From 3a169007f75b4e67f777c71c86676a008ec35ddd Mon Sep 17 00:00:00 2001
From: bklronin <therrmann23@gmail.com>
Date: Sun, 5 Jul 2026 19:36:27 +0200
Subject: [PATCH] - assembly draft

---
 .idea/workspace.xml                   |  18 +-
 src/fluency/main.py                   | 759 ++++++++++++++++++++++----
 src/fluency/models/data_model.py      |  92 +++-
 src/fluency/rendering/occ_renderer.py | 622 ++++++++++++++++++++-
 4 files changed, 1357 insertions(+), 134 deletions(-)

diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index ea9e0b1..3ee8ff9 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -4,12 +4,11 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- UI refinement, button position ui file as source no dirty drafting anymore">
+    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- assembly draft">
       <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/main.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/main.py" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/fluency/models/data_model.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/models/data_model.py" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" beforeDir="false" afterPath="$PROJECT_DIR$/src/fluency/rendering/occ_renderer.py" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -322,7 +321,15 @@
       <option name="project" value="LOCAL" />
       <updated>1783174566362</updated>
     </task>
-    <option name="localTasksCounter" value="27" />
+    <task id="LOCAL-00027" summary="- assembly draft">
+      <option name="closed" value="true" />
+      <created>1783239410744</created>
+      <option name="number" value="00027" />
+      <option name="presentableId" value="LOCAL-00027" />
+      <option name="project" value="LOCAL" />
+      <updated>1783239410744</updated>
+    </task>
+    <option name="localTasksCounter" value="28" />
     <servers />
   </component>
   <component name="TypeScriptGeneratedFilesManager">
@@ -365,6 +372,7 @@
     <MESSAGE value="- removed cadquery deoendency" />
     <MESSAGE value="- sketch enhacements" />
     <MESSAGE value="- UI refinement, button position ui file as source no dirty drafting anymore" />
-    <option name="LAST_COMMIT_MESSAGE" value="- UI refinement, button position ui file as source no dirty drafting anymore" />
+    <MESSAGE value="- assembly draft" />
+    <option name="LAST_COMMIT_MESSAGE" value="- assembly draft" />
   </component>
 </project>
\ No newline at end of file
diff --git a/src/fluency/main.py b/src/fluency/main.py
index 1b76261..22d2ba7 100644
--- a/src/fluency/main.py
+++ b/src/fluency/main.py
@@ -3547,11 +3547,14 @@ class Viewer3DWidget(QWidget):
     # Emitted when face-pick mode is cancelled (Esc) so the host can uncheck.
     pickFaceCancelled = Signal()
 
-    # Emitted when the user picks a face for a connector point (assembly).
-    # Payload: (origin, normal, x_dir, face_shape, owner_obj_id).
-    connectorPicked = Signal(tuple, tuple, tuple, object, str)
+    # Emitted when the user picks an entity for a connector point (assembly).
+    # Payload: (origin, normal, x_dir, entity_type, face_or_edge_or_vertex, owner_obj_id).
+    connectorPicked = Signal(tuple, tuple, tuple, str, object, str)
     # Emitted when connector pick mode is cancelled.
     connectorPickCancelled = Signal()
+    # Emitted on mouse move in connector mode to show snap preview.
+    # Payload: (origin, normal, entity_type, owner_obj_id) or None if nothing.
+    connectorHover = Signal(object)
 
     # Emitted when a body is clicked in assembly move mode.
     # Payload: owner_obj_id.
@@ -3569,6 +3572,11 @@ class Viewer3DWidget(QWidget):
         self.setAutoFillBackground(False)
         # Accept keyboard focus so navigation shortcuts (F, R, 1-7, P, O) work.
         self.setFocusPolicy(Qt.StrongFocus)
+        # Enable mouse tracking so ``mouseMoveEvent`` fires even without a
+        # button held — required for the connector-pick hover gizmo (and any
+        # status-bar hover feedback) to show under the cursor as the user
+        # moves the mouse over candidate snap entities before clicking.
+        self.setMouseTracking(True)
         # Try OCC renderer first; fall back to pygfx if unavailable.
         self._renderer: Any = None
         self._initialized = False
@@ -3579,9 +3587,11 @@ class Viewer3DWidget(QWidget):
         # When True, a left-click picks a planar face (for sketch-on-surface)
         # instead of orbiting the camera.  Set via set_pick_face_mode().
         self._pick_face_mode: bool = False
-        # When True, a left-click picks a face for a connector point
+        # When True, a left-click picks an entity for a connector point
         # (assembly component connection).
         self._connector_pick_mode: bool = False
+        # Current snap highlight object id (for hover during connector mode).
+        self._connector_snap_id: Optional[str] = None
         # When True, left-click on a body activates assembly drag-to-move.
         self._assembly_move_mode: bool = False
         # State for ongoing assembly drag.
@@ -3830,8 +3840,13 @@ class Viewer3DWidget(QWidget):
 
     def mouseMoveEvent(self, event):
         self._ensure_initialized()
-        # In face-pick/connector mode, keep dynamic highlighting.
-        if self._pick_face_mode or self._connector_pick_mode:
+        # In connector mode, show snap hover.
+        if self._connector_pick_mode:
+            self._handle_connector_hover(event)
+            super().mouseMoveEvent(event)
+            return
+        # In face-pick mode, keep dynamic highlighting.
+        if self._pick_face_mode:
             if hasattr(self._renderer, "handle_mouse_move"):
                 self._renderer.handle_mouse_move(event)
             super().mouseMoveEvent(event)
@@ -3914,37 +3929,170 @@ class Viewer3DWidget(QWidget):
     def set_connector_pick_mode(self, enabled: bool) -> None:
         """Toggle connector pick mode for placing connection points.
 
-        When enabled, clicking a face on a body in the assembly view
-        captures its origin and normal as a connection point for the
-        SolveSpace solver.
+        When enabled, clicking an entity (face, edge, vertex, hole)
+        on a body in the assembly view captures its position and
+        direction as a connection point for the SolveSpace solver.
         """
         self._connector_pick_mode = bool(enabled)
         if enabled:
             self.setCursor(Qt.CrossCursor)
         elif not self._pick_face_mode:
             self.unsetCursor()
+        if not enabled:
+            self._clear_connector_snap()
 
     def is_connector_pick_mode(self) -> bool:
         return self._connector_pick_mode
 
-    def _handle_connector_pick(self, event) -> None:
-        """Detect a planar face under the click and emit connectorPicked."""
+    def _clear_connector_snap(self) -> None:
+        """Remove the hover gizmo."""
+        fn = getattr(self._renderer, "clear_entity_gizmo", None)
+        if fn is not None:
+            fn()
+        # Backwards compat: also try the old method.
+        if self._connector_snap_id is not None:
+            fn2 = getattr(self._renderer, "remove_highlight_snap", None)
+            if fn2 is not None:
+                fn2(self._connector_snap_id)
+            self._connector_snap_id = None
+
+    def _handle_connector_hover(self, event) -> None:
+        """Update the hover snap gizmo during connector pick mode.
+
+        Probes a small neighbourhood around the cursor for ALL nearby snap
+        candidates (vertices, edge midpoints, face centres, hole openings)
+        and renders a dim marker on each plus a bright primary on the nearest
+        one — the general snap indicator.  Clicking then selects the
+        primary's position.
+        """
         self._ensure_initialized()
-        picker = getattr(self._renderer, "pick_planar_face", None)
-        if picker is None:
-            logger.warning("Renderer has no pick_planar_face support")
-            return
+        probe = getattr(self._renderer, "probe_snap_candidates", None)
         pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
-        info = picker(pos.x(), pos.y())
+
+        if probe is not None:
+            candidates = probe(pos.x(), pos.y())
+            if not candidates:
+                self._clear_connector_snap()
+                self.connectorHover.emit(None)
+                return
+            # Primary = the nearest candidate (probe sorts nearest-first).
+            info = candidates[0]
+        else:
+            # Fall back to single-pixel pick on renderers without the probe.
+            picker = getattr(self._renderer, "pick_entity", None)
+            if picker is None:
+                return
+            info = picker(pos.x(), pos.y())
+            candidates = [info] if info else []
+            if info is None or info.get("owner_obj_id") is None:
+                self._clear_connector_snap()
+                self.connectorHover.emit(None)
+                return
+
+        origin = info["position"]
+        normal = info.get("normal")
+        entity_type = info["type"]
+        owner = info.get("owner_obj_id", "")
+
+        # Show smart entity gizmo — dim candidate markers + bright primary.
+        self._clear_connector_snap()
+        gizmo_fn = getattr(self._renderer, "show_entity_gizmo", None)
+        if gizmo_fn is not None:
+            gizmo_fn(
+                entity_type=entity_type,
+                position=origin,
+                normal=normal,
+                x_dir=info.get("x_dir"),
+                radius=info.get("radius"),
+                candidates=candidates,
+            )
+        else:
+            # Fallback to old highlight_snap.
+            fn = getattr(self._renderer, "highlight_snap", None)
+            if fn is not None:
+                colors = {
+                    "planar_face": (0.0, 0.8, 1.0),      # cyan
+                    "cylindrical_face": (1.0, 0.4, 0.0),  # orange (hole)
+                    "edge": (0.0, 1.0, 0.4),               # green
+                    "vertex": (1.0, 1.0, 0.0),              # yellow
+                }
+                c = colors.get(entity_type, (1.0, 0.6, 0.0))
+                self._connector_snap_id = fn(origin, color=c, size=3.0)
+
+        self.connectorHover.emit({
+            "origin": origin,
+            "normal": normal,
+            "type": entity_type,
+            "owner_obj_id": owner,
+        })
+
+    def _handle_connector_pick(self, event) -> None:
+        """Detect an entity under the click and emit connectorPicked.
+
+        Uses the multi-pixel ``probe_snap_candidates`` so a click selects the
+        PRIMARY (nearest) snap target — the same one the hover gizmo
+        emphasised.  Falls back to single-pixel ``pick_entity`` then to
+        ``pick_planar_face`` on renderers without the probe.
+        """
+        self._ensure_initialized()
+        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
+        info: Optional[Dict[str, Any]] = None
+
+        probe = getattr(self._renderer, "probe_snap_candidates", None)
+        if probe is not None:
+            candidates = probe(pos.x(), pos.y())
+            if candidates:
+                info = candidates[0]  # nearest = primary
+
         if info is None:
-            logger.info("Connector pick: no planar face under cursor")
+            picker = getattr(self._renderer, "pick_entity", None)
+            if picker is None:
+                # Fallback to planar face only.
+                picker = getattr(self._renderer, "pick_planar_face", None)
+                if picker is None:
+                    logger.warning("Renderer has no entity picking support")
+                    return
+                pinfo = picker(pos.x(), pos.y())
+                if pinfo is None:
+                    logger.info("Connector pick: no planar face under cursor")
+                    return
+                owner_obj_id = pinfo.get("owner_obj_id", "")
+                self.connectorPicked.emit(
+                    tuple(pinfo["origin"]),
+                    tuple(pinfo["normal"]),
+                    tuple(pinfo["x_dir"]),
+                    "planar_face",
+                    pinfo["face"],
+                    owner_obj_id,
+                )
+                return
+            info = picker(pos.x(), pos.y())
+
+        if info is None:
+            logger.info("Connector pick: no entity under cursor")
             return
         owner_obj_id = info.get("owner_obj_id", "")
+        if not owner_obj_id:
+            return
+
+        entity_type = info["type"]
+        origin = info["position"]
+        normal = info.get("normal") or (0.0, 0.0, 1.0)
+        x_dir = info.get("x_dir") or (1.0, 0.0, 0.0)
+
+        # For vertices, pick a sensible normal from the parent face if possible.
+        if entity_type == "vertex" and normal is None:
+            normal = (0.0, 0.0, 1.0)
+
+        # Package the raw shape appropriately.
+        raw_shape = info.get("face") or info.get("edge") or info.get("vertex")
+
         self.connectorPicked.emit(
-            tuple(info["origin"]),
-            tuple(info["normal"]),
-            tuple(info["x_dir"]),
-            info["face"],
+            tuple(origin),
+            tuple(normal),
+            tuple(x_dir) if x_dir else (1.0, 0.0, 0.0),
+            entity_type,
+            raw_shape,
             owner_obj_id,
         )
 
@@ -4199,6 +4347,14 @@ class MainWindow(QMainWindow):
         # Drag-move state for assembly components
         self._asm_move_ac_id: Optional[str] = None
         self._asm_move_start_pos: Any = None
+        # Rigid-group drag state: maps every component id in the dragged
+        # rigid group to its start position, so the whole group translates
+        # together and connected partners keep their solved relative
+        # transforms.  Keyed by AssemblyComponent.id.
+        self._asm_move_group_start: Dict[str, Any] = {}
+        # Cached rigid-group membership for the current drag (avoids recomputing
+        # the BFS graph on every mouse-move event).
+        self._asm_move_group_ids: List[str] = []
         # Cache of render object IDs per assembly component, so drag updates
         # can replace only the moved component's shapes without clearing the
         # entire scene (avoids camera flicker).
@@ -4520,6 +4676,7 @@ class MainWindow(QMainWindow):
         self._btn_add_connector.clicked.connect(self._on_start_connector_placement)
         self._btn_del_connector.clicked.connect(self._on_delete_connector)
         self._viewer_3d.connectorPicked.connect(self._on_connector_picked)
+        self._viewer_3d.connectorHover.connect(self._on_connector_hover)
         self._viewer_3d.connectorPickCancelled.connect(
             lambda: self._btn_add_connector.setChecked(False)
         )
@@ -5068,7 +5225,12 @@ class MainWindow(QMainWindow):
     def _on_assembly_move_activated(self, owner_obj_id: str):
         """Called when the user clicks a body in move mode.
 
-        Parse the assembly component id and store its starting position.
+        Parse the assembly component id, compute the rigid group it belongs
+        to (transitively via mated connectors), and snapshot EVERY member's
+        start position so the whole group can translate together during the
+        drag.  The first-picked component of each mated pair stays as the
+        grounded reference frame for the solver; for a pure-translation
+        drag that just means we preserve all current relative transforms.
         """
         import numpy as np
 
@@ -5082,14 +5244,26 @@ class MainWindow(QMainWindow):
             return
 
         self._asm_move_ac_id = ac_id
+        # Rigid group membership (BFS over mated-connector connections).
+        group_ids = assembly.get_rigid_group(ac_id)
+        self._asm_move_group_ids = group_ids
+        self._asm_move_group_start = {}
+        for gid in group_ids:
+            g_ac = assembly.components.get(gid)
+            if g_ac is not None:
+                self._asm_move_group_start[gid] = np.array(g_ac.position, dtype=float)
+        # Keep the legacy single-component start for backwards compatibility.
         self._asm_move_start_pos = np.array(ac.position, dtype=float)
 
     def _on_assembly_move_dragged(self, owner_obj_id: str, dx: float, dy: float, dz: float):
-        """Called during a drag move.  Update only the dragged component in-place.
+        """Propagate a drag move across the entire rigid group, in-place.
 
-        Uses the targeted ``_update_assembly_component_in_viewer`` instead of
-        a full ``clear_scene`` + rebuild, so other shapes keep their render
-        objects and the camera stays perfectly still.
+        Every component in the dragged rigid group receives the SAME world
+        translation delta (relative to its own start position), so the mated
+        relative transforms are preserved exactly and SolveSpace's solved
+        alignment stays valid throughout the drag.  Each member is updated
+        in-place via ``_update_assembly_component_in_viewer`` so the camera
+        never flickers.
         """
         if self._asm_move_ac_id is None or self._asm_move_start_pos is None:
             return
@@ -5101,17 +5275,32 @@ class MainWindow(QMainWindow):
             return
 
         import numpy as np
-        # Apply delta relative to the start position.
-        ac.position = self._asm_move_start_pos + np.array([dx, dy, dz])
-        # Only update the dragged component's shapes — no scene clear.
-        self._update_assembly_component_in_viewer(ac_id)
+        delta = np.array([dx, dy, dz], dtype=float)
+        # Propagate the same delta to every rigid-group member.
+        group_ids = self._asm_move_group_ids or [ac_id]
+        for gid in group_ids:
+            start = self._asm_move_group_start.get(gid)
+            if start is None:
+                continue
+            g_ac = assembly.components.get(gid)
+            if g_ac is None:
+                continue
+            g_ac.position = start + delta
+            # Update only this component's shapes — no scene clear.
+            self._update_assembly_component_in_viewer(gid)
 
     def _on_assembly_move_finished(self, owner_obj_id: str):
         """Finalize the drag move."""
         if self._asm_move_ac_id is not None:
-            logger.info(f"Moved assembly component {self._asm_move_ac_id} to final position")
+            members = len(self._asm_move_group_ids) if self._asm_move_group_ids else 1
+            logger.info(
+                f"Moved assembly rigid group led by {self._asm_move_ac_id} "
+                f"({members} member(s)) to final position"
+            )
         self._asm_move_ac_id = None
         self._asm_move_start_pos = None
+        self._asm_move_group_start = {}
+        self._asm_move_group_ids = []
 
     # ────────────────────────────────────────────────────────────────────
     # Connector methods — two-click selection + preview dialog
@@ -5133,8 +5322,8 @@ class MainWindow(QMainWindow):
     def _on_start_connector_placement(self, checked: bool):
         """Toggle connector pick mode.
 
-        First click selects the first component's connection face.
-        Second click selects the second component and triggers alignment.
+        First click selects the first component's connection entity.
+        Second click selects the second component and triggers SolveSpace alignment.
         """
         if not self._assembly_view_active:
             self._btn_add_connector.setChecked(False)
@@ -5145,17 +5334,49 @@ class MainWindow(QMainWindow):
         # Reset any in-progress two-click state.
         self._connector_first_pick = None
         self._connector_second_ac_id = None
+        self._connector_align_pos = None
 
         self._viewer_3d.set_connector_pick_mode(checked)
         if checked:
             self._viewer_3d.setFocus()
             self._viewer_3d.activateWindow()
-            self.setStatusTip("Click on the first component's connection face")
+            self.setStatusTip("Click on the first component's connection point/face/edge/hole")
         else:
             self.setStatusTip("")
 
-    def _on_connector_picked(self, origin, normal, x_dir, face_shape, owner_obj_id):
-        """Handle a connector face pick — first or second click."""
+    def _on_connector_hover(self, info) -> None:
+        """Show entity-type feedback in the status bar during connector pick.
+
+        The gizmo itself is drawn by the viewer; this just reports what
+        entity is under the cursor so the user knows what they will snap to.
+        """
+        if info is None:
+            self.statusBar().showMessage("Move over a face / edge / hole / vertex to snap")
+            return
+        entity_type = info.get("type", "")
+        names = {
+            "planar_face": "Face",
+            "cylindrical_face": "Hole",
+            "edge": "Edge",
+            "vertex": "Vertex",
+        }
+        name = names.get(entity_type, "Entity")
+        ac_id = self._parse_ac_id(info.get("owner_obj_id", ""))
+        comp_name = ""
+        if ac_id is not None:
+            assembly = self._get_assembly()
+            ac = assembly.components.get(ac_id) if assembly else None
+            if ac is not None:
+                comp_name = f" on {ac.name}"
+        self.statusBar().showMessage(f"Snap target: {name}{comp_name} — click to pick")
+
+    def _on_connector_picked(self, origin, normal, x_dir, entity_type, raw_shape, owner_obj_id):
+        """Handle a connector entity pick — first or second click.
+
+        Snaps to faces, cylindrical holes, edges, or vertices.
+        Stores connector in component-local coordinates so it stays
+        valid when the component is moved by the solver.
+        """
         import numpy as np
 
         ac_id = self._parse_ac_id(owner_obj_id)
@@ -5171,19 +5392,37 @@ class MainWindow(QMainWindow):
                                 "The clicked component was not found in the assembly.")
             return
 
+        # Convert world-space connector to component-local coordinates.
+        # p_local = R^T @ (p_world - P)
+        pos_world = np.array(origin, dtype=float)
+        rot = ac.rotation
+        pos_local = rot.T @ (pos_world - ac.position)
+
+        n_world = np.array(normal, dtype=float)
+        n_local = rot.T @ n_world
+        n_local = n_local / max(np.linalg.norm(n_local), 1e-12)
+
+        x_world = np.array(x_dir, dtype=float) if x_dir else np.array([1.0, 0.0, 0.0])
+        x_local = rot.T @ x_world
+        x_local = x_local / max(np.linalg.norm(x_local), 1e-12)
+
         # ── First pick ──
         if self._connector_first_pick is None:
             self._connector_first_pick = {
                 "ac_id": ac_id,
-                "origin": tuple(origin),
-                "normal": tuple(normal),
-                "x_dir": tuple(x_dir),
+                "origin_local": tuple(pos_local),
+                "normal_local": tuple(n_local),
+                "x_dir_local": tuple(x_local),
+                "origin_world": tuple(origin),
+                "normal_world": tuple(normal),
+                "entity_type": entity_type,
                 "owner_obj_id": owner_obj_id,
             }
-            # Highlight the first face.
-            self._viewer_3d.highlight_face(face_shape)
-            self.setStatusTip("Now click on the second component's connection face")
-            logger.info(f"Connector first pick: {ac.name} at {origin}")
+            # Highlight the first face if planar.
+            if entity_type in ("planar_face", "cylindrical_face"):
+                self._viewer_3d.highlight_face(raw_shape)
+            self.setStatusTip("Now click on the second component's connection point/face/edge/hole")
+            logger.info(f"Connector first pick: {ac.name} at {origin} ({entity_type})")
             return
 
         # ── Second pick ──
@@ -5201,99 +5440,350 @@ class MainWindow(QMainWindow):
         self._btn_add_connector.setChecked(False)
         self.setStatusTip("")
 
-        logger.info(f"Connector second pick: {ac.name} at {origin}")
+        logger.info(f"Connector second pick: {ac.name} at {origin} ({entity_type})")
 
-        # Compute rough alignment transform (simulating SolveSpace).
-        # Move the second component so its connector face aligns with the
-        # first: translate so origin2 → origin1.
-        o1 = np.array(first["origin"])
-        o2 = np.array(origin)
-        align_delta = o1 - o2
+        # Build connector records (local coords).
+        second_pick = {
+            "ac_id": ac_id,
+            "origin_local": tuple(pos_local),
+            "normal_local": tuple(n_local),
+            "x_dir_local": tuple(x_local),
+            "origin_world": tuple(origin),
+            "normal_world": tuple(normal),
+            "entity_type": entity_type,
+            "owner_obj_id": owner_obj_id,
+        }
 
-        # Store the alignment position on the second component temporarily.
-        ac2 = assembly.components.get(ac_id)
-        if ac2 is not None:
-            self._connector_align_pos = np.array(ac2.position, dtype=float) + align_delta
-        else:
-            self._connector_align_pos = align_delta
+        # SolveSpace alignment: move second component so its connector
+        # aligns with the first. First component is fixed.
+        first_ac = assembly.components.get(first["ac_id"])
+        second_ac = ac
 
-        # Show the connector dialog with live preview callback.
-        rotation, offset = self._show_connector_dialog_with_preview(
-            first_ac=assembly.components.get(first["ac_id"]),
-            second_ac=ac2,
-            first_origin=first["origin"],
-            second_origin=o2,
-            first_normal=first["normal"],
-            second_normal=normal,
-            first_x_dir=first["x_dir"],
-            second_x_dir=x_dir,
-            align_delta=align_delta,
+        # Compute the world target for the second connector.
+        # It's at the first connector world position.
+        target_pos = np.array(first["origin_world"], dtype=float)
+        target_normal = np.array(first["normal_world"], dtype=float)
+        target_normal = target_normal / max(np.linalg.norm(target_normal), 1e-12)
+
+        # SolveSpace solver call.
+        solved = self._solve_assembly_alignment(
+            first_ac=first_ac,
+            second_ac=second_ac,
+            first_pick=first,
+            second_pick=second_pick,
+        )
+
+        if solved is None:
+            QMessageBox.warning(self, "Solver Error",
+                                "SolveSpace could not align the components.")
+            self._connector_first_pick = None
+            self._connector_second_ac_id = None
+            self._show_assembly_in_viewer(fit=True)
+            return
+
+        # Apply solved transform to second component.
+        second_ac.position = solved["position"]
+        second_ac.rotation = solved["rotation"]
+
+        # Show dialog with live preview (rotation offset along normal).
+        rotation, offset, flip = self._show_connector_dialog_with_preview(
+            first_ac=first_ac,
+            second_ac=second_ac,
+            first_pick=first,
+            second_pick=second_pick,
+            solved=solved,
         )
 
         if rotation is None:
             # User cancelled — restore original position.
-            if ac2 is not None:
-                self._show_assembly_in_viewer()
+            second_ac.position = np.array(solved["original_position"], dtype=float)
+            second_ac.rotation = np.array(solved["original_rotation"], dtype=float)
             self._connector_first_pick = None
             self._connector_second_ac_id = None
+            self._show_assembly_in_viewer(fit=True)
             return
 
-        # Create connectors on both components.
-        first_ac = assembly.components.get(first["ac_id"])
+        # Apply dialog adjustments (rotation + offset + flip).
+        import numpy as np
+        # Build rotation matrix: rotate second connector normal around
+        # the target normal axis by rotation degrees.
+        angle_rad = np.radians(rotation)
+        # Rodrigues' rotation formula around target_normal.
+        k = target_normal
+        K = np.array([[0, -k[2], k[1]], [k[2], 0, -k[0]], [-k[1], k[0], 0]])
+        R_axis = np.eye(3) + np.sin(angle_rad) * K + (1 - np.cos(angle_rad)) * (K @ K)
+
+        # Apply axis rotation to the solved rotation.
+        second_ac.rotation = R_axis @ second_ac.rotation
+
+        # Offset along the (possibly flipped) target normal.
+        flip_sign = -1.0 if flip else 1.0
+        second_ac.position = second_ac.position + flip_sign * target_normal * offset
+
+        # Create connectors on both components and link them as a mated pair.
+        conn1 = None
+        conn2 = None
         if first_ac:
             conn1 = first_ac.add_connector(
-                position=first["origin"],
-                normal=first["normal"],
-                x_dir=first["x_dir"],
+                position=first["origin_world"],
+                normal=first["normal_world"],
+                x_dir=first["x_dir_local"],
                 source_obj_id=first["owner_obj_id"],
-                name="Connector A",
+                name=f"Conn {entity_type} A",
             )
             conn1.axis_rotation = rotation
             conn1.offset = offset
+            # The first-picked connector is the grounded reference of the pair.
+            conn1.is_grounded = True
 
-        if ac2:
-            conn2 = ac2.add_connector(
-                position=tuple(o2),
-                normal=tuple(normal),
-                x_dir=tuple(x_dir),
+        if second_ac:
+            conn2 = second_ac.add_connector(
+                position=tuple(second_ac.position + second_ac.rotation @ np.array(second_pick["origin_local"])),
+                normal=tuple(second_ac.rotation @ np.array(second_pick["normal_local"])),
+                x_dir=tuple(second_ac.rotation @ np.array(second_pick["x_dir_local"])),
                 source_obj_id=owner_obj_id,
-                name="Connector B",
+                name=f"Conn {entity_type} B",
             )
             conn2.axis_rotation = rotation
             conn2.offset = offset
 
-            # Apply the aligned position (with dialog adjustments).
-            n2 = np.array(normal) / max(np.linalg.norm(normal), 1e-12)
-            ac2.position = self._connector_align_pos + n2 * offset
-            logger.info(f"Aligned '{ac2.name}' to connector position, offset={offset}mm")
+        # Cross-link the partners so the rigid-group move handler can follow
+        # the edge, and register the pair on the assembly graph.
+        if conn1 is not None and conn2 is not None:
+            conn1.partner_ac_id = second_ac.id
+            conn1.partner_connector_id = conn2.id
+            conn2.partner_ac_id = first_ac.id
+            conn2.partner_connector_id = conn1.id
+            assembly.add_connection(first_ac.id, second_ac.id)
 
-        logger.info(f"Connected component pair: {first['ac_id']} ↔ {ac_id}, rotation={rotation}°")
+        logger.info(f"Connected component pair: {first['ac_id']} ↔ {ac_id}, rotation={rotation}°, offset={offset}mm, flip={flip}")
         self._connector_first_pick = None
         self._connector_second_ac_id = None
         self._show_assembly_in_viewer(fit=True)
 
+    @staticmethod
+    def _rotation_between_vectors(a, b):
+        """Return a 3×3 rotation that maps vector *a* onto vector *b*.
+
+        Handles the two degenerate cases that plain Rodrigues' formula gets
+        wrong when the cross-product axis collapses to zero:
+
+        * ``a ≈ b``      → identity (no rotation needed).
+        * ``a ≈ -b``     → a 180° rotation about any axis orthogonal to *a*
+          (picked by a stable reference-vector projection).
+
+        Vectors are internally normalized so callers may pass non-unit input.
+        """
+        import numpy as _np
+        import math as _math
+        a = _np.asarray(a, dtype=float)
+        b = _np.asarray(b, dtype=float)
+        an = _np.linalg.norm(a); bn = _np.linalg.norm(b)
+        if an < 1e-12 or bn < 1e-12:
+            return _np.eye(3)
+        a = a / an; b = b / bn
+        dot = float(_np.dot(a, b))
+        cross = _np.cross(a, b)
+        cross_norm = _np.linalg.norm(cross)
+        if cross_norm < 1e-9:
+            if dot > 0.0:
+                # Already aligned.
+                return _np.eye(3)
+            # Anti-parallel: 180° about an axis orthogonal to *a*.
+            ref = _np.array([1.0, 0.0, 0.0]) if abs(a[0]) < 0.9 else _np.array([0.0, 1.0, 0.0])
+            axis = ref - a * _np.dot(ref, a)
+            axis = axis / max(_np.linalg.norm(axis), 1e-12)
+            K = _np.array([[0, -axis[2], axis[1]], [axis[2], 0, -axis[0]], [-axis[1], axis[0], 0]])
+            # sin(180°)=0, 1-cos(180°)=2  → R = I + 2 (K @ K)
+            return _np.eye(3) + 2.0 * (K @ K)
+        axis = cross / cross_norm
+        angle = _math.acos(max(-1.0, min(1.0, dot)))
+        K = _np.array([[0, -axis[2], axis[1]], [axis[2], 0, -axis[0]], [-axis[1], axis[0], 0]])
+        return _np.eye(3) + _np.sin(angle) * K + (1.0 - _np.cos(angle)) * (K @ K)
+
+    def _solve_assembly_alignment(
+        self,
+        first_ac: Any,
+        second_ac: Any,
+        first_pick: Dict[str, Any],
+        second_pick: Dict[str, Any],
+    ) -> Optional[Dict[str, Any]]:
+        """Use SolveSpace to align the second component to the first.
+
+        The first component is treated as fixed (grounded).  The second
+        component is moved so that its connector coincides with the first
+        connector (position + normal alignment).
+
+        Returns a dict with:
+        * ``position`` — new world position for second component.
+        * ``rotation`` — new 3×3 rotation matrix for second component.
+        * ``original_position`` / ``original_rotation`` — for cancellation.
+        """
+        import numpy as np
+        try:
+            from python_solvespace import SolverSystem, ResultFlag, Entity
+        except ImportError:
+            logger.warning("python_solvespace not available, falling back to direct alignment")
+            return self._align_direct(first_ac, second_ac, first_pick, second_pick)
+
+        # Save original transform for cancellation.
+        orig_pos = np.array(second_ac.position, dtype=float)
+        orig_rot = np.array(second_ac.rotation, dtype=float)
+
+        # World positions of connectors.
+        p1_world = np.array(first_pick["origin_world"], dtype=float)
+        n1_world = np.array(first_pick["normal_world"], dtype=float)
+        n1_world = n1_world / max(np.linalg.norm(n1_world), 1e-12)
+
+        p2_local = np.array(second_pick["origin_local"], dtype=float)
+        n2_local = np.array(second_pick["normal_local"], dtype=float)
+        n2_local = n2_local / max(np.linalg.norm(n2_local), 1e-12)
+
+        # Build solver.
+        #
+        # IMPORTANT: SolveSpace's SLVS_C_PARALLEL and SLVS_C_SAME_ORIENTATION
+        # both generate multi-equation residuals that trigger a hard C-level
+        # assertion in this python_solvespace build's Newton iterator
+        # ("Expected constraint to generate a single equation"), aborting the
+        # whole process.  We therefore avoid line-parallel / orientation
+        # constraints entirely and instead drive BOTH translation AND axis
+        # alignment with a pair of coincident point constraints:
+        #
+        #   * coincident(pt1,  pt2)   — forces the connector points together
+        #                                (3 translational DOF)
+        #   * coincident(pt1b, tip2)  — pins the *axis tip* of component 2
+        #                                onto a fixed point on component 1's
+        #                                connector axis, which forces the
+        #                                rotated axis direction to align
+        #                                with n1 (2 rotational DOF)
+        #
+        # That's 6 single-equation-coincident residuals against 6 free point
+        # parameters — a well-posed 0-DOF system — so it converges cleanly.
+        # The remaining free rotation around the axis is left for the
+        # rotation_spinner in the dialog.
+        sys = SolverSystem()
+
+        # Component 1 reference frame — fully grounded (dragged).  pt1 is the
+        # connector pivot, pt1b is one unit along the connector normal.
+        pt1 = sys.add_point_3d(float(p1_world[0]), float(p1_world[1]), float(p1_world[2]))
+        sys.dragged(pt1, Entity.FREE_IN_3D)
+        pt1b = sys.add_point_3d(
+            float(p1_world[0] + n1_world[0]),
+            float(p1_world[1] + n1_world[1]),
+            float(p1_world[2] + n1_world[2]),
+        )
+        sys.dragged(pt1b, Entity.FREE_IN_3D)
+
+        # Component 2 — free points, seeded near the current world connector.
+        p2_world_current = orig_pos + orig_rot @ p2_local
+        pt2 = sys.add_point_3d(float(p2_world_current[0]), float(p2_world_current[1]), float(p2_world_current[2]))
+        n2_world_current = orig_rot @ n2_local
+        tip2 = sys.add_point_3d(
+            float(p2_world_current[0] + n2_world_current[0]),
+            float(p2_world_current[1] + n2_world_current[1]),
+            float(p2_world_current[2] + n2_world_current[2]),
+        )
+
+        # Constraints: pivot coincidence + axis-tip coincidence.
+        sys.coincident(pt1, pt2, Entity.FREE_IN_3D)
+        sys.coincident(pt1b, tip2, Entity.FREE_IN_3D)
+
+        # Solve.
+        result = sys.solve()
+        if result != ResultFlag.OKAY:
+            logger.warning(f"SolveSpace solve failed: {result}")
+            return self._align_direct(first_ac, second_ac, first_pick, second_pick)
+
+        # Extract solved positions from the point entities' parameter tables.
+        # ``Entity`` does not expose .x/.y/.z — read them via SolverSystem.params.
+        p2_solved = np.array(sys.params(pt2.params), dtype=float)
+        tip2_solved = np.array(sys.params(tip2.params), dtype=float)
+        n2_solved = tip2_solved - p2_solved
+        n2_solved = n2_solved / max(np.linalg.norm(n2_solved), 1e-12)
+
+        # Compute the new component transform.
+        # The second connector in local coords is at p2_local with normal n2_local.
+        # In world space: P + R @ p2_local = p2_solved
+        #                 R @ n2_local   = n2_solved
+        # We need to find R and P.
+
+        # R must map n2_local → n2_solved.
+        # Use a rotation that aligns the two vectors.
+        from OCP.gp import gp_Vec, gp_Dir, gp_Ax1, gp_Trsf
+        # Compute the rotation mapping the connector's local axis to its
+        # solved world direction.  Use the robust helper so the degenerate
+        # anti-parallel case (cross → 0 but angle = 180°) is handled properly.
+        R_align = self._rotation_between_vectors(n2_local, n2_solved)
+
+        # The full rotation for the component.
+        new_rot = R_align @ orig_rot
+
+        # New position: P = p2_solved - R @ p2_local
+        new_pos = p2_solved - new_rot @ p2_local
+
+        return {
+            "position": new_pos,
+            "rotation": new_rot,
+            "original_position": orig_pos,
+            "original_rotation": orig_rot,
+        }
+
+    def _align_direct(
+        self,
+        first_ac: Any,
+        second_ac: Any,
+        first_pick: Dict[str, Any],
+        second_pick: Dict[str, Any],
+    ) -> Optional[Dict[str, Any]]:
+        """Direct geometric alignment (fallback when SolveSpace unavailable).
+
+        Moves the second component so its connector matches the first.
+        """
+        import numpy as np
+        orig_pos = np.array(second_ac.position, dtype=float)
+        orig_rot = np.array(second_ac.rotation, dtype=float)
+
+        p1_world = np.array(first_pick["origin_world"], dtype=float)
+        n1_world = np.array(first_pick["normal_world"], dtype=float)
+        n1_world = n1_world / max(np.linalg.norm(n1_world), 1e-12)
+
+        p2_local = np.array(second_pick["origin_local"], dtype=float)
+        n2_local = np.array(second_pick["normal_local"], dtype=float)
+        n2_local = n2_local / max(np.linalg.norm(n2_local), 1e-12)
+
+        # Align normals through the robust rotation helper so the
+        # anti-parallel case is handled correctly (see _rotation_between_vectors).
+        R_align = self._rotation_between_vectors(n2_local, n1_world)
+
+        new_rot = R_align @ orig_rot
+        p2_world_target = p1_world
+        new_pos = p2_world_target - new_rot @ p2_local
+
+        return {
+            "position": new_pos,
+            "rotation": new_rot,
+            "original_position": orig_pos,
+            "original_rotation": orig_rot,
+        }
+
     def _show_connector_dialog_with_preview(
         self,
         first_ac: Any,
         second_ac: Any,
-        first_origin: Tuple[float, float, float],
-        second_origin: Tuple[float, float, float],
-        first_normal: Tuple[float, float, float],
-        second_normal: Tuple[float, float, float],
-        first_x_dir: Tuple[float, float, float],
-        second_x_dir: Tuple[float, float, float],
-        align_delta: Any,
-    ) -> Tuple[Optional[float], Optional[float]]:
+        first_pick: Dict[str, Any],
+        second_pick: Dict[str, Any],
+        solved: Dict[str, Any],
+    ) -> Tuple[Optional[float], Optional[float], bool]:
         """Show connector dialog with live 3D preview of the alignment.
 
-        Returns (rotation_degrees, offset_mm) or (None, None) if cancelled.
+        Returns (rotation_degrees, offset_mm, flip) or (None, None, False) if cancelled.
         """
         from PySide6.QtWidgets import (QDialog, QVBoxLayout, QHBoxLayout,
                                         QLabel, QDoubleSpinBox, QPushButton,
                                         QFrame, QCheckBox)
 
         if second_ac is None:
-            return (None, None)
+            return (None, None, False)
 
         dialog = QDialog(self)
         dialog.setWindowTitle("Connector — Connection Properties")
@@ -5301,10 +5791,18 @@ class MainWindow(QMainWindow):
 
         layout = QVBoxLayout(dialog)
 
-        # Info label.
-        layout.addWidget(QLabel("Adjust the connection between the two components:"))
+        entity_names = {
+            "planar_face": "Face",
+            "cylindrical_face": "Hole",
+            "edge": "Edge",
+            "vertex": "Vertex",
+        }
+        t1 = entity_names.get(first_pick.get("entity_type", ""), "Entity")
+        t2 = entity_names.get(second_pick.get("entity_type", ""), "Entity")
+        layout.addWidget(QLabel(f"<b>{t1}</b> on {first_ac.name} → <b>{t2}</b> on {second_ac.name}"))
+        layout.addWidget(QLabel("Adjust the connection:"))
 
-        # Rotation around normal axis of the FIRST connector.
+        # Rotation around normal axis.
         rot_layout = QHBoxLayout()
         rot_layout.addWidget(QLabel("Rotation around axis (°):"))
         rotation_spin = QDoubleSpinBox()
@@ -5341,24 +5839,34 @@ class MainWindow(QMainWindow):
         btn_layout.addWidget(cancel_btn)
         layout.addLayout(btn_layout)
 
+        import numpy as np
+        target_normal = np.array(first_pick["normal_world"], dtype=float)
+        target_normal = target_normal / max(np.linalg.norm(target_normal), 1e-12)
+
         # ── Live preview callback ──
         def _update_preview(*args):
-            import numpy as np
             rot_deg = rotation_spin.value()
             off = offset_spin.value()
             flip = flip_check.isChecked()
 
-            # Compute the aligned position for second component.
-            base_pos = self._connector_align_pos if hasattr(self, '_connector_align_pos') else (
-                np.array(second_ac.position, dtype=float) + align_delta
-            )
-            # Apply offset along the second normal.
-            n2 = np.array(second_normal) / max(np.linalg.norm(second_normal), 1e-12)
-            new_pos = np.array(base_pos, dtype=float) + n2 * off
+            # Start from solved transform.
+            base_pos = np.array(solved["position"], dtype=float)
+            base_rot = np.array(solved["rotation"], dtype=float)
 
-            # Store preview position.
-            second_ac.position = new_pos
-            self._show_assembly_in_viewer()  # no fit — keep camera steady during live preview
+            # Apply axis rotation around target_normal.
+            angle_rad = np.radians(rot_deg)
+            k = target_normal
+            K = np.array([[0, -k[2], k[1]], [k[2], 0, -k[0]], [-k[1], k[0], 0]])
+            R_axis = np.eye(3) + np.sin(angle_rad) * K + (1 - np.cos(angle_rad)) * (K @ K)
+            preview_rot = R_axis @ base_rot
+
+            # Apply offset (with flip).
+            flip_sign = -1.0 if flip else 1.0
+            preview_pos = base_pos + flip_sign * target_normal * off
+
+            second_ac.position = preview_pos
+            second_ac.rotation = preview_rot
+            self._show_assembly_in_viewer()  # no fit — keep camera steady
 
         rotation_spin.valueChanged.connect(_update_preview)
         offset_spin.valueChanged.connect(_update_preview)
@@ -5370,15 +5878,9 @@ class MainWindow(QMainWindow):
         ok_btn.clicked.connect(dialog.accept)
         cancel_btn.clicked.connect(dialog.reject)
 
-        def _on_dialog_close():
-            nonlocal dialog
-            if dialog.result() != QDialog.DialogCode.Accepted:
-                # User cancelled — no changes applied, caller will restore.
-                pass
-
         if dialog.exec():
-            return (rotation_spin.value(), offset_spin.value())
-        return (None, None)
+            return (rotation_spin.value(), offset_spin.value(), flip_check.isChecked())
+        return (None, None, False)
 
     def _on_delete_connector(self):
         """Delete the connector nearest to the selected assembly component."""
@@ -5406,6 +5908,27 @@ class MainWindow(QMainWindow):
         if ok and label:
             idx = conn_labels.index(label)
             conn_id = conn_names[idx]
+            conn = ac.connectors.get(conn_id)
+            # Un-partner the mate and drop the rigid-group edge so stale
+            # connections don't linger in the BFS graph.
+            if conn is not None:
+                partner_ac_id = conn.partner_ac_id
+                partner_conn_id = conn.partner_connector_id
+                if partner_ac_id is not None and partner_conn_id is not None:
+                    partner_ac = assembly.components.get(partner_ac_id)
+                    if partner_ac is not None and partner_conn_id in partner_ac.connectors:
+                        pc = partner_ac.connectors[partner_conn_id]
+                        pc.partner_ac_id = None
+                        pc.partner_connector_id = None
+                        pc.is_grounded = False
+                # Remove the connection edge either side references this pair.
+                assembly.connections = [
+                    c for c in assembly.connections
+                    if not (
+                        (c.first_ac_id == active_id and c.second_ac_id == partner_ac_id)
+                        or (c.first_ac_id == partner_ac_id and c.second_ac_id == active_id)
+                    )
+                ] if partner_ac_id is not None else assembly.connections
             ac.remove_connector(conn_id)
             logger.info(f"Removed connector {conn_id}")
             self._show_assembly_in_viewer(fit=True)
diff --git a/src/fluency/models/data_model.py b/src/fluency/models/data_model.py
index 60749db..1a0a418 100644
--- a/src/fluency/models/data_model.py
+++ b/src/fluency/models/data_model.py
@@ -368,8 +368,16 @@ class Connector:
     # Which body/face this connector was placed on (renderer obj_id).
     source_obj_id: str = ""
 
-    # Future: connected to another Connector's id.
-    # connected_to: Optional[str] = None
+    # --- Rigid-group pairing (set when two connectors are mated) ---
+    # The id of the partner AssemblyComponent this connector is mated to.
+    # The FIRST-picked component is the grounded reference of the pair;
+    # 'is_grounded' marks that side so the move handler knows which half
+    # is the fixed frame of the rigid group.
+    partner_ac_id: Optional[str] = None
+    # The id of the partner Connector on the partner component.
+    partner_connector_id: Optional[str] = None
+    # True on the first-picked (grounded) connector of a mated pair.
+    is_grounded: bool = False
 
     created_at: datetime = field(default_factory=datetime.now)
     modified_at: datetime = field(default_factory=datetime.now)
@@ -430,6 +438,25 @@ class AssemblyComponent:
         return False
 
 
+@dataclass
+class AssemblyConnection:
+    """A mated connector pair linking two AssemblyComponents.
+
+    Records which component is the grounded reference (``first_ac_id``) and
+    which was solved against it (``second_ac_id``), plus the partner
+    connector ids so the linkage can be followed / removed symmetrically.
+    Used by the assembly-move handler to propagate translations across the
+    rigid group.
+    """
+
+    id: str = field(default_factory=lambda: str(uuid.uuid4()))
+    first_ac_id: str = ""    # grounded reference side
+    second_ac_id: str = ""   # solved side
+    first_connector_id: Optional[str] = None
+    second_connector_id: Optional[str] = None
+    created_at: datetime = field(default_factory=datetime.now)
+
+
 @dataclass
 class Assembly:
     """
@@ -447,9 +474,66 @@ class Assembly:
     components: Dict[str, AssemblyComponent] = field(default_factory=dict)
     active_assembly_component: Optional[str] = None
 
+    # Mated connector pairs — each entry links two AssemblyComponents so the
+    # assembly-move handler can propagate rigid-group translations.  The
+    # 'first_ac_id' side is the grounded reference of the pair.
+    connections: List["AssemblyConnection"] = field(default_factory=list)
+
     created_at: datetime = field(default_factory=datetime.now)
     modified_at: datetime = field(default_factory=datetime.now)
 
+    def add_connection(self, first_ac_id: str, second_ac_id: str) -> "AssemblyConnection":
+        """Record a mated connector pair between two component instances.
+
+        The first-picked component (``first_ac_id``) is treated as the
+        grounded reference of the pair.  Returns the AssemblyConnection for
+        further bookkeeping (e.g. attaching partner connector ids).
+        """
+        conn = AssemblyConnection(
+            first_ac_id=first_ac_id,
+            second_ac_id=second_ac_id,
+        )
+        self.connections.append(conn)
+        self.modified_at = datetime.now()
+        return conn
+
+    def remove_connections_for(self, ac_id: str) -> None:
+        """Drop every connection that involves *ac_id* (e.g. on removal)."""
+        self.connections = [
+            c for c in self.connections
+            if c.first_ac_id != ac_id and c.second_ac_id != ac_id
+        ]
+
+    def get_rigid_group(self, ac_id: str) -> List[str]:
+        """Return ids of all components rigidly linked to *ac_id* (BFS).
+
+        Includes *ac_id* itself.  Two components are linked when a mated
+        connector pair (in ``connections``) joins them; linkage is
+        transitive, so the whole connected subgraph forms one rigid group.
+        """
+        if ac_id not in self.components:
+            return []
+        # Build adjacency from the connection list.
+        adj: Dict[str, List[str]] = {}
+        for c in self.connections:
+            adj.setdefault(c.first_ac_id, []).append(c.second_ac_id)
+            adj.setdefault(c.second_ac_id, []).append(c.first_ac_id)
+        seen: List[str] = []
+        queue: List[str] = [ac_id]
+        while queue:
+            cur = queue.pop(0)
+            if cur in seen:
+                continue
+            seen.append(cur)
+            for nb in adj.get(cur, []):
+                if nb not in seen:
+                    queue.append(nb)
+        return seen
+
+    def is_grounded_reference(self, ac_id: str) -> bool:
+        """True if *ac_id* is the grounded (first-picked) side of any pair."""
+        return any(c.first_ac_id == ac_id for c in self.connections)
+
     def add_component_instance(
         self, component_id: str, name: Optional[str] = None
     ) -> AssemblyComponent:
@@ -472,6 +556,10 @@ class Assembly:
         """Remove a component instance from the assembly."""
         if assembly_component_id in self.components:
             del self.components[assembly_component_id]
+            # Also drop any mated-connector links that referenced this
+            # instance — otherwise stale connection edges would remain in
+            # the rigid-group graph and point at a missing component.
+            self.remove_connections_for(assembly_component_id)
             if self.active_assembly_component == assembly_component_id:
                 self.active_assembly_component = next(
                     iter(self.components.keys()), None
diff --git a/src/fluency/rendering/occ_renderer.py b/src/fluency/rendering/occ_renderer.py
index 84ffbc8..0e48a3e 100644
--- a/src/fluency/rendering/occ_renderer.py
+++ b/src/fluency/rendering/occ_renderer.py
@@ -48,6 +48,9 @@ class OCCRenderer(Renderer):
         self._highlight_ais: Any = None
         # Temporary transparent preview AIS for the live extrude/cut dialog.
         self._preview_ais: Any = None
+        # Smart entity picker gizmo objects (snap markers, axis lines, rings).
+        # Keyed by a synthetic id; values are raw AIS_InteractiveObject.
+        self._gizmo_objects: Dict[str, Any] = {}
 
     def initialize(self, parent_widget: Any) -> bool:
         """Initialise OCC viewer inside *parent_widget* (a QWidget)."""
@@ -251,16 +254,22 @@ class OCCRenderer(Renderer):
             logger.debug("polygon offset unavailable", exc_info=True)
 
         self._context.Display(ais, True)
-        # Activate selection modes so the viewer can detect/pick the whole
-        # shape (mode 0) and individual faces (mode for TopAbs_FACE) — needed
-        # for sketch-on-surface face picking.  Left-click orbits the camera
-        # (see handle_mouse_press), so active selection doesn't interfere.
+        # Activate selection modes so the viewer can detect/pick individual
+        # faces, edges and vertices.  Required for the smart entity picker
+        # gizmo (assembly connector picks) AND for sketch-on-surface face
+        # picking.  OCC assigns higher detection priority to vertices, then
+        # edges, then faces — so hovering near an edge/vertex picks the
+        # edge/vertex rather than the underlying face, which is what we want
+        # for snapping.  Left-click still orbits the camera (see
+        # handle_mouse_press); active selection is only consumed by the
+        # explicit pick methods (pick_entity / pick_planar_face).
         try:
-            from OCP.TopAbs import TopAbs_FACE
-            face_mode = AIS_Shape.SelectionMode_s(TopAbs_FACE)
-            self._context.Activate(ais, face_mode)
+            from OCP.TopAbs import TopAbs_FACE, TopAbs_EDGE, TopAbs_VERTEX
+            for topo in (TopAbs_VERTEX, TopAbs_EDGE, TopAbs_FACE):
+                mode = AIS_Shape.SelectionMode_s(topo)
+                self._context.Activate(ais, mode)
         except Exception:
-            logger.debug("face selection mode activation failed", exc_info=True)
+            logger.debug("selection mode activation failed", exc_info=True)
 
         defcol = color or (0.5, 0.5, 0.5)
         robj = OCCRenderObject(
@@ -467,7 +476,9 @@ class OCCRenderer(Renderer):
         self._context.Display(ais, True)
         self._preview_ais = ais
         if self._view is not None:
-            self._view.Repaint()
+            # OCC's V3d_View exposes ``Redraw`` (not ``Repaint``); calling
+            # the wrong name crashed the live extrude-cut preview callback.
+            self._view.Redraw()
 
     def clear_preview(self) -> None:
         """Remove the live extrude preview shape."""
@@ -484,6 +495,7 @@ class OCCRenderer(Renderer):
             return
         self.clear_preview()
         self.clear_face_highlight()
+        self.clear_entity_gizmo()
         # Remove every displayed AIS object. ``RemoveAll`` is the cleanest
         # path; fall back to iterating the displayed list if unavailable.
         try:
@@ -1007,6 +1019,598 @@ class OCCRenderer(Renderer):
             logger.debug("clear_face_highlight remove failed", exc_info=True)
         self._highlight_ais = None
 
+    # ─── General entity picking (for assembly connectors / snaps) ───────────
+
+    def pick_entity(self, x: int, y: int) -> Optional[Dict[str, Any]]:
+        """Pick the entity under screen pixel (x, y).
+
+        Returns a dict describing the detected geometry:
+
+        * ``type`` — one of ``planar_face``, ``cylindrical_face``,
+          ``edge``, ``vertex``.
+        * ``position`` — 3D point (face origin / edge midpoint / vertex).
+        * ``normal`` — direction vector (face normal / cylinder axis /
+          edge tangent / ``None`` for vertex).
+        * ``x_dir`` — stable in-plane reference direction.
+        * ``face`` / ``edge`` / ``vertex`` — the raw OCC sub-shape.
+        * ``owner_obj_id`` — the displayed body this belongs to.
+
+        Returns *None* if nothing detectable is under the cursor.
+        """
+        if self._view is None or self._context is None:
+            return None
+
+        self._context.MoveTo(x, y, self._view, True)
+        if not self._context.HasDetected():
+            return None
+
+        shape = self._context.DetectedShape()
+        if shape is None:
+            return None
+        return self._classify_detected_shape(shape)
+
+    def _classify_detected_shape(
+        self, shape: Any, owner_obj_id: Optional[str] = None,
+    ) -> Optional[Dict[str, Any]]:
+        """Classify a detected OCC sub-shape into a snap-candidate dict.
+
+        Shared by ``pick_entity`` (single-pixel) and ``probe_snap_candidates``
+        (multi-pixel grid probing).  Determines whether *shape* is a planar
+        face, cylindrical face (hole), edge, or vertex and returns the snap
+        info dict with ``position`` / ``normal`` / ``x_dir`` / ``type`` /
+        ``owner_obj_id`` (+ ``radius`` for holes).  When *owner_obj_id* is
+        omitted it is looked up from the context's currently-detected AIS.
+        """
+        if shape is None:
+            return None
+
+        from OCP.TopoDS import TopoDS_Face, TopoDS_Edge, TopoDS_Vertex, TopoDS
+        from OCP.TopAbs import TopAbs_FACE, TopAbs_EDGE, TopAbs_VERTEX
+        from OCP.BRepAdaptor import BRepAdaptor_Surface, BRepAdaptor_Curve
+        from OCP.GeomAbs import GeomAbs_Plane, GeomAbs_Cylinder
+        from OCP.BRep import BRep_Tool
+        from OCP.TopExp import TopExp_Explorer
+        from OCP.TopAbs import TopAbs_EDGE as TopAbs_EDGE_TYPE
+        from OCP.gp import gp_Pnt, gp_Dir
+        from OCP.Bnd import Bnd_Box
+        from OCP.BRepBndLib import BRepBndLib
+        from OCP.TopExp import TopExp
+        import numpy as np
+
+        # Helper: find owner object id if not supplied.
+        if owner_obj_id is None:
+            owner_obj_id = ""
+            try:
+                owner_ais = self._context.DetectedInteractive()
+            except Exception:
+                owner_ais = None
+            if owner_ais is not None:
+                for oid, robj in self._objects.items():
+                    if robj.ais_shape is owner_ais:
+                        owner_obj_id = oid
+                        break
+
+        # Try face first.
+        face = None
+        try:
+            face = TopoDS.Face_s(shape)
+            _ = BRepAdaptor_Surface(face)
+        except Exception:
+            face = None
+
+        if face is not None:
+            adaptor = BRepAdaptor_Surface(face)
+            stype = adaptor.GetType()
+
+            if stype == GeomAbs_Plane:
+                pln = adaptor.Plane()
+                n = pln.Axis().Direction()
+                from OCP.TopAbs import TopAbs_REVERSED
+                if face.Orientation() == TopAbs_REVERSED:
+                    n = n.Reversed()
+                nx, ny, nz = n.X(), n.Y(), n.Z()
+
+                # Center of face bbox projected onto plane.
+                bbox = Bnd_Box()
+                BRepBndLib.Add_s(face, bbox)
+                xmin, ymin, zmin, xmax, ymax, zmax = bbox.Get()
+                cx, cy, cz = (xmin + xmax) / 2.0, (ymin + ymax) / 2.0, (zmin + zmax) / 2.0
+                pln_origin = pln.Location()
+                d = (cx - pln_origin.X()) * nx + (cy - pln_origin.Y()) * ny + (cz - pln_origin.Z()) * nz
+                origin = (cx - d * nx, cy - d * ny, cz - d * nz)
+
+                # x_dir from first edge.
+                x_dir = None
+                try:
+                    expl = TopExp_Explorer(face, TopAbs_EDGE_TYPE)
+                    if expl.More():
+                        edge = TopoDS.Edge_s(expl.Current())
+                        v1 = TopExp.FirstVertex_s(edge, True)
+                        v2 = TopExp.LastVertex_s(edge, True)
+                        p1 = BRep_Tool.Pnt_s(v1)
+                        p2 = BRep_Tool.Pnt_s(v2)
+                        ex, ey, ez = p2.X() - p1.X(), p2.Y() - p1.Y(), p2.Z() - p1.Z()
+                        elen = (ex * ex + ey * ey + ez * ez) ** 0.5
+                        if elen > 1e-9:
+                            x_dir = (ex / elen, ey / elen, ez / elen)
+                except Exception:
+                    pass
+                if x_dir is None:
+                    px = pln.XAxis().Direction()
+                    x_dir = (px.X(), px.Y(), px.Z())
+
+                return {
+                    "type": "planar_face",
+                    "position": origin,
+                    "normal": (nx, ny, nz),
+                    "x_dir": x_dir,
+                    "face": face,
+                    "owner_obj_id": owner_obj_id,
+                }
+
+            elif stype == GeomAbs_Cylinder:
+                cyl = adaptor.Cylinder()
+                axis = cyl.Axis()
+                ax_dir = axis.Direction()
+                ax_pos = axis.Location()
+                radius = cyl.Radius()
+
+                # Parameter extents along the cylinder axis (v = height).
+                # BRepAdaptor_Surface exposes these via First/Last V
+                # *Parameter() — NOT a Bounds() method (that quirk crashed
+                # cylindrical-face picking).
+                vmin = adaptor.FirstVParameter()
+                vmax = adaptor.LastVParameter()
+
+                # Two candidate snap points: the centers of the cylinder's
+                # two end circles (the hole openings).  A bolt enters a
+                # hole from the camera-facing opening, so pick the END of
+                # the axis closest to the camera as the primary snap point.
+                # The axis location (ax_pos) is already on the cylinder axis
+                # at v=0; the other end is at v=vmax.
+                p0 = np.array([
+                    ax_pos.X(), ax_pos.Y(), ax_pos.Z(),
+                ], dtype=float)
+                p1 = np.array([
+                    ax_pos.X() + ax_dir.X() * (vmax - vmin),
+                    ax_pos.Y() + ax_dir.Y() * (vmax - vmin),
+                    ax_pos.Z() + ax_dir.Z() * (vmax - vmin),
+                ], dtype=float)
+
+                # Choose the camera-facing end.  The camera looks FROM its
+                # eye TOWARD its target, so the camera direction is
+                # (target - eye).  The end whose vector-from-camera is MOST
+                # OPPOSITE to (i.e. faces) the camera is the near opening.
+                cam_from = None
+                try:
+                    if self._view is not None:
+                        eye = self._view.Eye()
+                        at = self._view.At()
+                        cam_from = np.array([eye.X(), eye.Y(), eye.Z()], dtype=float)
+                        cam_to = np.array([at.X(), at.Y(), at.Z()], dtype=float)
+                except Exception:
+                    cam_from = None
+
+                if cam_from is not None:
+                    # End closest to the camera eye is the visible opening.
+                    d0 = float(np.linalg.norm(p0 - cam_from))
+                    d1 = float(np.linalg.norm(p1 - cam_from))
+                    near_end = p0 if d0 <= d1 else p1
+                else:
+                    # Fallback: axial midpoint.
+                    near_end = 0.5 * (p0 + p1)
+
+                origin = (float(near_end[0]), float(near_end[1]), float(near_end[2]))
+                # Normal = the cylinder axis direction.  This is the "bolt
+                # axis": the direction a bolt would travel INTO the hole.
+                # (Sign is the cylinder's own axis direction; a later flip can
+                # reverse it via the connector dialog's Flip checkbox.)
+                normal = (ax_dir.X(), ax_dir.Y(), ax_dir.Z())
+
+                # x_dir: radial direction from the axis center to the hole
+                # wall — gives a stable in-plane reference for the connector
+                # frame.  Use the cylinder's own XDirection if available.
+                try:
+                    px = cyl.Position().XDirection()
+                    x_dir = (px.X(), px.Y(), px.Z())
+                except Exception:
+                    x_dir = (1.0, 0.0, 0.0)
+
+                return {
+                    "type": "cylindrical_face",
+                    "position": origin,
+                    "normal": normal,
+                    "x_dir": x_dir,
+                    "face": face,
+                    "owner_obj_id": owner_obj_id,
+                    "radius": radius,
+                }
+
+        # Try edge.
+        edge = None
+        try:
+            edge = TopoDS.Edge_s(shape)
+            _ = BRepAdaptor_Curve(edge)
+        except Exception:
+            edge = None
+
+        if edge is not None:
+            curve = BRepAdaptor_Curve(edge)
+            # Midpoint parameter.
+            ufirst = curve.FirstParameter()
+            ulast = curve.LastParameter()
+            umid = (ufirst + ulast) / 2.0
+            p_mid = curve.Value(umid)
+            position = (p_mid.X(), p_mid.Y(), p_mid.Z())
+
+            # Tangent at midpoint.
+            try:
+                tangent = curve.DN(umid, 1)
+                tx, ty, tz = tangent.X(), tangent.Y(), tangent.Z()
+                tlen = (tx * tx + ty * ty + tz * tz) ** 0.5
+                if tlen > 1e-9:
+                    tangent = (tx / tlen, ty / tlen, tz / tlen)
+                else:
+                    tangent = None
+            except Exception:
+                tangent = None
+
+            # x_dir: perpendicular to tangent (arbitrary but stable).
+            x_dir = None
+            if tangent is not None:
+                t = np.array(tangent)
+                # Find a vector not parallel to t.
+                ref = np.array([1.0, 0.0, 0.0]) if abs(t[0]) < 0.9 else np.array([0.0, 1.0, 0.0])
+                x = np.cross(t, ref)
+                xlen = np.linalg.norm(x)
+                if xlen > 1e-9:
+                    x = x / xlen
+                    x_dir = (float(x[0]), float(x[1]), float(x[2]))
+
+            return {
+                "type": "edge",
+                "position": position,
+                "normal": tangent,
+                "x_dir": x_dir,
+                "edge": edge,
+                "owner_obj_id": owner_obj_id,
+            }
+
+        # Try vertex.
+        vertex = None
+        try:
+            vertex = TopoDS.Vertex_s(shape)
+            p = BRep_Tool.Pnt_s(vertex)
+            position = (p.X(), p.Y(), p.Z())
+            return {
+                "type": "vertex",
+                "position": position,
+                "normal": None,
+                "x_dir": None,
+                "vertex": vertex,
+                "owner_obj_id": owner_obj_id,
+            }
+        except Exception:
+            pass
+
+        return None
+
+    def _project_to_screen(self, p3d: Tuple[float, float, float]) -> Optional[Tuple[int, int]]:
+        """Project a 3D world point to (x, y) screen pixel.
+
+        Uses OCC's ``V3d_View.Convert`` (world → view coords).  Returns None
+        if the projection fails (e.g. behind the camera).
+        """
+        if self._view is None:
+            return None
+        try:
+            # OCC's Convert returns the window pixel coordinates.
+            xpix = self._view.Convert(float(p3d[0]), float(p3d[1]), float(p3d[2]))
+            # Some OCP builds return a tuple (x, y); others return two values.
+            if isinstance(xpix, (tuple, list)) and len(xpix) == 2:
+                return (int(xpix[0]), int(xpix[1]))
+            return None
+        except Exception:
+            # Fall back to ConvertWithProj or ProjTexte if Convert is unavailable.
+            return None
+
+    def probe_snap_candidates(
+        self, x: int, y: int, radius: int = 18,
+    ) -> List[Dict[str, Any]]:
+        """Probe a pixel grid around (x, y) and return visible snap candidates.
+
+        Samples a small ring + centre around the cursor, runs OCC's
+        ``MoveTo`` at each pixel, and classifies every distinct detected
+        sub-shape via :meth:`_classify_detected_shape`.  Results are
+        deduplicated by (owner_obj_id, type, rounded position) and sorted by
+        screen-space distance to the cursor, nearest first.
+
+        This is the general hover snap indicator: it surfaces nearby
+        vertices, edge midpoints, hole centres, and face centres so the
+        user can see the snap targets in the cursor neighbourhood — not
+        just the single entity directly under the crosshair.
+
+        Each entry is the same dict shape returned by ``pick_entity`` plus an
+        extra ``screen`` key carrying the (sx, sy) pixel where the entity was
+        first detected.
+        """
+        if self._view is None or self._context is None:
+            return []
+
+        # Sample pattern: the exact cursor pixel plus a small ring of
+        # offsets.  The ring catches nearby vertices/edges/holes that sit a
+        # few pixels away from where the user is pointing.
+        ring_offsets = [
+            (0, 0),
+            (-radius, 0), (radius, 0), (0, -radius), (0, radius),
+            (-radius, -radius), (radius, radius), (-radius, radius), (radius, -radius),
+            (-radius // 2, 0), (radius // 2, 0), (0, -radius // 2), (0, radius // 2),
+        ]
+
+        candidates: Dict[Tuple[str, str, Tuple[int, int, int]], Dict[str, Any]] = {}
+        for dx, dy in ring_offsets:
+            sx, sy = x + dx, y + dy
+            try:
+                self._context.MoveTo(sx, sy, self._view, True)
+            except Exception:
+                continue
+            if not self._context.HasDetected():
+                continue
+            shape = self._context.DetectedShape()
+            if shape is None:
+                continue
+            info = self._classify_detected_shape(shape)
+            if info is None:
+                continue
+            # Skip non-trackable hits (no owner — e.g. the workplane plane).
+            if not info.get("owner_obj_id"):
+                continue
+            pos = info.get("position") or (0.0, 0.0, 0.0)
+            # Dedupe key: owner + type + position rounded to 0.1 mm.
+            key = (
+                info.get("owner_obj_id", ""),
+                info.get("type", ""),
+                (round(pos[0], 1), round(pos[1], 1), round(pos[2], 1)),
+            )
+            if key not in candidates:
+                info["screen"] = (sx, sy)
+                candidates[key] = info
+
+        # Sort by screen-space distance to the cursor, nearest first.
+        results = list(candidates.values())
+        results.sort(key=lambda c: (c.get("screen", (x, y))[0] - x) ** 2 + (c.get("screen", (x, y))[1] - y) ** 2)
+        return results
+
+    def highlight_snap(self, position, color=None, size=3.0) -> Optional[str]:
+        """Show a small marker sphere at *position* as a snap indicator.
+
+        Returns an object id that can be removed later.
+        """
+        if self._context is None:
+            return None
+        from OCP.BRepPrimAPI import BRepPrimAPI_MakeSphere
+        from OCP.gp import gp_Pnt
+        from OCP.AIS import AIS_Shape
+        from OCP.Quantity import Quantity_Color, Quantity_TOC_RGB
+        try:
+            sphere = BRepPrimAPI_MakeSphere(gp_Pnt(*position), size).Shape()
+            ais = AIS_Shape(sphere)
+            c = color or (1.0, 0.6, 0.0)  # orange
+            ais.SetColor(Quantity_Color(c[0], c[1], c[2], Quantity_TOC_RGB))
+            ais.SetDisplayMode(1)
+            self._context.Display(ais, True)
+            if self._view is not None:
+                self._view.Update()
+            # Track this as a temporary object; use a synthetic id.
+            oid = f"__snap_{id(ais)}"
+            self._objects[oid] = _RenderObject(oid, ais, None, None)
+            return oid
+        except Exception as exc:
+            logger.debug(f"highlight_snap failed: {exc}")
+            return None
+
+    def remove_highlight_snap(self, obj_id: str) -> None:
+        """Remove a snap marker by its id."""
+        if obj_id in self._objects:
+            robj = self._objects.pop(obj_id)
+            if self._context is not None and robj.ais_shape is not None:
+                try:
+                    self._context.Remove(robj.ais_shape, True)
+                    if self._view is not None:
+                        self._view.Update()
+                except Exception:
+                    pass
+
+    # ─── Smart Entity Picker Gizmo ─────────────────────────────────────────
+
+    def clear_entity_gizmo(self) -> None:
+        """Remove all gizmo display objects (markers, axes, highlights)."""
+        had_any = bool(self._gizmo_objects)
+        for obj_id in list(self._gizmo_objects.keys()):
+            robj = self._gizmo_objects.pop(obj_id)
+            if self._context is not None and robj is not None:
+                try:
+                    self._context.Remove(robj, True)
+                except Exception:
+                    pass
+        if had_any and self._view is not None:
+            self._view.Update()
+
+    def show_entity_gizmo(
+        self,
+        entity_type: str,
+        position: Tuple[float, float, float],
+        normal: Optional[Tuple[float, float, float]] = None,
+        x_dir: Optional[Tuple[float, float, float]] = None,
+        color: Optional[Tuple[float, float, float]] = None,
+        radius: Optional[float] = None,
+        candidates: Optional[List[Dict[str, Any]]] = None,
+    ) -> None:
+        """Display a smart snap gizmo for the given entity type.
+
+        Renders a composite visual appropriate to the entity type:
+        * **planar_face**       — sphere at pick point + white normal axis + x_dir axis
+        * **cylindrical_face** — sphere at the camera-facing hole opening +
+          white bolt-axis line through the hole (the snap 'normal' points
+          along the hole like a bolt) + a ring of the hole radius at the
+          opening + a small radial reference line.
+        * **edge**              — sphere at edge midpoint + tangent axis line
+        * **vertex**            — sphere + RGB crosshair
+
+        When *candidates* is provided, every candidate is ALSO rendered with a
+        small DIM half-size sphere in its own per-type colour, while the
+        primary (this method's *position*/*entity_type*) is emphasised with a
+        larger bright sphere + axis indicators.  This is the general hover
+        snap indicator: it shows all snap targets in the cursor neighbourhood
+        (vertices, edge midpoints, face centres, hole openings) so the user
+        can see what they can snap to — click then selects the primary.
+
+        All previously shown gizmo objects are removed first so the gizmo
+        follows the cursor cleanly.
+        """
+        if self._context is None:
+            return
+        self.clear_entity_gizmo()
+
+        from OCP.gp import gp_Pnt, gp_Dir, gp_Ax2, gp_Circ
+        from OCP.BRepBuilderAPI import BRepBuilderAPI_MakeEdge
+        from OCP.AIS import AIS_Shape
+        from OCP.Quantity import Quantity_Color, Quantity_TOC_RGB
+        from OCP.BRepPrimAPI import BRepPrimAPI_MakeSphere
+
+        # Per-entity-type colours (shared by the dim candidate markers).
+        default_colors = {
+            "planar_face": (0.0, 0.8, 1.0),       # cyan
+            "cylindrical_face": (1.0, 0.5, 0.0),   # orange (hole / bolt axis)
+            "edge": (0.2, 1.0, 0.4),                # green
+            "vertex": (1.0, 1.0, 0.0),              # yellow
+        }
+        gizmo_color = color or default_colors.get(entity_type, (1.0, 0.6, 0.0))
+
+        def _make_sphere(p, c, size):
+            try:
+                s = BRepPrimAPI_MakeSphere(gp_Pnt(*p), size).Shape()
+                a = AIS_Shape(s)
+                a.SetColor(Quantity_Color(*c, Quantity_TOC_RGB))
+                a.SetDisplayMode(1)
+                self._context.Display(a, True)
+                self._gizmo_objects[f"__gizmo_sphere_{id(a)}"] = a
+            except Exception as exc:
+                logger.debug(f"gizmo sphere failed: {exc}")
+
+        px, py, pz = position
+
+        # ── 0. Dim candidate markers (every nearby snap target) ──
+        #
+        # Drawn FIRST so the bright primary sphere renders on top of them.
+        # Each candidate gets a small half-size sphere tinted by its own
+        # entity-type colour; the primary (this method's position) is drawn
+        # brighter & larger in step 1 below so it reads as the active snap.
+        if candidates:
+            for cand in candidates:
+                cpos = cand.get("position")
+                if cpos is None:
+                    continue
+                # Skip the primary itself — it gets its own bright marker.
+                if (round(cpos[0], 1), round(cpos[1], 1), round(cpos[2], 1)) == (
+                    round(px, 1), round(py, 1), round(pz, 1)
+                ):
+                    continue
+                cc = default_colors.get(cand.get("type", ""), (0.7, 0.7, 0.7))
+                _make_sphere(cpos, cc, 1.4)  # dim, small
+
+        # ── 1. Bright primary marker (sphere) ──
+        _make_sphere(position, gizmo_color, 2.8)
+
+        # ── 2. Axis indicator lines (primary only) ──
+        axis_length = 15.0
+
+        def _make_axis_line(
+            origin: Tuple[float, float, float],
+            direction: Tuple[float, float, float],
+            length: float,
+            line_color: Tuple[float, float, float],
+            label: str = "axis",
+        ) -> Optional[str]:
+            """Create a small line segment along *direction* from *origin*."""
+            try:
+                dx, dy, dz = direction
+                norm = (dx * dx + dy * dy + dz * dz) ** 0.5
+                if norm < 1e-9:
+                    return None
+                ux, uy, uz = dx / norm, dy / norm, dz / norm
+                ex = origin[0] + ux * length
+                ey = origin[1] + uy * length
+                ez = origin[2] + uz * length
+
+                edge = BRepBuilderAPI_MakeEdge(
+                    gp_Pnt(*origin), gp_Pnt(ex, ey, ez)
+                ).Edge()
+                ais = AIS_Shape(edge)
+                ais.SetColor(Quantity_Color(*line_color, Quantity_TOC_RGB))
+                ais.SetDisplayMode(0)  # wireframe
+                self._context.Display(ais, True)
+                gid = f"__gizmo_{label}_{id(ais)}"
+                self._gizmo_objects[gid] = ais
+                return gid
+            except Exception as exc:
+                logger.debug(f"gizmo axis line failed: {exc}")
+                return None
+
+        if entity_type == "planar_face" and normal is not None:
+            # Normal axis (white).
+            _make_axis_line(position, normal, axis_length, (1.0, 1.0, 1.0), "normal")
+            # X direction axis (slightly dimmer).
+            if x_dir is not None:
+                _make_axis_line(position, x_dir, axis_length * 0.6, gizmo_color, "xdir")
+
+        elif entity_type == "cylindrical_face" and normal is not None:
+            # Hole / bolt axis.  The snap point is the camera-facing opening,
+            # so draw the axis going INTO the hole (the +normal direction —
+            # the bolt travel direction) plus a short stub the other way for
+            # visual balance.  This reads as 'bolt axis through hole'.
+            _make_axis_line(position, normal, axis_length * 1.4, (1.0, 1.0, 1.0), "axis_in")
+            _make_axis_line(
+                position, (-normal[0], -normal[1], -normal[2]),
+                axis_length * 0.4, (0.6, 0.6, 0.6), "axis_stub",
+            )
+            # Radial reference (same colour as the marker).
+            if x_dir is not None:
+                _make_axis_line(position, x_dir, radius or (axis_length * 0.5), gizmo_color, "radial")
+
+        elif entity_type == "edge" and normal is not None:
+            # Tangent direction at midpoint.
+            _make_axis_line(position, normal, axis_length, gizmo_color, "tangent")
+
+        elif entity_type == "vertex":
+            # Small crosshair (three short axes) so a vertex snap reads as
+            # a coordinate point even before clicking.
+            _make_axis_line(position, (1, 0, 0), axis_length * 0.5, (1.0, 0.3, 0.3), "cross_x")
+            _make_axis_line(position, (0, 1, 0), axis_length * 0.5, (0.3, 1.0, 0.3), "cross_y")
+            _make_axis_line(position, (0, 0, 1), axis_length * 0.5, (0.3, 0.3, 1.0), "cross_z")
+
+        # ── 3. For cylindrical faces, ring of the hole radius at the opening ──
+        #
+        # Drawn at the camera-facing opening (the snap point), so the user
+        # sees the actual hole diameter they're snapping a bolt to.
+        if entity_type == "cylindrical_face" and normal is not None and radius is not None:
+            try:
+                center = gp_Pnt(px, py, pz)
+                ax2 = gp_Ax2(center, gp_Dir(*normal))
+                circ = gp_Circ(ax2, radius)
+                ring_edge = BRepBuilderAPI_MakeEdge(circ).Edge()
+                ring_ais = AIS_Shape(ring_edge)
+                ring_ais.SetColor(Quantity_Color(*gizmo_color, Quantity_TOC_RGB))
+                ring_ais.SetDisplayMode(0)  # wireframe
+                self._context.Display(ring_ais, True)
+                gid = f"__gizmo_ring_{id(ring_ais)}"
+                self._gizmo_objects[gid] = ring_ais
+            except Exception as exc:
+                logger.debug(f"gizmo ring failed: {exc}")
+
+        if self._view is not None:
+            self._view.Update()
+
     # ─── Mouse / keyboard event forwarding ──────────────────────────────
     #
     # CAD-style navigation: