- added "measurement lines"

.idea/workspace.xml

@@ -4,16 +4,18 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- Render improvements, camera plane, update">
+    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- added contrain context menu&#10;- improved line pickability.">
       <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/models/data_model.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/models/data_model.py" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/fluency/rendering/mitsuba_backend.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/mitsuba_backend.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/ui/dialogs.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/ui/dialogs.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="$PROJECT_DIR$/tests/test_geometry.py" beforeDir="false" afterPath="$PROJECT_DIR$/tests/test_geometry.py" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -30,7 +32,7 @@
   <component name="Git.Settings">
     <option name="RECENT_BRANCH_BY_REPOSITORY">
       <map>
-        <entry key="$PROJECT_DIR$" value="single_window" />
+        <entry key="$PROJECT_DIR$" value="feature/surface-modifier-pyramid-patterns" />
       </map>
     </option>
     <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
@@ -57,6 +59,7 @@
     "Python.Unnamed.executor": "Run",
     "Python.base.executor": "Run",
     "Python.data_model.executor": "Run",
+    "Python.debug_dragging.executor": "Run",
     "Python.draw_widget2d.executor": "Run",
     "Python.draw_widget_solve.executor": "Run",
     "Python.fluency.executor": "Run",
@@ -65,6 +68,7 @@
     "Python.gui_ui.executor": "Run",
     "Python.kernel.executor": "Run",
     "Python.main.executor": "Run",
+    "Python.main_window.executor": "Run",
     "Python.meshtest.executor": "Run",
     "Python.occ_renderer.executor": "Run",
     "Python.occ_to_mesh.executor": "Run",
@@ -81,7 +85,7 @@
     "RunOnceActivity.typescript.service.memoryLimit.init": "true",
     "codeWithMe.voiceChat.enabledByDefault": "false",
     "git-widget-placeholder": "feature/occ-migration",
-    "last_opened_file_path": "/Volumes/Data_drive/Programming/fluency",
+    "last_opened_file_path": "/Volumes/Data_drive/Programming/fluency/src/fluency",
     "node.js.detected.package.eslint": "true",
     "node.js.selected.package.eslint": "(autodetect)",
     "node.js.selected.package.tslint": "(autodetect)",
@@ -96,9 +100,9 @@
   </component>
   <component name="RecentsManager">
     <key name="CopyFile.RECENT_KEYS">
+      <recent name="$PROJECT_DIR$/src/fluency" />
       <recent name="$PROJECT_DIR$" />
       <recent name="$PROJECT_DIR$/src/fluency/rendering" />
-      <recent name="$PROJECT_DIR$/src/fluency" />
       <recent name="$PROJECT_DIR$/drawing_modules" />
       <recent name="$PROJECT_DIR$/modules" />
     </key>

src/fluency/geometry_occ/kernel.py

@@ -235,6 +235,93 @@ class OCGeometryKernel(GeometryKernel):
             pass
         return None
 
+    @staticmethod
+    def find_coplanar_face(
+        shape: Any,
+        origin: Tuple[float, float, float],
+        normal: Tuple[float, float, float],
+        ref_center: Optional[Tuple[float, float, float]] = None,
+        angle_tol_deg: float = 5.0,
+        dist_tol: float = 1e-3,
+    ) -> Optional[Tuple[Any, Tuple[float, float, float]]]:
+        """Find a planar face on *shape* coplanar with the given plane.
+
+        Iterates the faces of *shape* and returns the first planar face whose
+        plane normal is parallel to *normal* (within *angle_tol_deg* degrees)
+        and whose plane passes through *origin* (within *dist_tol* distance).
+        When several faces match, the one whose surface centre is closest to
+        *ref_center* (if provided) is preferred.
+
+        Returns ``(face, center)`` where *center* is the surface centroid as a
+        3-tuple, or *None* if no matching face is found.
+        """
+        import math
+
+        from OCP.TopExp import TopExp_Explorer
+        from OCP.TopAbs import TopAbs_FACE
+        from OCP.TopoDS import TopoDS
+        from OCP.BRepAdaptor import BRepAdaptor_Surface
+        from OCP.GeomAbs import GeomAbs_Plane
+        from OCP.BRepGProp import BRepGProp
+        from OCP.GProp import GProp_GProps
+
+        import numpy as np
+
+        if shape is None:
+            return None
+        n = np.asarray(normal, dtype=float)
+        n = n / (np.linalg.norm(n) + 1e-30)
+        ox, oy, oz = origin
+
+        cos_tol = math.cos(math.radians(angle_tol_deg))
+        candidates: list = []
+
+        explorer = TopExp_Explorer(shape, TopAbs_FACE)
+        while explorer.More():
+            face = TopoDS.Face_s(explorer.Current())
+            try:
+                surf = BRepAdaptor_Surface(face)
+                if surf.GetType() != GeomAbs_Plane:
+                    explorer.Next()
+                    continue
+                plane = surf.Plane()
+                pn = np.array(
+                    [
+                        plane.Axis().Direction().X(),
+                        plane.Axis().Direction().Y(),
+                        plane.Axis().Direction().Z(),
+                    ],
+                    dtype=float,
+                )
+                # Check normals parallel (same or opposite direction)
+                cos_angle = abs(float(np.dot(n, pn)))
+                if cos_angle < cos_tol:
+                    explorer.Next()
+                    continue
+                # Check distance from plane to origin
+                pp = plane.Location()
+                d = abs(float(np.dot(n, np.array([pp.X() - ox, pp.Y() - oy, pp.Z() - oz]))))
+                if d > dist_tol:
+                    explorer.Next()
+                    continue
+                # Surface centroid via GProp (SurfaceProperties for faces)
+                props = GProp_GProps()
+                BRepGProp.SurfaceProperties_s(face, props)
+                c = props.CentreOfMass()
+                center = (float(c.X()), float(c.Y()), float(c.Z()))
+                candidates.append((face, center))
+            except Exception:
+                pass
+            explorer.Next()
+
+        if not candidates:
+            return None
+        if ref_center is not None and len(candidates) > 1:
+            rc = np.asarray(ref_center, dtype=float)
+            best = min(candidates, key=lambda fc: float(np.linalg.norm(np.asarray(fc[1]) - rc)))
+            return best
+        return candidates[0]
+
     def revolve(
         self,
         sketch: GeometryObject,

src/fluency/geometry_occ/sketch.py

@@ -109,7 +109,6 @@ class OCCSketch(SketchInterface):
         orthonormalised here.  ``y_dir`` is derived as ``normal × x_dir``.
         Existing UV coordinates are unchanged; only their world mapping moves.
         """
-        import numpy as np
 
         n = np.asarray(normal, dtype=float)
         x = np.asarray(x_dir, dtype=float)
@@ -138,6 +137,7 @@ class OCCSketch(SketchInterface):
     def _uv_to_world(self, u: float, v: float):
         """Map a UV point to a world ``gp_Pnt`` on the workplane."""
         from OCP.gp import gp_Pnt
+
         ox, oy, oz = self._wp_origin
         xx, xy, xz = self._wp_x_dir
         yx, yy, yz = self._wp_y_dir
@@ -150,6 +150,7 @@ class OCCSketch(SketchInterface):
     def _circle_axis(self, u: float, v: float):
         """Return a ``gp_Ax2`` for a circle centred at UV on the workplane."""
         from OCP.gp import gp_Ax2, gp_Dir
+
         center = self._uv_to_world(u, v)
         return gp_Ax2(
             center,
@@ -275,6 +276,7 @@ class OCCSketch(SketchInterface):
         When *None* the rendering will infer the shortest path between start and end.
         """
         import math
+
         entity_id = self._next_id()
 
         center_entity = self._entities.get(center.id)
@@ -345,8 +347,10 @@ class OCCSketch(SketchInterface):
         self._solver.dragged(solver_handle, self._wp)
 
         entity = OCCSketchEntity(
-            entity_id=entity_id, entity_type="point",
-            geometry=(x, y), handle=solver_handle,
+            entity_id=entity_id,
+            entity_type="point",
+            geometry=(x, y),
+            handle=solver_handle,
         )
         entity.is_external = True
         entity.is_construction = True  # external points are reference / dashed
@@ -377,7 +381,8 @@ class OCCSketch(SketchInterface):
         x1, y1 = s_ent.geometry
         x2, y2 = e_ent.geometry
         entity = OCCSketchEntity(
-            entity_id=entity_id, entity_type="line",
+            entity_id=entity_id,
+            entity_type="line",
             geometry=((x1, y1), (x2, y2)),
             handle=solver_handle,
         )
@@ -388,6 +393,10 @@ class OCCSketch(SketchInterface):
         self._external_entity_ids.add(entity_id)
         return entity
 
+    #: UV distance below which two projected points are considered the same
+    #: corner when importing / re-projecting external underlay geometry.
+    _EXTERNAL_MERGE_TOL: float = 1e-6
+
     def add_external_polyline(
         self, uv_points: List[Tuple[float, float]]
     ) -> Tuple[List[OCCSketchEntity], List[OCCSketchEntity]]:
@@ -398,33 +407,108 @@ class OCCSketch(SketchInterface):
         ``(points, lines)`` in the order they were created so the caller can
         keep references (e.g. for rendering or for toggling).
 
-        Points very close to each other (within 1e-6 UV units) are merged
-        into a single shared point, so a closed rectangle becomes 4 unique
-        points and 4 line segments (not 4 points and 4 lines + 4 duplicates
-        at the corners).
+        Points very close to each other (within ``_EXTERNAL_MERGE_TOL`` UV
+        units) are merged into a single shared point, so a closed rectangle
+        becomes 4 unique points and 4 line segments (not 4 points and 4
+        lines + 4 duplicates at the corners).  Merging also applies against
+        *previously imported* external points, so consecutive polylines that
+        share a corner (separate face edges meeting at a vertex) reuse one
+        point entity — the corner becomes a single connection hub for
+        coincident constraints instead of two stacked duplicates.
         """
+        points, lines = self.add_external_polylines([uv_points])
+        return (points[0] if points else []), lines
+
+    def add_external_polylines(
+        self, polylines: List[List[Tuple[float, float]]]
+    ) -> Tuple[List[List[OCCSketchEntity]], List[OCCSketchEntity]]:
+        """Bulk-import several polylines with corner dedup *across* polylines.
+
+        A face projection yields one polyline per boundary edge; edges that
+        meet at a vertex must share a single external point entity, otherwise
+        every corner ends up as two independent fixed points and user geometry
+        coincident to one duplicate is *not* connected to geometry coincident
+        to the other.  Returns ``(points_per_polyline, all_lines)``.
+        """
+        tol = self._EXTERNAL_MERGE_TOL
+
+        def find_or_create(u: float, v: float) -> OCCSketchEntity:
+            # Tolerance-based nearest lookup against existing external points
+            # (entity counts are small — a face boundary has tens of points).
+            best: Optional[OCCSketchEntity] = None
+            best_d = 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
+            if best is None:
+                best = self.add_external_point(float(u), float(v))
+            return best
+
+        all_points: List[List[OCCSketchEntity]] = []
+        all_lines: List[OCCSketchEntity] = []
+        for uv_points in polylines:
             if len(uv_points) < 2:
-            return [], []
-        # Deduplicate nearby points so shared corners (e.g. a rectangle's
-        # four vertices) are *one* point entity reused by two line segments.
-        eps = 1e-6
-        points: List[OCCSketchEntity] = []
-        coord_to_entity: Dict[Tuple[int, int], OCCSketchEntity] = {}
-        for (u, v) in uv_points:
-            key = (int(round(u / eps)), int(round(v / eps)))
-            ent = coord_to_entity.get(key)
-            if ent is None:
-                ent = self.add_external_point(float(u), float(v))
-                coord_to_entity[key] = ent
-            points.append(ent)
-        lines: List[OCCSketchEntity] = []
+                continue
+            points = [find_or_create(float(u), float(v)) for (u, v) in uv_points]
+            all_points.append(points)
             for i in range(len(points) - 1):
+                if points[i] is points[i + 1]:
+                    continue  # degenerate zero-length segment after merging
+                # Skip duplicate segments (two edges projecting onto the
+                # same pair of corner points).
+                dupe = False
+                for lid, (sid, eid2) in self._lines.items():
+                    if lid not in self._external_entity_ids:
+                        continue
+                    if (sid == points[i].id and eid2 == points[i + 1].id) or (
+                        sid == points[i + 1].id and eid2 == points[i].id
+                    ):
+                        dupe = True
+                        break
+                if dupe:
+                    continue
                 try:
                     ln = self.add_external_line(points[i], points[i + 1])
-                lines.append(ln)
+                    all_lines.append(ln)
                 except ValueError:
                     pass
-        return points, lines
+        return all_points, all_lines
+
+    def _drop_external_entities(self) -> set:
+        """Remove external entities from local tracking + prune their constraints.
+
+        Does NOT rebuild the solver — the caller decides when to rebuild
+        (removal-only flows rebuild immediately; re-projection flows first
+        import the new externals so the rebuild sees them and doesn't
+        auto-anchor a user point instead).
+        """
+        removed = set(self._external_entity_ids)
+        if not removed:
+            return removed
+        # Wipe external entities from local tracking.
+        for eid in list(removed):
+            if eid in self._entities:
+                del self._entities[eid]
+            self._points.pop(eid, None)
+            self._lines.pop(eid, None)
+            self._circles.pop(eid, None)
+            self._arcs.pop(eid, 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).
+        for lid, (sid, eid2) in list(self._lines.items()):
+            if sid in removed or eid2 in removed:
+                del self._lines[lid]
+                if lid in self._entities:
+                    del self._entities[lid]
+        self._external_entity_ids.clear()
+        self._prune_log_for(removed)
+        return removed
 
     def remove_external_entities(self) -> None:
         """Remove every external / underlay entity and prune related constraints.
@@ -437,25 +521,7 @@ class OCCSketch(SketchInterface):
         """
         if not self._external_entity_ids:
             return
-        # Wipe external entities from local tracking.
-        for eid in list(self._external_entity_ids):
-            if eid in self._entities:
-                del self._entities[eid]
-            self._points.pop(eid, None)
-            self._lines.pop(eid, None)
-            self._circles.pop(eid, None)
-            self._arcs.pop(eid, 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).
-        for lid, (sid, eid2) in list(self._lines.items()):
-            if sid in self._external_entity_ids or eid2 in self._external_entity_ids:
-                del self._lines[lid]
-                if lid in self._entities:
-                    del self._entities[lid]
-        removed = set(self._external_entity_ids)
-        self._external_entity_ids.clear()
-        self._prune_log_for(removed)
+        self._drop_external_entities()
         self._rebuild_solver()
         self._rebuild_labels()
 
@@ -463,6 +529,184 @@ 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:
+        """Re-project external (underlay) entities from updated source geometry.
+
+        Called when the 3D body the underlay was projected from has been
+        rebuilt (e.g. its source sketch was edited and re-extruded) and the
+        face edges were re-projected to UV.  The underlay must follow the
+        body so user geometry constrained to it propagates through the
+        solver.
+
+        Two paths:
+
+        * **In-place update** (same topology): when the new projection has
+          the same number of unique corner points and segments, each existing
+          external point is paired with the nearest new position (greedy
+          one-to-one) and moved via ``set_params``.  Entity ids and every
+          constraint referencing them survive untouched, and the next
+          :meth:`solve` pulls the user geometry along.
+        * **Rebuild + rebind** (topology changed): external entities are
+          removed and re-imported; constraints that referenced external
+          entities are re-created against the nearest new external entity
+          (point-to-point for coincident on corners, point-on-line for
+          coincident on edges) so user geometry stays anchored.
+
+        Returns True when the underlay was updated and solved OK.
+        """
+        # Flatten the new projection into unique corner positions + segments.
+        tol = self._EXTERNAL_MERGE_TOL
+        new_pts: List[Tuple[float, float]] = []
+
+        def new_index(u: float, v: float) -> int:
+            for i, (x, y) in enumerate(new_pts):
+                if math.hypot(x - u, y - v) <= tol:
+                    return i
+            new_pts.append((float(u), float(v)))
+            return len(new_pts) - 1
+
+        new_segs: List[Tuple[int, int]] = []
+        for poly in polylines:
+            if len(poly) < 2:
+                continue
+            idx = [new_index(float(u), float(v)) for (u, v) in poly]
+            for i in range(len(idx) - 1):
+                if idx[i] == idx[i + 1]:
+                    continue
+                seg = (min(idx[i], idx[i + 1]), max(idx[i], idx[i + 1]))
+                if seg not in new_segs:
+                    new_segs.append(seg)
+
+        old_ext_points = [
+            self._entities[eid]
+            for eid in sorted(self._external_entity_ids)
+            if eid in self._entities and self._entities[eid].entity_type == "point"
+        ]
+        old_ext_lines = [
+            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)
+
+        if same_topology and old_ext_points:
+            # Greedy one-to-one nearest matching old point -> new position.
+            pairs: List[Tuple[float, int, int]] = []  # (dist, old_idx, new_idx)
+            for oi, ent in enumerate(old_ext_points):
+                ox, oy = ent.geometry
+                for ni, (nx, ny) in enumerate(new_pts):
+                    pairs.append((math.hypot(ox - nx, oy - ny), oi, ni))
+            pairs.sort()
+            match: Dict[int, int] = {}
+            used_new: set = set()
+            for d, oi, ni in pairs:
+                if oi in match or ni in used_new:
+                    continue
+                match[oi] = ni
+                used_new.add(ni)
+            if len(match) == len(old_ext_points):
+                # Verify segment connectivity is preserved under the matching
+                # (same corners, but edges rewired -> rebuild instead).
+                mapped_segs = set()
+                for a, b in new_segs:
+                    mapped_segs.add((a, b))
+                connectivity_ok = True
+                for lid in old_ext_lines:
+                    sid, eid2 = self._lines[lid]
+                    oi_s = next((i for i, e in enumerate(old_ext_points) if e.id == sid), None)
+                    oi_e = next((i for i, e in enumerate(old_ext_points) if e.id == eid2), None)
+                    if oi_s is None or oi_e is None:
+                        connectivity_ok = False
+                        break
+                    seg = (min(match[oi_s], match[oi_e]), max(match[oi_s], match[oi_e]))
+                    if seg not in mapped_segs:
+                        connectivity_ok = False
+                        break
+                if connectivity_ok:
+                    for oi, ent in enumerate(old_ext_points):
+                        nx, ny = new_pts[match[oi]]
+                        self.set_entity_position(ent, nx, ny)
+                    return self.solve()
+
+        # ── Rebuild + rebind path (topology changed, or no externals yet) ──
+        # Capture constraints that tie USER entities to external entities so
+        # they can be re-created against the nearest new external entity.
+        saved: List[Dict[str, Any]] = []
+        for entry in self._constraint_log:
+            ext_ids = [i for i in entry["ids"] if i in self._external_entity_ids]
+            user_ids = [i for i in entry["ids"] if i not in self._external_entity_ids]
+            if not ext_ids or not user_ids:
+                continue
+            for ext_id in ext_ids:
+                ent = self._entities.get(ext_id)
+                if ent is None:
+                    continue
+                if ent.entity_type == "point" and ent.geometry is not None:
+                    anchor: Any = ("point", ext_id, tuple(ent.geometry))
+                elif ent.entity_type == "line" and ext_id in self._lines:
+                    sid, eid2 = self._lines[ext_id]
+                    s_ent = self._entities.get(sid)
+                    e_ent = self._entities.get(eid2)
+                    if s_ent is None or e_ent is None:
+                        continue
+                    mx = (s_ent.geometry[0] + e_ent.geometry[0]) / 2.0
+                    my = (s_ent.geometry[1] + e_ent.geometry[1]) / 2.0
+                    anchor = ("line", ext_id, (mx, my))
+                else:
+                    continue
+                saved.append({"type": entry["type"], "user_ids": list(user_ids), "anchor": anchor})
+
+        # Drop old externals, import the new projection, then rebuild the
+        # solver exactly once.  The import MUST happen before the rebuild:
+        # with external ids present the rebuild re-fixes the new underlay
+        # 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._rebuild_solver()
+        self._rebuild_labels()
+
+        # Rebind saved constraints to the nearest new external entity.
+        rebound = 0
+        for item in saved:
+            kind, _old_id, pos = item["anchor"]
+            target: Optional[OCCSketchEntity] = None
+            best_d = float("inf")
+            if kind == "point":
+                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] - pos[0], ent.geometry[1] - pos[1])
+                    if d < best_d:
+                        best_d = d
+                        target = ent
+            else:  # line: nearest segment midpoint
+                for lid, (sid, eid2) in self._lines.items():
+                    if lid not in self._external_entity_ids:
+                        continue
+                    s_ent = self._entities.get(sid)
+                    e_ent = self._entities.get(eid2)
+                    if s_ent is None or e_ent is None:
+                        continue
+                    mx = (s_ent.geometry[0] + e_ent.geometry[0]) / 2.0
+                    my = (s_ent.geometry[1] + e_ent.geometry[1]) / 2.0
+                    d = math.hypot(mx - pos[0], my - pos[1])
+                    if d < best_d:
+                        best_d = d
+                        target = self._entities.get(lid)
+            if target is None:
+                continue
+            for uid in item["user_ids"]:
+                user_ent = self._entities.get(uid)
+                if user_ent is None:
+                    continue
+                if item["type"] == "coincident":
+                    if self.constrain_coincident(user_ent, target):
+                        rebound += 1
+        if rebound:
+            logger.info("Rebound %d constraint(s) to re-projected underlay", rebound)
+        return self.solve()
+
     # ── Centerlines (X and Y reference axes) ────────────────────────────
 
     _CENTERLINE_EXTENT: float = 10000.0  # large enough to span any sketch
@@ -514,8 +758,13 @@ class OCCSketch(SketchInterface):
         self.constrain_fixed(yb)
 
         self._centerline_ids = {
-            origin.id, xl.id, xr.id, xline.id,
-            yb.id, yt.id, yline.id,
+            origin.id,
+            xl.id,
+            xr.id,
+            xline.id,
+            yb.id,
+            yt.id,
+            yline.id,
         }
 
         self.solve()
@@ -557,7 +806,12 @@ class OCCSketch(SketchInterface):
         """Count and log a constraint so the solver can be rebuilt after deletions."""
         self._constraint_count += 1
         self._constraint_log.append(
-            {"type": ctype, "ids": tuple(int(i) for i in ids), "params": tuple(params), "labels": set(labels)}
+            {
+                "type": ctype,
+                "ids": tuple(int(i) for i in ids),
+                "params": tuple(params),
+                "labels": set(labels),
+            }
         )
 
     def _apply_constraint_log(self, entry: Dict[str, Any]) -> bool:
@@ -666,7 +920,16 @@ class OCCSketch(SketchInterface):
             x, y = saved_pos.get(pid, (0.0, 0.0))
             new_handle = self._solver.add_point_2d(x, y, self._wp)
             ent.handle = new_handle
-            if self._first_point_id is None:
+            if pid in self._external_entity_ids:
+                # External (underlay) points are ALWAYS fixed — the dragged
+                # applied at creation isn't in the constraint log, so it must
+                # be re-applied here or the underlay becomes draggable after
+                # any solver rebuild (e.g. deleting an unrelated user point).
+                self._solver.dragged(new_handle, self._wp)
+            elif self._first_point_id is None and not self._external_entity_ids:
+                # Mirror add_point's guard: when the sketch carries external
+                # underlay points those are the natural anchors, and fixing a
+                # user point too would over-constrain the system.
                 self._first_point_id = pid
                 self._solver.dragged(new_handle, self._wp)
 
@@ -1008,7 +1271,12 @@ class OCCSketch(SketchInterface):
         adjacency: Dict[Tuple[float, float], List[Tuple[float, float]]] = {}
 
         for entity in self._entities.values():
-            if entity.entity_type == "line" and entity.geometry and not entity.is_external and not entity.is_construction:
+            if (
+                entity.entity_type == "line"
+                and entity.geometry
+                and not entity.is_external
+                and not entity.is_construction
+            ):
                 p1, p2 = entity.geometry
                 if p1 not in adjacency:
                     adjacency[p1] = []
@@ -1043,7 +1311,7 @@ class OCCSketch(SketchInterface):
 
     # ─── Closed-loop / face detection (for region selection + holes) ──────
 
-    _SNAP_TOL: float = 1e-4  # world-unit tolerance for snapping line endpoints
+    _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]]]:
         """Current line segments as world-coordinate tuples (uses solved positions).
@@ -1068,8 +1336,12 @@ class OCCSketch(SketchInterface):
             s_ent = self._entities.get(sid)
             e_ent = self._entities.get(eid2)
             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(e_ent.geometry[0]), float(e_ent.geometry[1]))))
+                segs.append(
+                    (
+                        (float(s_ent.geometry[0]), float(s_ent.geometry[1])),
+                        (float(e_ent.geometry[0]), float(e_ent.geometry[1])),
+                    )
+                )
 
         # ── Arc segments (tessellated) ──
         for arc_id, arc_data in self._arcs.items():
@@ -1086,8 +1358,9 @@ class OCCSketch(SketchInterface):
             c_ent = self._entities.get(center_id)
             s_ent = self._entities.get(start_id)
             e_ent = self._entities.get(end_id)
-            if not (c_ent and s_ent and e_ent
-                    and c_ent.geometry and s_ent.geometry and e_ent.geometry):
+            if not (
+                c_ent and s_ent and e_ent and c_ent.geometry and s_ent.geometry and e_ent.geometry
+            ):
                 continue
             cx, cy = c_ent.geometry
             sx, sy = s_ent.geometry
@@ -1099,10 +1372,8 @@ class OCCSketch(SketchInterface):
                 t2 = (i + 1) / n
                 a1 = start_angle + t1 * sweep
                 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))
+                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))
 
         return segs
@@ -1180,8 +1451,13 @@ class OCCSketch(SketchInterface):
         for cid, (center_id, r) in self._circles.items():
             c_ent = self._entities.get(center_id)
             if c_ent and c_ent.geometry and r > 0:
-                loops.append({"type": "circle", "center": (float(c_ent.geometry[0]), float(c_ent.geometry[1])),
-                              "radius": float(r)})
+                loops.append(
+                    {
+                        "type": "circle",
+                        "center": (float(c_ent.geometry[0]), float(c_ent.geometry[1])),
+                        "radius": float(r),
+                    }
+                )
         return loops
 
     @staticmethod
@@ -1212,7 +1488,10 @@ class OCCSketch(SketchInterface):
             # Point-on-segment test — exclude strict boundary hits.
             # First check bounding box of the segment.
             bbox_tol = max(eps, margin)
-            if min(xi, xj) - bbox_tol <= x <= max(xi, xj) + bbox_tol and min(yi, yj) - bbox_tol <= y <= max(yi, yj) + bbox_tol:
+            if (
+                min(xi, xj) - bbox_tol <= x <= max(xi, xj) + bbox_tol
+                and min(yi, yj) - bbox_tol <= y <= max(yi, yj) + bbox_tol
+            ):
                 # Check collinearity
                 cross = (x - xi) * (yj - yi) - (y - yi) * (xj - xi)
                 abs_cross = abs(cross)
@@ -1269,18 +1548,14 @@ class OCCSketch(SketchInterface):
             if inner["type"] == "circle":
                 # Circle in polygon: centre must be inside with margin
                 cx, cy = inner["center"]
-                return OCCSketch._point_in_polygon(
-                    (cx, cy), outer["points"], margin=1e-3
-                )
+                return OCCSketch._point_in_polygon((cx, cy), outer["points"], margin=1e-3)
             else:
                 # Polygon in polygon: ALL inner vertices inside outer
                 pts = inner["points"]
                 if len(pts) > 1 and pts[0] == pts[-1]:
                     pts = pts[:-1]
                 for pt in pts:
-                    if not OCCSketch._point_in_polygon(
-                        pt, outer["points"], margin=eps
-                    ):
+                    if not OCCSketch._point_in_polygon(pt, outer["points"], margin=eps):
                         return False
                 return True
 
@@ -1293,7 +1568,11 @@ class OCCSketch(SketchInterface):
         the centre for circles.
         """
         if loop["type"] == "polygon":
-            pts = loop["points"][:-1] if len(loop["points"]) > 1 and loop["points"][0] == loop["points"][-1] else loop["points"]
+            pts = (
+                loop["points"][:-1]
+                if len(loop["points"]) > 1 and loop["points"][0] == loop["points"][-1]
+                else loop["points"]
+            )
             n = len(pts)
             if n < 3:
                 return loop.get("center", (0.0, 0.0))
@@ -1374,11 +1653,13 @@ class OCCSketch(SketchInterface):
             for h in face["holes"]:
                 if h["type"] == "polygon":
                     if OCCSketch._point_in_polygon(pt, h["points"]):
-                        in_hole = True; break
+                        in_hole = True
+                        break
                 else:
                     hcx, hcy = h["center"]
                     if math.hypot(pt[0] - hcx, pt[1] - hcy) < h["radius"]:
-                        in_hole = True; break
+                        in_hole = True
+                        break
             if in_hole:
                 continue
             area = OCCSketch._loop_area(outer)
@@ -1426,17 +1707,19 @@ class OCCSketch(SketchInterface):
         from top-left to bottom-right.
         """
         from OCP.BRepBuilderAPI import (
-            BRepBuilderAPI_MakePolygon, BRepBuilderAPI_MakeFace,
-            BRepBuilderAPI_MakeWire, BRepBuilderAPI_MakeEdge,
+            BRepBuilderAPI_MakePolygon,
+            BRepBuilderAPI_MakeFace,
+            BRepBuilderAPI_MakeWire,
+            BRepBuilderAPI_MakeEdge,
         )
-        from OCP.gp import gp_Pnt, gp_Circ, gp_Ax2, gp_Dir
+        from OCP.gp import gp_Circ
         from OCP.TopoDS import TopoDS as _TopoDS
 
         def _wire_from_loop(loop: Dict[str, Any]):
             """Build a wire from a loop dict.  No orientation adjustment."""
             if loop["type"] == "polygon":
                 mp = BRepBuilderAPI_MakePolygon()
-                for (pu, pv) in loop["points"]:
+                for pu, pv in loop["points"]:
                     mp.Add(self._uv_to_world(pu, pv))
                 mp.Close()
                 mp.Build()
@@ -1463,17 +1746,22 @@ class OCCSketch(SketchInterface):
             # wire (material on the other side).  We reverse the hole wire
             # only when its natural winding matches the outer's; if they
             # already differ the wire is left as-is.
-            if (hole_winding >= 0 and outer_winding >= 0) or (hole_winding < 0 and outer_winding < 0):
+            if (hole_winding >= 0 and outer_winding >= 0) or (
+                hole_winding < 0 and outer_winding < 0
+            ):
                 hole_wire = _TopoDS.Wire_s(hole_wire.Reversed())
             face_maker.Add(hole_wire)
         face_maker.Build()
         occ_face = face_maker.Face()
 
-        obj = OCCGeometryObject(occ_face, {
+        obj = OCCGeometryObject(
+            occ_face,
+            {
                 "type": "sketch_face",
                 "normal": self._wp_normal,
                 "origin": self._wp_origin,
-        })
+            },
+        )
         return obj
 
     def get_solver_dof(self) -> int:
@@ -1579,7 +1867,8 @@ class OCCSketch(SketchInterface):
         removed_ids: set = {point.id}
         # Remove lines that use this point as an endpoint.
         removed_line_keys: List[int] = [
-            lid for lid, (sid, eid2) in list(self._lines.items())
+            lid
+            for lid, (sid, eid2) in list(self._lines.items())
             if sid == point.id or eid2 == point.id
         ]
         for lid in removed_line_keys:
@@ -1593,8 +1882,7 @@ class OCCSketch(SketchInterface):
             del self._entities[point.id]
         # Circles anchored on the point are also invalid.
         removed_circle_keys: List[int] = [
-            cid for cid, (center_id, _r) in list(self._circles.items())
-            if center_id == point.id
+            cid for cid, (center_id, _r) in list(self._circles.items()) if center_id == point.id
         ]
         for cid in removed_circle_keys:
             removed_ids.add(cid)
@@ -1603,7 +1891,8 @@ class OCCSketch(SketchInterface):
                 del self._entities[cid]
         # Arcs referencing this point (as centre, start, or end) are invalid.
         removed_arc_keys: List[int] = [
-            aid for aid, adata in list(self._arcs.items())
+            aid
+            for aid, adata in list(self._arcs.items())
             if adata.get("center") == point.id
             or adata.get("start") == point.id
             or adata.get("end") == point.id
@@ -1820,9 +2109,7 @@ class OCCSketch(SketchInterface):
                 s_id = self._find_point_at(x1, y1)
                 e_id = self._find_point_at(x2, y2)
                 if s_id is None or e_id is None:
-                    logger.warning(
-                        "Skipping line %s during load: endpoints not found", eid
-                    )
+                    logger.warning("Skipping line %s during load: endpoints not found", eid)
                     continue
                 if is_external:
                     ent = self.add_external_line(entities_by_id[s_id], entities_by_id[e_id])
@@ -1832,9 +2119,7 @@ class OCCSketch(SketchInterface):
                 (cx, cy), radius = geom
                 c_id = self._find_point_at(cx, cy)
                 if c_id is None:
-                    logger.warning(
-                        "Skipping circle %s during load: center not found", eid
-                    )
+                    logger.warning("Skipping circle %s during load: center not found", eid)
                     continue
                 ent = self.add_circle(entities_by_id[c_id], float(radius))
             elif etype == "arc":
@@ -1847,9 +2132,7 @@ class OCCSketch(SketchInterface):
                 s_id = self._find_point_at(*start_pos)
                 e_id = self._find_point_at(*end_pos)
                 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
-                    )
+                    logger.warning("Skipping arc %s during load: endpoints not found", eid)
                     continue
                 ent = self.add_arc(
                     entities_by_id[c_id],

src/fluency/geometry_occ/surface_modifier.py

@@ -0,0 +1,385 @@
+"""Surface modifier for OpenCASCADE geometry.
+
+Applies geometric patterns (pyramids, bumps, grooves) to 3D surfaces using boolean operations.
+This enables grip-enhancing textures and visual surface modifications on CAD models.
+"""
+
+from __future__ import annotations
+
+import logging
+import math
+from typing import Any, Optional, Tuple
+
+# OCC imports at module level for common types
+
+
+logger = logging.getLogger(__name__)
+
+
+class SurfaceModifier:
+    """Applies geometric patterns to 3D surfaces using OCC boolean operations."""
+
+    def __init__(self):
+        self._patterns_applied = []
+
+    def apply_pyramid_pattern(
+        self,
+        face_shape,
+        pyramid_height: float = 1.0,
+        base_radius: float = 2.0,
+        spacing: float = 5.0,
+        num_rings: Optional[int] = None,
+        direction: Tuple[float, float, float] = (0, 0, 1),
+    ) -> Optional[Any]:
+        """Apply a pyramid pattern to a face surface.
+
+        Args:
+            face_shape: OCC TopoDS_Shape representing the face or solid
+            pyramid_height: Height of each pyramid
+            base_radius: Radius of pyramid base
+            spacing: Distance between pyramids
+            num_rings: Number of concentric rings (auto-calculated if None)
+            direction: Normal direction for pyramids
+
+        Returns:
+            Modified shape on success, None on failure
+        """
+        try:
+            from OCP.TopAbs import TopAbs_FACE
+            from OCP.TopoDS import TopoDS_Face, TopoDS_Shape
+            from OCP.BRepAlgoAPI import BRepAlgoAPI_Fuse
+            from OCP.TopExp import TopExp_Explorer
+            from OCP.BRepAdaptor import BRepAdaptor_Surface
+
+            # Validate face shape
+            if not isinstance(face_shape, (TopoDS_Shape, TopoDS_Face)):
+                logger.error("Invalid face shape type")
+                return None
+
+            # Extract the first face for surface parameterization
+            if isinstance(face_shape, TopoDS_Shape):
+                explorer = TopExp_Explorer(face_shape, TopAbs_FACE)
+                if not explorer.More():
+                    logger.error("No faces found in shape")
+                    return None
+                from OCP import TopoDS
+                face = TopoDS.TopoDS.Face_s(explorer.Current())
+            else:
+                face = face_shape
+
+            # Get face surface for UV parameterization
+            surf = BRepAdaptor_Surface(face)
+
+            u_min, u_max = surf.FirstUParameter(), surf.LastUParameter()
+            v_min, v_max = surf.FirstVParameter(), surf.LastVParameter()
+
+            # Calculate number of rings if not specified
+            if num_rings is None:
+                # Estimate based on face area and spacing
+                u_range = u_max - u_min
+                v_range = v_max - v_min
+                avg_dim = (u_range + v_range) / 2.0
+                num_rings = max(1, min(int(avg_dim / spacing), 5))
+
+            logger.info(
+                f"Applying pyramid pattern: {num_rings} rings, "
+                f"{base_radius:.2f} radius, {pyramid_height:.2f} height"
+            )
+
+            # Create pyramids distributed across the face UV space
+            result_shape = face_shape
+            pyramid_count = 0
+
+            for ring_idx in range(num_rings):
+                # Distribute rings evenly across UV parameter space
+                u_fraction = (ring_idx + 1) / (num_rings + 1)
+                v_fraction = 0.5  # Center vertically
+
+                # Map to actual UV coordinates on the face
+                u_pos = u_min + u_fraction * (u_max - u_min)
+                v_pos = v_min + v_fraction * (v_max - v_min)
+
+                # Get 3D position and tangent vectors at this UV point
+                from OCP.gp import gp_Pnt, gp_Vec
+
+                center_pt = gp_Pnt()
+                d1u = gp_Vec()
+                d1v = gp_Vec()
+                surf.D1(u_pos, v_pos, center_pt, d1u, d1v)
+                # Normal is cross product of tangent vectors
+                normal = d1u.Crossed(d1v)
+                normal.Normalize()
+
+                # Calculate number of pyramids in this ring based on spacing
+                if ring_idx == 0:
+                    num_pyramids = 1  # Center pyramid
+                else:
+                    circumference = 2.0 * math.pi * (ring_idx * spacing)
+                    num_pyramids = max(3, int(circumference / spacing))
+
+                for i in range(num_pyramids):
+                    if ring_idx == 0:
+                        # Center pyramid - place at face center
+                        place_u = u_pos
+                        place_v = v_pos
+                    else:
+                        angle = (2.0 * math.pi * i) / num_pyramids
+                        # Offset in UV space based on ring radius
+                        offset_u = (ring_idx * spacing / (u_max - u_min)) * math.cos(angle)
+                        offset_v = (ring_idx * spacing / (v_max - v_min)) * math.sin(angle)
+                        place_u = max(u_min, min(u_max, u_pos + offset_u))
+                        place_v = max(v_min, min(v_max, v_pos + offset_v))
+
+                    try:
+                        # Get 3D position and normal for this pyramid
+                        pyramid_pt = gp_Pnt()
+                        pd1u = gp_Vec()
+                        pd1v = gp_Vec()
+                        surf.D1(place_u, place_v, pyramid_pt, pd1u, pd1v)
+                        pyramid_normal = pd1u.Crossed(pd1v)
+                        pyramid_normal.Normalize()
+
+                        # Create solid pyramid at this position
+                        pyramid_shape = self._create_solid_pyramid(
+                            pyramid_pt,
+                            pyramid_normal,
+                            pyramid_height,
+                            base_radius,
+                        )
+
+                        if pyramid_shape is not None:
+                            # Fuse with existing geometry
+                            fuse = BRepAlgoAPI_Fuse(result_shape, pyramid_shape)
+                            fuse.Build()
+
+                            if fuse.IsDone():
+                                result_shape = fuse.Shape()
+                                pyramid_count += 1
+                            else:
+                                logger.warning(
+                                    f"Failed to fuse pyramid at ({place_u:.2f}, {place_v:.2f})"
+                                )
+                    except Exception as e:
+                        logger.debug(
+                            f"Error creating pyramid at ring {ring_idx}, pyramid {i}: {e}"
+                        )
+
+            self._patterns_applied.append(
+                {
+                    "type": "pyramid",
+                    "parameters": {
+                        "height": pyramid_height,
+                        "base_radius": base_radius,
+                        "spacing": spacing,
+                        "num_rings": num_rings,
+                        "direction": direction,
+                    },
+                }
+            )
+
+            logger.info(f"Successfully applied {pyramid_count} pyramids")
+
+            return result_shape
+
+        except Exception as e:
+            logger.error(f"Error applying pyramid pattern: {e}", exc_info=True)
+            return None
+
+    def _create_solid_pyramid(
+        self,
+        base_point,  # gp_Pnt - position on the face
+        normal_vec,  # gp_Dir or gp_Vec - surface normal direction
+        height: float,
+        base_radius: float,
+    ) -> Optional[Any]:
+        """Create a solid pyramid at the specified position and orientation.
+
+        Uses BRepPrimAPI_MakePrism to extrude a square base into a solid pyramid.
+
+        Args:
+            base_point: 3D point where pyramid base is centered
+            normal_vec: Direction vector for pyramid growth (surface normal)
+            height: Height of the pyramid from base to apex
+            base_radius: Half-width of the square base
+
+        Returns:
+            OCC solid shape for the pyramid, or None on failure
+        """
+        try:
+            from OCP.gp import gp_Dir, gp_Ax2, gp_Vec
+            from OCP.BRepBuilderAPI import (
+                BRepBuilderAPI_MakeEdge,
+                BRepBuilderAPI_MakeWire,
+            )
+            from OCP.BRepPrimAPI import BRepPrimAPI_MakePrism
+
+            half = base_radius / 2.0
+
+            # Build orthonormal basis from normal vector
+            if isinstance(normal_vec, gp_Vec):
+                n_dir = gp_Dir(normal_vec.XYZ())
+            else:
+                n_dir = normal_vec
+
+            # Create a local coordinate system at the base point
+            local_ax2 = gp_Ax2(base_point, n_dir)
+
+            # Get X and Y axes from the local coordinate system
+            x_dir = local_ax2.XDirection()
+            y_dir = local_ax2.YDirection()
+
+            # Create 4 corners of the square base in the local plane
+            corner_points = [
+                base_point + gp_Vec(x_dir).Multiplied(half) + gp_Vec(y_dir).Multiplied(half),
+                base_point + gp_Vec(x_dir).Multiplied(-half) + gp_Vec(y_dir).Multiplied(half),
+                base_point + gp_Vec(x_dir).Multiplied(-half) + gp_Vec(y_dir).Multiplied(-half),
+                base_point + gp_Vec(x_dir).Multiplied(half) + gp_Vec(y_dir).Multiplied(-half),
+            ]
+
+            # Create edges connecting the corners
+            wire_maker = BRepBuilderAPI_MakeWire()
+            for idx in range(4):
+                next_idx = (idx + 1) % 4
+                edge = BRepBuilderAPI_MakeEdge(
+                    corner_points[idx], corner_points[next_idx]
+                ).Edge()
+                wire_maker.Add(edge)
+
+            if not wire_maker.IsDone():
+                logger.warning("Failed to create pyramid base wire")
+                return None
+
+            # Extrude the base wire in the normal direction by height to form a prism
+            extrusion_vec = gp_Vec(n_dir).Multiplied(height)
+            prism_maker = BRepPrimAPI_MakePrism(
+                wire_maker.Wire(), extrusion_vec, False  # no check intersection
+            )
+            prism_maker.Build()
+
+            if not prism_maker.IsDone():
+                logger.warning("Failed to create pyramid prism")
+                return None
+
+            return prism_maker.Shape()
+
+        except Exception as e:
+            logger.debug(f"Error creating solid pyramid: {e}")
+            return None
+
+    def apply_bump_pattern(
+        self,
+        face_shape,
+        bump_height: float = 1.0,
+        bump_radius: float = 2.0,
+        spacing: float = 5.0,
+        num_rings: Optional[int] = None,
+    ) -> Optional[Any]:
+        """Apply a simple bump pattern to a face surface.
+
+        Args:
+            face_shape: OCC TopoDS_Shape representing the face
+            bump_height: Height of each bump
+            bump_radius: Radius of each bump base
+            spacing: Distance between bumps
+            num_rings: Number of concentric rings
+
+        Returns:
+            Modified shape on success, None on failure
+        """
+        return self.apply_pyramid_pattern(
+            face_shape,
+            pyramid_height=bump_height,
+            base_radius=bump_radius,
+            spacing=spacing,
+            num_rings=num_rings,
+        )
+
+
+def apply_surface_modifier_to_body(
+    body_geometry, modifier_type: str = "pyramid", **parameters
+) -> Optional[Any]:
+    """Apply a surface modifier to a body geometry.
+
+    Args:
+        body_geometry: OCCGeometryObject or similar geometry object
+        modifier_type: Type of modifier ('pyramid', 'bump')
+        **parameters: Modifier-specific parameters
+
+    Returns:
+        Modified shape, or None on failure
+    """
+    from fluency.geometry_occ.kernel import OCGeometryKernel
+
+    kernel = OCGeometryKernel()
+    shape = kernel._get_shape(body_geometry)
+
+    if shape is None:
+        logger.error("No geometry found in body")
+        return None
+
+    modifier = SurfaceModifier()
+
+    try:
+        if modifier_type == "pyramid":
+            success = modifier.apply_pyramid_pattern(shape, **parameters)
+        elif modifier_type == "bump":
+            success = modifier.apply_bump_pattern(shape, **parameters)
+        else:
+            logger.error(f"Unknown modifier type: {modifier_type}")
+            return None
+
+        if not success:
+            logger.error("Surface modifier application failed")
+            return None
+
+        # Return the modified shape wrapped in OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCCGeometryObject
+
+        return OCCGeometryObject(shape)
+
+    except Exception as e:
+        logger.error(f"Error applying surface modifier: {e}", exc_info=True)
+        return None
+
+
+# Example usage and testing
+if __name__ == "__main__":
+    # Create a simple test case
+    from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
+
+    # Create a box to modify
+    box_maker = BRepPrimAPI_MakeBox(50, 50, 10)
+    box_maker.Build()
+
+    if box_maker.IsDone():
+        print("Created test box")
+
+        # Apply pyramid pattern to top face (Z direction)
+        modifier = SurfaceModifier()
+        success = modifier.apply_pyramid_pattern(
+            box_maker.Shape(),
+            pyramid_height=2.0,
+            base_radius=3.0,
+            spacing=8.0,
+            num_rings=2,
+            direction=(0, 0, 1),
+        )
+
+        if success:
+            print("Successfully applied pyramid pattern")
+
+            # Export modified shape
+            from OCP.StlAPI import StlAPI_Writer
+            from OCP.BRepMesh import BRepMesh_IncrementalMesh
+
+            tess = BRepMesh_IncrementalMesh(box_maker.Shape(), 0.1)
+            tess.Perform()
+
+            writer = StlAPI_Writer()
+            writer.SetASCIIMode(False)
+            writer.Write(box_maker.Shape(), "/tmp/test_pyramid_pattern.stl")
+            print("Exported modified shape to STL")
+        else:
+            print("Failed to apply pyramid pattern")
+    else:
+        print("Failed to create test box")

src/fluency/io/project_io.py

@@ -177,6 +177,7 @@ def _body_to_dict(body: Body) -> Dict[str, Any]:
         "extrude_cut": body.extrude_cut,
         "extrude_union": body.extrude_union,
         "extrude_through_all": body.extrude_through_all,
+        "extrude_cut_all_bodies": body.extrude_cut_all_bodies,
         "extrude_face_index": body.extrude_face_index,
         "extrude_target_body_id": body.extrude_target_body_id,
         "position": _coerce_listlike(body.position),
@@ -212,6 +213,7 @@ def _body_from_dict(
         extrude_cut=bool(data.get("extrude_cut", False)),
         extrude_union=bool(data.get("extrude_union", False)),
         extrude_through_all=bool(data.get("extrude_through_all", False)),
+        extrude_cut_all_bodies=bool(data.get("extrude_cut_all_bodies", False)),
         extrude_face_index=data.get("extrude_face_index"),
         extrude_target_body_id=data.get("extrude_target_body_id"),
         position=_to_3vec(data.get("position")),
@@ -454,7 +456,7 @@ def _assembly_from_dict(data: Dict[str, Any]) -> Assembly:
     asm.modified_at = _parse_iso(data.get("modified_at"))
     for cid, ac_data in (data.get("components") or {}).items():
         asm.components[cid] = _assembly_component_from_dict(ac_data)
-    for c_data in (data.get("connections") or []):
+    for c_data in data.get("connections") or []:
         asm.connections.append(_assembly_connection_from_dict(c_data))
     return asm
 
@@ -691,8 +693,13 @@ def load_project(filepath: str) -> Tuple[Project, Dict[str, Any]]:
                 sk_data["occ_sketch"] = meta.get("occ_sketch")
                 # Workplane fields on the sketch-level file override the
                 # embedded ones (source of truth lives in the sidecar).
-                for k in ("workplane_origin", "workplane_normal", "workplane_x_dir",
-                          "is_solved", "is_fully_constrained"):
+                for k in (
+                    "workplane_origin",
+                    "workplane_normal",
+                    "workplane_x_dir",
+                    "is_solved",
+                    "is_fully_constrained",
+                ):
                     if k in meta:
                         sk_data[k] = meta[k]
 

src/fluency/models/data_model.py

@@ -232,6 +232,7 @@ class Body:
     extrude_cut: bool = False
     extrude_union: bool = False
     extrude_through_all: bool = False
+    extrude_cut_all_bodies: bool = False  # cut through all bodies in component
     extrude_face_index: Optional[int] = None  # which sketch face was selected
     extrude_target_body_id: Optional[str] = None  # for cut/union: target body id
     needs_update: bool = False  # True when source sketch changed since last extrude

src/fluency/ui/dialogs.py

@@ -4,18 +4,13 @@ from __future__ import annotations
 
 import logging
 import math
-from typing import Any, Dict, List, Optional, Tuple
+from typing import Tuple
 
-from PySide6.QtCore import Qt, QPoint, QPointF
-from PySide6.QtGui import QColor, QFont, QKeySequence
 from PySide6.QtWidgets import (
     QButtonGroup,
     QCheckBox,
-    QComboBox,
     QDialog,
-    QDialogButtonBox,
     QDoubleSpinBox,
-    QFormLayout,
     QFrame,
     QGridLayout,
     QHBoxLayout,
@@ -24,11 +19,11 @@ from PySide6.QtWidgets import (
     QPushButton,
     QRadioButton,
     QVBoxLayout,
-    QWidget,
 )
 
 logger = logging.getLogger(__name__)
 
+
 class ExtrudeDialog(QDialog):
     """Dialog for extrude options.
 
@@ -76,6 +71,13 @@ class ExtrudeDialog(QDialog):
         )
         layout.addWidget(self.through_all_checkbox)
 
+        self.cut_all_bodies_checkbox = QCheckBox("Cut All Bodies")
+        self.cut_all_bodies_checkbox.setToolTip(
+            "Apply the boolean cut to every body in the current component, "
+            "not just the one the sketch was drawn on.  Requires Perform Cut."
+        )
+        layout.addWidget(self.cut_all_bodies_checkbox)
+
         self.rounded_checkbox = QCheckBox("Round Edges")
         layout.addWidget(self.rounded_checkbox)
 
@@ -103,6 +105,7 @@ class ExtrudeDialog(QDialog):
             self.cut_checkbox,
             self.union_checkbox,
             self.through_all_checkbox,
+            self.cut_all_bodies_checkbox,
             self.rounded_checkbox,
         ):
             # The spinbox has valueChanged; the checkboxes have stateChanged.
@@ -144,7 +147,7 @@ class ExtrudeDialog(QDialog):
                 pass
         super().hideEvent(event)
 
-    def get_values(self) -> Tuple[float, bool, bool, bool, bool, bool, bool]:
+    def get_values(self) -> Tuple[float, bool, bool, bool, bool, bool, bool, bool]:
         return (
             self.length_input.value(),
             self.symmetric_checkbox.isChecked(),
@@ -152,6 +155,7 @@ class ExtrudeDialog(QDialog):
             self.cut_checkbox.isChecked(),
             self.union_checkbox.isChecked(),
             self.through_all_checkbox.isChecked(),
+            self.cut_all_bodies_checkbox.isChecked(),
             self.rounded_checkbox.isChecked(),
         )
 
@@ -404,7 +408,6 @@ class WorkplaneOrientationDialog(QDialog):
     def _on_ok(self):
         """Compute the final orientation and accept."""
         import numpy as np
-        import math
 
         if self._custom_radio.isChecked():
             # Custom: start from XY normal and rotate by the two angles.
@@ -413,18 +416,22 @@ class WorkplaneOrientationDialog(QDialog):
             # Start from +Z normal, rotate around X then Y
             n = np.array([0.0, 0.0, 1.0])
             # Rotate around X
-            rx = np.array([
+            rx = np.array(
+                [
                     [1, 0, 0],
                     [0, math.cos(ax), -math.sin(ax)],
                     [0, math.sin(ax), math.cos(ax)],
-            ])
+                ]
+            )
             n = rx @ n
             # Rotate around Y
-            ry = np.array([
+            ry = np.array(
+                [
                     [math.cos(ay), 0, math.sin(ay)],
                     [0, 1, 0],
                     [-math.sin(ay), 0, math.cos(ay)],
-            ])
+                ]
+            )
             n = ry @ n
             n = n / np.linalg.norm(n)
             # x_dir: cross product of normal with world Y, or world Z if normal ~ Y
@@ -454,23 +461,26 @@ class WorkplaneOrientationDialog(QDialog):
         whether called before or after ``_on_ok``.
         """
         import numpy as np
-        import math
 
         if self._custom_radio.isChecked():
             ax = math.radians(self._angle_x.value())
             ay = math.radians(self._angle_y.value())
             n = np.array([0.0, 0.0, 1.0])
-            rx = np.array([
+            rx = np.array(
+                [
                     [1, 0, 0],
                     [0, math.cos(ax), -math.sin(ax)],
                     [0, math.sin(ax), math.cos(ax)],
-            ])
+                ]
+            )
             n = rx @ n
-            ry = np.array([
+            ry = np.array(
+                [
                     [math.cos(ay), 0, math.sin(ay)],
                     [0, 1, 0],
                     [-math.sin(ay), 0, math.cos(ay)],
-            ])
+                ]
+            )
             n = ry @ n
             n = n / np.linalg.norm(n)
             world_y = np.array([0.0, 1.0, 0.0])
@@ -492,6 +502,8 @@ class WorkplaneOrientationDialog(QDialog):
             if btn is not None:
                 return (btn.normal, btn.x_dir, self._name_input.text().strip() or "Workplane")
             # Fallback: XY default.
-            return ((0.0, 0.0, 1.0), (1.0, 0.0, 0.0), self._name_input.text().strip() or "Workplane")
-
-
+            return (
+                (0.0, 0.0, 1.0),
+                (1.0, 0.0, 0.0),
+                self._name_input.text().strip() or "Workplane",
+            )

src/fluency/ui/main_window.py

@@ -183,6 +183,157 @@ def _make_body_thumbnail(
         return None
 
 
+def _make_component_thumbnail(
+    component,
+    kernel,
+    size: QSize = QSize(96, 96),
+):
+    """Render a small isometric thumbnail of all bodies in a component.
+
+    Combines the meshes of all visible bodies and renders them together.
+    Returns a QPixmap or None on failure.
+    """
+    try:
+        import numpy as np
+        from PIL import Image, ImageDraw
+        from PySide6.QtGui import QImage, QPixmap
+
+        # Collect meshes from all visible bodies with geometry
+        all_verts = []
+        all_faces = []
+        vertex_offset = 0
+
+        for body in component.bodies.values():
+            if not body.visible or not body.geometry:
+                continue
+            verts, faces = body.get_mesh(kernel)
+            if verts is None or len(verts) == 0:
+                continue
+
+            verts = np.asarray(verts, dtype=np.float64)
+            faces = np.asarray(faces, dtype=np.int32)
+
+            # Apply body transform
+            if hasattr(body, "position") and body.position is not None:
+                if hasattr(body, "rotation") and body.rotation is not None:
+                    verts = verts @ body.rotation.T
+                verts = verts + body.position
+
+            all_verts.append(verts)
+            all_faces.append(faces + vertex_offset)
+            vertex_offset += len(verts)
+
+        if not all_verts:
+            return None
+
+        verts = np.concatenate(all_verts, axis=0)
+        faces = np.concatenate(all_faces, axis=0)
+
+        mins = verts.min(axis=0)
+        maxs = verts.max(axis=0)
+        center = (mins + maxs) / 2
+        extent = maxs - mins
+        max_dim = max(extent)
+        if max_dim < 1e-10:
+            return None
+
+        # Normalize vertices to [-1, 1] range centered at origin
+        v = (verts - center) / (max_dim * 0.7)
+
+        # Simple isometric projection (rotation + orthographic)
+        angle_y = np.radians(-45)
+        angle_x = np.radians(25)
+        cos_y, sin_y = np.cos(angle_y), np.sin(angle_y)
+        cos_x, sin_x = np.cos(angle_x), np.sin(angle_x)
+
+        # Rotate Y
+        x1 = v[:, 0] * cos_y - v[:, 2] * sin_y
+        z1 = v[:, 0] * sin_y + v[:, 2] * cos_y
+        y1 = v[:, 1]
+
+        # Rotate X
+        y2 = y1 * cos_x - z1 * sin_x
+        z2 = y1 * sin_x + z1 * cos_x
+        x2 = x1
+
+        # Project to 2D (orthographic)
+        w_px, h_px = size.width(), size.height()
+
+        # Compute 2D bounding box of projected vertices for tight framing
+        all_px = x2
+        all_py = -y2
+        px_min, px_max = all_px.min(), all_px.max()
+        py_min, py_max = all_py.min(), all_py.max()
+        span_x = px_max - px_min
+        span_y = py_max - py_min
+        if span_x < 1e-10 or span_y < 1e-10:
+            return None
+
+        # Scale to fill ~90% of the image
+        margin = 0.10
+        avail_w = w_px * (1.0 - margin)
+        avail_h = h_px * (1.0 - margin)
+        scale = min(avail_w / span_x, avail_h / span_y)
+
+        center_x = (px_min + px_max) / 2
+        center_y = (py_min + py_max) / 2
+        px = (all_px * scale + w_px / 2 - center_x * scale).astype(np.float64)
+        py = (all_py * scale + h_px / 2 - center_y * scale).astype(np.float64)
+        depth = z2  # for painter's algorithm
+
+        # Dark grey background
+        img = Image.new("RGBA", (w_px, h_px), (55, 55, 60, 255))
+        draw = ImageDraw.Draw(img)
+
+        # Compute face normals for backface culling & shading
+        v0 = np.stack([px[faces[:, 0]], py[faces[:, 0]], depth[faces[:, 0]]], axis=1)
+        v1 = np.stack([px[faces[:, 1]], py[faces[:, 1]], depth[faces[:, 1]]], axis=1)
+        v2 = np.stack([px[faces[:, 2]], py[faces[:, 2]], depth[faces[:, 2]]], axis=1)
+
+        # 2D cross product for winding
+        cross = (v1[:, 0] - v0[:, 0]) * (v2[:, 1] - v0[:, 1]) - (v1[:, 1] - v0[:, 1]) * (
+            v2[:, 0] - v0[:, 0]
+        )
+
+        # Average depth per face
+        avg_depth = (v0[:, 2] + v1[:, 2] + v2[:, 2]) / 3.0
+
+        # Sort faces by depth (painter's algorithm: draw far faces first)
+        order = np.argsort(-avg_depth)
+
+        # Ceramic white body with shading
+        base_r, base_g, base_b = 220, 218, 215
+
+        for i in order:
+            # Backface culling
+            if cross[i] <= 0:
+                continue
+
+            pts = [
+                (float(px[faces[i, 0]]), float(py[faces[i, 0]])),
+                (float(px[faces[i, 1]]), float(py[faces[i, 1]])),
+                (float(px[faces[i, 2]]), float(py[faces[i, 2]])),
+            ]
+
+            # Shading: stronger contrast for depth perception
+            brightness = 0.5 + 0.5 * max(0.0, min(1.0, (avg_depth[i] + 1) / 2))
+            r = int(base_r * brightness)
+            g = int(base_g * brightness)
+            b = int(base_b * brightness)
+
+            draw.polygon(pts, fill=(r, g, b, 255))
+
+        # Convert PIL image to QPixmap
+        data = img.tobytes("raw", "RGBA")
+        qimg = QImage(data, w_px, h_px, w_px * 4, QImage.Format_RGBA8888)
+        pixmap = QPixmap.fromImage(qimg.copy())
+        return pixmap
+
+    except Exception as e:
+        logger.debug(f"Component thumbnail generation failed: {e}")
+        return None
+
+
 # ── Button sizing & styling constants ────────────────────────────────
 _BTN_MIN = 40  # minimum button dimension (px)
 _BTN_MAX = 160  # maximum button dimension (px)
@@ -246,7 +397,7 @@ def _scroll_to_button(btn: QPushButton, scroll_area: QScrollArea) -> None:
 def _create_component_button(
     num: int,
     name: str,
-    body,
+    component,
     kernel,
     group: QButtonGroup,
     layout: QHBoxLayout,
@@ -261,7 +412,10 @@ def _create_component_button(
     btn.clicked.connect(click_handler)
     _set_button_style(btn)
 
-    pixmap = _make_body_thumbnail(body, kernel, QSize(96, 96))
+    # Render thumbnail from all bodies in the component
+    has_geometry = any(b.visible and b.geometry for b in component.bodies.values())
+    if has_geometry:
+        pixmap = _make_component_thumbnail(component, kernel, QSize(96, 96))
         if pixmap is not None:
             btn.setIcon(pixmap)
             btn.setIconSize(QSize(96, 96))
@@ -727,7 +881,7 @@ class MainWindow(QMainWindow):
         self._btn_del_sketch = ui.pb_del_sketch
         # ── Body tools ──
         self._btn_update_body = ui.pb_update_body
-        self._btn_edit_sketch_3 = ui.pb_edt_sktch_3
+        self._btn_body_hide = ui.pb_body_hide
         self._btn_del_body = ui.pb_del_body
         # ── Component tools ──
         self._btn_new_compo = ui.pb_new_compo
@@ -891,7 +1045,10 @@ class MainWindow(QMainWindow):
         self._btn_move.clicked.connect(self._translate_body)
         self._btn_array.clicked.connect(self._pattern_array)
         self._btn_offset.clicked.connect(self._offset_sketch)
-        self._btn_edit_sketch_3.clicked.connect(self._edit_sketch)
+        # Per-body hide/show toggle: the user clicks pb_body_hide next
+        # to a body name in the right-hand list.  We update the body's
+        # ``visible`` flag and ask the viewer to show/hide the mesh.
+        self._btn_body_hide.clicked.connect(self._on_body_hide_button_clicked)
 
         # Snap toggle
         self._btn_snap.clicked.connect(lambda c: self._sketch_widget.set_snap_mode("point", c))
@@ -998,11 +1155,12 @@ class MainWindow(QMainWindow):
         if component_index >= len(comp_ids):
             return
         comp = self._project.components[comp_ids[component_index]]
-        first_body = next(iter(comp.bodies.values()), None)
-        if not first_body or not first_body.geometry:
+        # Check if component has any bodies with geometry
+        has_geometry = any(b.visible and b.geometry for b in comp.bodies.values())
+        if not has_geometry:
             return
         btn = self._component_buttons[component_index]
-        pixmap = _make_body_thumbnail(first_body, self._kernel, QSize(96, 96))
+        pixmap = _make_component_thumbnail(comp, self._kernel, QSize(96, 96))
         if pixmap is not None:
             btn.setIcon(pixmap)
             btn.setIconSize(QSize(96, 96))
@@ -1076,18 +1234,13 @@ class MainWindow(QMainWindow):
                 self._sketch_list.addItem(sketch.name)
 
             for body_id, body in self._current_component.bodies.items():
-                # QListWidgetItem with a checkbox so the user can toggle
-                # each body's visibility in the 3D viewer.  The item's
-                # data role stores the body id so the toggle handler can
+                # QListWidgetItem with a data role so the toggle handler can
                 # look up the right body without relying on display text.
                 display_name = body.name
                 if body.needs_update:
                     display_name = f"⚠ {body.name}"
                 item = QListWidgetItem(display_name)
                 item.setData(Qt.UserRole, body_id)
-                # Qt.Checked = visible, Qt.Unchecked = hidden.  Default
-                # is whatever the body model says.
-                item.setCheckState(Qt.Checked if body.visible else Qt.Unchecked)
                 # Greying out a hidden body's name is a nice UX touch.
                 if not body.visible:
                     item.setForeground(QColor("#6c7086"))
@@ -1103,6 +1256,8 @@ class MainWindow(QMainWindow):
         changes to all assembly instances, and recalculates connectors.
         """
         self._update_bodies_from_sketch()
+        self._update_sketches_from_bodies()
+        self._update_bodies_from_sketch()  # re-extrude bodies whose sketches just moved
         self._redraw_bodies()
         self._propagate_to_assembly()
         self._recalculate_connectors()
@@ -1172,6 +1327,49 @@ class MainWindow(QMainWindow):
                             target = b
                             break
 
+            # Handle cut_all_bodies: apply the cut to every body in the
+            # component, not just the target.
+            if body.extrude_cut and body.extrude_cut_all_bodies:
+                try:
+                    if body.extrude_through_all and target is not None:
+                        cut_length = self._through_all_length(target, sketch)
+                        cut_symmetric = True
+                        cut_invert = False
+                    else:
+                        cut_length = body.extrude_length or 10.0
+                        cut_symmetric = body.extrude_symmetric
+                        cut_invert = body.extrude_invert
+                    tool_geom = self._kernel.extrude(
+                        face_geom,
+                        -cut_length if cut_invert else cut_length,
+                        symmetric=cut_symmetric,
+                    )
+                    if tool_geom is None:
+                        logger.warning(f"Body '{body.name}': cut-all tool geometry is empty")
+                        continue
+                    cut_count = 0
+                    for other_id, other in list(self._current_component.bodies.items()):
+                        if other.geometry is None:
+                            continue
+                        try:
+                            other.geometry = self._kernel.boolean_difference(
+                                other.geometry, tool_geom
+                            )
+                            other.needs_update = False
+                            other.modified_at = datetime.now()
+                            cut_count += 1
+                        except Exception:
+                            pass  # body doesn't intersect tool, skip
+                    body.needs_update = False
+                    body.modified_at = datetime.now()
+                    updated += 1
+                    logger.info(
+                        f"Re-extruded cut-all body '{body.name}': cut {cut_count} body(ies)"
+                    )
+                except Exception as exc:
+                    logger.exception(f"Body '{body.name}': re-extrude cut-all failed: {exc}")
+                continue  # skip the single-target path below
+
             # Compute the new result.
             try:
                 if body.extrude_through_all and target is not None:
@@ -1215,6 +1413,87 @@ class MainWindow(QMainWindow):
         if updated > 0:
             logger.info(f"Updated {updated} body(ies) from sketch")
 
+    def _update_sketches_from_bodies(self) -> None:
+        """Re-project underlay construction lines from updated 3D bodies.
+
+        For every sketch in the current component that carries a
+        ``_source_face`` (a face-projected underlay) and a
+        ``_source_body_id``, find the corresponding face on the updated
+        body geometry, re-project its edges to UV, and update the sketch's
+        external entities *in place* (preserving entity ids so existing
+        constraints survive).  The solver is re-run so any user geometry
+        anchored to the underlay follows the body.
+        """
+        if not self._current_component:
+            return
+        from fluency.geometry_occ.kernel import OCGeometryKernel
+
+        kernel = OCGeometryKernel()
+        updated = 0
+        for sketch in self._current_component.sketches.values():
+            src_body_id = getattr(sketch, "_source_body_id", None)
+            src_face = getattr(sketch, "_source_face", None)
+            if src_body_id is None or src_face is None:
+                continue
+            if sketch.occ_sketch is None:
+                continue
+            body = self._current_component.bodies.get(src_body_id)
+            if body is None or body.geometry is None:
+                continue
+            body_shape = kernel._get_shape(body.geometry)
+            if body_shape is None:
+                continue
+            # Find the face on the updated body that matches the original
+            # face's plane (normal parallel, origin coplanar).
+            wp = sketch.occ_sketch.get_workplane()
+            origin, normal = wp[0], wp[1]
+            ref_center = getattr(sketch, "_source_face_center", None)
+            match = OCGeometryKernel.find_coplanar_face(
+                body_shape,
+                origin,
+                normal,
+                ref_center=ref_center,
+            )
+            if match is None:
+                logger.debug(
+                    "Sketch '%s': no matching face on body '%s', skipping",
+                    sketch.name,
+                    body.name,
+                )
+                continue
+            new_face, new_center = match
+            sketch._source_face = new_face
+            sketch._source_face_center = new_center
+            # Re-project the new face's edges into UV.
+            from fluency.ui.sketch_widget import _project_face_to_uv
+
+            try:
+                polys = _project_face_to_uv(new_face, wp)
+            except Exception as exc:
+                logger.debug("re-projection failed for sketch '%s': %s", sketch.name, exc)
+                continue
+            if not polys:
+                continue
+            # Update external entities in-place (preserves ids + constraints).
+            ok = sketch.occ_sketch.update_external_entities(polys)
+            if ok:
+                updated += 1
+                logger.info(
+                    "Re-projected underlay for sketch '%s' from body '%s'",
+                    sketch.name,
+                    body.name,
+                )
+            # If the sketch is currently loaded in the widget, refresh
+            # the underlay data so the view reflects the new projection
+            # WITHOUT re-importing (which would break constraints).
+            if sketch.occ_sketch is self._sketch_widget._sketch:
+                self._sketch_widget._source_face = new_face
+                self._sketch_widget._source_underlay_uv = polys
+                self._sketch_widget._rebuild_from_sketch()
+                self._sketch_widget.update()
+        if updated > 0:
+            logger.info("Re-projected underlays for %d sketch(es)", updated)
+
     def _propagate_to_assembly(self):
         """Refresh all assembly instances that reference the current component.
 
@@ -1390,12 +1669,12 @@ class MainWindow(QMainWindow):
         btn.clicked.connect(self._on_assembly_component_clicked)
         _set_button_style(btn)
 
-        # Thumbnail from the component's first body.
+        # Thumbnail from all bodies in the component.
         src_comp = self._current_component
         if src_comp:
-            first_body = next(iter(src_comp.bodies.values()), None)
-            if first_body and first_body.geometry:
-                pixmap = _make_body_thumbnail(first_body, self._kernel, QSize(96, 96))
+            has_geometry = any(b.visible and b.geometry for b in src_comp.bodies.values())
+            if has_geometry:
+                pixmap = _make_component_thumbnail(src_comp, self._kernel, QSize(96, 96))
                 if pixmap is not None:
                     btn.setIcon(pixmap)
                     btn.setIconSize(QSize(96, 96))
@@ -3225,6 +3504,17 @@ class MainWindow(QMainWindow):
         sketch.set_workplane(origin, normal, x_dir)
         # Keep the face reference for the projection underlay (Phase 3).
         sketch._source_face = face_shape
+        # Store the face centroid for re-matching when the body updates.
+        try:
+            from OCP.BRepGProp import BRepGProp
+            from OCP.GProp import GProp_GProps
+
+            props = GProp_GProps()
+            BRepGProp.VolumeProperties_s(face_shape, props)
+            c = props.CentreOfMass()
+            sketch._source_face_center = (float(c.X()), float(c.Y()), float(c.Z()))
+        except Exception:
+            sketch._source_face_center = tuple(float(v) for v in origin)
         # Remember which body the sketch lives on so a later cut / combine
         # extrude auto-targets it.  ``source_body`` may be None if the
         # pick landed on an untracked shape (e.g. an imported STEP that
@@ -3452,11 +3742,9 @@ class MainWindow(QMainWindow):
                     break
 
     def _on_body_visibility_changed(self, item: QListWidgetItem) -> None:
-        """Toggle a body's 3D visibility when the user flips its checkbox.
+        """Toggle a body's 3D visibility when the user clicks pb_body_hide.
 
-        itemChanged also fires for selection (not just check-state) changes,
-        so we filter on the check state being the changed role.  The body
-        is looked up via the UserRole data we set in _refresh_lists.
+        The body is looked up via the UserRole data we set in _refresh_lists.
         """
         if self._current_component is None:
             return
@@ -3466,16 +3754,11 @@ class MainWindow(QMainWindow):
         body = self._current_component.bodies.get(body_id)
         if body is None:
             return
-        new_visible = item.checkState() == Qt.Checked
+        new_visible = not body.visible  # toggle
         if body.visible == new_visible:
             return  # no change
         body.visible = new_visible
-        # Greying out hidden bodies gives a quick visual hint in the list.
         item.setForeground(QColor("#1e1e2e") if new_visible else QColor("#6c7086"))
-        # Apply to the 3D viewer: if the body has a rendered object, hide
-        # or show it.  Bodies without a render_object (e.g. just-created,
-        # not yet displayed) don't need viewer updates; they'll pick up
-        # the visibility at the next redraw.
         if body.render_object is not None:
             ok = self._viewer_3d.set_visibility(body.render_object, new_visible)
             if not ok:
@@ -3486,6 +3769,12 @@ class MainWindow(QMainWindow):
                 )
         logger.info(f"{'Visible' if new_visible else 'Hidden'}: {body.name}")
 
+    def _on_body_hide_button_clicked(self) -> None:
+        """Handle click on pb_body_hide button - toggle visibility of selected body."""
+        current_item = self._body_list.currentItem()
+        if current_item is not None:
+            self._on_body_visibility_changed(current_item)
+
     # ─── Extrude / cut helpers (shared by live preview + apply) ────────
 
     def _resolve_extrude_target(
@@ -3558,6 +3847,7 @@ class MainWindow(QMainWindow):
         cut: bool,
         union: bool,
         through_all: bool,
+        cut_all_bodies: bool = False,
     ) -> Optional[Dict[str, Any]]:
         """Compute the *previewable* result of an extrude/cut/union.
 
@@ -3566,6 +3856,7 @@ class MainWindow(QMainWindow):
           - "target_body": the Body being modified (None for plain extrude)
           - "tool_geom": the extruded profile geometry (the boolean tool)
           - "tool_shape": same, as a TopoDS_Shape (for show/remove)
+          - "all_targets": list of all bodies affected when cut_all_bodies
         Or *None* if the geometry can't be built (e.g. empty sketch).
 
         Mutates nothing on the project — safe to call repeatedly for the
@@ -3577,6 +3868,15 @@ class MainWindow(QMainWindow):
             return None
         # Resolve target (only meaningful for cut / union).
         target = self._resolve_extrude_target(sketch) if (cut or union) else None
+        # When cut_all_bodies, collect all bodies in the component as targets.
+        all_targets: list = []
+        if cut_all_bodies and cut and self._current_component is not None:
+            all_targets = [
+                b for b in self._current_component.bodies.values() if b.geometry is not None
+            ]
+            # Use the first non-tool body as the primary target for preview.
+            if target is None and all_targets:
+                target = all_targets[0]
         # Determine the extrude length and direction.
         if through_all and target is not None:
             # Pass-through: symmetric extrude large enough to clear the body
@@ -3617,6 +3917,7 @@ class MainWindow(QMainWindow):
                 "target_body": target,
                 "tool_geom": tool_geom,
                 "tool_shape": tool_shape,
+                "all_targets": all_targets,
             }
         # Plain extrude: the tool IS the result.
         return {
@@ -3625,6 +3926,7 @@ class MainWindow(QMainWindow):
             "target_body": None,
             "tool_geom": tool_geom,
             "tool_shape": tool_shape,
+            "all_targets": [],
         }
 
     def _start_extrude_preview(self, dialog: ExtrudeDialog, sketch: Sketch, face_geom: Any) -> None:
@@ -3639,17 +3941,24 @@ class MainWindow(QMainWindow):
         # which case we leave them alone).
         state = {"dimmed": []}
 
-        def _apply_dim(target: Optional[Body]):
-            # Undo any prior dim, then dim the new target.
-            for bid, tval in state["dimmed"]:
+        def _apply_dim(targets):
+            """Dim one or more bodies for preview clarity."""
+            # Undo any prior dim.
+            for bid, _tval in state["dimmed"]:
                 body = self._current_component.bodies.get(bid) if self._current_component else None
                 if body is not None and body.render_object is not None:
                     self._viewer_3d.set_transparency(body.render_object, 0.0)
             state["dimmed"].clear()
-            if target is not None and target.render_object is not None:
-                ok = self._viewer_3d.set_transparency(target.render_object, 0.6)
+            # Normalize to a list.
+            if targets is None:
+                targets = []
+            elif isinstance(targets, Body):
+                targets = [targets]
+            for t in targets:
+                if t is not None and t.render_object is not None:
+                    ok = self._viewer_3d.set_transparency(t.render_object, 0.6)
                     if ok:
-                    state["dimmed"].append((target.id, 0.6))
+                        state["dimmed"].append((t.id, 0.6))
 
         def _clear():
             self._viewer_3d.clear_preview()
@@ -3663,7 +3972,7 @@ class MainWindow(QMainWindow):
             if values is None:
                 _clear()
                 return
-            length, symmetric, invert, cut, union, through_all, _rounded = values
+            length, symmetric, invert, cut, union, through_all, cut_all_bodies, _rounded = values
             result = self._compute_extrude_result(
                 sketch,
                 face_geom,
@@ -3673,12 +3982,18 @@ class MainWindow(QMainWindow):
                 bool(cut),
                 bool(union),
                 bool(through_all),
+                cut_all_bodies=bool(cut_all_bodies),
             )
             if result is None or result["result_shape"] is None:
                 self._viewer_3d.clear_preview()
                 _apply_dim(None)
                 return
             self._viewer_3d.show_preview(result["result_shape"])
+            # Dim all affected bodies when cut_all_bodies is active.
+            all_targets = result.get("all_targets", [])
+            if all_targets:
+                _apply_dim(all_targets)
+            else:
                 _apply_dim(result["target_body"])
 
         dialog.set_preview_callback(_callback)
@@ -3731,10 +4046,13 @@ class MainWindow(QMainWindow):
             logger.info("Extrude dialog cancelled")
             return
 
-        length, symmetric, invert, cut, union, through_all, rounded = dialog.get_values()
+        length, symmetric, invert, cut, union, through_all, cut_all_bodies, rounded = (
+            dialog.get_values()
+        )
         logger.info(
             f"Extrude params: length={length}, symmetric={symmetric}, "
-            f"invert={invert}, cut={cut}, union={union}, through_all={through_all}"
+            f"invert={invert}, cut={cut}, union={union}, through_all={through_all}, "
+            f"cut_all_bodies={cut_all_bodies}"
         )
 
         # Capture the face index before the dialog closes (the selected
@@ -3751,6 +4069,7 @@ class MainWindow(QMainWindow):
                 bool(cut),
                 bool(union),
                 bool(through_all),
+                cut_all_bodies=bool(cut_all_bodies),
             )
             if result is None or result["result_geom"] is None:
                 logger.warning("Extrude produced no geometry")
@@ -3758,12 +4077,41 @@ class MainWindow(QMainWindow):
                 return
 
             target = result["target_body"]
-            if target is not None:
-                # Cut / union: commit the result onto the *target* body in
-                # place (don't create a separate tool body — the previous
-                # implementation did, and that was the user-perceived
-                # "added without cut" bug once the spurious body was
-                # deleted).
+            all_targets = result.get("all_targets", [])
+
+            if target is not None and bool(cut) and all_targets:
+                # Cut all bodies: apply the boolean difference to every body
+                # in the component that has geometry.
+                tool_geom = result["tool_geom"]
+                updated_count = 0
+                for body in all_targets:
+                    try:
+                        new_geom = self._kernel.boolean_difference(body.geometry, tool_geom)
+                        body.geometry = new_geom
+                    except Exception as exc:
+                        logger.debug("Cut-all: boolean failed for %s: %s", body.name, exc)
+                        continue
+                    body.extrude_length = length
+                    body.extrude_symmetric = symmetric
+                    body.extrude_invert = invert
+                    body.extrude_cut = True
+                    body.extrude_union = False
+                    body.extrude_through_all = bool(through_all)
+                    body.extrude_cut_all_bodies = True
+                    body.extrude_face_index = face_index
+                    body.source_sketch = sketch
+                    body.source_operation = "cut"
+                    body.extrude_target_body_id = body.id
+                    if body.render_object is not None:
+                        self._viewer_3d.remove_mesh(body.render_object)
+                    shape = self._kernel._get_shape(body.geometry)
+                    body.render_object = self._viewer_3d.show_shape(shape, body.color, body.name)
+                    updated_count += 1
+                logger.info(f"Cut-all applied to {updated_count} body(ies)")
+                body_name = f"{updated_count} body(ies)"
+            elif target is not None:
+                # Single-body cut / union: commit the result onto the *target*
+                # body in place.
                 target.geometry = result["result_geom"]
                 # Store extrude params so the body can be rebuilt later.
                 target.extrude_length = length
@@ -3772,6 +4120,7 @@ class MainWindow(QMainWindow):
                 target.extrude_cut = bool(cut)
                 target.extrude_union = bool(union)
                 target.extrude_through_all = bool(through_all)
+                target.extrude_cut_all_bodies = False
                 target.extrude_face_index = face_index
                 target.source_sketch = sketch
                 target.source_operation = "cut" if cut else "union"
@@ -3797,6 +4146,7 @@ class MainWindow(QMainWindow):
                         extrude_cut=False,
                         extrude_union=False,
                         extrude_through_all=bool(through_all),
+                        extrude_cut_all_bodies=False,
                         extrude_face_index=face_index,
                     )
                 )
@@ -4356,12 +4706,12 @@ class MainWindow(QMainWindow):
 
             # Rebuild component buttons (one per component, with thumbnails).
             for idx, comp in enumerate(self._project.components.values(), start=1):
-                first_body = next(iter(comp.bodies.values()), None)
-                if first_body and first_body.geometry:
+                has_geometry = any(b.visible and b.geometry for b in comp.bodies.values())
+                if has_geometry:
                     btn = _create_component_button(
                         idx,
                         comp.name,
-                        first_body,
+                        comp,
                         self._kernel,
                         self._component_group,
                         self._component_box_layout,
@@ -4409,12 +4759,16 @@ class MainWindow(QMainWindow):
                     btn.clicked.connect(self._on_assembly_component_clicked)
                     _set_button_style(btn)
 
-                    # Thumbnail from the source component's first body.
+                    # Thumbnail from the source component's all bodies.
                     src_comp = self._project.components.get(ac.component_id)
                     if src_comp:
-                        first_body = next(iter(src_comp.bodies.values()), None)
-                        if first_body and first_body.geometry:
-                            pixmap = _make_body_thumbnail(first_body, self._kernel, QSize(96, 96))
+                        has_geometry = any(
+                            b.visible and b.geometry for b in src_comp.bodies.values()
+                        )
+                        if has_geometry:
+                            pixmap = _make_component_thumbnail(
+                                src_comp, self._kernel, QSize(96, 96)
+                            )
                             if pixmap is not None:
                                 btn.setIcon(pixmap)
                                 btn.setIconSize(QSize(96, 96))
@@ -4512,7 +4866,7 @@ class MainWindow(QMainWindow):
                 btn = _create_component_button(
                     btn_num,
                     name,
-                    body,
+                    comp,
                     self._kernel,
                     self._component_group,
                     self._component_box_layout,

src/fluency/ui/sketch_widget.py

@@ -185,6 +185,7 @@ class Sketch2DWidget(QWidget):
         # Rectangle first-click snap target (stored so the second click
         # doesn't overwrite it and the correct corner gets constrained).
         self._rect_first_snap_target: Optional[OCCSketchEntity] = None
+        self._rect_first_line_target: Optional[OCCSketchEntity] = None
 
         # Offset preview state (live preview while the OffsetDialog is open).
         self._offset_preview_points: List[Tuple[float, float]] = []
@@ -375,15 +376,18 @@ class Sketch2DWidget(QWidget):
         # Clear any prior external entities before importing fresh ones so a
         # repeated face pick doesn't pile up duplicate construction lines.
         self._sketch.remove_external_entities()
-        imported = 0
-        for poly in self._source_underlay_uv:
-            if len(poly) < 2:
-                continue
-            try:
-                _, lines = self._sketch.add_external_polyline(
+        # Import ALL polylines in one call so corners shared between edges
+        # become a single external point entity (one connection hub per
+        # corner) instead of stacked duplicates.
+        polys = [
             [(float(u), float(v)) for (u, v) in poly]
-                )
-                imported += len(lines)
+            for poly in self._source_underlay_uv
+            if len(poly) >= 2
+        ]
+        imported = 0
+        try:
+            _, lines = self._sketch.add_external_polylines(polys)
+            imported = len(lines)
         except Exception as exc:
             logger.debug("underlay polyline import failed: %s", exc)
         logger.info("Imported %d construction-line segments from source face", imported)
@@ -560,6 +564,7 @@ class Sketch2DWidget(QWidget):
         self._mode = None
         self._clear_move_state()
         self._rect_first_snap_target = None
+        self._rect_first_line_target = None
         self.clear_offset_preview()
         self.update()
 
@@ -597,6 +602,7 @@ class Sketch2DWidget(QWidget):
         self._snap_horizontal = False
         self._snap_vertical = False
         self._rect_first_snap_target = None
+        self._rect_first_line_target = None
         self._arc_accum_sweep = 0.0
         self._arc_prev_angle = None
 
@@ -671,22 +677,16 @@ class Sketch2DWidget(QWidget):
     # ─── Snapping ─────────────────────────────────────────────────────────
 
     def _find_nearest_point(self, pos: QPoint, max_distance: int = 15) -> Optional[QPoint]:
-        if not self._snap_mode.get("point", False):
+        # 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)
+        if entity is None or entity.geometry is None:
             return None
-        nearest = None
-        min_dist = max_distance
-        for entity in self._points:
-            if entity.geometry:
         x, y = entity.geometry
-                point = QPoint(int(round(x)), int(round(y)))
-                screen_point = self._world_to_screen(point)
-                dist = math.sqrt(
-                    (pos.x() - screen_point.x()) ** 2 + (pos.y() - screen_point.y()) ** 2
-                )
-                if dist < min_dist:
-                    min_dist = dist
-                    nearest = point
-        return nearest
+        return QPoint(int(round(x)), int(round(y)))
 
     def _find_nearest_point_entity(
         self, pos: QPoint, max_distance: int = 15
@@ -721,6 +721,14 @@ class Sketch2DWidget(QWidget):
         if not self._snap_mode.get("mpoint", False):
             return None
         for p1, p2 in self._lines:
+            line_ent = self._find_line_sketch_entity(p1, p2)
+            # Skip hidden underlay lines (consistent with point snap) and
+            # centerlines (their midpoint is the origin — covered by point snap).
+            if line_ent is not None and (
+                (self._is_external(line_ent) and not self._underlay_visible)
+                or self._is_centerline(line_ent)
+            ):
+                continue
             if p1.geometry and p2.geometry:
                 x1, y1 = p1.geometry
                 x2, y2 = p2.geometry
@@ -731,6 +739,52 @@ class Sketch2DWidget(QWidget):
                     return mid
         return None
 
+    def _find_line_snap(
+        self, pos: QPoint, max_distance: int = 15
+    ) -> Optional[Tuple[QPoint, OCCSketchEntity]]:
+        """Snap onto the nearest line (projected point on the line).
+
+        Returns ``(world_point_on_line, line_entity)`` for the closest line
+        within ``max_distance`` screen pixels, or None.  External (underlay)
+        lines participate when the underlay is visible — this is what lets a
+        click anywhere along a projected construction edge anchor the new
+        point with a point-on-line constraint.  Centerlines count as
+        infinite reference axes (perpendicular projection, no clamping).
+        """
+        if not self._snap_mode.get("point", False):
+            return None
+        wx, wy = self._screen_to_world_f(pos)
+        best: Optional[Tuple[QPoint, OCCSketchEntity]] = None
+        best_dist = float(max_distance)
+        for p1, p2 in self._lines:
+            line_ent = self._find_line_sketch_entity(p1, p2)
+            if line_ent is None:
+                continue
+            if self._is_external(line_ent) and not self._underlay_visible:
+                continue
+            if p1.geometry is None or p2.geometry is None:
+                continue
+            x1, y1 = p1.geometry
+            x2, y2 = p2.geometry
+            dx = x2 - x1
+            dy = y2 - y1
+            len_sq = dx * dx + dy * dy
+            if len_sq == 0:
+                continue
+            if self._is_centerline(line_ent):
+                # Infinite reference axis: unclamped perpendicular projection.
+                t = ((wx - x1) * dx + (wy - y1) * dy) / len_sq
+            else:
+                t = max(0.0, min(1.0, ((wx - x1) * dx + (wy - y1) * dy) / len_sq))
+            proj_x = x1 + t * dx
+            proj_y = y1 + t * dy
+            screen_proj = self._world_to_screen(QPoint(int(round(proj_x)), int(round(proj_y))))
+            dist = math.sqrt((pos.x() - screen_proj.x()) ** 2 + (pos.y() - screen_proj.y()) ** 2)
+            if dist < best_dist:
+                best_dist = dist
+                best = (QPoint(int(round(proj_x)), int(round(proj_y))), line_ent)
+        return best
+
     def _apply_angle_snap(self, start: QPoint, end: QPoint) -> QPoint:
         if not self._snap_mode.get("angle", False):
             return end
@@ -771,6 +825,14 @@ class Sketch2DWidget(QWidget):
             mid_snap = self._find_midpoint_snap(pos)
             if mid_snap:
                 return self._world_to_screen(mid_snap)
+        # Line snap: click anywhere along a line (incl. projected construction
+        # edges) lands exactly on it and carries a point-on-line constraint
+        # target so the new endpoint is actually connected, not just close.
+        line_snap = self._find_line_snap(pos)
+        if line_snap is not None:
+            snap_pt, line_ent = line_snap
+            self._snap_line_target = line_ent
+            return self._world_to_screen(snap_pt)
         if start:
             if self._snap_mode.get("horiz", False):
                 horiz = self._apply_horizontal_snap(start, result)
@@ -860,6 +922,44 @@ class Sketch2DWidget(QWidget):
             if nearest is not None:
                 return nearest
 
+        # Line snap (excluding lines whose both endpoints are being moved)
+        if self._snap_mode.get("point", False):
+            wx, wy = self._screen_to_world_f(pos)
+            best_line: Optional[Tuple[QPoint, OCCSketchEntity]] = None
+            best_line_dist = float(self._snap_distance)
+            for p1, p2 in self._lines:
+                if p1.id in exclude_ids and p2.id in exclude_ids:
+                    continue
+                line_ent = self._find_line_sketch_entity(p1, p2)
+                if line_ent is None:
+                    continue
+                if self._is_external(line_ent) and not self._underlay_visible:
+                    continue
+                if p1.geometry is None or p2.geometry is None:
+                    continue
+                x1, y1 = p1.geometry
+                x2, y2 = p2.geometry
+                dx = x2 - x1
+                dy = y2 - y1
+                len_sq = dx * dx + dy * dy
+                if len_sq == 0:
+                    continue
+                if self._is_centerline(line_ent):
+                    t = ((wx - x1) * dx + (wy - y1) * dy) / len_sq
+                else:
+                    t = max(0.0, min(1.0, ((wx - x1) * dx + (wy - y1) * dy) / len_sq))
+                proj_x = x1 + t * dx
+                proj_y = y1 + t * dy
+                sp = self._world_to_screen(QPoint(int(round(proj_x)), int(round(proj_y))))
+                d = math.sqrt((pos.x() - sp.x()) ** 2 + (pos.y() - sp.y()) ** 2)
+                if d < best_line_dist:
+                    best_line_dist = d
+                    best_line = (QPoint(int(round(proj_x)), int(round(proj_y))), line_ent)
+            if best_line is not None:
+                snap_pt, line_ent = best_line
+                self._snap_line_target = line_ent
+                return self._world_to_screen(snap_pt)
+
         # Horizontal / vertical / angle snaps are relative to the original anchor
         result = pos
         if self._snap_mode.get("horiz", False):
@@ -1116,6 +1216,8 @@ class Sketch2DWidget(QWidget):
         fm = QFontMetrics(QFont("Monospace", 9))
         # Track how many tags already share an anchor so we stack them vertically.
         stack_count: Dict[Tuple[int, int], int] = {}
+        # Compute sketch centroid once so all pills stack inside the shape.
+        centroid_screen = self._sketch_centroid_screen()
 
         for idx, entry in enumerate(self._sketch._constraint_log):
             # One bad log entry (e.g. a dangling id after a delete, an
@@ -1128,6 +1230,11 @@ class Sketch2DWidget(QWidget):
                 params = entry["params"]
                 anchor: Optional[QPoint] = None
                 label = ""
+                # World-space endpoints for distance dimension lines.
+                # Initialised every iteration so stale values from a prior
+                # distance constraint are never accidentally reused.
+                tag_p1: Optional[QPoint] = None
+                tag_p2: Optional[QPoint] = None
 
                 if ctype == "horizontal":
                     anchor = self._line_world_mid(ids[0])
@@ -1149,7 +1256,10 @@ class Sketch2DWidget(QWidget):
                     # 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)
-                    label = f"dst {params[0]:.1f}" if params else "dst"
+                    label = "dstc"
+                    # Store world-space positions for dimension-line rendering.
+                    tag_p1 = a
+                    tag_p2 = b
                 elif ctype == "parallel":
                     anchor = self._line_world_mid(ids[0])
                     label = "par"
@@ -1184,6 +1294,13 @@ class Sketch2DWidget(QWidget):
                 else:
                     continue
 
+                # For distance constraints, allow rendering even without an
+                # anchor — we only need tag_p1/tag_p2 for the dimension line.
+                if anchor is None:
+                    if ctype != "distance":
+                        continue
+                    # Use first valid endpoint as fallback anchor for the pill.
+                    anchor = tag_p1 if tag_p1 is not None else tag_p2
                     if anchor is None:
                         continue
                 sc = self._world_to_screen(anchor)
@@ -1194,11 +1311,34 @@ class Sketch2DWidget(QWidget):
                 text = f"> {label} <"
                 w = fm.horizontalAdvance(text) + 10
                 h = 16
-                # Stack successive tags above the anchor so they don't overlap.
-                cx = sc.x()
-                cy = sc.y() - 14 - slot * (h + 2)
+                # Push pill toward the sketch centroid (inside the closed
+                # shape) so it sits inside — dimensions are outside.
+                if centroid_screen is not None:
+                    dir_x = centroid_screen.x() - sc.x()
+                    dir_y = centroid_screen.y() - sc.y()
+                    dist = math.sqrt(dir_x * dir_x + dir_y * dir_y)
+                    if dist > 0.5:
+                        nx, ny = dir_x / dist, dir_y / dist
+                    else:
+                        # Anchor is at the centroid — default to upward.
+                        nx, ny = 0.0, -1.0
+                else:
+                    # No centroid available — default to upward.
+                    nx, ny = 0.0, -1.0
+                # Place the first pill 14 px inside from anchor,
+                # stack subsequent pills further in.
+                offset = 14 + slot * (h + 2)
+                cx = sc.x() + nx * offset
+                cy = sc.y() + ny * offset
                 rect = QRect(cx - w // 2, cy - h // 2, w, h)
-                tags.append({"idx": idx, "label": text, "rect": rect, "center": QPoint(cx, cy)})
+                tag_entry = {"idx": idx, "label": text, "rect": rect, "center": QPoint(cx, cy)}
+                # Attach world-space endpoints so paintEvent can draw dimension lines.
+                if ctype == "distance":
+                    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
+                tags.append(tag_entry)
             except Exception as exc:
                 # Catch any failure while building this one tag (bad
                 # geometry, missing entity, numpy round weirdness, etc.)
@@ -1817,11 +1957,20 @@ class Sketch2DWidget(QWidget):
                     self._solve_and_sync()
                     self._snap_point_target = None
                 else:
-                    # Auto-constrain: point snap during move → coincident
-                    if self._snap_point_target is not None and self._move_anchor is not None:
-                        self._sketch.constrain_coincident(
-                            self._move_anchor, self._snap_point_target
-                        )
+                    # Auto-constrain: snap → coincident / point-on-line
+                    target = None
+                    if self._snap_point_target is not None:
+                        target = self._snap_point_target
+                    elif self._snap_line_target is not None and self._move_anchor is not None:
+                        # Don't constrain a point onto a line it belongs to.
+                        line_ent = self._snap_line_target
+                        ep = self._sketch._lines.get(line_ent.id)
+                        if ep is None or (
+                            self._move_anchor.id != ep[0] and self._move_anchor.id != ep[1]
+                        ):
+                            target = line_ent
+                    if target is not None and self._move_anchor is not None:
+                        self._sketch.constrain_coincident(self._move_anchor, target)
                         self._solve_and_sync()
                 # Snap modes are honoured during the move (see _apply_move_snaps
                 # in mouseMoveEvent), so the committed positions are already snapped.
@@ -2100,6 +2249,32 @@ class Sketch2DWidget(QWidget):
 
     # ─── Drawing handlers ─────────────────────────────────────────────────
 
+    def _auto_constrain_new_point(self, point: OCCSketchEntity, solve: bool = False) -> None:
+        """Anchor a freshly created point to whatever the cursor snapped to.
+
+        Point-to-point (coincident) wins; otherwise a line snap produces a
+        point-on-line constraint (the solver's coincident accepts a point and
+        a line).  Without the line fallback, a click along a projected
+        construction edge placed a free point that merely *looked* connected
+        — the endpoint never moved with the edge and loops broke on drag.
+        """
+        if self._sketch is None:
+            return
+        target = None
+        if self._snap_point_target is not None:
+            target = self._snap_point_target
+        elif self._snap_line_target is not None:
+            # Don't constrain a point onto a line it is itself an endpoint of
+            # (degenerate / redundant for the solver).
+            line_ent = self._snap_line_target
+            ep = self._sketch._lines.get(line_ent.id)
+            if ep is None or (point.id != ep[0] and point.id != ep[1]):
+                target = line_ent
+        if target is not None:
+            self._sketch.constrain_coincident(point, target)
+            if solve:
+                self._solve_and_sync()
+
     def _handle_line_click(self, pos: QPoint):
         self._ensure_sketch_with_centerlines()
 
@@ -2112,10 +2287,8 @@ class Sketch2DWidget(QWidget):
             self._points.append(point)
             self._draw_buffer.append(pos)
 
-            # Auto-constrain: point snap → coincident on start point
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(point, self._snap_point_target)
-                self._solve_and_sync()
+            # Auto-constrain: snap → coincident / point-on-line on start point
+            self._auto_constrain_new_point(point, solve=True)
         else:
             point = self._sketch.add_point(pos.x(), pos.y())
             point.is_construction = self._is_construct
@@ -2125,9 +2298,8 @@ class Sketch2DWidget(QWidget):
                 line = self._sketch.add_line(self._points[-2], self._points[-1])
                 self._lines.append((self._points[-2], self._points[-1]))
 
-                # Auto-constrain: point snap → coincident on end point
-                if self._snap_point_target is not None:
-                    self._sketch.constrain_coincident(self._points[-1], self._snap_point_target)
+                # Auto-constrain: snap → coincident / point-on-line on end point
+                self._auto_constrain_new_point(self._points[-1])
 
                 # Auto-constrain: detect horizontal / vertical from geometry
                 if self._snap_mode.get("horiz", False) or self._snap_mode.get("vert", False):
@@ -2157,6 +2329,7 @@ class Sketch2DWidget(QWidget):
                 self._undo_manager.save_state()
             self._draw_buffer.append(pos)
             self._rect_first_snap_target = self._snap_point_target
+            self._rect_first_line_target = self._snap_line_target
         else:
             p1 = self._draw_buffer[0]
             p2 = pos
@@ -2179,13 +2352,13 @@ class Sketch2DWidget(QWidget):
                 self._lines.append((pts[i], pts[(i + 1) % 4]))
                 line_entities.append(line)
 
-            # Auto-constrain: point snap → coincident on the correct corners.
-            # pts[0] = first click snapped position
-            # pts[2] = second click snapped position
+            # Auto-constrain: snap → coincident / point-on-line on the
+            # correct corners.  pts[0] = first click, pts[2] = second click.
             if self._rect_first_snap_target is not None:
                 self._sketch.constrain_coincident(pts[0], self._rect_first_snap_target)
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(pts[2], self._snap_point_target)
+            elif self._rect_first_line_target is not None:
+                self._sketch.constrain_coincident(pts[0], self._rect_first_line_target)
+            self._auto_constrain_new_point(pts[2])
 
             # Auto-constrain: detect horizontal / vertical from geometry
             if self._snap_mode.get("horiz", False):
@@ -2225,10 +2398,8 @@ class Sketch2DWidget(QWidget):
             self._points.append(center)
             self._draw_buffer.append(pos)
 
-            # Auto-constrain: point snap → coincident on center
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(center, self._snap_point_target)
-                self._solve_and_sync()
+            # Auto-constrain: snap → coincident / point-on-line on center
+            self._auto_constrain_new_point(center, solve=True)
         else:
             center = self._points[-1]
             cx, cy = center.geometry if center.geometry else (0, 0)
@@ -2257,10 +2428,8 @@ class Sketch2DWidget(QWidget):
             self._points.append(center)
             self._draw_buffer.append(pos)
 
-            # Auto-constrain: point snap → coincident on center
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(center, self._snap_point_target)
-                self._solve_and_sync()
+            # Auto-constrain: snap → coincident / point-on-line on center
+            self._auto_constrain_new_point(center, solve=True)
         elif len(self._draw_buffer) == 1:
             # Click 2: place start point (defines radius + start angle)
             start = self._sketch.add_point(pos.x(), pos.y())
@@ -2274,9 +2443,8 @@ class Sketch2DWidget(QWidget):
             self._arc_prev_angle = math.atan2(pos.y() - cy, pos.x() - cx)
             self._arc_accum_sweep = 0.0
 
-            # Auto-constrain: point snap → coincident on start
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(start, self._snap_point_target)
+            # Auto-constrain: snap → coincident / point-on-line on start
+            self._auto_constrain_new_point(start)
 
             self._solve_and_sync()
         else:
@@ -2321,9 +2489,8 @@ class Sketch2DWidget(QWidget):
                 self._sketch.add_arc(center, radius, start_point, end, sweep=sweep)
                 self._arcs.append((center, radius, start_point, end, sweep))
 
-            # Auto-constrain: point snap → coincident on end point
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(end, self._snap_point_target)
+            # Auto-constrain: snap → coincident / point-on-line on end point
+            self._auto_constrain_new_point(end)
 
             self._solve_and_sync()
 
@@ -2352,9 +2519,7 @@ class Sketch2DWidget(QWidget):
             self._points.append(c1)
             self._draw_buffer.append(pos)
 
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(c1, self._snap_point_target)
-                self._solve_and_sync()
+            self._auto_constrain_new_point(c1, solve=True)
 
             self.sketch_updated.emit()
             self.update()
@@ -2367,8 +2532,7 @@ class Sketch2DWidget(QWidget):
             self._points.append(c2)
             self._draw_buffer.append(pos)
 
-            if self._snap_point_target is not None:
-                self._sketch.constrain_coincident(c2, self._snap_point_target)
+            self._auto_constrain_new_point(c2)
 
             self._solve_and_sync()
             self.sketch_updated.emit()
@@ -2850,41 +3014,145 @@ class Sketch2DWidget(QWidget):
     def _point_distance(self, p1: QPoint, p2: QPoint) -> float:
         return math.sqrt((p1.x() - p2.x()) ** 2 + (p1.y() - p2.y()) ** 2)
 
-    def _draw_distance_measurement(self, painter: QPainter, p1: QPoint, p2: QPoint):
-        """Draw dimension lines and distance value between two world-coord points."""
+    def _sketch_centroid_screen(self) -> Optional[QPointF]:
+        """Screen-space centroid of all non-external sketch points.
+
+        ``_points`` maps point_id → (x, y) tuple.  We look up the entity
+        in ``_entities`` to check ``is_external`` and get the geometry.
+        """
+        if not self._sketch:
+            return None
+        sx = sy = 0.0
+        n = 0
+        for pid, geom in self._sketch._points.items():
+            ent = self._sketch._entities.get(pid)
+            if ent is not None and self._is_external(ent):
+                continue
+            if isinstance(geom, tuple) and len(geom) == 2:
+                x, y = geom
+                if isinstance(x, (int, float)) and isinstance(y, (int, float)):
+                    sp = self._world_to_screen(QPoint(int(round(x)), int(round(y))))
+                    sx += sp.x()
+                    sy += sp.y()
+                    n += 1
+        return QPointF(sx / n, sy / n) if n > 0 else None
+
+    def _draw_technical_dimension(
+        self,
+        painter: QPainter,
+        p1: QPoint,
+        p2: QPoint,
+        value: float,
+        color: QColor = QColor("#a6e3a1"),
+    ):
+        """Draw an ISO-style dimension between two world-space points.
+
+        Renders extension lines from each endpoint, a dimension line offset
+        from the measured edge (on the side *away* from the sketch centroid),
+        arrowheads at both ends, and the value with "mm" centred on the
+        dimension line.
+        """
         sp1 = self._world_to_screen(p1)
         sp2 = self._world_to_screen(p2)
 
         dx = sp2.x() - sp1.x()
         dy = sp2.y() - sp1.y()
-        length = math.sqrt(dx * dx + dy * dy)
-        if length == 0:
+        screen_len = math.sqrt(dx * dx + dy * dy)
+        if screen_len < 1:
             return
 
-        # Perpendicular direction for offset lines
-        perp_dx = -dy / length
-        perp_dy = dx / length
-        offset = 25.0
+        # Unit vectors along and perpendicular to the dimension line.
+        ux = dx / screen_len
+        uy = dy / screen_len
+        px = -uy
+        py = ux
 
-        p1a = QPointF(sp1.x() + perp_dx, sp1.y() + perp_dy)
-        p1b = QPointF(sp1.x() + perp_dx * offset, sp1.y() + perp_dy * offset)
-        p2a = QPointF(sp2.x() + perp_dx, sp2.y() + perp_dy)
-        p2b = QPointF(sp2.x() + perp_dx * offset, sp2.y() + perp_dy * offset)
-        mid = QPointF((p1b.x() + p2b.x()) / 2, (p1b.y() + p2b.y()) / 2)
+        # Flip the perpendicular so the dimension line is on the side
+        # *away* from the sketch centroid (outside the closed shape).
+        centroid = self._sketch_centroid_screen()
+        if centroid is not None:
+            # Cross product: positive → centroid is left of p1→p2
+            cross = dx * (centroid.y() - sp1.y()) - dy * (centroid.x() - sp1.x())
+            if cross > 0:
+                px, py = -px, -py
+        else:
+            # Fallback: pick the side with the smaller screen coord.
+            if py > 0 or (py == 0 and px < 0):
+                px, py = -px, -py
 
-        pen_dim = QPen(QColor("#a6e3a1"), 1.5, Qt.DotLine)
+        # ── Scale factors ──
+        ext_gap = 4.0
+        ext_overrun = 5.0
+        dim_offset = 25.0
+        arrow_len = 6.0
+        arrow_w = 2.0
+        gap = 40.0
+
+        # ── Extension lines ──
+        e1s = QPointF(sp1.x() + px * ext_gap, sp1.y() + py * ext_gap)
+        e1e = QPointF(
+            sp1.x() + px * (dim_offset + ext_overrun), sp1.y() + py * (dim_offset + ext_overrun)
+        )
+        e2s = QPointF(sp2.x() + px * ext_gap, sp2.y() + py * ext_gap)
+        e2e = QPointF(
+            sp2.x() + px * (dim_offset + ext_overrun), sp2.y() + py * (dim_offset + ext_overrun)
+        )
+
+        pen_ext = QPen(color, 0.8)
+        painter.setPen(pen_ext)
+        painter.drawLine(e1s, e1e)
+        painter.drawLine(e2s, e2e)
+
+        # ── Dimension line (with gap for text) ──
+        d1 = QPointF(sp1.x() + px * dim_offset, sp1.y() + py * dim_offset)
+        d2 = QPointF(sp2.x() + px * dim_offset, sp2.y() + py * dim_offset)
+        dmid = QPointF((d1.x() + d2.x()) / 2, (d1.y() + d2.y()) / 2)
+
+        pen_dim = QPen(color, 1.2)
         painter.setPen(pen_dim)
-        painter.drawLine(p1a.toPoint(), p1b.toPoint())
-        painter.drawLine(p2a.toPoint(), p2b.toPoint())
-        painter.drawLine(p1b.toPoint(), p2b.toPoint())
 
-        # Draw distance text
-        dist = self._point_distance(p1, p2)
+        le = QPointF(dmid.x() - ux * (gap / 2), dmid.y() - uy * (gap / 2))
+        painter.drawLine(d1, le)
+        rs = QPointF(dmid.x() + ux * (gap / 2), dmid.y() + uy * (gap / 2))
+        painter.drawLine(rs, d2)
+
+        # ── Arrowheads ──
+        def _arrow(tip: QPointF, idx: float, idy: float):
+            bx = tip.x() - idx * arrow_len
+            by = tip.y() - idy * arrow_len
+            b1 = QPointF(bx + px * arrow_w, by + py * arrow_w)
+            b2 = QPointF(bx - px * arrow_w, by - py * arrow_w)
+            path = QPainterPath()
+            path.moveTo(tip)
+            path.lineTo(b1)
+            path.lineTo(b2)
+            path.closeSubpath()
+            painter.setPen(Qt.NoPen)
+            painter.setBrush(QBrush(color))
+            painter.drawPath(path)
+            painter.setPen(pen_dim)
+
+        _arrow(d1, ux, uy)
+        _arrow(d2, -ux, -uy)
+
+        # ── Dimension text ──
         painter.save()
-        painter.translate(mid)
-        painter.scale(1, -1)
-        painter.setPen(QPen(QColor("#a6e3a1"), 1))
-        painter.drawText(0, 0, f"{dist:.2f}")
+        try:
+            painter.translate(dmid)
+            angle = math.degrees(math.atan2(uy, ux))
+            if angle > 90 or angle < -90:
+                angle += 180
+            painter.rotate(angle)
+            painter.setPen(QPen(color, 1))
+            f = QFont("Helvetica", 11)
+            f.setBold(True)
+            painter.setFont(f)
+            text = f"{value:.2f} mm"
+            fm = QFontMetrics(f)
+            tw = fm.horizontalAdvance(text)
+            th = fm.height()
+            painter.drawText(int(-tw / 2), int(th / 3), text)
+        finally:
             painter.restore()
 
     def paintEvent(self, event):
@@ -3097,6 +3365,23 @@ class Sketch2DWidget(QWidget):
             painter.setPen(QPen(QColor("#f38ba8") if hovered else QColor("#f9e2af"), 1))
             painter.drawText(rect, Qt.AlignCenter, tag["label"])
 
+        # ── Technical dimension lines for distance constraints ──
+        # Draw proper measurement lines (extension lines + dimension line
+        # with arrowheads + centred text) for every distance constraint.
+        for tag in self._constraint_tags:
+            if "p1_world" in tag and "p2_world" in tag:
+                try:
+                    self._draw_technical_dimension(
+                        painter,
+                        tag["p1_world"],
+                        tag["p2_world"],
+                        tag["distance"],
+                    )
+                except Exception:
+                    import traceback
+
+                    traceback.print_exc()
+
         # ── Circles ──
         for center_ent, radius in self._circles:
             if center_ent.geometry:

tests/test_geometry.py

@@ -1,7 +1,6 @@
 """Tests for Fluency CAD geometry kernel."""
 
 import pytest
-import numpy as np
 
 from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
 from fluency.geometry_occ.sketch import OCCSketch
@@ -195,10 +194,14 @@ class TestOCCSketch:
         sk = OCCSketch()
         sk.set_workplane((10.0, 0.0, 5.0), normal, x_dir)
         # 20x20 square in UV
-        p0 = sk.add_point(-10, -10); p1 = sk.add_point(10, -10)
-        p2 = sk.add_point(10, 10);   p3 = sk.add_point(-10, 10)
-        sk.add_line(p0, p1); sk.add_line(p1, p2)
-        sk.add_line(p2, p3); sk.add_line(p3, p0)
+        p0 = sk.add_point(-10, -10)
+        p1 = sk.add_point(10, -10)
+        p2 = sk.add_point(10, 10)
+        p3 = sk.add_point(-10, 10)
+        sk.add_line(p0, p1)
+        sk.add_line(p1, p2)
+        sk.add_line(p2, p3)
+        sk.add_line(p3, p0)
 
         geom = sk.get_geometry()
         # The face must carry the plane normal for the kernel.
@@ -220,10 +223,14 @@ class TestOCCSketch:
 
         sk = OCCSketch()
         sk.set_workplane((0, 0, 0), (0, 0, 1), (1, 0, 0))
-        a = sk.add_point(-10, -10); b = sk.add_point(10, -10)
-        c = sk.add_point(10, 10);   d = sk.add_point(-10, 10)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(-10, -10)
+        b = sk.add_point(10, -10)
+        c = sk.add_point(10, 10)
+        d = sk.add_point(-10, 10)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
         ctr = sk.add_point(0, 0)
         sk.add_circle(ctr, 3.0)
 
@@ -290,10 +297,14 @@ class TestExternalEntities:
         # Underlay: a 20x20 square projected from a face (closed polyline).
         sk.add_external_polyline([(0, 0), (20, 0), (20, 20), (0, 20), (0, 0)])
         # User profile: a 5x5 square — this is what should be extruded.
-        a = sk.add_point(2, 2); b = sk.add_point(8, 2)
-        c = sk.add_point(8, 8); d = sk.add_point(2, 8)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(2, 2)
+        b = sk.add_point(8, 2)
+        c = sk.add_point(8, 8)
+        d = sk.add_point(2, 8)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
         faces = sk.detect_faces()
         # Only the user-drawn face (5x5 square) should be detected.
         assert len(faces) == 1
@@ -310,10 +321,14 @@ class TestExternalEntities:
     def test_external_entities_excluded_from_get_polygon_points(self):
         sk = OCCSketch()
         sk.add_external_polyline([(0, 0), (100, 0), (100, 100), (0, 100), (0, 0)])
-        a = sk.add_point(1, 1); b = sk.add_point(2, 1)
-        c = sk.add_point(2, 2); d = sk.add_point(1, 2)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(1, 1)
+        b = sk.add_point(2, 1)
+        c = sk.add_point(2, 2)
+        d = sk.add_point(1, 2)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
         poly = sk.get_polygon_points()
         # The user square (1..2 range) should appear, not the 0..100 underlay.
         assert all(1.0 <= p.x <= 2.0 for p in poly)
@@ -328,10 +343,14 @@ class TestExternalEntities:
         # Underlay (NOT to be extruded).
         sk.add_external_polyline([(0, 0), (10, 0), (10, 10), (0, 10), (0, 0)])
         # User profile: a 2x2 square inside the underlay.
-        a = sk.add_point(1, 1); b = sk.add_point(3, 1)
-        c = sk.add_point(3, 3); d = sk.add_point(1, 3)
-        sk.add_line(a, b); sk.add_line(b, c)
-        sk.add_line(c, d); sk.add_line(d, a)
+        a = sk.add_point(1, 1)
+        b = sk.add_point(3, 1)
+        c = sk.add_point(3, 3)
+        d = sk.add_point(1, 3)
+        sk.add_line(a, b)
+        sk.add_line(b, c)
+        sk.add_line(c, d)
+        sk.add_line(d, a)
         geom = sk.get_geometry()
         # Volume = 2 * 2 * 4 = 16, NOT 10 * 10 * 4 = 400.
         kernel = OCGeometryKernel()
@@ -498,10 +517,9 @@ class TestExtrudeCutFix:
         and the tool is no longer needed.
         """
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCGeometryKernel
         from OCP.GProp import GProp_GProps
         from OCP.BRepGProp import BRepGProp
-        import math
 
         k = OCGeometryKernel()
         target_shape = BRepPrimAPI_MakeBox(100, 100, 100).Shape()
@@ -511,17 +529,18 @@ class TestExtrudeCutFix:
         # expected volume easy to compute.
         from OCP.BRepPrimAPI import BRepPrimAPI_MakePrism
         from OCP.gp import gp_Pnt, gp_Vec
+
         # 20x20 square at (0,0,0), extruded along +Z by 200.
         from OCP.BRepBuilderAPI import BRepBuilderAPI_MakePolygon
+
         mp = BRepBuilderAPI_MakePolygon()
-        for (x, y) in [(0, 0), (20, 0), (20, 20), (0, 20)]:
+        for x, y in [(0, 0), (20, 0), (20, 20), (0, 20)]:
             mp.Add(gp_Pnt(x, y, 0))
         mp.Close()
         from OCP.BRepBuilderAPI import BRepBuilderAPI_MakeFace
+
         face = BRepBuilderAPI_MakeFace(mp.Wire()).Face()
-        tool_shape = BRepPrimAPI_MakePrism(
-            face, gp_Vec(0, 0, 200)
-        ).Shape()
+        tool_shape = BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, 200)).Shape()
         tool_obj = OCCGeometryObject(tool_shape, {"type": "prism"})
 
         # Before cut: target is 100^3 = 1_000_000.
@@ -536,9 +555,7 @@ class TestExtrudeCutFix:
         # After cut: target is 1_000_000 - 20*20*100 = 960_000
         # (the prism only intersects the box in z=[0,100], i.e. 100 deep).
         g1 = GProp_GProps()
-        BRepGProp.VolumeProperties_s(
-            k._get_shape(target_obj_geometry), g1
-        )
+        BRepGProp.VolumeProperties_s(k._get_shape(target_obj_geometry), g1)
         assert abs(g1.Mass() - 960_000.0) < 1.0
 
     def test_boolean_difference_does_not_leave_separate_cavity_body(self):
@@ -551,10 +568,9 @@ class TestExtrudeCutFix:
         target, so a single body remains.
         """
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from OCP.BRepAlgoAPI import BRepAlgoAPI_Cut
         from OCP.TopExp import TopExp_Explorer
         from OCP.TopAbs import TopAbs_SOLID
-        from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
+        from fluency.geometry_occ.kernel import OCGeometryKernel
 
         k = OCGeometryKernel()
         target_shape = BRepPrimAPI_MakeBox(100, 100, 100).Shape()
@@ -562,6 +578,7 @@ class TestExtrudeCutFix:
 
         # Tool: small box at the centre, fully inside the target.
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox as BBox
+
         tool_shape = BBox(20, 20, 20).Shape()
         tool_obj = OCCGeometryObject(tool_shape, {})
 
@@ -595,91 +612,59 @@ class TestBodyVisibilityToggle:
 
     def _make_window(self):
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import MainWindow
+
         return MainWindow()
 
     def test_body_list_uses_checkable_items(self):
-        """Each body list item must be a checkable QListWidgetItem."""
+        """Each body list item has a data role for the toggle handler."""
         from PySide6.QtCore import Qt
+
         win = self._make_window()
         # Add a fake body to the current component so the list isn't empty.
         from fluency.models.data_model import Body
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
+
+        box = OCCGeometryObject(BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {})
         win._current_component.bodies["a"] = Body(name="A", geometry=box)
         win._refresh_lists()
         items = win._body_list.findItems("A", Qt.MatchExactly)
         assert len(items) == 1
-        # Item is checkable (so the user can toggle visibility).
-        assert items[0].flags() & Qt.ItemIsUserCheckable
         # And the body id is stored on the item for the toggle handler.
         assert items[0].data(Qt.UserRole) == "a"
-        # Default state is checked (= visible).
-        assert items[0].checkState() == Qt.Checked
+        # Default state is visible.
+        assert win._current_component.bodies["a"].visible is True
 
     def test_toggling_visibility_updates_body_model(self):
-        """Flipping the checkbox should set body.visible accordingly."""
+        """Toggling visibility via _on_body_visibility_changed updates the model."""
         from PySide6.QtCore import Qt
+
         win = self._make_window()
         from fluency.models.data_model import Body
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
+
+        box = OCCGeometryObject(BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {})
         win._current_component.bodies["a"] = Body(name="A", geometry=box)
         win._refresh_lists()
         item = win._body_list.findItems("A", Qt.MatchExactly)[0]
 
         # Toggle off.
-        item.setCheckState(Qt.Unchecked)
         win._on_body_visibility_changed(item)
         assert win._current_component.bodies["a"].visible is False
 
         # Toggle back on.
-        item.setCheckState(Qt.Checked)
         win._on_body_visibility_changed(item)
         assert win._current_component.bodies["a"].visible is True
 
-    def test_visibility_no_op_when_unchanged(self):
-        """Re-emitting the same state must not trigger a viewer call.
-
-        The set_visibility call into the viewer is cheap but not free;
-        spamming it on every selection change would be wasteful.  The
-        handler short-circuits when the new state matches the model's.
-        """
-        from PySide6.QtCore import Qt
-        win = self._make_window()
-        from fluency.models.data_model import Body
-        from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
-        from fluency.geometry_occ.kernel import OCCGeometryObject
-        box = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(10, 10, 10).Shape(), {}
-        )
-        win._current_component.bodies["a"] = Body(name="A", geometry=box)
-        win._refresh_lists()
-        item = win._body_list.findItems("A", Qt.MatchExactly)[0]
-
-        # Force the model's visibility to False to mimic a desync.
-        win._current_component.bodies["a"].visible = False
-        # Set the checkbox to Unchecked — this matches the model, so the
-        # handler should short-circuit (not call set_visibility).
-        item.setCheckState(Qt.Unchecked)
-        # We can't directly assert "viewer was not called" without
-        # monkey-patching; instead assert that re-firing the handler
-        # doesn't raise and the state is consistent.
-        win._on_body_visibility_changed(item)
-        assert win._current_component.bodies["a"].visible is False
-
 
 def math_hypot(x, y):
     import math
+
     return math.hypot(x, y)
 
 
@@ -698,10 +683,13 @@ class TestConstraintTagRendering:
     def _make_widget_with_sketch(self, sk):
         """Build a Sketch2DWidget in offscreen mode and attach *sk* to it."""
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import Sketch2DWidget
+
         w = Sketch2DWidget()
         w.set_sketch(sk)
         return w
@@ -824,6 +812,7 @@ class TestConstraintTagRendering:
         class _BadRound:
             def __round__(self, ndigits=0):
                 raise TypeError("cannot round")
+
         sk._entities[c.id].geometry = (_BadRound(), _BadRound())
         tags = w._compute_constraint_tags()
         assert all(t["center"] is not None for t in tags)
@@ -865,12 +854,13 @@ class TestExtrudeRedesign:
 
     def _make_window_with_box(self, box_side=100.0):
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import MainWindow
         from fluency.models.data_model import Sketch, Body
-        from fluency.geometry_occ.kernel import OCCGeometryObject
         from fluency.geometry_occ.sketch import OCCSketch
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
 
@@ -896,7 +886,6 @@ class TestExtrudeRedesign:
         return win, sketch, sk, box_obj
 
     def _add_circle(self, sk, r=10.0):
-        from fluency.geometry_occ.sketch import OCCSketch
         c = sk.add_point(0, 0)
         sk.add_circle(c, r)
         sk.solve()
@@ -905,6 +894,7 @@ class TestExtrudeRedesign:
     def _geometry_volume(self, win, geom):
         from OCP.GProp import GProp_GProps
         from OCP.BRepGProp import BRepGProp
+
         sh = win._kernel._get_shape(geom)
         g = GProp_GProps()
         BRepGProp.VolumeProperties_s(sh, g)
@@ -919,37 +909,48 @@ class TestExtrudeRedesign:
         so a 5 mm cut makes a real 5 mm-deep pocket.
         """
         import math
+
         win, sketch, sk, box_obj = self._make_window_with_box(100.0)
         face_geom = self._add_circle(sk, r=10.0)
         # Plain cut, length=5, NOT inverted.  Pre-redesign this would have
         # removed nothing; post-redesign it must remove a 5 mm cylinder.
         result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=5.0, symmetric=False, invert=False,
-            cut=True, union=False, through_all=False,
+            sketch,
+            face_geom,
+            length=5.0,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=False,
         )
         assert result is not None
         assert result["target_body"] is not None
         assert result["target_body"].name == "Box1"
         vol = self._geometry_volume(win, result["result_geom"])
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 5.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 5.0
         assert abs(vol - expected) < 1.0
 
     def test_cut_through_all_passes_through(self):
-        """"Through All" cut fully passes through the body."""
+        """ "Through All" cut fully passes through the body."""
         import math
+
         win, sketch, sk, box_obj = self._make_window_with_box(100.0)
         face_geom = self._add_circle(sk, r=10.0)
         result = win._compute_extrude_result(
-            sketch, face_geom,
+            sketch,
+            face_geom,
             length=5.0,  # ignored when through_all
-            symmetric=False, invert=False,
-            cut=True, union=False, through_all=True,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=True,
         )
         assert result is not None
         vol = self._geometry_volume(win, result["result_geom"])
         # Full through cylinder = pi * r^2 * box_depth.
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 100.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 100.0
         assert abs(vol - expected) < 1.0
 
     def test_cut_auto_targets_source_body_not_existing_zero(self):
@@ -960,30 +961,23 @@ class TestExtrudeRedesign:
         """
         import math
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import MainWindow
         from fluency.models.data_model import Sketch, Body
-        from fluency.geometry_occ.kernel import OCCGeometryObject
         from fluency.geometry_occ.sketch import OCCSketch
         from OCP.BRepPrimAPI import BRepPrimAPI_MakeBox
 
         win = MainWindow()
         # First body in the dict: a 50-millimetre box ALSO.
-        first = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(50, 50, 50).Shape(), {}
-        )
-        win._current_component.bodies["first"] = Body(
-            name="First", geometry=first
-        )
+        first = OCCGeometryObject(BRepPrimAPI_MakeBox(50, 50, 50).Shape(), {})
+        win._current_component.bodies["first"] = Body(name="First", geometry=first)
         # Source body: a 100-millimetre box (drawn over).
-        src = OCCGeometryObject(
-            BRepPrimAPI_MakeBox(100, 100, 100).Shape(), {}
-        )
-        win._current_component.bodies["src"] = Body(
-            name="Src", geometry=src
-        )
+        src = OCCGeometryObject(BRepPrimAPI_MakeBox(100, 100, 100).Shape(), {})
+        win._current_component.bodies["src"] = Body(name="Src", geometry=src)
         # Sketch circle on top of the SOURCE box (0,0 so normal +Z).
         sk = OCCSketch()
         sk.set_workplane((50, 50, 100), (0, 0, 1), (1, 0, 0))
@@ -999,16 +993,21 @@ class TestExtrudeRedesign:
 
         face_geom = sk.get_geometry()
         result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=5.0, symmetric=False, invert=False,
-            cut=True, union=False, through_all=True,
+            sketch,
+            face_geom,
+            length=5.0,
+            symmetric=False,
+            invert=False,
+            cut=True,
+            union=False,
+            through_all=True,
         )
         assert result is not None
         # Target is the source box, NOT the dict's first body.
         assert result["target_body"].name == "Src"
         vol = self._geometry_volume(win, result["result_geom"])
         # 100^3 - pi*100*100 (through-all full-depth cut on the 100 box).
-        expected = 100.0 ** 3 - math.pi * (10.0 ** 2) * 100.0
+        expected = 100.0**3 - math.pi * (10.0**2) * 100.0
         assert abs(vol - expected) < 1.0
 
     def test_union_default_builds_outward(self):
@@ -1019,17 +1018,23 @@ class TestExtrudeRedesign:
         rather than "subtracting" from the existing box.
         """
         import math
+
         win, sketch, sk, box_obj = self._make_window_with_box(100.0)
         face_geom = self._add_circle(sk, r=10.0)
         result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=10.0, symmetric=False, invert=False,
-            cut=False, union=True, through_all=False,
+            sketch,
+            face_geom,
+            length=10.0,
+            symmetric=False,
+            invert=False,
+            cut=False,
+            union=True,
+            through_all=False,
         )
         assert result is not None
         vol = self._geometry_volume(win, result["result_geom"])
         # 100^3 + pi*100*10 — material added on top.
-        expected = 100.0 ** 3 + math.pi * (10.0 ** 2) * 10.0
+        expected = 100.0**3 + math.pi * (10.0**2) * 10.0
         assert abs(vol - expected) < 1.0
 
     def test_plain_extrude_untouched_by_source_body(self):
@@ -1037,9 +1042,14 @@ class TestExtrudeRedesign:
         win, sketch, sk, box_obj = self._make_window_with_box(100.0)
         face_geom = self._add_circle(sk, r=10.0)
         result = win._compute_extrude_result(
-            sketch, face_geom,
-            length=10.0, symmetric=False, invert=False,
-            cut=False, union=False, through_all=False,
+            sketch,
+            face_geom,
+            length=10.0,
+            symmetric=False,
+            invert=False,
+            cut=False,
+            union=False,
+            through_all=False,
         )
         assert result is not None
         # No boolean target; result is the standalone tool extrusion.
@@ -1047,7 +1057,8 @@ class TestExtrudeRedesign:
         vol = self._geometry_volume(win, result["result_geom"])
         # Standalone cylinder 10 mm tall.
         import math
-        assert abs(vol - math.pi * (10.0 ** 2) * 10.0) < 1.0
+
+        assert abs(vol - math.pi * (10.0**2) * 10.0) < 1.0
 
     def test_freshly_picked_sketch_is_auto_selected(self):
         """After _on_face_picked, the new sketch is the current list row.
@@ -1055,7 +1066,6 @@ class TestExtrudeRedesign:
         The user should be able to click Extrude/Cut immediately without
         first hunting for the new sketch in the left list.
         """
-        from fluency.geometry_occ.kernel import OCCGeometryObject
         win, _, sk, box_obj = self._make_window_with_box(100.0)
         # Simulate _on_face_picked by calling it through a fake face
         # shape — but the simplest behavioural check is to call the
@@ -1063,6 +1073,7 @@ class TestExtrudeRedesign:
         # set as _current_sketch, and it appears (and is selected) in
         # the list after _refresh_lists + setCurrentRow.
         from fluency.models.data_model import Sketch
+
         sketch = Sketch(name="Sketch on face 99")
         sketch._source_body_id = "b1"
         sketch.set_workplane((50, 50, 100), (0, 0, 1), (1, 0, 0))
@@ -1084,8 +1095,10 @@ class TestExtrudeRedesign:
     def test_preview_callback_invoked_on_value_change(self):
         """The live preview callback fires on spinbox/checkbox changes."""
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import ExtrudeDialog
 
@@ -1110,8 +1123,10 @@ class TestExtrudeRedesign:
     def test_preview_hidden_event_sends_none(self):
         """hideEvent should deliver None to the callback so the host clears."""
         import os
+
         os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
         from PySide6.QtWidgets import QApplication
+
         app = QApplication.instance() or QApplication([])
         from fluency.main import ExtrudeDialog