option name="presentableId" value="LOCAL-00006" />
-      <option name="project" value="LOCAL" />
-      <updated>1735601786207</updated>
-    </task>
     <task id="LOCAL-00007" summary="- changing compos for sketches works">
       <option name="closed" value="true" />
       <created>1735652081552</created>
@@ -482,7 +430,95 @@
       <option name="project" value="LOCAL" />
       <updated>1785915859137</updated>
     </task>
-    <option name="localTasksCounter" value="45" />
+    <task id="LOCAL-00045" summary="- arc improvements, fillets, operations, bodys">
+      <option name="closed" value="true" />
+      <created>1785941246695</created>
+      <option name="number" value="00045" />
+      <option name="presentableId" value="LOCAL-00045" />
+      <option name="project" value="LOCAL" />
+      <updated>1785941246695</updated>
+    </task>
+    <task id="LOCAL-00046" summary="- arc improvements, fillets, operations, bodys">
+      <option name="closed" value="true" />
+      <created>1785948828454</created>
+      <option name="number" value="00046" />
+      <option name="presentableId" value="LOCAL-00046" />
+      <option name="project" value="LOCAL" />
+      <updated>1785948828454</updated>
+    </task>
+    <task id="LOCAL-00047" summary="- arc improvements, fillets, operations, bodys">
+      <option name="closed" value="true" />
+      <created>1786110295218</created>
+      <option name="number" value="00047" />
+      <option name="presentableId" value="LOCAL-00047" />
+      <option name="project" value="LOCAL" />
+      <updated>1786110295218</updated>
+    </task>
+    <task id="LOCAL-00048" summary="- arc improvements, fillets, operations, bodys">
+      <option name="closed" value="true" />
+      <created>1786125317688</created>
+      <option name="number" value="00048" />
+      <option name="presentableId" value="LOCAL-00048" />
+      <option name="project" value="LOCAL" />
+      <updated>1786125317688</updated>
+    </task>
+    <task id="LOCAL-00049" summary="- Operation highlighting, body highlighting">
+      <option name="closed" value="true" />
+      <created>1786180549405</created>
+      <option name="number" value="00049" />
+      <option name="presentableId" value="LOCAL-00049" />
+      <option name="project" value="LOCAL" />
+      <updated>1786180549405</updated>
+    </task>
+    <task id="LOCAL-00050" summary="- tech draw draft">
+      <option name="closed" value="true" />
+      <created>1786888483687</created>
+      <option name="number" value="00050" />
+      <option name="presentableId" value="LOCAL-00050" />
+      <option name="project" value="LOCAL" />
+      <updated>1786888483688</updated>
+    </task>
+    <task id="LOCAL-00051" summary="- tech draw draft v2">
+      <option name="closed" value="true" />
+      <created>1786910497589</created>
+      <option name="number" value="00051" />
+      <option name="presentableId" value="LOCAL-00051" />
+      <option name="project" value="LOCAL" />
+      <updated>1786910497589</updated>
+    </task>
+    <task id="LOCAL-00052" summary="- tech draw draft v2">
+      <option name="closed" value="true" />
+      <created>1786984519780</created>
+      <option name="number" value="00052" />
+      <option name="presentableId" value="LOCAL-00052" />
+      <option name="project" value="LOCAL" />
+      <updated>1786984519781</updated>
+    </task>
+    <task id="LOCAL-00053" summary="- tech draw draft v2">
+      <option name="closed" value="true" />
+      <created>1786995561375</created>
+      <option name="number" value="00053" />
+      <option name="presentableId" value="LOCAL-00053" />
+      <option name="project" value="LOCAL" />
+      <updated>1786995561376</updated>
+    </task>
+    <task id="LOCAL-00054" summary="- tech drawing and render improv">
+      <option name="closed" value="true" />
+      <created>1787058413911</created>
+      <option name="number" value="00054" />
+      <option name="presentableId" value="LOCAL-00054" />
+      <option name="project" value="LOCAL" />
+      <updated>1787058413911</updated>
+    </task>
+    <task id="LOCAL-00055" summary="Fiexed highlighting of operations">
+      <option name="closed" value="true" />
+      <created>1787091089061</created>
+      <option name="number" value="00055" />
+      <option name="presentableId" value="LOCAL-00055" />
+      <option name="project" value="LOCAL" />
+      <updated>1787091089061</updated>
+    </task>
+    <option name="localTasksCounter" value="56" />
     <servers />
   </component>
   <component name="TypeScriptGeneratedFilesManager">
@@ -503,11 +539,6 @@
     <ignored-roots>
       <path value="$PROJECT_DIR$/pythonProject" />
     </ignored-roots>
-    <MESSAGE value="- changing compos for sketches works" />
-    <MESSAGE value="- changing compos including sketches and bodies" />
-    <MESSAGE value="- Drawing bodys depending on the selected compo&#10;- Cut working&#10;- Edit sketch working" />
-    <MESSAGE value="- delete sketch working&#10;- added mid point snap&#10;- added hovering line with distance" />
-    <MESSAGE value="- Added new buttons and settings" />
     <MESSAGE value="- Added construction lines switching&#10;- Moved callbacks into sketchwidget from main.&#10;- Changed reset on right click" />
     <MESSAGE value="- Added contrain displayed next to line&#10;- Slight change to point check from solver." />
     <MESSAGE value="- Added enabling of midpsnap and prepared others&#10;- Show dimesnion on hover" />
@@ -528,6 +559,11 @@
     <MESSAGE value="- Render improvements, camera plane, update" />
     <MESSAGE value="- added &quot;measurement lines&quot;" />
     <MESSAGE value="- arc improvements, fillets, operations, bodys" />
-    <option name="LAST_COMMIT_MESSAGE" value="- arc improvements, fillets, operations, bodys" />
+    <MESSAGE value="- Operation highlighting, body highlighting" />
+    <MESSAGE value="- tech draw draft" />
+    <MESSAGE value="- tech draw draft v2" />
+    <MESSAGE value="- tech drawing and render improv" />
+    <MESSAGE value="Fiexed highlighting of operations" />
+    <option name="LAST_COMMIT_MESSAGE" value="Fiexed highlighting of operations" />
   </component>
 </project>

.layout_new.py

@@ -0,0 +1,376 @@
+# ── 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 = (
+    _LAYOUT_MARGIN_MM,
+    _TB_TOP_MM + _TB_CLEARANCE_MM,
+    _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

.render_check.py

@@ -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))

.smoke_layout.py

@@ -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")

.test_connector_relocate.py

@@ -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")

.test_demo_repro.py

@@ -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")

.test_instance_ops.py

@@ -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()

.test_relocate_fallback.py

@@ -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")

.test_underlay_curves.py

@@ -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")

WARP.md

@@ -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

gui.ui

@@ -1170,41 +1170,27 @@
        <string>Modify</string>
       </property>
       <layout class="QGridLayout" name="gridLayout_3">
-       <item row="1" column="0">
+       <item row="2" column="1">
-        <widget class="QPushButton" name="pb_combop">
+        <widget class="QPushButton" name="pb_chamfer_op">
          <property name="text">
-          <string>Comb</string>
+          <string>Chamfer</string>
          </property>
         </widget>
        </item>
        <item row="2" column="0">
-        <widget class="QPushButton" name="pb_arrayop">
-         <property name="text">
-          <string>Array</string>
-         </property>
-        </widget>
-       </item>
-       <item row="1" column="1">
-        <widget class="QPushButton" name="pb_moveop">
-         <property name="text">
-          <string>Mve</string>
-         </property>
-        </widget>
-       </item>
-       <item row="2" column="1">
-        <widget class="QPushButton" name="pb_revop">
-         <property name="text">
-          <string>Rev</string>
-         </property>
-        </widget>
-       </item>
-       <item row="3" column="0">
         <widget class="QPushButton" name="pb_fillet_op">
          <property name="text">
           <string>Fillet</string>
          </property>
         </widget>
        </item>
+       <item row="6" column="0">
+        <widget class="QPushButton" name="pb_thread">
+         <property name="text">
+          <string>Thread</string>
+         </property>
+        </widget>
+       </item>
        <item row="0" column="0">
         <widget class="QPushButton" name="pb_extrdop">
          <property name="text">
@@ -1212,6 +1198,13 @@
          </property>
         </widget>
        </item>
+       <item row="4" column="1">
+        <widget class="QPushButton" name="pb_revop">
+         <property name="text">
+          <string>Rev</string>
+         </property>
+        </widget>
+       </item>
        <item row="0" column="1">
         <widget class="QPushButton" name="pb_cutop">
          <property name="text">
@@ -1219,17 +1212,31 @@
          </property>
         </widget>
        </item>
-       <item row="3" column="1">
+       <item row="4" column="0">
-        <widget class="QPushButton" name="pb_chamfer">
+        <widget class="QPushButton" name="pb_arrayop">
          <property name="text">
-          <string>Chamfer</string>
+          <string>Arry</string>
          </property>
         </widget>
        </item>
-       <item row="4" column="0">
+       <item row="1" column="0">
-        <widget class="QPushButton" name="pb_thread">
+        <widget class="QPushButton" name="pb_combop">
          <property name="text">
-          <string>Thread</string>
+          <string>Comb</string>
+         </property>
+        </widget>
+       </item>
+       <item row="1" column="1">
+        <widget class="QPushButton" name="pb_moveop">
+         <property name="text">
+          <string>Mve</string>
+         </property>
+        </widget>
+       </item>
+       <item row="6" column="1">
+        <widget class="QPushButton" name="pb_mirror_op">
+         <property name="text">
+          <string>Mirror</string>
          </property>
         </widget>
        </item>

gui_ui.py

@@ -628,50 +628,55 @@ class Ui_fluencyCAD(object):
         self.groupBox.setMaximumSize(QSize(200, 16777215))
         self.gridLayout_3 = QGridLayout(self.groupBox)
         self.gridLayout_3.setObjectName(u"gridLayout_3")
-        self.pb_combop = QPushButton(self.groupBox)
+        self.pb_chamfer_op = QPushButton(self.groupBox)
-        self.pb_combop.setObjectName(u"pb_combop")
+        self.pb_chamfer_op.setObjectName(u"pb_chamfer_op")
 
-        self.gridLayout_3.addWidget(self.pb_combop, 1, 0, 1, 1)
+        self.gridLayout_3.addWidget(self.pb_chamfer_op, 2, 1, 1, 1)
-
-        self.pb_arrayop = QPushButton(self.groupBox)
-        self.pb_arrayop.setObjectName(u"pb_arrayop")
-
-        self.gridLayout_3.addWidget(self.pb_arrayop, 2, 0, 1, 1)
-
-        self.pb_moveop = QPushButton(self.groupBox)
-        self.pb_moveop.setObjectName(u"pb_moveop")
-
-        self.gridLayout_3.addWidget(self.pb_moveop, 1, 1, 1, 1)
-
-        self.pb_revop = QPushButton(self.groupBox)
-        self.pb_revop.setObjectName(u"pb_revop")
-
-        self.gridLayout_3.addWidget(self.pb_revop, 2, 1, 1, 1)
 
         self.pb_fillet_op = QPushButton(self.groupBox)
         self.pb_fillet_op.setObjectName(u"pb_fillet_op")
 
-        self.gridLayout_3.addWidget(self.pb_fillet_op, 3, 0, 1, 1)
+        self.gridLayout_3.addWidget(self.pb_fillet_op, 2, 0, 1, 1)
+
+        self.pb_thread = QPushButton(self.groupBox)
+        self.pb_thread.setObjectName(u"pb_thread")
+
+        self.gridLayout_3.addWidget(self.pb_thread, 6, 0, 1, 1)
 
         self.pb_extrdop = QPushButton(self.groupBox)
         self.pb_extrdop.setObjectName(u"pb_extrdop")
 
         self.gridLayout_3.addWidget(self.pb_extrdop, 0, 0, 1, 1)
 
+        self.pb_revop = QPushButton(self.groupBox)
+        self.pb_revop.setObjectName(u"pb_revop")
+
+        self.gridLayout_3.addWidget(self.pb_revop, 4, 1, 1, 1)
+
         self.pb_cutop = QPushButton(self.groupBox)
         self.pb_cutop.setObjectName(u"pb_cutop")
 
         self.gridLayout_3.addWidget(self.pb_cutop, 0, 1, 1, 1)
 
-        self.pb_chamfer = QPushButton(self.groupBox)
+        self.pb_arrayop = QPushButton(self.groupBox)
-        self.pb_chamfer.setObjectName(u"pb_chamfer")
+        self.pb_arrayop.setObjectName(u"pb_arrayop")
 
-        self.gridLayout_3.addWidget(self.pb_chamfer, 3, 1, 1, 1)
+        self.gridLayout_3.addWidget(self.pb_arrayop, 4, 0, 1, 1)
 
-        self.pb_thread = QPushButton(self.groupBox)
+        self.pb_combop = QPushButton(self.groupBox)
-        self.pb_thread.setObjectName(u"pb_thread")
+        self.pb_combop.setObjectName(u"pb_combop")
 
-        self.gridLayout_3.addWidget(self.pb_thread, 4, 0, 1, 1)
+        self.gridLayout_3.addWidget(self.pb_combop, 1, 0, 1, 1)
+
+        self.pb_moveop = QPushButton(self.groupBox)
+        self.pb_moveop.setObjectName(u"pb_moveop")
+
+        self.gridLayout_3.addWidget(self.pb_moveop, 1, 1, 1, 1)
+
+        self.pb_mirror_op = QPushButton(self.groupBox)
+        self.pb_mirror_op.setObjectName(u"pb_mirror_op")
+
+        self.gridLayout_3.addWidget(self.pb_mirror_op, 6, 1, 1, 1)
 
 
         self.gridLayout.addWidget(self.groupBox, 0, 3, 1, 1)
@@ -922,15 +927,16 @@ class Ui_fluencyCAD(object):
         self.pb_offset_tool.setText(QCoreApplication.translate("fluencyCAD", u"Offst", None))
         self.assembly_box.setTitle(QCoreApplication.translate("fluencyCAD", u"Assembly", None))
         self.groupBox.setTitle(QCoreApplication.translate("fluencyCAD", u"Modify", None))
-        self.pb_combop.setText(QCoreApplication.translate("fluencyCAD", u"Comb", None))
+        self.pb_chamfer_op.setText(QCoreApplication.translate("fluencyCAD", u"Chamfer", None))
-        self.pb_arrayop.setText(QCoreApplication.translate("fluencyCAD", u"Array", None))
-        self.pb_moveop.setText(QCoreApplication.translate("fluencyCAD", u"Mve", None))
-        self.pb_revop.setText(QCoreApplication.translate("fluencyCAD", u"Rev", None))
         self.pb_fillet_op.setText(QCoreApplication.translate("fluencyCAD", u"Fillet", None))
-        self.pb_extrdop.setText(QCoreApplication.translate("fluencyCAD", u"Extrd", None))
-        self.pb_cutop.setText(QCoreApplication.translate("fluencyCAD", u"Cut", None))
-        self.pb_chamfer.setText(QCoreApplication.translate("fluencyCAD", u"Chamfer", None))
         self.pb_thread.setText(QCoreApplication.translate("fluencyCAD", u"Thread", None))
+        self.pb_extrdop.setText(QCoreApplication.translate("fluencyCAD", u"Extrd", None))
+        self.pb_revop.setText(QCoreApplication.translate("fluencyCAD", u"Rev", None))
+        self.pb_cutop.setText(QCoreApplication.translate("fluencyCAD", u"Cut", None))
+        self.pb_arrayop.setText(QCoreApplication.translate("fluencyCAD", u"Arry", None))
+        self.pb_combop.setText(QCoreApplication.translate("fluencyCAD", u"Comb", None))
+        self.pb_moveop.setText(QCoreApplication.translate("fluencyCAD", u"Mve", None))
+        self.pb_mirror_op.setText(QCoreApplication.translate("fluencyCAD", u"Mirror", None))
         self.groupBox_10.setTitle(QCoreApplication.translate("fluencyCAD", u"Bodys / Operations", None))
         self.groupBox_8.setTitle(QCoreApplication.translate("fluencyCAD", u"Tools", None))
         self.pb_body_hide.setText(QCoreApplication.translate("fluencyCAD", u"Hide", None))

src/fluency/geometry_occ/kernel.py

@@ -16,8 +16,35 @@ from fluency.geometry.base import (
     Point3D,
 )
 
+
+
 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."""
@@ -446,52 +473,82 @@ class OCGeometryKernel(GeometryKernel):
     def fillet(
         self, body: GeometryObject, radius: float, edges: Optional[List[Any]] = None
     ) -> GeometryObject:
-        """Apply fillet to edges."""
+        """Apply fillet to edges. Skips edges that cannot be filleted."""
-        shape = self._get_shape(body)
         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:
+        # Collect candidate edges
-            for edge in edges:
+        if edges is not None:
-                fillet.Add(radius, edge)
+            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, TopoDS.Edge_s(explorer.Current()))
+                e = TopoDS.Edge_s(explorer.Current())
+                if _curve_is_linear(e):
+                    candidates.append(e)
                 explorer.Next()
 
-        fillet.Build()
+        # Add all edges, then Build once — avoids OCC internal crashes
-        return OCCGeometryObject(fillet.Shape(), {"type": "fillet"})
+        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."""
+        """Apply chamfer to edges. Skips edges that cannot be chamfered."""
-        shape = self._get_shape(body)
         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:
+        # Collect candidate edges
-            for edge in edges:
+        if edges is not None:
-                chamfer.Add(size, edge)
+            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, TopoDS.Edge_s(explorer.Current()))
+                e = TopoDS.Edge_s(explorer.Current())
+                if _curve_is_linear(e):
+                    candidates.append(e)
                 explorer.Next()
 
-        chamfer.Build()
+        # Add all edges, then Build once — avoids OCC internal crashes
-        return OCCGeometryObject(chamfer.Shape(), {"type": "chamfer"})
+        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

src/fluency/geometry_occ/sketch.py

@@ -327,9 +327,16 @@ class OCCSketch(SketchInterface):
         start_point: SketchEntity,
         end_point: SketchEntity,
         sweep: Optional[float] = None,
+        register: bool = True,
     ) -> OCCSketchEntity:
         """Add an arc (added to solver + tracked).
 
+        *register* False keeps the arc tracked-only (no solver entity, no
+        handle) — for reference geometry whose three reference points are
+        all already fixed, e.g. external underlay arcs: registering the
+        arc on top of three dragged points over-constrains the solver
+        (SolveSpace reports the system as inconsistent).
+
         The arc is registered with SolveSpace so its three reference points
         are linked: start, end, and centre.  SolveSpace's arc entity
         implicitly enforces ``distance(start, centre) = distance(end, centre)``,
@@ -362,7 +369,11 @@ class OCCSketch(SketchInterface):
 
         if center_entity is None or start_entity is None or end_entity is None:
             raise ValueError("Arc points not found in sketch")
-        if center_entity.handle is None or start_entity.handle is None or end_entity.handle is None:
+        if register and (
+            center_entity.handle is None
+            or start_entity.handle is None
+            or end_entity.handle is None
+        ):
             raise ValueError("Arc endpoints must already be in the solver")
 
         cx, cy = center_entity.geometry
@@ -386,17 +397,20 @@ class OCCSketch(SketchInterface):
         # whenever the workplane orientation changes.  The normal is
         # invalidated by ``clear`` / ``_rebuild_solver`` /
         # ``set_workplane`` (the workplane reference changes).
-        if self._wp_normal_handle is None:
+        if register:
-            self._wp_normal_handle = self._make_arc_normal_3d()
+            if self._wp_normal_handle is None:
-        nm: Any = self._wp_normal_handle
+                self._wp_normal_handle = self._make_arc_normal_3d()
-        assert nm is not None  # _make_arc_normal_3d always returns a handle
+            nm: Any = self._wp_normal_handle
-        arc_handle = self._solver.add_arc(
+            assert nm is not None  # _make_arc_normal_3d always returns a handle
-            nm,
+            arc_handle = self._solver.add_arc(
-            center_entity.handle,
+                nm,
-            start_entity.handle,
+                center_entity.handle,
-            end_entity.handle,
+                start_entity.handle,
-            self._wp,
+                end_entity.handle,
-        )
+                self._wp,
+            )
+        else:
+            arc_handle = None
 
         entity = OCCSketchEntity(
             entity_id=entity_id,
@@ -418,6 +432,9 @@ class OCCSketch(SketchInterface):
             "end": end_point.id,
             "radius": radius,
             "sweep": sweep,
+            # Tracked-only arcs (register=False) have no solver entity and
+            # are skipped by ``_rebuild_solver``.
+            "in_solver": register,
             # ``original_sweep`` captures the angular span the user drew
             # the arc with.  When the host geometry (e.g. a rectangle
             # the arc is attached to) resizes, ``_sync_solved_positions``
@@ -587,6 +604,70 @@ class OCCSketch(SketchInterface):
                     pass
         return all_points, all_lines
 
+    def _import_external_curves(
+        self,
+        circles: List[Dict[str, Any]],
+        arcs: List[Dict[str, Any]],
+    ) -> None:
+        """Import projected circle/arc dicts as external underlay entities.
+
+        Mirrors the widget's initial underlay import: a circle becomes a
+        fixed external centre point plus a tracked circle entity; an arc
+        becomes a fixed external centre point, endpoint entities (shared
+        with the polyline corners already imported, so the arc connects
+        to the adjacent lines), and an arc entity.  Must be called after
+        ``add_external_polylines`` and before ``_rebuild_solver`` — the
+        rebuild re-registers arcs in the fresh solver and re-fixes every
+        external point.
+        """
+        for c in circles:
+            try:
+                center_uv = (float(c["center"][0]), float(c["center"][1]))
+                center_pt = self.add_external_point(center_uv[0], center_uv[1])
+                self.add_circle(center_pt, float(c["radius"]))
+            except Exception as exc:
+                logger.debug("external circle import failed: %s", exc)
+
+        # Generous tolerance: arc endpoints come from a fresh projection of
+        # the face and must land on the existing corner points despite float
+        # drift (same rule as the widget's initial import).
+        merge_tol = 1e-3
+
+        def find_pt(u: float, v: float) -> Optional[OCCSketchEntity]:
+            best: Optional[OCCSketchEntity] = None
+            best_d = merge_tol
+            for eid in self._external_entity_ids:
+                ent = self._entities.get(eid)
+                if ent is None or ent.entity_type != "point" or ent.geometry is None:
+                    continue
+                d = math.hypot(ent.geometry[0] - u, ent.geometry[1] - v)
+                if d <= best_d:
+                    best_d = d
+                    best = ent
+            return best
+
+        for a in arcs:
+            try:
+                center_uv = (float(a["center"][0]), float(a["center"][1]))
+                start_uv = (float(a["start"][0]), float(a["start"][1]))
+                end_uv = (float(a["end"][0]), float(a["end"][1]))
+                center_pt = self.add_external_point(center_uv[0], center_uv[1])
+                start_pt = find_pt(start_uv[0], start_uv[1])
+                if start_pt is None:
+                    start_pt = self.add_external_point(start_uv[0], start_uv[1])
+                end_pt = find_pt(end_uv[0], end_uv[1])
+                if end_pt is None:
+                    end_pt = self.add_external_point(end_uv[0], end_uv[1])
+                # register=False: all three reference points are external
+                # (dragged/fixed) — registering the arc on top would
+                # over-constrain the solver (inconsistent).
+                self.add_arc(
+                    center_pt, float(a["radius"]), start_pt, end_pt,
+                    sweep=None, register=False,
+                )
+            except Exception as exc:
+                logger.debug("external arc import failed: %s", exc)
+
     def _drop_external_entities(self) -> set:
         """Remove external entities from local tracking + prune their constraints.
 
@@ -606,6 +687,21 @@ class OCCSketch(SketchInterface):
             self._lines.pop(eid, None)
             self._circles.pop(eid, None)
             self._arcs.pop(eid, None)
+        # Underlay circle/arc entities are tracked (not tagged external):
+        # drop any whose reference points just went away, or a re-import
+        # would pile stale duplicates on top of the fresh ones.
+        for cid, (cent_id, _radius) in list(self._circles.items()):
+            if cent_id in removed:
+                del self._circles[cid]
+                self._entities.pop(cid, None)
+        for aid, arc_data in list(self._arcs.items()):
+            if (
+                arc_data.get("center") in removed
+                or arc_data.get("start") in removed
+                or arc_data.get("end") in removed
+            ):
+                del self._arcs[aid]
+                self._entities.pop(aid, None)
         # Also clean lines that USE an external point as an endpoint but
         # somehow aren't themselves external (defensive — shouldn't happen
         # via the public API, but rebuild_solver needs a clean graph).
@@ -637,7 +733,7 @@ class OCCSketch(SketchInterface):
         """Return the set of external (underlay) entity ids currently in the sketch."""
         return set(self._external_entity_ids)
 
-    def update_external_entities(self, polylines: List[List[Tuple[float, float]]]) -> bool:
+    def update_external_entities(self, polylines: List[Any]) -> bool:
         """Re-project external (underlay) entities from updated source geometry.
 
         Called when the 3D body the underlay was projected from has been
@@ -646,6 +742,11 @@ class OCCSketch(SketchInterface):
         body so user geometry constrained to it propagates through the
         solver.
 
+        *polylines* is the raw output of ``_project_face_to_uv``: a mixed
+        list of plain polylines (lists of ``(u, v)``) and curve dicts
+        (``{"type": "circle", ...}`` / ``{"type": "arc", ...}``) for
+        circular/arc face edges.
+
         Two paths:
 
         * **In-place update** (same topology): when the new projection has
@@ -663,6 +764,22 @@ class OCCSketch(SketchInterface):
         Returns True when the underlay was updated and solved OK.
         """
         # Flatten the new projection into unique corner positions + segments.
+        # The projection mixes plain polylines with curve dicts; polylines
+        # carry the corner/segment topology used below, curve dicts are
+        # only handled by the rebuild + rebind path.
+        polys: List[List[Tuple[float, float]]] = []
+        circles: List[Dict[str, Any]] = []
+        arcs: List[Dict[str, Any]] = []
+        for entry in polylines:
+            if isinstance(entry, dict):
+                etype = entry.get("type")
+                if etype == "circle":
+                    circles.append(entry)
+                elif etype == "arc":
+                    arcs.append(entry)
+            elif isinstance(entry, (list, tuple)):
+                polys.append(list(entry))
+
         tol = self._EXTERNAL_MERGE_TOL
         new_pts: List[Tuple[float, float]] = []
 
@@ -674,7 +791,7 @@ class OCCSketch(SketchInterface):
             return len(new_pts) - 1
 
         new_segs: List[Tuple[int, int]] = []
-        for poly in polylines:
+        for poly in polys:
             if len(poly) < 2:
                 continue
             idx = [new_index(float(u), float(v)) for (u, v) in poly]
@@ -694,7 +811,13 @@ class OCCSketch(SketchInterface):
             lid for lid in sorted(self._lines.keys()) if lid in self._external_entity_ids
         ]
 
-        same_topology = len(new_pts) == len(old_ext_points) and len(new_segs) == len(old_ext_lines)
+        # Curve entries force the rebuild path: the in-place branch only
+        # moves point/line entities and cannot represent a circle or arc.
+        same_topology = (
+            not (circles or arcs)
+            and len(new_pts) == len(old_ext_points)
+            and len(new_segs) == len(old_ext_lines)
+        )
 
         if same_topology and old_ext_points:
             # Greedy one-to-one nearest matching old point -> new position.
@@ -769,7 +892,8 @@ class OCCSketch(SketchInterface):
         # points and (per the add_point guard) does not auto-anchor a user
         # point — which would conflict with the re-bound coincidents below.
         self._drop_external_entities()
-        self.add_external_polylines(polylines)
+        self.add_external_polylines(polys)
+        self._import_external_curves(circles, arcs)
         self._rebuild_solver()
         self._rebuild_labels()
 
@@ -952,7 +1076,17 @@ class OCCSketch(SketchInterface):
         elif ctype == "distance":
             if h(ids[0]) is None or h(ids[1]) is None:
                 return False
-            self._solver.distance(h(ids[0]), h(ids[1]), params[0], self._wp)
+            ent0 = self._entities.get(ids[0])
+            ent1 = self._entities.get(ids[1])
+            # Normalise (line, point) -> (point, line) like constrain_distance
+            # does, and drop legacy line-line entries the solver can't hold.
+            if ent0 is not None and ent1 is not None:
+                if ent0.entity_type == "line" and ent1.entity_type == "line":
+                    return False
+                if ent0.entity_type == "line" and ent1.entity_type == "point":
+                    self._solver.distance(h(ids[1]), h(ids[0]), params[0], self._wp)
+                else:
+                    self._solver.distance(h(ids[0]), h(ids[1]), params[0], self._wp)
         elif ctype == "angle":
             if h(ids[0]) is None or h(ids[1]) is None:
                 return False
@@ -1115,6 +1249,8 @@ class OCCSketch(SketchInterface):
             assert nm is not None
             for aid in sorted(self._arcs.keys()):
                 arc_data = self._arcs[aid]
+                if not arc_data.get("in_solver", True):
+                    continue  # tracked-only (underlay) arc — no solver state
                 c_id = arc_data.get("center")
                 s_id = arc_data.get("start")
                 e_id = arc_data.get("end")
@@ -1175,16 +1311,92 @@ class OCCSketch(SketchInterface):
             entity.constraints.append("vrt")
         return True
 
+    def _point_line_signed_offset(
+        self, point_ent: OCCSketchEntity, line_ent: OCCSketchEntity
+    ) -> float:
+        """Signed perpendicular offset of *point_ent* from *line_ent*, in the
+        solver's sign convention — i.e. the ``valA`` that pins the point on
+        its current side of the line.
+
+        Mirrors SolveSpace's ``PT_LINE_DISTANCE`` equation exactly
+        (a = line start, b = line end, d = a - b):
+
+            proj = dv·(ua − u) − du·(va − v),   m = |d|
+            offset = proj / m
+
+        Returns 0.0 when the line is degenerate or the point lies on it
+        (the side is then undefined — callers fall back to the unsigned
+        value).
+        """
+        if line_ent.id not in self._lines:
+            return 0.0
+        sid, eid2 = self._lines[line_ent.id]
+        s_ent = self._entities.get(sid)
+        e_ent = self._entities.get(eid2)
+        if s_ent is None or e_ent is None or not s_ent.geometry or not e_ent.geometry:
+            return 0.0
+        ua, va = s_ent.geometry
+        ub, vb = e_ent.geometry
+        u, v = point_ent.geometry
+        du = ua - ub
+        dv = va - vb
+        m = math.hypot(du, dv)
+        if m < 1e-12:
+            return 0.0
+        return (dv * (ua - u) - du * (va - v)) / m
+
     def constrain_distance(
         self, entity1: SketchEntity, entity2: SketchEntity, distance: float
     ) -> bool:
-        """Constrain distance between two entities."""
+        """Constrain distance between two entities.
+
+        python-solvespace's ``distance`` accepts point-point and point-line
+        (in that order) only, so line-point pairs are normalised and line-line
+        pairs are rejected with a warning instead of raising TypeError.
+
+        A point constrained to itself with a non-zero value is always
+        inconsistent — reject it up front so the UI never creates a constraint
+        the solver cannot satisfy.
+        """
         e1 = self._entities.get(entity1.id)
         e2 = self._entities.get(entity2.id)
         if e1 is None or e2 is None or e1.handle is None or e2.handle is None:
             return False
-        self._solver.distance(e1.handle, e2.handle, distance, self._wp)
+        if e1 is e2 and e1.entity_type == "point" and distance != 0.0:
-        self._record_constraint("distance", (entity1.id, entity2.id), (distance,))
+            logger.warning("distance: refusing point-to-itself constraint")
+            return False
+
+        t1, t2 = e1.entity_type, e2.entity_type
+        if t1 == "line" and t2 == "line":
+            logger.warning(
+                "distance: line-to-line distance is not supported by the solver "
+                "(select a point and a line instead)"
+            )
+            return False
+
+        # python-solvespace only accepts (point, line) ordering.
+        if t1 == "line" and t2 == "point":
+            e1, e2 = e2, e1
+            entity1, entity2 = entity2, entity1
+
+        # Point-to-line distance is SIGNED in SolveSpace: the constraint
+        # equation is (signed perpendicular offset) = valA, so a positive
+        # valA always drives the point onto one fixed side of the line
+        # (for a vertical line, always +x).  Pass a value whose sign
+        # matches the side the point is currently on so the constraint
+        # pins it there instead of flipping it across the line.  The sign
+        # is recorded with the value so a solver rebuild reproduces the
+        # same side.
+        solver_value = distance
+        if e2.entity_type == "line" and e1.entity_type == "point" and distance != 0.0:
+            signed = self._point_line_signed_offset(e1, e2)
+            if abs(signed) > 1e-9:
+                solver_value = math.copysign(distance, signed)
+
+        self._solver.distance(e1.handle, e2.handle, solver_value, self._wp)
+        # Record in the normalised (point-first) order so replayed / legacy
+        # constraint logs are consistent.
+        self._record_constraint("distance", (entity1.id, entity2.id), (solver_value,))
         return True
 
     def constrain_angle(self, line1: SketchEntity, line2: SketchEntity, angle: float) -> bool:
@@ -1863,7 +2075,7 @@ class OCCSketch(SketchInterface):
 
     _SNAP_TOL: float = 1e-2  # world-unit tolerance for snapping line endpoints in loop detection
 
-    def _line_segments(self) -> List[Tuple[Tuple[float, float], Tuple[float, float]]]:
+    def _line_segments(self) -> List[Tuple[float, float, float, float, int]]:
         """Current line segments as world-coordinate tuples (uses solved positions).
 
         Returns both straight line segments AND tessellated arc segments so
@@ -1871,10 +2083,13 @@ class OCCSketch(SketchInterface):
         and external entities are excluded — they're reference geometry and
         must not affect the sketch profile.
 
+        Each segment is ``(x1, y1, x2, y2, entity_id)`` — the entity_id lets
+        callers trace which sketch entity produced each segment.
+
         Tessellation density: roughly 12 segments per π radians of arc sweep,
         which gives smooth-looking closed loops for face detection.
         """
-        segs: List[Tuple[Tuple[float, float], Tuple[float, float]]] = []
+        segs: List[Tuple[float, float, float, float, int]] = []
 
         # ── Straight line segments ──
         for line_id, (sid, eid2) in self._lines.items():
@@ -1888,8 +2103,9 @@ class OCCSketch(SketchInterface):
             if s_ent and e_ent and s_ent.geometry and e_ent.geometry:
                 segs.append(
                     (
-                        (float(s_ent.geometry[0]), float(s_ent.geometry[1])),
+                        float(s_ent.geometry[0]), float(s_ent.geometry[1]),
-                        (float(e_ent.geometry[0]), float(e_ent.geometry[1])),
+                        float(e_ent.geometry[0]), float(e_ent.geometry[1]),
+                        line_id,
                     )
                 )
 
@@ -1924,7 +2140,7 @@ class OCCSketch(SketchInterface):
                 a2 = start_angle + t2 * sweep
                 p1 = (cx + radius * math.cos(a1), cy + radius * math.sin(a1))
                 p2 = (cx + radius * math.cos(a2), cy + radius * math.sin(a2))
-                segs.append((p1, p2))
+                segs.append((p1[0], p1[1], p2[0], p2[1], arc_id))
 
         return segs
 
@@ -1932,8 +2148,8 @@ class OCCSketch(SketchInterface):
         """Detect closed loops: polygon cycles from connected lines + each circle.
 
         Each loop is one of:
-          {"type": "polygon", "points": [(x,y), ...]}  (closed, last == first)
+          {"type": "polygon", "points": [(x,y), ...], "entity_ids": [int, ...]}  (closed, last == first)
-          {"type": "circle", "center": (x,y), "radius": r}
+          {"type": "circle", "center": (x,y), "radius": r, "entity_ids": [int]}
         Line endpoint coordinates are snapped to ``_SNAP_TOL`` so a closed
         rectangle's four corners join into one cycle even after solver floating
         point jitter. Only connected components where every node has degree 2
@@ -1949,11 +2165,13 @@ class OCCSketch(SketchInterface):
 
             reprs: Dict[Any, Tuple[float, float]] = {}  # key -> averaged world pt
             edges: List[Tuple[Any, Any]] = []
-            for p1, p2 in segs:
+            edge_eids: Dict[Tuple[Any, Any], int] = {}  # (k1,k2) -> entity_id
-                k1, k2 = key(p1), key(p2)
+            for x1, y1, x2, y2, eid in segs:
-                reprs.setdefault(k1, p1)
+                k1, k2 = key((x1, y1)), key((x2, y2))
-                reprs.setdefault(k2, p2)
+                reprs.setdefault(k1, (x1, y1))
+                reprs.setdefault(k2, (x2, y2))
                 edges.append((k1, k2))
+                edge_eids[(k1, k2) if k1 < k2 else (k2, k1)] = eid
 
             # Undirected adjacency.
             adj: Dict[Any, List[Any]] = {}
@@ -1980,8 +2198,9 @@ class OCCSketch(SketchInterface):
                         if nb not in comp_seen:
                             stack.append(nb)
                 if all(len(adj[n]) == 2 for n in comp) and len(comp) >= 3:
-                    # Order the cycle by following each node's neighbor not yet visited.
+                    # Order the cycle by following each node's neighbour not yet visited.
                     ordered: List[Any] = []
+                    eids: List[int] = []
                     cur = comp[0]
                     prev = None
                     for _ in range(len(comp)):
@@ -1989,16 +2208,26 @@ class OCCSketch(SketchInterface):
                         nbrs = [nb for nb in adj[cur] if nb != prev]
                         if not nbrs:
                             break
+                        ekey = (cur, nbrs[0]) if cur < nbrs[0] else (nbrs[0], cur)
+                        if ekey in edge_eids:
+                            eids.append(edge_eids[ekey])
                         prev = cur
                         cur = nbrs[0]
                     if len(ordered) == len(comp):
                         pts = [reprs[k] for k in ordered]
                         pts.append(pts[0])
-                        loops.append({"type": "polygon", "points": pts})
+                        loops.append(
+                            {"type": "polygon", "points": pts, "entity_ids": sorted(set(eids))}
+                        )
                 seen |= comp_seen
 
         # Circles are closed loops of their own.
         for cid, (center_id, r) in self._circles.items():
+            circle_ent = self._entities.get(cid)
+            if circle_ent is not None and circle_ent.is_construction:
+                continue
+            if cid in self._external_entity_ids:
+                continue
             c_ent = self._entities.get(center_id)
             if c_ent and c_ent.geometry and r > 0:
                 loops.append(
@@ -2006,6 +2235,7 @@ class OCCSketch(SketchInterface):
                         "type": "circle",
                         "center": (float(c_ent.geometry[0]), float(c_ent.geometry[1])),
                         "radius": float(r),
+                        "entity_ids": [cid],
                     }
                 )
         return loops
@@ -2156,8 +2386,7 @@ class OCCSketch(SketchInterface):
         that is the rectangle minus the circle — exactly the
         "shape within a shape = closed without inner" behavior. A shape nested
         inside a hole (depth 2) becomes its own solid face again.
-
+        Returns a list of ``{"outer": loop, "holes": [loop, ...], "depth": int, "entity_ids": [int, ...]}``.
-        Returns a list of ``{"outer": loop, "holes": [loop, ...], "depth": int}``.
         """
         loops = self.get_closed_loops()
         if not loops:
@@ -2181,7 +2410,11 @@ class OCCSketch(SketchInterface):
                 # directly nested: depth one greater, and outer contains inner.
                 if depths[j] == depths[i] + 1 and OCCSketch._loop_contains(inner, outer):
                     holes.append(inner)
-            faces.append({"outer": outer, "holes": holes, "depth": depths[i]})
+            # Face entity_ids = union of outer + hole loop entity_ids.
+            eids = set(outer.get("entity_ids", []))
+            for h in holes:
+                eids.update(h.get("entity_ids", []))
+            faces.append({"outer": outer, "holes": holes, "depth": depths[i], "entity_ids": sorted(eids)})
         return faces
 
     def find_face_at(self, x: float, y: float) -> Optional[Dict[str, Any]]:
@@ -2618,6 +2851,9 @@ class OCCSketch(SketchInterface):
                             "end": tuple(e_ent.geometry),
                             "radius": radius_val,
                             "sweep": sweep_val,
+                            # Tracked-only underlay arcs must not be
+                            # re-registered with the solver on load.
+                            "in_solver": bool(arc_data.get("in_solver", True)),
                         }
             entities_payload.append(
                 {
@@ -2834,12 +3070,30 @@ class OCCSketch(SketchInterface):
                     if c_id is None or s_id is None or e_id is None:
                         logger.warning("Skipping arc %s during load: endpoints not found", eid)
                         return
+                    in_solver = bool(geom.get("in_solver", True))
+                    if "in_solver" not in geom:
+                        # Old files: an arc whose three reference points are
+                        # all external is an underlay arc — re-registering it
+                        # over-constrains the solver (inconsistent).
+                        c_ent_r = entities_by_id.get(c_id)
+                        s_ent_r = entities_by_id.get(s_id)
+                        e_ent_r = entities_by_id.get(e_id)
+                        if (
+                            c_ent_r is not None
+                            and s_ent_r is not None
+                            and e_ent_r is not None
+                            and getattr(c_ent_r, "is_external", False)
+                            and getattr(s_ent_r, "is_external", False)
+                            and getattr(e_ent_r, "is_external", False)
+                        ):
+                            in_solver = False
                     ent = self.add_arc(
                         entities_by_id[c_id],
                         radius,
                         entities_by_id[s_id],
                         entities_by_id[e_id],
                         sweep=sweep,
+                        register=in_solver,
                     )
                 else:
                     logger.warning("Unknown sketch entity type %r; skipping", etype)

src/fluency/io/project_io.py

@@ -43,9 +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
@@ -226,10 +229,15 @@ def _feature_to_dict(feat: Feature) -> Dict[str, Any]:
         "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),
     }
 
 
@@ -253,11 +261,26 @@ def _feature_from_dict(data: Dict[str, Any], sketches: Dict[str, Sketch]) -> Fea
         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]
@@ -472,6 +495,8 @@ def _connector_to_dict(conn: Connector) -> Dict[str, Any]:
         "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),
@@ -492,6 +517,8 @@ def _connector_from_dict(data: Dict[str, Any]) -> Connector:
         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")
@@ -510,12 +537,22 @@ 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(
-def _assembly_component_from_dict(data: Dict[str, Any]) -> AssemblyComponent:
+    data: Dict[str, Any],
+    component: Optional[Component] = None,
+    sketch_geometry_loader: Optional[Callable[[str], Optional[OCCGeometryObject]]] = None,
+) -> AssemblyComponent:
     ac = AssemblyComponent(
         id=_saved_id(data),
         component_id=data.get("component_id", ""),
@@ -527,6 +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
 
 
@@ -564,8 +631,11 @@ 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(
-def _assembly_from_dict(data: Dict[str, Any]) -> Assembly:
+    data: Dict[str, Any],
+    components: Optional[Dict[str, Component]] = None,
+    sketch_geometry_loader: Optional[Callable[[str], Optional[OCCGeometryObject]]] = None,
+) -> Assembly:
     asm = Assembly(
         id=_saved_id(data),
         name=data.get("name", "Untitled Assembly"),
@@ -574,12 +644,133 @@ def _assembly_from_dict(data: Dict[str, Any]) -> Assembly:
     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)
+        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,
@@ -592,6 +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 {},
@@ -752,6 +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")
@@ -817,8 +1043,9 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:
 
         # 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():
+        # Applies to both component sketches and instance-local sketches.
-            for sk_id, sk_data in (comp_data.get("sketches") or {}).items():
+        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
@@ -845,6 +1072,12 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:
                     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", ""),
@@ -864,7 +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

src/fluency/models/data_model.py

@@ -229,17 +229,21 @@ class Feature:
       - "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 array.  ``pattern_type`` is "linear" or
-                  "circular"; ``count`` is the total number of items
+                 "circular"; ``count`` is the total number of items
-                  (original + copies).  Linear uses ``direction``
+                 (original + copies).  Linear uses ``direction``
-                  (unit vector) and ``spacing`` (mm between adjacent
+                 (unit vector) and ``spacing`` (mm between adjacent
-                  items); circular reuses ``axis`` + ``origin`` for the
+                 items); circular reuses ``axis`` + ``origin`` for the
-                  rotation axis and ``angle`` for the total angular
+                 rotation axis and ``angle`` for the total angular
-                  span in degrees (copies evenly distributed).
+                 span in degrees (copies evenly distributed).
       - "base":   frozen geometry snapshot (``geometry`` field) — used
-                  to migrate legacy bodies whose original base feature
+                 to migrate legacy bodies whose original base feature
-                  is unknown.  Never the result of a user operation.
+                 is unknown.  Never the result of a user operation.
     """
 
     id: str = field(default_factory=lambda: str(uuid.uuid4()))
@@ -271,6 +275,14 @@ class Feature:
     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
@@ -281,6 +293,11 @@ class Feature:
     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)
 
 
@@ -470,6 +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.
@@ -489,6 +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:
@@ -512,6 +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)
 
@@ -522,6 +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(
@@ -531,6 +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()
@@ -544,6 +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:
@@ -707,6 +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)
@@ -783,36 +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:
+    # ── Drawing helpers ──
-        """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
 
-    def remove_component(self, component_id: str) -> bool:
+    def get_drawing_for(self, source_kind: str, source_id: str) -> Optional["TechnicalDrawing"]:
-        """Remove a component from the project."""
+        """Return the drawing bound to *(source_kind, source_id)*, if any."""
-        if component_id in self.components:
+        for drawing in self.drawings:
-            del self.components[component_id]
+            if drawing.source_kind == source_kind and drawing.source_id == source_id:
-            if self.active_component == component_id:
+                return drawing
-                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]
         return None
 
-    def set_active_component(self, component_id: Optional[str]) -> None:
+    def add_drawing(self, drawing: "TechnicalDrawing") -> "TechnicalDrawing":
-        """Set the active component."""
+        """Register *drawing* with the project and return it."""
-        self.active_component = component_id
+        self.drawings.append(drawing)
         self.modified_at = datetime.now()
+        return drawing
+
 
     def export_step(self, filepath: str) -> bool:
         """Export all visible bodies to STEP."""
@@ -881,3 +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)

src/fluency/rendering/occ_renderer.py

@@ -157,17 +157,24 @@ class OCCRenderer(Renderer):
         self._highlight_ais: Any = None
         # Overlays for the fillet tool's two picked faces (one AIS per face).
         self._faces_highlight_ais: List[Any] = []
+        # Hot-pink translucent overlay for operation-history highlighting.
+        self._op_highlight_ais: Any = None
         # Temporary transparent preview AIS for the live extrude/cut dialog.
         self._preview_ais: Any = None
         # Smart entity picker gizmo objects (snap markers, axis lines, rings).
         # Keyed by a synthetic id; values are raw AIS_InteractiveObject.
         self._gizmo_objects: Dict[str, Any] = {}
+        # Persistent connector gizmo objects (first pick) – not cleared by hover.
+        self._persistent_gizmo_objects: Dict[str, Any] = {}
         # World-anchored sketch reference gizmo (a triad at the sketch
         # midpoint): part kind ("center" / "axis_x" / … / "plane_xy" …) →
         # dict {"ais": [AIS…], "color": rgb, "pick": descriptor}.
         self._sketch_gizmo_parts: Dict[str, Any] = {}
         # Part kind currently highlighted on hover (for restore-on-leave).
         self._sketch_gizmo_highlighted: Optional[str] = None
+        # Cache for shape classification to avoid re-classifying same OCC sub-shapes
+        # during repeated probe/hover calls. Key = (id(shape), owner_obj_id).
+        self._classify_cache: dict = {}
 
     def initialize(self, parent_widget: Any) -> bool:
         """Initialise OCC viewer inside *parent_widget* (a QWidget)."""
@@ -333,10 +340,16 @@ class OCCRenderer(Renderer):
         shape: Any,
         color: Optional[Tuple[float, float, float]] = None,
         name: Optional[str] = None,
+        auto_fit: bool = True,
     ) -> str:
         """Display an OCC ``TopoDS_Shape`` directly via ``AIS_Shape``.
 
         Returns a unique object ID (or *name* if provided).
+ 
+        With *auto_fit* (default), the first object added to an empty
+        scene triggers a camera fit.  Pass ``auto_fit=False`` when
+        rebuilding a scene under explicit camera control (e.g. the
+        assembly view), so the rebuild doesn't move the camera.
         """
         from OCP.AIS import AIS_Shape
         from OCP.Quantity import Quantity_Color, Quantity_TOC_RGB
@@ -396,7 +409,7 @@ class OCCRenderer(Renderer):
         self._objects[obj_id] = robj
 
         # Fit camera on first shape added.
-        if len(self._objects) == 1:
+        if auto_fit and len(self._objects) == 1:
             try:
                 self.fit_camera()
             except Exception:
@@ -543,6 +556,16 @@ class OCCRenderer(Renderer):
             return False
         return True
 
+    def set_color(
+        self, obj_id: str, color: Tuple[float, float, float]
+    ) -> bool:
+        """Set the colour of an object by ID.  Returns True on success."""
+        obj = self._objects.get(obj_id)
+        if obj is None:
+            return False
+        self.set_object_color(obj, color)
+        return True
+
     # ─── Live preview (extrude/cut preview) ──────────────────────────────
 
     _PREVIEW_ID = "__extrude_preview__"
@@ -608,6 +631,7 @@ class OCCRenderer(Renderer):
             return
         self.clear_preview()
         self.clear_face_highlight()
+        self.clear_operation_highlight()
         self.clear_entity_gizmo()
         # The sketch reference gizmo is scene-anchored — drop it with the rest.
         self.remove_sketch_gizmo()
@@ -1385,6 +1409,60 @@ class OCCRenderer(Renderer):
                 logger.debug("clear_faces_highlight remove failed", exc_info=True)
         self._faces_highlight_ais = []
 
+
+    # ─── Operation history highlight ─────────────────────────────────────
+
+    def highlight_operation_shape(
+        self, shape: Any, color: Tuple[float, float, float] = (1.0, 0.08, 0.58)
+    ) -> None:
+        """Overlay a translucent hot-pink *shape* on the 3D view.
+
+        Used to show the intermediate geometry at a selected operation in
+        the feature-history list.  The overlay is an independent
+        ``AIS_Shape`` with polygon offset so it draws on top of the
+        coincident body surface without z-fighting.  Replaces any previous
+        operation highlight.
+        """
+        if self._context is None:
+            return
+        self.clear_operation_highlight()
+        from OCP.AIS import AIS_Shape
+        from OCP.Quantity import Quantity_Color, Quantity_TOC_RGB
+
+        ais = AIS_Shape(shape)
+        try:
+            ais.SetMaterial(self._default_material())
+        except Exception:
+            logger.debug("op highlight material set failed", exc_info=True)
+        ais.SetColor(Quantity_Color(*color, Quantity_TOC_RGB))
+        ais.SetDisplayMode(1)  # shaded
+        try:
+            ais.SetTransparency(0.2)
+        except Exception:
+            logger.debug("op highlight transparency set failed", exc_info=True)
+        try:
+            ais.SetSelectability(0)
+        except Exception:
+            logger.debug("op highlight selectability set failed", exc_info=True)
+        try:
+            ais.SetPolygonOffsets(3, 1.0, -0.5)
+        except Exception:
+            logger.debug("op highlight polygon offset failed", exc_info=True)
+        self._context.Display(ais, False)
+        self._op_highlight_ais = ais
+        if self._view is not None:
+            self._view.Redraw()
+
+    def clear_operation_highlight(self) -> None:
+        """Remove the operation-history overlay, if any."""
+        if self._context is None or self._op_highlight_ais is None:
+            return
+        try:
+            self._context.Remove(self._op_highlight_ais, True)
+        except Exception:
+            logger.debug("clear_operation_highlight remove failed", exc_info=True)
+        self._op_highlight_ais = None
+
     # ─── General entity picking (for assembly connectors / snaps) ───────────
 
     def pick_entity(self, x: int, y: int) -> Optional[Dict[str, Any]]:
@@ -1447,6 +1525,10 @@ class OCCRenderer(Renderer):
         """
         if shape is None:
             return []
+        # Cache lookup
+        cache_key = (id(shape), owner_obj_id)
+        if cache_key in self._classify_cache:
+            return self._classify_cache[cache_key]
 
         from OCP.TopoDS import TopoDS
         from OCP.BRepAdaptor import BRepAdaptor_Surface, BRepAdaptor_Curve
@@ -1508,7 +1590,7 @@ class OCCRenderer(Renderer):
                 # x_dir: viewport-aligned so connector gizmo matches screen.
                 x_dir = _compute_viewport_aligned_xdir((nx, ny, nz), self._view)
 
-                return [
+                res = [
                     {
                         "type": "planar_face",
                         "position": origin,
@@ -1518,6 +1600,8 @@ class OCCRenderer(Renderer):
                         "owner_obj_id": owner_obj_id,
                     }
                 ]
+                self._classify_cache[cache_key] = res
+                return res
 
             elif stype == GeomAbs_Cylinder:
                 cyl = adaptor.Cylinder()
@@ -1625,6 +1709,7 @@ class OCCRenderer(Renderer):
                             "radius": radius,
                         }
                     )
+                self._classify_cache[cache_key] = results
                 return results
 
         # Try edge.
@@ -1668,7 +1753,7 @@ class OCCRenderer(Renderer):
                     x = x / xlen
                     x_dir = (float(x[0]), float(x[1]), float(x[2]))
 
-            return [
+            res = [
                 {
                     "type": "edge",
                     "position": position,
@@ -1678,6 +1763,8 @@ class OCCRenderer(Renderer):
                     "owner_obj_id": owner_obj_id,
                 }
             ]
+            self._classify_cache[cache_key] = res
+            return res
 
         # Try vertex.
         vertex = None
@@ -1685,7 +1772,7 @@ class OCCRenderer(Renderer):
             vertex = TopoDS.Vertex_s(shape)
             p = BRep_Tool.Pnt_s(vertex)
             position = (p.X(), p.Y(), p.Z())
-            return [
+            res = [
                 {
                     "type": "vertex",
                     "position": position,
@@ -1695,9 +1782,12 @@ class OCCRenderer(Renderer):
                     "owner_obj_id": owner_obj_id,
                 }
             ]
+            self._classify_cache[cache_key] = res
+            return res
         except Exception:
             pass
 
+        self._classify_cache[cache_key] = []
         return []
 
     def probe_snap_candidates(
@@ -2400,6 +2490,114 @@ class OCCRenderer(Renderer):
         if self._view is not None:
             self._view.Update()
 
+    def show_persistent_entity_gizmo(
+        self,
+        entity_type: str,
+        position: Tuple[float, float, float],
+        normal: Optional[Tuple[float, float, float]] = None,
+        x_dir: Optional[Tuple[float, float, float]] = None,
+        radius: Optional[float] = None,
+        color: Tuple[float, float, float] = (0.0, 1.0, 0.0),
+    ) -> None:
+        """Display a persistent green gizmo for a confirmed first connector pick.
+
+        Unlike show_entity_gizmo, this does not clear the hover gizmo and stores
+        its AIS objects in _persistent_gizmo_objects so they survive hover updates.
+        """
+        if self._context is None:
+            return
+        # Clear previous persistent gizmo
+        self.clear_persistent_entity_gizmo()
+
+        gizmo_scale = self._get_gizmo_scale(position)
+        from OCP.gp import gp_Pnt, gp_Dir, gp_Ax2, gp_Circ
+        from OCP.BRepBuilderAPI import BRepBuilderAPI_MakeEdge
+        from OCP.AIS import AIS_Shape
+        from OCP.Quantity import Quantity_Color, Quantity_TOC_RGB
+        from OCP.BRepPrimAPI import BRepPrimAPI_MakeSphere
+
+        def _store(obj, key):
+            self._context.Display(obj, True)
+            self._persistent_gizmo_objects[key] = obj
+
+        def _make_sphere(p, c, size):
+            try:
+                s = BRepPrimAPI_MakeSphere(gp_Pnt(*p), size).Shape()
+                a = AIS_Shape(s)
+                a.SetColor(Quantity_Color(*c, Quantity_TOC_RGB))
+                a.SetDisplayMode(1)
+                _store(a, f"__pg_sphere_{id(a)}")
+            except Exception as exc:
+                logger.debug(f"persistent gizmo sphere failed: {exc}")
+
+        px, py, pz = position
+        _make_sphere(position, color, 5.6 * gizmo_scale)
+
+        axis_length = 30.0 * gizmo_scale
+
+        def _make_axis_line(origin, direction, length, line_color, label):
+            try:
+                dx, dy, dz = direction
+                norm = (dx*dx + dy*dy + dz*dz) ** 0.5
+                if norm < 1e-9:
+                    return
+                ux, uy, uz = dx/norm, dy/norm, dz/norm
+                ex = origin[0] + ux * length
+                ey = origin[1] + uy * length
+                ez = origin[2] + uz * length
+                edge = BRepBuilderAPI_MakeEdge(gp_Pnt(*origin), gp_Pnt(ex, ey, ez)).Edge()
+                ais = AIS_Shape(edge)
+                ais.SetColor(Quantity_Color(*line_color, Quantity_TOC_RGB))
+                ais.SetDisplayMode(0)
+                _store(ais, f"__pg_{label}_{id(ais)}")
+            except Exception as exc:
+                logger.debug(f"persistent gizmo axis failed: {exc}")
+
+        if entity_type == "planar_face" and normal is not None:
+            _make_axis_line(position, normal, axis_length, (1.0, 1.0, 1.0), "normal")
+            if x_dir is not None:
+                _make_axis_line(position, x_dir, axis_length * 0.6, color, "xdir")
+        elif entity_type == "cylindrical_face" and normal is not None:
+            _make_axis_line(position, normal, axis_length * 1.4, (1.0, 1.0, 1.0), "axis_in")
+            _make_axis_line(position, (-normal[0], -normal[1], -normal[2]), axis_length * 0.4, (0.6, 0.6, 0.6), "axis_stub")
+            if x_dir is not None:
+                _make_axis_line(position, x_dir, radius or (axis_length * 0.5), color, "radial")
+            # ring
+            if radius is not None:
+                try:
+                    center = gp_Pnt(px, py, pz)
+                    ax2 = gp_Ax2(center, gp_Dir(*normal))
+                    circ = gp_Circ(ax2, radius)
+                    ring_edge = BRepBuilderAPI_MakeEdge(circ).Edge()
+                    ring_ais = AIS_Shape(ring_edge)
+                    ring_ais.SetColor(Quantity_Color(*color, Quantity_TOC_RGB))
+                    ring_ais.SetDisplayMode(0)
+                    _store(ring_ais, f"__pg_ring_{id(ring_ais)}")
+                except Exception as exc:
+                    logger.debug(f"persistent gizmo ring failed: {exc}")
+        elif entity_type == "edge" and normal is not None:
+            _make_axis_line(position, normal, axis_length, color, "tangent")
+        elif entity_type == "vertex":
+            _make_axis_line(position, (1,0,0), axis_length * 0.5, (1.0,0.3,0.3), "cross_x")
+            _make_axis_line(position, (0,1,0), axis_length * 0.5, (0.3,1.0,0.3), "cross_y")
+            _make_axis_line(position, (0,0,1), axis_length * 0.5, (0.3,0.3,1.0), "cross_z")
+
+        if self._view is not None:
+            self._view.Update()
+
+    def clear_persistent_entity_gizmo(self) -> None:
+        """Remove the persistent first-pick gizmo."""
+        if self._context is None:
+            return
+        for obj in list(self._persistent_gizmo_objects.values()):
+            try:
+                self._context.Erase(obj, True)
+            except Exception:
+                pass
+        self._persistent_gizmo_objects.clear()
+        if self._view is not None:
+            self._view.Update()
+
     # ─── Selection mode control ───────────────────────────────────────────
     #
     # When connector gizmo mode is active, standard OCC face/edge/vertex
@@ -2636,6 +2834,13 @@ class OCCRenderer(Renderer):
                 (c.get("screen", (x, y))[0] - x) ** 2 + (c.get("screen", (x, y))[1] - y) ** 2
             )
         )
+        # Early exit if we already found a very close candidate — avoids unnecessary work.
+        if results:
+            best = results[0]
+            best_sp = best.get("screen", (x, y))
+            best_dist2 = (best_sp[0] - x) ** 2 + (best_sp[1] - y) ** 2
+            if best_dist2 <= 25:  # within 5 px
+                return [best]
         return results
 
     def recognize_composite_features(

src/fluency/sketch_solver.py

@@ -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
+            if isinstance(entity_a, SolverLine) and isinstance(entity_b, SolverLine):
-            handle_b = entity_b.handle if isinstance(entity_b, SolverPoint) else entity_b.handle
+                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

src/fluency/tests/test_iso5457_sheet.py

@@ -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()

src/fluency/ui/dialogs.py

@@ -641,6 +641,246 @@ class ArrayDialog(QDialog):
         }
 
 
+class MirrorDialog(QDialog):
+    """Dialog for the mirror tool: plane selection with live preview.
+
+    Mirrors the selected body across a plane.  The user can pick a
+    plane from:
+
+      - A list of existing workplanes (combo box, passed by the caller)
+      - Six axis-aligned presets (XY, XZ, YZ and their negatives)
+      - Custom origin + normal enterable through spinboxes
+
+    ``keep_original`` (checked by default) boolean-unions the original
+    solid with its mirror image so you get a symmetric part from half
+    the modeling work.
+
+    A live-preview callback (``set_preview_callback``) fires on every
+    change so the host can show the mirrored shape in the 3D view
+    before committing.
+
+    ``get_values()`` returns a dict:
+    ``{"mirror_plane_origin", "mirror_plane_normal", "keep_original"}``.
+    """
+
+    def __init__(
+        self,
+        parent: Optional[QWidget] = None,
+        workplanes: Optional[list] = None,
+    ):
+        super().__init__(parent)
+        self.setWindowTitle("Mirror Options")
+        self.setMinimumWidth(400)
+
+        self._preview_callback: Optional[Callable[[Any], None]] = None
+        self._workplanes: list = workplanes if workplanes is not None else []
+
+        # Preset plane definitions: (label, normal, origin)
+        self._presets: list = [
+            ("XY (Top)", (0, 0, 1), (0, 0, 0)),
+            ("XZ (Front)", (0, 1, 0), (0, 0, 0)),
+            ("YZ (Right)", (1, 0, 0), (0, 0, 0)),
+            ("-XY (Bottom)", (0, 0, -1), (0, 0, 0)),
+            ("-XZ (Back)", (0, -1, 0), (0, 0, 0)),
+            ("-YZ (Left)", (-1, 0, 0), (0, 0, 0)),
+        ]
+
+        layout = QVBoxLayout(self)
+
+        # ── Plane source ──
+        src_layout = QHBoxLayout()
+        src_layout.addWidget(QLabel("Mirror plane:"))
+        self._wp_combo = QComboBox()
+        if self._workplanes:
+            for name, _origin, _normal in self._workplanes:
+                self._wp_combo.addItem(name)
+        else:
+            self._wp_combo.addItem("(no workplanes)")
+            self._wp_combo.setEnabled(False)
+        self._wp_combo.setToolTip("Pick an existing workplane as the mirror plane.")
+        src_layout.addWidget(self._wp_combo, 1)
+        layout.addLayout(src_layout)
+
+        # ── Preset radio buttons ──
+        preset_label = QLabel("Preset planes:")
+        layout.addWidget(preset_label)
+
+        self._preset_group = QButtonGroup(self)
+        preset_grid = QGridLayout()
+        for idx, (label, normal, origin) in enumerate(self._presets):
+            btn = QRadioButton(label)
+            btn.setChecked(idx == 0)  # XY default
+            self._preset_group.addButton(btn, idx)
+            preset_grid.addWidget(btn, idx // 2, idx % 2)
+        layout.addLayout(preset_grid)
+
+        # ── Custom origin ──
+        line1 = QFrame()
+        line1.setFrameShape(QFrame.Shape.HLine)
+        line1.setFrameShadow(QFrame.Shadow.Sunken)
+        layout.addWidget(line1)
+
+        origin_label = QLabel("Plane origin (mm):")
+        layout.addWidget(origin_label)
+        origin_row = QHBoxLayout()
+        origin_row.addWidget(QLabel("X:"))
+        self._origin_x = QDoubleSpinBox()
+        self._origin_x.setRange(-100000.0, 100000.0)
+        self._origin_x.setDecimals(2)
+        self._origin_x.setValue(0.0)
+        origin_row.addWidget(self._origin_x)
+        origin_row.addWidget(QLabel("Y:"))
+        self._origin_y = QDoubleSpinBox()
+        self._origin_y.setRange(-100000.0, 100000.0)
+        self._origin_y.setDecimals(2)
+        self._origin_y.setValue(0.0)
+        origin_row.addWidget(self._origin_y)
+        origin_row.addWidget(QLabel("Z:"))
+        self._origin_z = QDoubleSpinBox()
+        self._origin_z.setRange(-100000.0, 100000.0)
+        self._origin_z.setDecimals(2)
+        self._origin_z.setValue(0.0)
+        origin_row.addWidget(self._origin_z)
+        layout.addLayout(origin_row)
+
+        # ── Custom normal ──
+        normal_label = QLabel("Plane normal:")
+        layout.addWidget(normal_label)
+        normal_row = QHBoxLayout()
+        normal_row.addWidget(QLabel("X:"))
+        self._normal_x = QDoubleSpinBox()
+        self._normal_x.setRange(-1.0, 1.0)
+        self._normal_x.setSingleStep(1.0)
+        self._normal_x.setDecimals(0)
+        self._normal_x.setValue(0.0)
+        normal_row.addWidget(self._normal_x)
+        normal_row.addWidget(QLabel("Y:"))
+        self._normal_y = QDoubleSpinBox()
+        self._normal_y.setRange(-1.0, 1.0)
+        self._normal_y.setSingleStep(1.0)
+        self._normal_y.setDecimals(0)
+        self._normal_y.setValue(0.0)
+        normal_row.addWidget(self._normal_y)
+        normal_row.addWidget(QLabel("Z:"))
+        self._normal_z = QDoubleSpinBox()
+        self._normal_z.setRange(-1.0, 1.0)
+        self._normal_z.setSingleStep(1.0)
+        self._normal_z.setDecimals(0)
+        self._normal_z.setValue(1.0)
+        normal_row.addWidget(self._normal_z)
+        layout.addLayout(normal_row)
+
+        # ── Keep original ──
+        self._keep_original_cb = QCheckBox("Keep original")
+        self._keep_original_cb.setChecked(True)
+        self._keep_original_cb.setToolTip(
+            "When checked, the original solid is kept and union'd with its mirror image."
+        )
+        layout.addWidget(self._keep_original_cb)
+
+        # ── Buttons ──
+        line2 = QFrame()
+        line2.setFrameShape(QFrame.Shape.HLine)
+        line2.setFrameShadow(QFrame.Shadow.Sunken)
+        layout.addWidget(line2)
+
+        btn_layout = QHBoxLayout()
+        ok_btn = QPushButton("Mirror")
+        ok_btn.clicked.connect(self.accept)
+        cancel_btn = QPushButton("Cancel")
+        cancel_btn.clicked.connect(self.reject)
+        btn_layout.addWidget(ok_btn)
+        btn_layout.addWidget(cancel_btn)
+        layout.addLayout(btn_layout)
+
+        # ── Wire signals ──
+        self._wp_combo.currentIndexChanged.connect(self._on_workplane_selected)
+        self._preset_group.buttonClicked.connect(self._on_preset_changed)
+        for w in (self._origin_x, self._origin_y, self._origin_z,
+                  self._normal_x, self._normal_y, self._normal_z):
+            w.valueChanged.connect(self._emit_preview)
+        self._keep_original_cb.toggled.connect(self._emit_preview)
+
+        # Set initial values from the first preset (XY)
+        self._on_preset_changed(self._preset_group.button(0))
+
+    # ── Helpers ─────────────────────────────────────────────────────
+
+    def _on_workplane_selected(self, index: int) -> None:
+        """Fill origin / normal from the selected workplane."""
+        if index < 0 or index >= len(self._workplanes):
+            return
+        _name, origin, normal = self._workplanes[index]
+        self._origin_x.setValue(float(origin[0]))
+        self._origin_y.setValue(float(origin[1]))
+        self._origin_z.setValue(float(origin[2]))
+        self._normal_x.setValue(float(normal[0]))
+        self._normal_y.setValue(float(normal[1]))
+        self._normal_z.setValue(float(normal[2]))
+        self._emit_preview()
+
+    def _on_preset_changed(self, btn: QRadioButton) -> None:
+        """Fill origin / normal from the selected preset."""
+        idx = self._preset_group.id(btn)
+        if idx < 0 or idx >= len(self._presets):
+            return
+        _label, normal, origin = self._presets[idx]
+        self._origin_x.setValue(float(origin[0]))
+        self._origin_y.setValue(float(origin[1]))
+        self._origin_z.setValue(float(origin[2]))
+        self._normal_x.setValue(float(normal[0]))
+        self._normal_y.setValue(float(normal[1]))
+        self._normal_z.setValue(float(normal[2]))
+        self._emit_preview()
+
+    def _emit_preview(self) -> None:
+        """Fire the preview callback (if installed) with current values."""
+        if self._preview_callback is None:
+            return
+        values = self.get_values()
+        self._preview_callback(values)
+
+    def set_preview_callback(self, callback: Optional[Callable[[Any], None]]) -> None:
+        """Install a callback for live 3D preview of the mirrored shape.
+
+        The callback receives a ``dict`` with keys
+        ``mirror_plane_origin``, ``mirror_plane_normal``, and
+        ``keep_original``, or *None* to clear the preview.
+        """
+        self._preview_callback = callback
+        if callback is not None:
+            self._emit_preview()
+
+    def get_values(self) -> Dict[str, Any]:
+        """Return the current mirror parameters as a dict.
+
+        Keys: ``mirror_plane_origin`` (3-tuple), ``mirror_plane_normal``
+        (3-tuple, auto-normalized), ``keep_original`` (bool).
+        """
+        normal = (
+            self._normal_x.value(),
+            self._normal_y.value(),
+            self._normal_z.value(),
+        )
+        # Auto-normalize the normal vector (zero-vector → +Z).
+        import math as _math
+        nx, ny, nz = normal
+        norm = _math.sqrt(nx * nx + ny * ny + nz * nz)
+        if norm < 1e-12:
+            normal = (0.0, 0.0, 1.0)
+        else:
+            normal = (nx / norm, ny / norm, nz / norm)
+        return {
+            "mirror_plane_origin": (
+                self._origin_x.value(),
+                self._origin_y.value(),
+                self._origin_z.value(),
+            ),
+            "mirror_plane_normal": normal,
+            "keep_original": self._keep_original_cb.isChecked(),
+        }
+
+
 class WorkplaneOrientationDialog(QDialog):
     """Modal dialog to choose the orientation of a new workplane.
 

src/fluency/ui/render_window.py

@@ -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._stop_thread(self._preview_thread)
-            self._preview_thread.terminate()
-            self._preview_thread.wait(2000)
         elif self._active_mode == "render" and self._render_thread:
-            self._render_thread.cancel()
+            self._stop_thread(self._render_thread)
-            self._render_thread.terminate()
-            self._render_thread.wait(2000)
         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():
+            # block=True: at window close a thread must not outlive the app.
-                thread.cancel()
+            self._stop_thread(thread, block=True)
-                thread.terminate()
-                thread.wait(2000)
 
         # 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._start_meshing()
-        self._schedule_auto_preview()
 
     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):
+        # block=True: at tab exit / app shutdown a thread must not outlive
-            if thread and thread.isRunning():
+        # the owning widget.
-                thread.cancel()
+        for thread in (self._mesh_thread, self._preview_thread, self._render_thread):
-                thread.terminate()
+            self._stop_thread(thread, block=True)
-                thread.wait(2000)
+        self._mesh_thread = None
-        if self._mesh_path and os.path.exists(self._mesh_path):
+        self._preview_thread = None
-            try:
+        self._render_thread = None
-                os.unlink(self._mesh_path)
+        self._active_mode = None
-            except OSError:
+        # Delete temp PLY files (single shape plus all assembly parts).
-                pass
+        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):
+    def _start_meshing(self):
-        if self._shape is None:
+        """Kick off background tessellation of the current shape/assembly.
-            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 _prepare_assembly_mesh(self, parts: list):
+        The GUI thread is never blocked: the tab shows "Tessellating…"
-        """Tessellate multiple shapes to separate PLY files.
+        until the mesh is ready, then the auto-preview is scheduled.
-
-        *parts* is a list of ``(TopoDS_Shape, Optional[str])`` tuples.
-        Each material preset name is resolved via ``get_preset``.
         """
-        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 = []
+    def _on_mesh_ready(self, mesh_path: str, gen: int) -> None:
-        first_bounds = None
+        """Background tessellation finished (single shape)."""
-        for shape, mat_name in parts:
+        if gen != self._mesh_generation:
-            try:
+            # The load was replaced mid-tessellation — discard the stale mesh.
-                mesh_path = occ_shape_to_ply(shape, linear_deflection=0.1, angular_deflection=0.15)
+            _unlink_quiet(mesh_path)
-                material = get_preset(mat_name) if mat_name else get_preset("Brushed Steel")
+            return
-                self._assembly_parts.append((mesh_path, material))
+        self._mesh_path = mesh_path
-                if first_bounds is None:
+        if self._camera is None and self._backend is not None:
-                    first_bounds = occ_shape_bounds(shape)
+            mn, mx = occ_shape_bounds(self._shape)
-            except Exception as e:
+            self._camera = self._backend.default_camera_from_bounds(mn, mx)
-                logger.warning(f"Failed to tessellate assembly part: {e}")
+            self._populate_camera_controls()
-        if first_bounds and self._camera is None:
+        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._stop_thread(self._preview_thread)
-            self._preview_thread.terminate()
-            self._preview_thread.wait(2000)
         elif self._active_mode == "render" and self._render_thread:
-            self._render_thread.cancel()
+            self._stop_thread(self._render_thread)
-            self._render_thread.terminate()
-            self._render_thread.wait(2000)
         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)

src/fluency/ui/sketch_widget.py

@@ -260,6 +260,7 @@ class Sketch2DWidget(QWidget):
         self._move_anchor_orig: Optional[QPoint] = None
         self._move_orig_positions: Dict[int, Tuple[float, float]] = {}
         self._move_active: bool = False
+        self._move_did_move: bool = False
 
         # Auto-constraint tracking on snap
         self._snap_point_target: Optional[OCCSketchEntity] = None
@@ -547,8 +548,12 @@ class Sketch2DWidget(QWidget):
                         end_uv[0], end_uv[1]
                     )
                 # sweep=None → renderer computes shortest-path arc
+                # register=False: all three reference points are external
+                # (fixed) — registering the arc on top would
+                # over-constrain the solver (inconsistent).
                 self._sketch.add_arc(
-                    center_pt, radius, start_pt, end_pt, sweep=None
+                    center_pt, radius, start_pt, end_pt,
+                    sweep=None, register=False,
                 )
                 imported += 1
             except Exception as exc:
@@ -811,6 +816,7 @@ class Sketch2DWidget(QWidget):
         self._move_anchor_orig = None
         self._move_orig_positions = {}
         self._move_active = False
+        self._move_did_move = False
         self._hovered_face = None
         self._snap_point_target = None
         self._snap_line_target = None
@@ -863,19 +869,17 @@ class Sketch2DWidget(QWidget):
         constraint multi-select, then emits ``constrain_done`` so the
         toolbar buttons uncheck themselves.
         """
-        if not self._is_drawing_tool_active():
+        was_active = self._is_drawing_tool_active()
-            return
-        self._mode = None
         self._draw_buffer = []
         self._dynamic_line_end = None
         self._selected_entities = []
         self._hovered_constraint_idx = -1
         self._arc_accum_sweep = 0.0
         self._arc_prev_angle = None
-        # Invalidate any pending dimension-input prompt so the value
-        # dialog (if one is open elsewhere) doesn't latch onto stale state.
         self._pending_distance_val = None
-        self.constrain_done.emit()
+        if was_active:
+            self._mode = None
+            self.constrain_done.emit()
         self.update()
 
     def set_construct_mode(self, enabled: bool):
@@ -930,13 +934,12 @@ class Sketch2DWidget(QWidget):
 
     # ─── Snapping ─────────────────────────────────────────────────────────
 
-    def _find_nearest_point(self, pos: QPoint, max_distance: int = 15) -> Optional[QPoint]:
+    def _find_nearest_point(self, pos: QPoint, max_distance: int = 15, exclude_ids: Optional[set[int]] = None) -> Optional[QPoint]:
-        # Delegates to _find_nearest_point_entity so the position snap and
         # the constraint target ALWAYS agree — previously this loop ignored
         # underlay visibility, so a hidden underlay corner would snap the
         # cursor position while the entity lookup returned None and no
         # coincident constraint was created (silent disconnect).
-        entity = self._find_nearest_point_entity(pos, max_distance)
+        entity = self._find_nearest_point_entity(pos, max_distance, exclude_ids=exclude_ids)
         if entity is None:
             return None
         xy = self._flat_xy(entity.geometry)
@@ -946,7 +949,7 @@ class Sketch2DWidget(QWidget):
         return QPoint(int(round(x)), int(round(y)))
 
     def _find_nearest_point_entity(
-        self, pos: QPoint, max_distance: int = 15
+        self, pos: QPoint, max_distance: int = 15, exclude_ids: Optional[set[int]] = None
     ) -> Optional[OCCSketchEntity]:
         """Find the nearest point entity to a screen position.
 
@@ -962,6 +965,8 @@ class Sketch2DWidget(QWidget):
         for entity in self._points:
             if self._is_external(entity) and not self._underlay_visible:
                 continue
+            if exclude_ids and entity.id in exclude_ids:
+                continue
             xy = self._flat_xy(entity.geometry)
             if xy is None:
                 continue
@@ -1066,7 +1071,7 @@ class Sketch2DWidget(QWidget):
             return end
         return QPoint(start.x(), end.y())
 
-    def _apply_all_snaps(self, pos: QPoint, start: Optional[QPoint] = None) -> QPoint:
+    def _apply_all_snaps(self, pos: QPoint, start: Optional[QPoint] = None, exclude_ids: Optional[set[int]] = None) -> QPoint:
         result = pos
         # Reset auto-constraint tracking
         self._snap_point_target = None
@@ -1074,10 +1079,16 @@ class Sketch2DWidget(QWidget):
         self._snap_horizontal = False
         self._snap_vertical = False
 
-        point_snap = self._find_nearest_point(pos)
+        point_snap = self._find_nearest_point(pos, exclude_ids=exclude_ids)
         if point_snap:
             self._snap_point_target = self._find_nearest_point_entity(pos)
             return self._world_to_screen(point_snap)
+        # When exclude_ids is active (constraint multi-select), don't fall
+        # through to midpoint / line snap — those redirect the click to a
+        # position the handler's point lookup won't find.  The handler uses
+        # its own world-space entity lookup with the same exclude set.
+        if exclude_ids:
+            return result
         if self._snap_mode.get("mpoint", False):
             mid_snap = self._find_midpoint_snap(pos)
             if mid_snap:
@@ -1240,27 +1251,84 @@ class Sketch2DWidget(QWidget):
 
     # ─── Solver helpers ───────────────────────────────────────────────────
 
-    def _get_point_entity_at(self, world_pos: QPoint) -> Optional[OCCSketchEntity]:
+    def _get_point_entity_at(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None) -> Optional[OCCSketchEntity]:
         """Find nearest point entity to world position.
 
         External (underlay) points are pickable when the underlay is visible
         so the user can use them as constraint anchors (e.g. the corner of a
         projected face); they're skipped when the underlay is hidden.
+
+        When several points are within tolerance (e.g. a user-drawn corner
+        sitting exactly on the centerline origin), user-drawn points win
+        over centerline / external reference points — otherwise a click on
+        your own corner would silently grab the reference point underneath
+        it and the distance would apply to the wrong entity.
         """
+        best: Optional[OCCSketchEntity] = None
+        best_dist = float("inf")
+        ref_best: Optional[OCCSketchEntity] = None
+        ref_best_dist = float("inf")
+        tolerance = self._pick_tolerance_world(10)
         for entity in self._points:
             if self._is_external(entity) and not self._underlay_visible:
                 continue
+            if exclude_ids and entity.id in exclude_ids:
+                continue
             xy = self._flat_xy(entity.geometry)
             if xy is None:
                 continue
             x, y = xy
             dist = math.sqrt((world_pos.x() - x) ** 2 + (world_pos.y() - y) ** 2)
-            if dist < self._pick_tolerance_world(10):
+            if dist >= tolerance:
-                return entity
+                continue
-        return None
+            if self._is_external(entity) or self._is_centerline(entity):
+                # Reference geometry — fallback only, never preferred.
+                if dist < ref_best_dist:
+                    ref_best, ref_best_dist = entity, dist
+            else:
+                # User-drawn point — preferred over reference geometry.
+                if dist < best_dist:
+                    best, best_dist = entity, dist
+        return best if best is not None else ref_best
+
+    def _get_point_entity_at_fallback(
+        self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None
+    ) -> Optional[OCCSketchEntity]:
+        """Same as :meth:`_get_point_entity_at` but with 3× tolerance.
+
+        Used by the distance constraint handler when the standard lookup fails
+        during multi-select — the snap may not have fired (the excluded entity
+        was the only one within screen range), so ``world_snapped`` is the raw
+        click position which can be further from the intended target than the
+        snapped position would have been.
+        """
+        best: Optional[OCCSketchEntity] = None
+        best_dist = float("inf")
+        ref_best: Optional[OCCSketchEntity] = None
+        ref_best_dist = float("inf")
+        tolerance = self._pick_tolerance_world(30)
+        for entity in self._points:
+            if self._is_external(entity) and not self._underlay_visible:
+                continue
+            if exclude_ids and entity.id in exclude_ids:
+                continue
+            xy = self._flat_xy(entity.geometry)
+            if xy is None:
+                continue
+            x, y = xy
+            dist = math.sqrt((world_pos.x() - x) ** 2 + (world_pos.y() - y) ** 2)
+            if dist >= tolerance:
+                continue
+            if self._is_external(entity) or self._is_centerline(entity):
+                if dist < ref_best_dist:
+                    ref_best, ref_best_dist = entity, dist
+            else:
+                if dist < best_dist:
+                    best, best_dist = entity, dist
+        return best if best is not None else ref_best
 
     def _get_line_entity_at(
-        self, world_pos: QPoint
+        self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None
     ) -> Optional[Tuple[OCCSketchEntity, OCCSketchEntity]]:
         """Find a line near the given world position.
 
@@ -1273,12 +1341,27 @@ class Sketch2DWidget(QWidget):
         uses perpendicular distance to the infinite line (no segment
         clamping) with a zoom-adjusted tolerance so they are pickable at
         any zoom level.
+
+        When several lines are within tolerance (e.g. a user-drawn edge
+        lying exactly on the X axis), user-drawn lines win over centerline
+        / external reference lines — otherwise a click on your own edge
+        would silently grab the reference axis underneath it.
         """
+        best: Optional[Tuple[OCCSketchEntity, OCCSketchEntity]] = None
+        best_dist = float("inf")
+        ref_best: Optional[Tuple[OCCSketchEntity, OCCSketchEntity]] = None
+        ref_best_dist = float("inf")
         for p1_ent, p2_ent in self._lines:
             line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
             is_ext = bool(line_ent is not None and self._is_external(line_ent))
             if is_ext and not self._underlay_visible:
                 continue
+            # NOTE: exclude_ids is accepted for API consistency but NOT applied
+            # here — it contains POINT ids (the already-selected entity for
+            # multi-click constraint tools).  Filtering lines by their endpoint
+            # ids would prevent the user from picking a line that shares the
+            # selected point, which is a valid operation for point-on-line /
+            # midpoint / distance constraints.
             if p1_ent.geometry and p2_ent.geometry:
                 x1, y1 = p1_ent.geometry
                 x2, y2 = p2_ent.geometry
@@ -1300,7 +1383,9 @@ class Sketch2DWidget(QWidget):
                     # perpendicular distance directly (no segment clamping).
                     tol = self._pick_tolerance_world(12)
                     if perp_dist < tol:
-                        return (p1_ent, p2_ent)
+                        cand = (p1_ent, p2_ent)
+                        if perp_dist < ref_best_dist:
+                            ref_best, ref_best_dist = cand, perp_dist
                 else:
                     # Regular lines: clamp the projection to the segment
                     # and check distance to that clamped point.
@@ -1317,8 +1402,15 @@ class Sketch2DWidget(QWidget):
                         self._pick_tolerance_world(8) if is_ext else self._pick_tolerance_world(14)
                     )
                     if seg_dist < tol:
-                        return (p1_ent, p2_ent)
+                        cand = (p1_ent, p2_ent)
-        return None
+                        # Prefer user-drawn lines over reference geometry.
+                        if is_ext:
+                            if seg_dist < ref_best_dist:
+                                ref_best, ref_best_dist = cand, seg_dist
+                        else:
+                            if seg_dist < best_dist:
+                                best, best_dist = cand, seg_dist
+        return best if best is not None else ref_best
 
     def _find_line_sketch_entity(
         self, p1_ent: OCCSketchEntity, p2_ent: OCCSketchEntity
@@ -1399,6 +1491,43 @@ class Sketch2DWidget(QWidget):
         x1, y1 = s_ent.geometry
         x2, y2 = e_ent.geometry
         return QPoint(int(round((x1 + x2) / 2)), int(round((y1 + y2) / 2)))
+    def _line_world_endpoints(
+        self, line_id: int
+    ) -> Optional[Tuple[Tuple[float, float], Tuple[float, float]]]:
+        """World-space endpoint coordinates of the line with the given id."""
+        if not self._sketch or line_id not in self._sketch._lines:
+            return None
+        sid, eid2 = self._sketch._lines[line_id]
+        s_ent = self._sketch._entities.get(sid)
+        e_ent = self._sketch._entities.get(eid2)
+        if not s_ent or not e_ent or not s_ent.geometry or not e_ent.geometry:
+            return None
+        x1, y1 = s_ent.geometry
+        x2, y2 = e_ent.geometry
+        if not all(isinstance(v, (int, float)) for v in (x1, y1, x2, y2)):
+            return None
+        return (float(x1), float(y1)), (float(x2), float(y2))
+
+    def _perpendicular_foot_world(self, point: QPoint, line_id: int) -> Optional[QPoint]:
+        """Perpendicular foot of *point* projected onto the line, world-space.
+
+        The foot lies on the *infinite* line through the two endpoints — when
+        the point projects beyond the segment the dimension line legitimately
+        extends past the endpoint.  Returns None if the line geometry is
+        unavailable.
+        """
+        ends = self._line_world_endpoints(line_id)
+        if ends is None:
+            return None
+        (x1, y1), (x2, y2) = ends
+        dx = x2 - x1
+        dy = y2 - y1
+        denom = dx * dx + dy * dy
+        if denom < 1e-12:
+            # Degenerate (zero-length) line — fall back to its start point.
+            return QPoint(int(round(x1)), int(round(y1)))
+        t = ((point.x() - x1) * dx + (point.y() - y1) * dy) / denom
+        return QPoint(int(round(x1 + t * dx)), int(round(y1 + t * dy)))
 
     def _point_world(self, pid: int) -> Optional[QPoint]:
         """World-space position of the point entity with the given id.
@@ -1508,13 +1637,32 @@ class Sketch2DWidget(QWidget):
                     anchor = self._line_world_mid(ids[1])
                     label = "mid"
                 elif ctype == "distance":
-                    # Distance may be point-to-point OR point-to-line (e.g.
+                    # Distance may be point-to-point OR point-to-line.  For a
-                    # point-on-line coincident surfaces as a coincident entry;
+                    # point-to-line distance the dimension line must run from
-                    # a future point-to-line distance would do the same).
+                    # the selected point to its perpendicular foot on the line
-                    # Use _entity_anchor so a line id routes to the line
+                    # (i.e. at 90° to the line) — NOT to the line's midpoint,
-                    # midpoint instead of crashing on round(<tuple>).
+                    # which would render the measured distance at an arbitrary
+                    # angle.  Use _entity_anchor so a line id routes to the
+                    # line midpoint as a fallback instead of crashing on
+                    # round(<tuple>).
                     a = self._entity_anchor(ids[0])
                     b = self._entity_anchor(ids[1])
+                    ent_a = self._sketch._entities.get(ids[0])
+                    ent_b = self._sketch._entities.get(ids[1])
+                    ta = ent_a.entity_type if ent_a is not None else None
+                    tb = ent_b.entity_type if ent_b is not None else None
+                    if ta == "point" and tb == "line":
+                        if a is not None:
+                            foot = self._perpendicular_foot_world(a, ids[1])
+                            if foot is not None:
+                                b = foot
+                    elif ta == "line" and tb == "point":
+                        # Legacy (line, point) log ordering — same geometry,
+                        # mirrored.
+                        if b is not None:
+                            foot = self._perpendicular_foot_world(b, ids[0])
+                            if foot is not None:
+                                a = foot
                     # NOTE: use `is not None`, not truthiness — QPoint(0,0) is falsy in PySide6.
                     if a is not None and b is not None:
                         anchor = QPoint((a.x() + b.x()) // 2, (a.y() + b.y()) // 2)
@@ -1599,7 +1747,10 @@ class Sketch2DWidget(QWidget):
                     if tag_p1 is not None and tag_p2 is not None:
                         tag_entry["p1_world"] = tag_p1
                         tag_entry["p2_world"] = tag_p2
-                        tag_entry["distance"] = params[0] if params else 0.0
+                        # The stored value carries the side-sign (negative
+                        # when the point is on the "negative" side of the
+                        # line) — the dimension text shows the magnitude.
+                        tag_entry["distance"] = abs(params[0]) if params else 0.0
                 tags.append(tag_entry)
             except Exception as exc:
                 # Catch any failure while building this one tag (bad
@@ -2105,9 +2256,15 @@ class Sketch2DWidget(QWidget):
                     self.update()
                     return
 
+            # Exclude already-selected entities from snap/lookup during constraint multi-select
+            # so the user can pick a second entity distinct from the first.
+            _exclude_ids: Optional[set[int]] = None
+            if self._mode and self._mode.startswith("constrain_") and self._selected_entities:
+                _exclude_ids = {e.id for e in self._selected_entities}
             snapped_pos = self._apply_all_snaps(
                 event.pos(),
                 self._world_to_screen(self._draw_buffer[0]) if self._draw_buffer else None,
+                exclude_ids=_exclude_ids,
             )
             world_snapped = (
                 self._screen_to_world(snapped_pos) if snapped_pos != event.pos() else world_pos
@@ -2126,23 +2283,23 @@ class Sketch2DWidget(QWidget):
             elif self._mode == "select":
                 self._handle_select_click(world_snapped)
             elif self._mode == "constrain_coincident":
-                self._handle_constraint_coincident(world_snapped)
+                self._handle_constraint_coincident(world_snapped, exclude_ids=_exclude_ids)
             elif self._mode == "constrain_horizontal":
                 self._handle_constraint_horizontal(world_snapped)
             elif self._mode == "constrain_vertical":
                 self._handle_constraint_vertical(world_snapped)
             elif self._mode == "constrain_distance":
-                self._handle_constraint_distance(world_snapped)
+                self._handle_constraint_distance(world_snapped, exclude_ids=_exclude_ids)
             elif self._mode == "constrain_midpoint":
-                self._handle_constraint_midpoint(world_snapped)
+                self._handle_constraint_midpoint(world_snapped, exclude_ids=_exclude_ids)
             elif self._mode == "constrain_perpendicular":
                 self._handle_constraint_perpendicular(world_snapped)
             elif self._mode == "constrain_parallel":
                 self._handle_constraint_parallel(world_snapped)
             elif self._mode == "constrain_ptline":
-                self._handle_constraint_ptline(world_snapped)
+                self._handle_constraint_ptline(world_snapped, exclude_ids=_exclude_ids)
             elif self._mode == "constrain_symmetric":
-                self._handle_constraint_symmetric(world_snapped)
+                self._handle_constraint_symmetric(world_snapped, exclude_ids=_exclude_ids)
             elif self._mode == "constrain_diameter":
                 self._handle_constraint_diameter(world_snapped)
 
@@ -2166,6 +2323,8 @@ class Sketch2DWidget(QWidget):
             target_world = self._screen_to_world(snapped_screen)
             dx = target_world.x() - self._move_anchor_orig.x()
             dy = target_world.y() - self._move_anchor_orig.y()
+            if dx != 0 or dy != 0:
+                self._move_did_move = True
             for ent in self._moving_points:
                 if ent.id in self._move_orig_positions and ent.geometry is not None:
                     ox, oy = self._move_orig_positions[ent.id]
@@ -2363,8 +2522,7 @@ class Sketch2DWidget(QWidget):
                     # the user expects from dragging a single corner.
                     if self._move_anchor is not None and self._move_anchor.geometry is not None:
                         ax, ay = self._move_anchor.geometry
-                        if not self._sketch.is_entity_dragged(self._move_anchor.id):
+                        if self._move_did_move and not self._sketch.is_entity_dragged(self._move_anchor.id):
-                            self._sketch.constrain_fixed(self._move_anchor)
                             # constrain_fixed reads the current params via
                             # the dragged() call, so re-sync to be safe.
                             self._solve_and_sync()
@@ -3254,10 +3412,13 @@ class Sketch2DWidget(QWidget):
 
     # ─── Constraint handlers (with solver calls) ──────────────────────────
 
-    def _handle_constraint_coincident(self, world_pos: QPoint):
+    def _handle_constraint_coincident(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None):
-        ent = self._get_point_entity_at(world_pos)
+        ent = self._get_point_entity_at(world_pos, exclude_ids=exclude_ids)
         if ent is None:
             return
+        if ent in self._selected_entities:
+            self.update()
+            return
         self._selected_entities.append(ent)
         if len(self._selected_entities) >= 2:
             e1, e2 = self._selected_entities[:2]
@@ -3310,7 +3471,6 @@ class Sketch2DWidget(QWidget):
         line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
         if line_ent is None:
             return
-        # Save state before adding constraint
         if self._undo_manager:
             self._undo_manager.save_state()
         if self._sketch:
@@ -3327,18 +3487,62 @@ class Sketch2DWidget(QWidget):
         self.constrain_done.emit()
         self.update()
 
-    def _handle_constraint_distance(self, world_pos: QPoint):
+    def _handle_constraint_distance(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None):
-        point_ent = self._get_point_entity_at(world_pos)
+        point_ent = self._get_point_entity_at(world_pos, exclude_ids=exclude_ids)
+        if point_ent is None:
+            # The snap may not have fired (excluded entity was the only one
+            # within screen range, or the standard tolerance is too tight after
+            # a viewport change like re-projecting a face).  Retry with 3×.
+            point_ent = self._get_point_entity_at_fallback(world_pos, exclude_ids=exclude_ids)
         if point_ent:
-            # Point clicked: collect points; constraint applied after 2nd point.
+            if point_ent in self._selected_entities:
+                self.update()
+                return
             self._selected_entities.append(point_ent)
         else:
-            line_hit = self._get_line_entity_at(world_pos)
+            line_hit = self._get_line_entity_at(world_pos, exclude_ids=exclude_ids)
             if line_hit:
                 p1_ent, p2_ent = line_hit
                 line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
                 if line_ent is not None:
-                    # Line clicked: constrain its length (endpoint distance).
+                    if self._selected_entities:
+                        # A point is already selected: this line is the
+                        # SECOND entity of a point-to-line distance.
+                        prev_ent = self._selected_entities[0]
+                        dist, ok = QInputDialog.getDouble(
+                            self,
+                            "Point-to-line distance",
+                            "Distance (mm):",
+                            self._constraint_distance_value,
+                            0,
+                            10000,
+                            2,
+                        )
+                        if ok and self._sketch:
+                            # Save state before adding constraint
+                            if self._undo_manager:
+                                self._undo_manager.save_state()
+                            self._sketch.constrain_distance(prev_ent, line_ent, dist)
+                            self._solve_and_sync()
+                            logger.info(f"Point-line distance {dist:.2f}mm")
+                        self._selected_entities = []
+                        self._mode = None
+                        self.constrain_done.emit()
+                        self.update()
+                        return
+                    # No selection: a lone line click sets its length
+                    # (distance between its endpoint points).  Reference
+                    # lines (centerlines / underlay projections) are fixed
+                    # and have no meaningful "length" — skip them; the
+                    # user must pick a point first to constrain against
+                    # them (point-to-line distance).
+                    if self._is_centerline(line_ent) or self._is_external(line_ent):
+                        logger.info(
+                            "distance: select a point first, then this reference line "
+                            "for a point-to-line distance"
+                        )
+                        self.update()
+                        return
                     dist, ok = QInputDialog.getDouble(
                         self,
                         "Distance",
@@ -3378,12 +3582,12 @@ class Sketch2DWidget(QWidget):
             self.constrain_done.emit()
         self.update()
 
-    def _handle_constraint_midpoint(self, world_pos: QPoint):
+    def _handle_constraint_midpoint(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None):
-        point_ent = self._get_point_entity_at(world_pos)
+        point_ent = self._get_point_entity_at(world_pos, exclude_ids=exclude_ids)
         if point_ent and not self._selected_entities:
             self._selected_entities.append(point_ent)
         elif self._selected_entities:
-            line_hit = self._get_line_entity_at(world_pos)
+            line_hit = self._get_line_entity_at(world_pos, exclude_ids=exclude_ids)
             if line_hit:
                 p1_ent, p2_ent = line_hit
                 line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
@@ -3454,13 +3658,13 @@ class Sketch2DWidget(QWidget):
             self.constrain_done.emit()
         self.update()
 
-    def _handle_constraint_ptline(self, world_pos: QPoint):
+    def _handle_constraint_ptline(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None):
         """Point-on-line coincident (point on line)."""
-        point_ent = self._get_point_entity_at(world_pos)
+        point_ent = self._get_point_entity_at(world_pos, exclude_ids=exclude_ids)
         if point_ent and not self._selected_entities:
             self._selected_entities.append(point_ent)
         elif self._selected_entities:
-            line_hit = self._get_line_entity_at(world_pos)
+            line_hit = self._get_line_entity_at(world_pos, exclude_ids=exclude_ids)
             if line_hit:
                 p1_ent, p2_ent = line_hit
                 line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
@@ -3477,11 +3681,11 @@ class Sketch2DWidget(QWidget):
                 self.constrain_done.emit()
         self.update()
 
-    def _handle_constraint_symmetric(self, world_pos: QPoint):
+    def _handle_constraint_symmetric(self, world_pos: QPoint, exclude_ids: Optional[set[int]] = None):
         """Symmetric constraint: select entity1, entity2, then mirror line."""
         # Click 3: mirror line
         if len(self._selected_entities) == 2:
-            line_hit = self._get_line_entity_at(world_pos)
+            line_hit = self._get_line_entity_at(world_pos, exclude_ids=exclude_ids)
             if line_hit:
                 p1_ent, p2_ent = line_hit
                 mirror_line = self._find_line_sketch_entity(p1_ent, p2_ent)
@@ -3503,8 +3707,11 @@ class Sketch2DWidget(QWidget):
             self.update()
             return
         # Clicks 1-2: select point entities
-        point_ent = self._get_point_entity_at(world_pos)
+        point_ent = self._get_point_entity_at(world_pos, exclude_ids=exclude_ids)
         if point_ent:
+            if point_ent in self._selected_entities:
+                self.update()
+                return
             self._selected_entities.append(point_ent)
             n_selected = len(self._selected_entities)
             if n_selected < 2:
@@ -4026,6 +4233,32 @@ class Sketch2DWidget(QWidget):
                     painter.setPen(QPen(QColor("#cdd6f4"), 2))
                 painter.drawLine(sp1, sp2)
 
+        # ── Selected-entity highlight (multi-click constraint tools) ──
+        # While collecting entities for a distance constraint the first pick
+        # gets highlighted so the user can see it registered before clicking
+        # the second entity.  Points get a bright ring, lines a bright
+        # overlay stroke.
+        if self._selected_entities and self._is_drawing_tool_active():
+            for ent in self._selected_entities:
+                if ent.entity_type == "point":
+                    xy = self._flat_xy(ent.geometry)
+                    if xy is None:
+                        continue
+                    x, y = xy
+                    sp = self._world_to_screen(QPoint(int(round(x)), int(round(y))))
+                    painter.setPen(QPen(QColor("#f9e2af"), 2))
+                    painter.setBrush(Qt.NoBrush)
+                    painter.drawEllipse(sp, 9, 9)
+                elif ent.entity_type == "line":
+                    p1e, p2e = self._get_line_endpoints(ent)
+                    if p1e and p2e and p1e.geometry and p2e.geometry:
+                        x1, y1 = p1e.geometry
+                        x2, y2 = p2e.geometry
+                        sp1 = self._world_to_screen(QPoint(int(round(x1)), int(round(y1))))
+                        sp2 = self._world_to_screen(QPoint(int(round(x2)), int(round(y2))))
+                        painter.setPen(QPen(QColor("#f9e2af"), 3))
+                        painter.drawLine(sp1, sp2)
+
         # ── Constraint tags (log-driven; drawn upright in screen space) ──
         # Tags are recomputed here so paint stays in sync with the latest solve.
         # While a drawing or constraint tool is active the badges are hidden
@@ -4382,13 +4615,18 @@ class Sketch2DWidget(QWidget):
                 painter.drawPath(path)
 
         # ── Selected entities ──
+        # Point entities only (rings); line selection is highlighted by the
+        # dedicated constraint-selection block above.  Guard with _flat_xy so
+        # a line entity (tuple-of-tuples geometry) can never reach round().
         for entity in self._selected_entities:
-            if entity.geometry:
+            xy = self._flat_xy(entity.geometry)
-                x, y = entity.geometry
+            if xy is None:
-                screen_pos = self._world_to_screen(QPoint(int(round(x)), int(round(y))))
+                continue
-                painter.setPen(QPen(QColor("#f9e2af"), 2))
+            x, y = xy
-                painter.setBrush(Qt.NoBrush)
+            screen_pos = self._world_to_screen(QPoint(int(round(x)), int(round(y))))
-                painter.drawEllipse(screen_pos, 12, 12)
+            painter.setPen(QPen(QColor("#f9e2af"), 2))
+            painter.setBrush(Qt.NoBrush)
+            painter.drawEllipse(screen_pos, 12, 12)
 
         # ── DOF display ──
         if self._sketch:

src/fluency/ui/viewer_widget.py

@@ -189,17 +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.
@@ -279,6 +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).
 
@@ -862,6 +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:
@@ -901,6 +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)

tests/test_technical_drawing.py

@@ -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)
+