- added contrain context menu

- improved line pickability.

src/fluency/ui/sketch_widget.py

@@ -6,11 +6,10 @@ import logging
 import math
 from typing import Any, Dict, List, Optional, Tuple
 
-from PySide6.QtCore import Qt, Signal, Slot, QPoint, QPointF, QSize, QRect
+from PySide6.QtCore import Qt, Signal, QPoint, QPointF, QRect
 from PySide6.QtGui import (
     QBrush,
     QColor,
-    QCursor,
     QFont,
     QFontMetrics,
     QPainter,
@@ -20,6 +19,8 @@ from PySide6.QtGui import (
 )
 from PySide6.QtWidgets import (
     QInputDialog,
+    QMenu,
+    QMessageBox,
     QWidget,
 )
 
@@ -31,7 +32,9 @@ logger = logging.getLogger(__name__)
 
 def _project_face_to_uv(
     face: Any,
-    workplane: Tuple[Tuple[float, float, float], Tuple[float, float, float], Tuple[float, float, float]],
+    workplane: Tuple[
+        Tuple[float, float, float], Tuple[float, float, float], Tuple[float, float, float]
+    ],
 ) -> List[List[Tuple[float, float]]]:
     """Project a planar ``TopoDS_Face``'s boundary edges into the UV frame.
 
@@ -107,17 +110,25 @@ class Sketch2DWidget(QWidget):
         self._points: List[OCCSketchEntity] = []
         self._lines: List[Tuple[OCCSketchEntity, OCCSketchEntity]] = []
         self._circles: List[Tuple[OCCSketchEntity, float]] = []
-        self._arcs: List[Tuple[OCCSketchEntity, float, OCCSketchEntity, OCCSketchEntity, float]] = []  # (center, radius, start_point, end_point, sweep)
+        self._arcs: List[
+            Tuple[OCCSketchEntity, float, OCCSketchEntity, OCCSketchEntity, float]
+        ] = []  # (center, radius, start_point, end_point, sweep)
         # Accumulated sweep tracking during arc draw (smoothly follows cursor)
         self._arc_accum_sweep: float = 0.0
         self._arc_prev_angle: Optional[float] = None
 
         self._draw_buffer: List[QPoint] = []
         self._hovered_point: Optional[QPoint] = None
-        self._hovered_point_entity: Optional[OCCSketchEntity] = None  # point entity under cursor (for Delete)
+        self._hovered_point_entity: Optional[OCCSketchEntity] = (
+            None  # point entity under cursor (for Delete)
+        )
         self._hovered_line: Optional[Tuple[QPoint, QPoint]] = None
-        self._hovered_line_entity: Optional[OCCSketchEntity] = None  # line entity under cursor (for Delete)
+        self._hovered_line_entity: Optional[OCCSketchEntity] = (
-        self._hovered_constraint_idx: int = -1  # constraint-log index hovered over its tag (for Delete)
+            None  # line entity under cursor (for Delete)
+        )
+        self._hovered_constraint_idx: int = (
+            -1
+        )  # constraint-log index hovered over its tag (for Delete)
         self._constraint_tags: List[Dict[str, Any]] = []  # cached tag rects for paint + hit-test
         self._hovered_face: Any = None  # detected face dict (see OCCSketch.detect_faces) or None
         self._selected_face: Any = None
@@ -254,11 +265,7 @@ class Sketch2DWidget(QWidget):
         # Snapshot the entity list before modifying (add_point adds to
         # _entities, which would change dict size mid-iteration).
         for eid, entity in list(self._sketch._entities.items()):
-            if (
+            if entity.is_external and entity.entity_type == "point" and entity.geometry is not None:
-                entity.is_external
-                and entity.entity_type == "point"
-                and entity.geometry is not None
-            ):
                 x, y = entity.geometry
                 new_pt = self._sketch.add_point(x, y)
                 new_pt.is_construction = False
@@ -379,9 +386,7 @@ class Sketch2DWidget(QWidget):
                 imported += len(lines)
             except Exception as exc:
                 logger.debug("underlay polyline import failed: %s", exc)
-        logger.info(
+        logger.info("Imported %d construction-line segments from source face", imported)
-            "Imported %d construction-line segments from source face", imported
-        )
         # Pull the new external entities into the UI lists so they're
         # snap/hover/paint targets.
         self._rebuild_from_sketch()
@@ -654,6 +659,15 @@ class Sketch2DWidget(QWidget):
             int(self.height() / 2 - pos.y() * self._zoom + self._offset.y()),
         )
 
+    def _pick_tolerance_world(self, min_pixels: float = 10.0) -> float:
+        """Screen-pixel pick tolerance converted to world coordinates.
+
+        Keeps the clickable zone roughly constant in screen space regardless
+        of zoom level.  A small floor (0.5 world units) prevents the
+        tolerance from vanishing when fully zoomed out.
+        """
+        return max(0.5, min_pixels / max(self._zoom, 0.01))
+
     # ─── Snapping ─────────────────────────────────────────────────────────
 
     def _find_nearest_point(self, pos: QPoint, max_distance: int = 15) -> Optional[QPoint]:
@@ -674,7 +688,9 @@ class Sketch2DWidget(QWidget):
                     nearest = point
         return nearest
 
-    def _find_nearest_point_entity(self, pos: QPoint, max_distance: int = 15) -> Optional[OCCSketchEntity]:
+    def _find_nearest_point_entity(
+        self, pos: QPoint, max_distance: int = 15
+    ) -> Optional[OCCSketchEntity]:
         """Find the nearest point entity to a screen position.
 
         External (underlay) points are pickable when the underlay is visible
@@ -877,11 +893,13 @@ class Sketch2DWidget(QWidget):
             if entity.geometry:
                 x, y = entity.geometry
                 dist = math.sqrt((world_pos.x() - x) ** 2 + (world_pos.y() - y) ** 2)
-                if dist < 5:  # tolerance in world coords
+                if dist < self._pick_tolerance_world(10):
                     return entity
         return None
 
-    def _get_line_entity_at(self, world_pos: QPoint) -> Optional[Tuple[OCCSketchEntity, OCCSketchEntity]]:
+    def _get_line_entity_at(
+        self, world_pos: QPoint
+    ) -> Optional[Tuple[OCCSketchEntity, OCCSketchEntity]]:
         """Find a line near the given world position.
 
         External (underlay) lines are pickable when the underlay is visible
@@ -910,15 +928,15 @@ class Sketch2DWidget(QWidget):
                 # Compute perpendicular distance to the infinite line.
                 line_len_sq = dx * dx + dy * dy
                 # Perpendicular distance: |(P - P1) × (P2 - P1)| / |P2 - P1|
-                perp_dist = abs(dx * (y1 - world_pos.y()) - dy * (x1 - world_pos.x())) / math.sqrt(line_len_sq)
+                perp_dist = abs(dx * (y1 - world_pos.y()) - dy * (x1 - world_pos.x())) / math.sqrt(
+                    line_len_sq
+                )
 
                 is_cl = line_ent is not None and self._is_centerline(line_ent)
                 if is_cl:
                     # Centerlines are infinite reference axes: use the
                     # perpendicular distance directly (no segment clamping).
-                    # Zoom-adjusted tolerance: at least 20 pixels in screen space
+                    tol = self._pick_tolerance_world(12)
-                    # so the axes are easily pickable regardless of zoom level.
-                    tol = max(10.0, 20.0 / max(self._zoom, 0.01))
                     if perp_dist < tol:
                         return (p1_ent, p2_ent)
                 else:
@@ -928,8 +946,15 @@ class Sketch2DWidget(QWidget):
                     t = max(0.0, min(1.0, t))
                     proj_x = x1 + t * dx
                     proj_y = y1 + t * dy
-                    seg_dist = math.sqrt((world_pos.x() - proj_x)**2 + (world_pos.y() - proj_y)**2)
+                    seg_dist = math.sqrt(
-                    if seg_dist < 10:  # tolerance
+                        (world_pos.x() - proj_x) ** 2 + (world_pos.y() - proj_y) ** 2
+                    )
+                    # External (underlay) lines get a tighter tolerance so
+                    # they don't steal picks from user-drawn sketch lines.
+                    tol = (
+                        self._pick_tolerance_world(8) if is_ext else self._pick_tolerance_world(14)
+                    )
+                    if seg_dist < tol:
                         return (p1_ent, p2_ent)
         return None
 
@@ -965,7 +990,9 @@ class Sketch2DWidget(QWidget):
                 return self._sketch._entities.get(sid), self._sketch._entities.get(eid2)
         return None, None
 
-    def _find_line_entity_for_line_xy(self, p1_xy: Tuple[float, float], p2_xy: Tuple[float, float]) -> Optional[OCCSketchEntity]:
+    def _find_line_entity_for_line_xy(
+        self, p1_xy: Tuple[float, float], p2_xy: Tuple[float, float]
+    ) -> Optional[OCCSketchEntity]:
         """Find the OCCSketchEntity for a line defined by its endpoint tuples."""
         for eid, start_end in self._sketch._lines.items():
             sid, eid2 = start_end
@@ -974,15 +1001,25 @@ class Sketch2DWidget(QWidget):
             if s_ent and e_ent and s_ent.geometry and e_ent.geometry:
                 sx, sy = s_ent.geometry
                 ex, ey = e_ent.geometry
-                if (abs(sx - p1_xy[0]) < 0.1 and abs(sy - p1_xy[1]) < 0.1 and
+                if (
-                    abs(ex - p2_xy[0]) < 0.1 and abs(ey - p2_xy[1]) < 0.1):
+                    abs(sx - p1_xy[0]) < 0.1
+                    and abs(sy - p1_xy[1]) < 0.1
+                    and abs(ex - p2_xy[0]) < 0.1
+                    and abs(ey - p2_xy[1]) < 0.1
+                ):
                     return s_ent  # Return the line entity reference
-                if (abs(sx - p2_xy[0]) < 0.1 and abs(sy - p2_xy[1]) < 0.1 and
+                if (
-                    abs(ex - p1_xy[0]) < 0.1 and abs(ey - p1_xy[1]) < 0.1):
+                    abs(sx - p2_xy[0]) < 0.1
+                    and abs(sy - p2_xy[1]) < 0.1
+                    and abs(ex - p1_xy[0]) < 0.1
+                    and abs(ey - p1_xy[1]) < 0.1
+                ):
                     return s_ent
         return None
 
-    def _get_constraints_for_line(self, p1_ent: OCCSketchEntity, p2_ent: OCCSketchEntity) -> List[str]:
+    def _get_constraints_for_line(
+        self, p1_ent: OCCSketchEntity, p2_ent: OCCSketchEntity
+    ) -> List[str]:
         """Get constraint labels from both endpoint entities."""
         return list(set(p1_ent.constraints + p2_ent.constraints))
 
@@ -1040,7 +1077,9 @@ class Sketch2DWidget(QWidget):
             # tag is dropped rather than the paint event crashing.
             logger.debug(
                 "_point_world: could not round geometry for entity %s (%r, %r)",
-                pid, x, y,
+                pid,
+                x,
+                y,
             )
             return None
 
@@ -1091,46 +1130,57 @@ class Sketch2DWidget(QWidget):
                 label = ""
 
                 if ctype == "horizontal":
-                    anchor = self._line_world_mid(ids[0]); label = "hrz"
+                    anchor = self._line_world_mid(ids[0])
+                    label = "hrz"
                 elif ctype == "vertical":
-                    anchor = self._line_world_mid(ids[0]); label = "vrt"
+                    anchor = self._line_world_mid(ids[0])
+                    label = "vrt"
                 elif ctype == "midpoint":
-                    anchor = self._line_world_mid(ids[1]); label = "mid"
+                    anchor = self._line_world_mid(ids[1])
+                    label = "mid"
                 elif ctype == "distance":
                     # Distance may be point-to-point OR point-to-line (e.g.
                     # point-on-line coincident surfaces as a coincident entry;
                     # a future point-to-line distance would do the same).
                     # Use _entity_anchor so a line id routes to the line
                     # midpoint instead of crashing on round(<tuple>).
-                    a = self._entity_anchor(ids[0]); b = self._entity_anchor(ids[1])
+                    a = self._entity_anchor(ids[0])
+                    b = self._entity_anchor(ids[1])
                     # 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"
                 elif ctype == "parallel":
-                    anchor = self._line_world_mid(ids[0]); label = "par"
+                    anchor = self._line_world_mid(ids[0])
+                    label = "par"
                 elif ctype == "perpendicular":
-                    anchor = self._line_world_mid(ids[0]); label = "perp"
+                    anchor = self._line_world_mid(ids[0])
+                    label = "perp"
                 elif ctype == "angle":
                     anchor = self._line_world_mid(ids[0])
                     label = f"ang {params[0]:.0f}" if params else "ang"
                 elif ctype == "equal":
-                    anchor = self._line_world_mid(ids[0]); label = "eql"
+                    anchor = self._line_world_mid(ids[0])
+                    label = "eql"
                 elif ctype == "coincident":
                     # Coincident can be point-to-point OR point-on-line (when
                     # a line is one of the targets).  Use _entity_anchor so
                     # the line's midpoint is used as a fallback anchor when
                     # one of the ids is a line.
-                    a = self._entity_anchor(ids[0]); b = self._entity_anchor(ids[1])
+                    a = self._entity_anchor(ids[0])
+                    b = self._entity_anchor(ids[1])
                     if a is not None and b is not None:
                         anchor = QPoint((a.x() + b.x()) // 2, (a.y() + b.y()) // 2)
                     label = "coin"
                 elif ctype == "symmetric":
-                    anchor = self._line_world_mid(ids[2]); label = "sym"
+                    anchor = self._line_world_mid(ids[2])
+                    label = "sym"
                 elif ctype == "fixed":
-                    anchor = self._point_world(ids[0]); label = "fix"
+                    anchor = self._point_world(ids[0])
+                    label = "fix"
                 elif ctype == "equal_radius":
-                    anchor = self._point_world(ids[0]); label = "eqr"
+                    anchor = self._point_world(ids[0])
+                    label = "eqr"
                 else:
                     continue
 
@@ -1157,7 +1207,10 @@ class Sketch2DWidget(QWidget):
                 # other tags as normal.
                 logger.debug(
                     "Skipped constraint tag #%s (%s) due to %s: %s",
-                    idx, entry.get("type"), type(exc).__name__, exc,
+                    idx,
+                    entry.get("type"),
+                    type(exc).__name__,
+                    exc,
                 )
                 continue
         return tags
@@ -1242,7 +1295,7 @@ class Sketch2DWidget(QWidget):
             if c_ent.geometry and r > 0:
                 cx, cy = c_ent.geometry
                 d = math.sqrt((world.x() - cx) ** 2 + (world.y() - cy) ** 2)
-                if abs(d - r) < 8:
+                if abs(d - r) < self._pick_tolerance_world(16):
                     return c_ent, QPoint(int(round(cx)), int(round(cy)))
         return None
 
@@ -1271,6 +1324,162 @@ class Sketch2DWidget(QWidget):
         self.update()
         return ok
 
+    # ─── Context menu: loop detection & constraint presets ─────────────────
+
+    def _find_loop_from_point(self, point_entity: OCCSketchEntity) -> Optional[List[int]]:
+        """Trace a 4-sided closed loop starting from *point_entity*.
+
+        Returns ``[p1_id, l1_id, p2_id, l2_id, p3_id, l3_id, p4_id, l4_id]``
+        (alternating point/line ids, 8 elements for a quadrilateral) if found,
+        otherwise ``None``.
+        """
+        if self._sketch is None:
+            return None
+        start_id = point_entity.id
+        lines = self._sketch._lines  # line_id -> (p1_id, p2_id)
+
+        # Collect all lines touching the start point and the 'other' endpoint.
+        connected: List[Tuple[int, int]] = []
+        for lid, (p1, p2) in lines.items():
+            if p1 == start_id:
+                connected.append((lid, p2))
+            elif p2 == start_id:
+                connected.append((lid, p1))
+
+        if len(connected) < 2:
+            return None
+
+        # DFS from each first edge looking for a 4-edge cycle back to start.
+        for first_lid, second_pid in connected:
+            path: List[int] = [start_id, first_lid, second_pid]
+            if self._trace_loop_recursive(path, lines, start_id, depth=1):
+                # Strip the duplicate start point at the end so the path is
+                # exactly [p1,l1,p2,l2,p3,l3,p4,l4] (8 elements).
+                return path[:-1]
+        return None
+
+    @staticmethod
+    def _trace_loop_recursive(
+        path: List[int],
+        lines: Dict[int, Tuple[int, int]],
+        start_id: int,
+        depth: int,
+    ) -> bool:
+        """Recursively extend *path* looking for a 4-edge cycle.
+
+        ``path`` alternates point-id, line-id, point-id, …
+        Returns ``True`` when a valid 4-edge cycle back to *start_id* is found.
+        """
+        if depth >= 4:
+            return path[-1] == start_id
+
+        current_pid = path[-1]
+        prev_lid = path[-2]
+
+        for lid, (p1, p2) in lines.items():
+            if lid == prev_lid:
+                continue
+            if p1 == current_pid:
+                next_pid = p2
+            elif p2 == current_pid:
+                next_pid = p1
+            else:
+                continue
+
+            path.append(lid)
+            path.append(next_pid)
+            if Sketch2DWidget._trace_loop_recursive(path, lines, start_id, depth + 1):
+                return True
+            path.pop()
+            path.pop()
+        return False
+
+    def _classify_loop_lines(
+        self, loop: List[int]
+    ) -> Tuple[List[OCCSketchEntity], List[OCCSketchEntity]]:
+        """Classify the four lines of *loop* as horizontal-ish / vertical-ish.
+
+        Uses an angle heuristic: lines within ±45° of the u-axis are
+        "horizontal", the other two are "vertical".
+
+        Returns ``(horiz_entities, vert_entities)``.
+        """
+        horiz: List[OCCSketchEntity] = []
+        vert: List[OCCSketchEntity] = []
+        if self._sketch is None:
+            return horiz, vert
+
+        for i in range(1, len(loop), 2):  # line ids at indices 1, 3, 5, 7
+            lid = loop[i]
+            ent = self._sketch._entities.get(lid)
+            if ent is None:
+                continue
+            p1_id, p2_id = self._sketch._lines[lid]
+            p1_ent = self._sketch._entities.get(p1_id)
+            p2_ent = self._sketch._entities.get(p2_id)
+            if not p1_ent or not p2_ent or not p1_ent.geometry or not p2_ent.geometry:
+                continue
+            x1, y1 = p1_ent.geometry
+            x2, y2 = p2_ent.geometry
+            angle = abs(math.atan2(y2 - y1, x2 - x1))
+            if angle < math.pi / 4 or angle > 3 * math.pi / 4:
+                horiz.append(ent)
+            else:
+                vert.append(ent)
+        return horiz, vert
+
+    def _constrain_loop(self, loop: List[int], variant: str) -> None:
+        """Apply constraint preset *variant* to the 4-sided *loop*.
+
+        Variants:
+        - ``"square"`` — H + V + equal-length
+        - ``"rectangle"`` — H + V
+        - ``"rectangle_construction"`` — H + V + diagonal construction lines
+        - ``"trapezoid"`` — parallel pair on the horizontal lines only
+        """
+        if self._sketch is None:
+            return
+        sketch = self._sketch
+        horiz, vert = self._classify_loop_lines(loop)
+        if len(horiz) != 2 or len(vert) != 2:
+            logger.warning("Loop classification failed – cannot constrain")
+            return
+
+        if self._undo_manager:
+            self._undo_manager.save_state()
+
+        # Point entities in loop order (indices 0, 2, 4, 6)
+        point_ents = [sketch._entities.get(loop[i]) for i in range(0, len(loop), 2)]
+
+        if variant == "trapezoid":
+            # Only parallel constraint on the horizontal pair.
+            sketch.constrain_parallel(horiz[0], horiz[1])
+        else:
+            # Square / Rectangle / Rectangle+Construction all start with H + V.
+            sketch.constrain_horizontal(horiz[0])
+            sketch.constrain_horizontal(horiz[1])
+            sketch.constrain_vertical(vert[0])
+            sketch.constrain_vertical(vert[1])
+
+            if variant == "square":
+                # Force one adjacent pair equal → all four equal via H + V.
+                sketch.constrain_equal_length(horiz[0], vert[0])
+
+            elif variant == "rectangle_construction":
+                # Add the two diagonals as construction lines.
+                p1, p2, p3, p4 = point_ents
+                if p1 and p2 and p3 and p4:
+                    d1 = sketch.add_line(p1, p3)
+                    d2 = sketch.add_line(p2, p4)
+                    d1.is_construction = True
+                    d2.is_construction = True
+
+        self._solve_and_sync()
+        sketch_updated = getattr(self, "sketch_updated", None)
+        if sketch_updated is not None:
+            sketch_updated.emit()
+        self.update()
+
     # ─── Mouse events ─────────────────────────────────────────────────────
 
     def mousePressEvent(self, event):
@@ -1283,14 +1492,16 @@ class Sketch2DWidget(QWidget):
             return
 
         if event.button() == Qt.RightButton:
+            # Only clear drawing-state, preserve any point selection for the
+            # context menu (contextMenuEvent is invoked by Qt after this).
+            if self._mode in ("line", "rectangle", "circle", "arc", "slot"):
                 self._mode = None
                 self._draw_buffer = []
                 self._dynamic_line_end = None
-            self._selected_entities = []
                 self._arc_accum_sweep = 0.0
                 self._arc_prev_angle = None
                 self.constrain_done.emit()
-            self.update()
+            # Do NOT return — let Qt deliver the contextMenuEvent.
             return
 
         if event.button() == Qt.LeftButton:
@@ -1298,9 +1509,12 @@ class Sketch2DWidget(QWidget):
             if self._mode in ("select", None) and self._sketch:
                 # ① Tight point check (4 px) — a deliberate grab on a point.
                 tight_ent = self._find_nearest_point_entity(event.pos(), max_distance=4)
-                if (tight_ent is not None and tight_ent.geometry
+                if (
+                    tight_ent is not None
+                    and tight_ent.geometry
                     and not self._is_external(tight_ent)
-                        and not self._is_centerline(tight_ent)):
+                    and not self._is_centerline(tight_ent)
+                ):
                     x, y = tight_ent.geometry
                     moving = self._collect_connected_points(tight_ent)
                     orig: Dict[int, Tuple[float, float]] = {}
@@ -1324,9 +1538,11 @@ class Sketch2DWidget(QWidget):
                 # selection zone.  External (underlay) entities are fixed
                 # references and can't be dragged.
                 target = self._find_move_target(event.pos())
-                if (target is not None
+                if (
+                    target is not None
                     and not self._is_external(target[0])
-                        and not self._is_centerline(target[0])):
+                    and not self._is_centerline(target[0])
+                ):
                     anchor_ent, anchor_world = target
                     moving = self._collect_connected_points(anchor_ent)
                     orig: Dict[int, Tuple[float, float]] = {}
@@ -1362,7 +1578,8 @@ class Sketch2DWidget(QWidget):
                     return
 
             snapped_pos = self._apply_all_snaps(
-                event.pos(), self._world_to_screen(self._draw_buffer[0]) if self._draw_buffer else None
+                event.pos(),
+                self._world_to_screen(self._draw_buffer[0]) if self._draw_buffer else None,
             )
             world_snapped = (
                 self._screen_to_world(snapped_pos) if snapped_pos != event.pos() else world_pos
@@ -1410,12 +1627,14 @@ class Sketch2DWidget(QWidget):
             return
 
         # Handle element move (grab all points of the element, snap the anchor)
-        if self._move_active and self._move_anchor is not None and self._move_anchor_orig is not None:
+        if (
+            self._move_active
+            and self._move_anchor is not None
+            and self._move_anchor_orig is not None
+        ):
             anchor_orig_screen = self._world_to_screen(self._move_anchor_orig)
             exclude_ids = set(e.id for e in self._moving_points)
-            snapped_screen = self._apply_move_snaps(
+            snapped_screen = self._apply_move_snaps(event.pos(), anchor_orig_screen, exclude_ids)
-                event.pos(), anchor_orig_screen, exclude_ids
-            )
             target_world = self._screen_to_world(snapped_screen)
             dx = target_world.x() - self._move_anchor_orig.x()
             dy = target_world.y() - self._move_anchor_orig.y()
@@ -1442,9 +1661,11 @@ class Sketch2DWidget(QWidget):
                 ew = self._dynamic_line_end
                 cx_f, cy_f = cw.x(), cw.y()
                 sx_f, sy_f = sw.x(), sw.y()
-                r = math.sqrt((sx_f - cx_f) ** 2 + (sy_f - cy_f) ** 2) if (
+                r = (
-                    (sx_f - cx_f) ** 2 + (sy_f - cy_f) ** 2 > 0
+                    math.sqrt((sx_f - cx_f) ** 2 + (sy_f - cy_f) ** 2)
-                ) else 1.0
+                    if ((sx_f - cx_f) ** 2 + (sy_f - cy_f) ** 2 > 0)
+                    else 1.0
+                )
                 dx = ew.x() - cx_f
                 dy = ew.y() - cy_f
                 d = math.sqrt(dx * dx + dy * dy)
@@ -1541,7 +1762,7 @@ class Sketch2DWidget(QWidget):
                         if c_ent.geometry and r > 0:
                             cx, cy = c_ent.geometry
                             d = math.sqrt((world_pos.x() - cx) ** 2 + (world_pos.y() - cy) ** 2)
-                            if abs(d - r) < 8:
+                            if abs(d - r) < self._pick_tolerance_world(16):
                                 over_circle = True
                                 break
                     self._hovered_face = None
@@ -1595,7 +1816,9 @@ class Sketch2DWidget(QWidget):
                 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)
+                        self._sketch.constrain_coincident(
+                            self._move_anchor, self._snap_point_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.
@@ -1614,7 +1837,7 @@ class Sketch2DWidget(QWidget):
         delta = event.angleDelta().y()
         factor = 1.1 if delta > 0 else 0.9
         self._zoom *= factor
-        self._zoom = max(0.1, min(10.0, self._zoom))
+        self._zoom = max(0.05, min(200.0, self._zoom))
         self.update()
 
     def keyPressEvent(self, event):
@@ -1632,8 +1855,9 @@ class Sketch2DWidget(QWidget):
                     return
 
         # Redo: Ctrl+Shift+Z or Ctrl+Y
-        if (event.key() == Qt.Key_Z and event.modifiers() & (Qt.ControlModifier | Qt.ShiftModifier)) or \
+        if (
-           (event.key() == Qt.Key_Y and event.modifiers() & Qt.ControlModifier):
+            event.key() == Qt.Key_Z and event.modifiers() & (Qt.ControlModifier | Qt.ShiftModifier)
+        ) or (event.key() == Qt.Key_Y and event.modifiers() & Qt.ControlModifier):
             if self._undo_manager and self._undo_manager.can_redo:
                 self._undo_manager.redo()
                 self._rebuild_from_sketch()
@@ -1648,7 +1872,11 @@ class Sketch2DWidget(QWidget):
         # line > point. Works in Move mode or when no tool is selected; ignored
         # while actively drawing so an in-progress line isn't clobbered.
         if event.key() in (Qt.Key_Delete, Qt.Key_Backspace):
-            if self._mode in ("select", None) and not self._draw_buffer and self._sketch is not None:
+            if (
+                self._mode in ("select", None)
+                and not self._draw_buffer
+                and self._sketch is not None
+            ):
                 if self._hovered_constraint_idx >= 0:
                     self._delete_hovered_constraint()
                     event.accept()
@@ -1664,7 +1892,11 @@ class Sketch2DWidget(QWidget):
 
         # C key toggles the hovered line between normal and construction mode.
         if event.key() == Qt.Key_C:
-            if self._mode in ("select", None) and not self._draw_buffer and self._sketch is not None:
+            if (
+                self._mode in ("select", None)
+                and not self._draw_buffer
+                and self._sketch is not None
+            ):
                 if self._hovered_line_entity is not None:
                     self._toggle_hovered_line_construction()
                     event.accept()
@@ -1672,6 +1904,83 @@ class Sketch2DWidget(QWidget):
 
         super().keyPressEvent(event)
 
+    def contextMenuEvent(self, event):
+        """Right-click context menu — constraint presets for quadrilateral loops."""
+        if self._sketch is None:
+            return
+
+        world_pos = self._screen_to_world(event.pos())
+        point_entity = self._get_point_entity_at(world_pos)
+
+        # Only offer the constraint menu when clicking directly on a sketch
+        # point that belongs to a closed 4-sided loop.
+        if point_entity is None or self._is_external(point_entity):
+            return
+
+        loop = self._find_loop_from_point(point_entity)
+        menu = QMenu(self)
+
+        constraint_actions = []
+        if loop is not None and len(loop) == 8:
+            horiz, vert = self._classify_loop_lines(loop)
+            valid = len(horiz) == 2 and len(vert) == 2
+
+            a_square = menu.addAction("Constrain as Square")
+            a_square.setEnabled(valid)
+            constraint_actions.append((a_square, "square"))
+
+            a_rect = menu.addAction("Constrain as Rectangle")
+            a_rect.setEnabled(valid)
+            constraint_actions.append((a_rect, "rectangle"))
+
+            a_rect_c = menu.addAction("Constrain as Rectangle + Construction")
+            a_rect_c.setEnabled(valid)
+            constraint_actions.append((a_rect_c, "rectangle_construction"))
+
+            a_trap = menu.addAction("Constrain as Trapezoid")
+            a_trap.setEnabled(valid)
+            constraint_actions.append((a_trap, "trapezoid"))
+
+            menu.addSeparator()
+        elif loop is not None:
+            # Loop detected but not a quadrilateral → inform the user.
+            QMessageBox.information(
+                self,
+                "Not a Quadrilateral",
+                "The selected point belongs to a shape with "
+                f"{len(loop) // 2} sides.\n"
+                "Only four-sided loops can be constrained with these presets.",
+            )
+            return
+        # else: no loop at all — fall through to the basic point actions.
+
+        fix_action = menu.addAction("Fix Point")
+        delete_action = menu.addAction("Delete Point")
+
+        action = menu.exec_(event.globalPos())
+        if action is None:
+            return
+
+        for act, variant in constraint_actions:
+            if action is act:
+                assert loop is not None  # guaranteed by constraint_actions population
+                self._constrain_loop(loop, variant)
+                return
+
+        if action == fix_action:
+            if self._undo_manager:
+                self._undo_manager.save_state()
+            self._sketch.constrain_fixed(point_entity)
+            self._solve_and_sync()
+            self.update()
+        elif action == delete_action:
+            if self._undo_manager:
+                self._undo_manager.save_state()
+            self._sketch.delete_point(point_entity)
+            self._rebuild_from_sketch()
+            self._solve_and_sync()
+            self.update()
+
     def _delete_hovered_constraint(self):
         """Delete the hovered constraint (by log index) and recompute the rest."""
         idx = self._hovered_constraint_idx
@@ -1779,9 +2088,7 @@ class Sketch2DWidget(QWidget):
         # Flip the construction flag on the line entity itself.
         new_val = not line_ent.is_construction
         line_ent.is_construction = new_val
-        logger.info(
+        logger.info(f"Toggled line {line_ent.id} construction -> {new_val}")
-            f"Toggled line {line_ent.id} construction -> {new_val}"
-        )
         self._hovered_line = None
         self._hovered_line_entity = None
         self._solve_and_sync()
@@ -2080,6 +2387,7 @@ class Sketch2DWidget(QWidget):
             # Degenerate: centers on top of each other → draw a circle
             # using the midpoint-to-cursor distance as radius.
             import math as _m
+
             r_fallback = _m.hypot(pos.x() - c1_pos.x(), pos.y() - c1_pos.y())
             if r_fallback > 0:
                 self._sketch.add_circle(c1_ent, r_fallback)
@@ -2093,8 +2401,8 @@ class Sketch2DWidget(QWidget):
 
         # Perpendicular distance from cursor to the centerline C1↔C2.
         import math as _m
-        r = abs((pos.x() - c1_pos.x()) * dy_c
+
-                - (pos.y() - c1_pos.y()) * dx_c) / _m.sqrt(L_sq)
+        r = abs((pos.x() - c1_pos.x()) * dy_c - (pos.y() - c1_pos.y()) * dx_c) / _m.sqrt(L_sq)
         if r < 0.5:
             r = 0.5  # minimum radius so the slot doesn't collapse
 
@@ -2137,9 +2445,7 @@ class Sketch2DWidget(QWidget):
         for corner_pt in (pt1, pb1, pt2, pb2):
             if corner_pt.geometry is not None:
                 cgx, cgy = corner_pt.geometry
-                snap_target = self._get_point_entity_at(
+                snap_target = self._get_point_entity_at(QPoint(int(round(cgx)), int(round(cgy))))
-                    QPoint(int(round(cgx)), int(round(cgy)))
-                )
                 if snap_target is not None and snap_target.id != corner_pt.id:
                     self._sketch.constrain_coincident(corner_pt, snap_target)
 
@@ -2322,8 +2628,15 @@ class Sketch2DWidget(QWidget):
                 line_ent = self._find_line_sketch_entity(p1_ent, p2_ent)
                 if line_ent is not None:
                     # Line clicked: constrain its length (endpoint distance).
-                    dist, ok = QInputDialog.getDouble(self, "Distance", "Distance (mm):",
+                    dist, ok = QInputDialog.getDouble(
-                                                       self._constraint_distance_value, 0, 10000, 2)
+                        self,
+                        "Distance",
+                        "Distance (mm):",
+                        self._constraint_distance_value,
+                        0,
+                        10000,
+                        2,
+                    )
                     if ok and self._sketch:
                         # Save state before adding constraint
                         if self._undo_manager:
@@ -2339,8 +2652,9 @@ class Sketch2DWidget(QWidget):
 
         if len(self._selected_entities) >= 2:
             e1, e2 = self._selected_entities[:2]
-            dist, ok = QInputDialog.getDouble(self, "Distance", "Distance (mm):",
+            dist, ok = QInputDialog.getDouble(
-                                               self._constraint_distance_value, 0, 10000, 2)
+                self, "Distance", "Distance (mm):", self._constraint_distance_value, 0, 10000, 2
+            )
             if ok and self._sketch:
                 # Save state before adding constraint
                 if self._undo_manager:
@@ -2495,12 +2809,11 @@ class Sketch2DWidget(QWidget):
             if c_ent.geometry and r > 0:
                 cx, cy = c_ent.geometry
                 d = math.sqrt((world_pos.x() - cx) ** 2 + (world_pos.y() - cy) ** 2)
-                if abs(d - r) < 8:  # Clicked on circle circumference
+                if abs(d - r) < self._pick_tolerance_world(16):  # Clicked on circle circumference
                     # Prompt for diameter value
                     current_diameter = r * 2.0
                     diameter, ok = QInputDialog.getDouble(
-                        self, "Diameter", "Diameter (mm):",
+                        self, "Diameter", "Diameter (mm):", current_diameter, 0, 10000, 2
-                        current_diameter, 0, 10000, 2
                     )
                     if ok and self._sketch:
                         # Save state before adding constraint
@@ -2515,9 +2828,7 @@ class Sketch2DWidget(QWidget):
                                 self._circles[i] = (ent, new_radius)
                                 break
                         # Record constraint for undo/redo
-                        self._sketch._record_constraint(
+                        self._sketch._record_constraint("diameter", (c_ent.id,), (diameter,))
-                            "diameter", (c_ent.id,), (diameter,)
-                        )
                         self._solve_and_sync()
                         logger.info(f"Diameter constraint: {diameter:.2f}mm")
                     self._selected_entities = []
@@ -2635,6 +2946,27 @@ class Sketch2DWidget(QWidget):
                 painter.drawLine(0, sy, self.width(), sy)
                 wy += grid_10
 
+        # ── Draw 1mm fine grid (only at high zoom for precision work) ──
+        grid_1 = 1  # 1mm fine grid
+        px_1 = grid_1 * self._zoom
+        if px_1 >= MIN_PX_SPACING:
+            pen_fine = QPen(QColor("#353548"), 0.3)
+            start_x = math.floor(min(top_left.x(), bottom_right.x()) / grid_1) * grid_1
+            end_x = math.ceil(max(top_left.x(), bottom_right.x()) / grid_1) * grid_1
+            start_y = math.floor(min(top_left.y(), bottom_right.y()) / grid_1) * grid_1
+            end_y = math.ceil(max(top_left.y(), bottom_right.y()) / grid_1) * grid_1
+            painter.setPen(pen_fine)
+            wx = start_x
+            while wx <= end_x:
+                sx = int(wx * self._zoom + self.width() / 2 + self._offset.x())
+                painter.drawLine(sx, 0, sx, self.height())
+                wx += grid_1
+            wy = start_y
+            while wy <= end_y:
+                sy = int(self.height() / 2 - wy * self._zoom + self._offset.y())
+                painter.drawLine(0, sy, self.width(), sy)
+                wy += grid_1
+
         # ── Centerlines (X and Y reference axes through origin) ──
         # X centerline = horizontal (red dashed), Y centerline = vertical (green dashed).
         # Both span the full viewport so they are always visible as reference guides.
@@ -2660,10 +2992,12 @@ class Sketch2DWidget(QWidget):
         # underlay on top of the entity-based lines.
         if self._source_underlay_uv and self._underlay_visible:
             if self._source_underlay_uv[0] and len(self._source_underlay_uv[0]) >= 3:
-                fill_poly = QPolygonF([
+                fill_poly = QPolygonF(
+                    [
                         self._world_to_screen(QPoint(int(round(u)), int(round(v))))
                         for (u, v) in self._source_underlay_uv[0]
-                ])
+                    ]
+                )
                 painter.setBrush(QBrush(QColor(250, 179, 135, 28)))
                 painter.setPen(Qt.NoPen)
                 painter.drawPolygon(fill_poly)
@@ -2713,9 +3047,7 @@ class Sketch2DWidget(QWidget):
                     continue
                 if entity.geometry:
                     x, y = entity.geometry
-                    screen_pos = self._world_to_screen(
+                    screen_pos = self._world_to_screen(QPoint(int(round(x)), int(round(y))))
-                        QPoint(int(round(x)), int(round(y)))
-                    )
                     painter.setPen(QPen(QColor("#fab387"), 1))
                     painter.setBrush(QBrush(QColor("#fab387")))
                     painter.drawEllipse(screen_pos, 4, 4)
@@ -2736,7 +3068,11 @@ class Sketch2DWidget(QWidget):
                 sp1 = self._world_to_screen(QPoint(int(round(x1)), int(round(y1))))
                 sp2 = self._world_to_screen(QPoint(int(round(x2)), int(round(y2))))
 
-                is_construction = p1_ent.is_construction or p2_ent.is_construction or (line_ent is not None and line_ent.is_construction)
+                is_construction = (
+                    p1_ent.is_construction
+                    or p2_ent.is_construction
+                    or (line_ent is not None and line_ent.is_construction)
+                )
                 if is_construction:
                     painter.setPen(QPen(QColor("#6c7086"), 1, Qt.DashLine))
                 else:
@@ -2811,8 +3147,10 @@ class Sketch2DWidget(QWidget):
                     QPoint(int(round(preview[i][0])), int(round(preview[i][1])))
                 )
                 p2 = self._world_to_screen(
-                    QPoint(int(round(preview[(i + 1) % len(preview)][0])),
+                    QPoint(
-                           int(round(preview[(i + 1) % len(preview)][1])))
+                        int(round(preview[(i + 1) % len(preview)][0])),
+                        int(round(preview[(i + 1) % len(preview)][1])),
+                    )
                 )
                 painter.drawLine(p1, p2)
 
@@ -2827,8 +3165,42 @@ class Sketch2DWidget(QWidget):
             p1 = self._world_to_screen(self._draw_buffer[0])
             p2 = self._world_to_screen(self._dynamic_line_end)
             painter.setPen(QPen(QColor("#a6e3a1"), 2, Qt.DashLine))
-            painter.drawRect(min(p1.x(), p2.x()), min(p1.y(), p2.y()),
+            painter.drawRect(
-                             abs(p2.x() - p1.x()), abs(p2.y() - p1.y()))
+                min(p1.x(), p2.x()), min(p1.y(), p2.y()), abs(p2.x() - p1.x()), abs(p2.y() - p1.y())
+            )
+            # ── Dimension labels for rectangle preview ──
+            w1 = self._draw_buffer[0]
+            w2 = self._dynamic_line_end
+            width_mm = abs(w2.x() - w1.x())
+            height_mm = abs(w2.y() - w1.y())
+            rx = min(p1.x(), p2.x())
+            ry = min(p1.y(), p2.y())
+            rw = abs(p2.x() - p1.x())
+            rh = abs(p2.y() - p1.y())
+            painter.save()
+            painter.setPen(QPen(QColor("#f9e2af"), 1))
+            font = painter.font()
+            font.setPointSize(9)
+            painter.setFont(font)
+            # Horizontal label (top edge, centered)
+            if rw > 20:
+                h_label = f"{width_mm:.1f} mm"
+                h_rect = painter.fontMetrics().boundingRect(h_label)
+                h_x = rx + rw / 2 - h_rect.width() / 2
+                h_y = ry - 8 if ry > 20 else ry + rh + 16
+                painter.drawText(int(h_x), int(h_y), h_label)
+            # Vertical label (right edge, centered)
+            if rh > 20:
+                v_label = f"{height_mm:.1f} mm"
+                v_rect = painter.fontMetrics().boundingRect(v_label)
+                v_x = (
+                    rx + rw + 8
+                    if rx + rw + v_rect.width() + 16 < self.width()
+                    else rx - v_rect.width() - 8
+                )
+                v_y = ry + rh / 2 + v_rect.height() / 2
+                painter.drawText(int(v_x), int(v_y), v_label)
+            painter.restore()
 
         if self._draw_buffer and self._dynamic_line_end and self._mode == "circle":
             center = self._world_to_screen(self._draw_buffer[0])
@@ -2897,8 +3269,7 @@ class Sketch2DWidget(QWidget):
                 dy_c = c2.y() - c1.y()
                 L = math.sqrt(dx_c * dx_c + dy_c * dy_c)
                 if L > 0:
-                    r = abs((cursor.x() - c1.x()) * dy_c
+                    r = abs((cursor.x() - c1.x()) * dy_c - (cursor.y() - c1.y()) * dx_c) / L
-                            - (cursor.y() - c1.y()) * dx_c) / L
                     if r < 0.5:
                         r = 0.5
                     perp_x = -dy_c / L
@@ -2983,9 +3354,11 @@ class Sketch2DWidget(QWidget):
                 outer = face["outer"]
                 if outer["type"] == "polygon":
                     pts = outer["points"]
-                    sp0 = self._world_to_screen(QPoint(int(round(pts[0][0])), int(round(pts[0][1]))))
+                    sp0 = self._world_to_screen(
+                        QPoint(int(round(pts[0][0])), int(round(pts[0][1])))
+                    )
                     path.moveTo(sp0.x(), sp0.y())
-                    for (px, py) in pts[1:]:
+                    for px, py in pts[1:]:
                         sp = self._world_to_screen(QPoint(int(round(px)), int(round(py))))
                         path.lineTo(sp.x(), sp.y())
                     path.closeSubpath()
@@ -2998,9 +3371,11 @@ class Sketch2DWidget(QWidget):
                 for hole in face["holes"]:
                     if hole["type"] == "polygon":
                         pts = hole["points"]
-                        sp0 = self._world_to_screen(QPoint(int(round(pts[0][0])), int(round(pts[0][1]))))
+                        sp0 = self._world_to_screen(
+                            QPoint(int(round(pts[0][0])), int(round(pts[0][1])))
+                        )
                         path.moveTo(sp0.x(), sp0.y())
-                        for (px, py) in pts[1:]:
+                        for px, py in pts[1:]:
                             sp = self._world_to_screen(QPoint(int(round(px)), int(round(py))))
                             path.lineTo(sp.x(), sp.y())
                         path.closeSubpath()