Fix routing, replace ILayoutAlgorithm, and resolve Note divider issue

.cspell.yaml

@@ -72,6 +72,7 @@ words:
   - collinear
   - collinearity
   - collinearly
+  - pathfinding
   # Non-ASCII terms retained verbatim in extracted source comments
   - façade
   - Köpf

docs/design/rendering-layout/connector-router.md

@@ -62,8 +62,13 @@ implementations are:
    the margin. The result is then clamped into the chosen face's usable connectable extents (again
    applying the same clearance inset when an extent is long enough) and projected inward to the real
    outline. The chosen `PortSide` is retained so the route exits and enters perpendicular to the face.
-2. **Obstacle set.** Builds a `Rect` per box, excluding the connection's two endpoint boxes matched
-   by reference identity, so the connector is free to leave and enter the boxes it joins.
+2. **Obstacle set.** Builds a `Rect` per box, including the connection's own two endpoint boxes. The
+   connector remains free to leave and enter the boxes it joins because the underlying
+   `OrthogonalEdgeRouter` steps each anchor off its face by a perpendicular stub longer than any
+   clearance level it tries before pathfinding, then reattaches the true anchor when assembling the
+   final path; treating endpoints as ordinary obstacles closes the gap through which an unrelated,
+   already-routed connector's soft obstacles could otherwise squeeze a later connector into its own
+   target box's interior.
 3. **Dispatch.** Routes through the router realizing `options.EdgeRouting`. Today `Orthogonal` maps to
    the internal `OrthogonalEdgeRouter.RouteWithStatus`, which is the implementation behind the enum
    value and remains internal to the Layout system. The dispatch is a single-arm switch structured so

docs/gallery/README.md

@@ -34,6 +34,13 @@ layer with a dummy bend point created by an unrelated long edge (LongSource to L
 clusters isolated nodes at the end of the layer's order, and coordinate assignment squeezes any resulting gap down to
 the standard node spacing, instead of inheriting the dummy's unrelated port-alignment floor as an inflated gap.
 
+![Nine edges docking on a compartment box without crossing its interior](parallel-edges-into-compartment-box.svg)
+
+Regression coverage for the parallel-edges-into-compartment-box fix: nine unmerged edges from a small Source box
+converge on a taller Target box's nine-row compartment. ConnectorRouter now treats every box, including a connection's
+own endpoints, as a hard obstacle for the whole route (not just the final docking stub), so a connector squeezed by
+other already-routed connectors can no longer detour straight through its own target box's interior.
+
 ## Flow direction
 
 The same directed graph laid out in two flow directions, selected with the direction option, plus a nested container

docs/reqstream/rendering-layout/connector-router.yaml

@@ -63,14 +63,17 @@ sections:
 
       - id: Rendering-Layout-ConnectorRouter-ExcludesEndpoints
         title: >-
-          ConnectorRouter shall exclude a connection's two endpoint boxes, matched by instance
-          identity, from the obstacle set used to route that connection.
+          ConnectorRouter shall treat a connection's own endpoint boxes as ordinary obstacles while
+          still letting the connector leave and enter their faces, by routing through a perpendicular
+          approach stub that clears each endpoint before the true anchor is reattached.
         justification: |
-          A connector must be free to leave and enter the boxes it joins; treating the endpoint boxes
-          as obstacles would block the connector's own anchors. Endpoints are matched by reference so
-          no domain concept enters the routing.
+          Excluding endpoint boxes entirely left a gap through which an unrelated, already-routed
+          connector's soft obstacles could squeeze a later connector into its own target box's
+          interior. Treating endpoints as solid obstacles and relying on the router's existing
+          stub-then-dock approach keeps the connector's own docking free while closing that gap.
         tests:
-          - Route_EndpointBoxes_AreExcludedFromObstacles
+          - Route_EndpointBoxes_ReachBoundaryAnchorsViaApproachStub
+          - Route_NineParallelEdgesIntoCompartmentBox_DoNotCrossTargetInterior
 
       - id: Rendering-Layout-ConnectorRouter-CarriesStyling
         title: >-

docs/verification/rendering-layout/connector-router.md

@@ -26,7 +26,7 @@ obstacle avoidance, and produced `LayoutLine` styling are all observed on real o
 
 A verification run passes when every named scenario below asserts without unexpected exception, and
 the referenced tests cover each `Rendering-Layout-ConnectorRouter-*` requirement. Any wrong anchor
-face, waypoint that enters a non-endpoint obstacle interior, incorrect line styling passthrough,
+face, waypoint that enters an obstacle's strict interior, incorrect line styling passthrough,
 out-of-order batch result, or non-argument-null exception for invalid input constitutes a failure.
 
 ### Test Scenarios
@@ -51,9 +51,12 @@ out-of-order batch result, or non-argument-null exception for invalid input cons
 - **Obstacle avoidance** (`Rendering-Layout-ConnectorRouter-AvoidsObstacles`):
   `Route_ObstacleBetweenEndpoints_RoutesAroundInterior` confirms the route is orthogonal and never
   enters an intervening box's interior.
-- **Endpoint exclusion** (`Rendering-Layout-ConnectorRouter-ExcludesEndpoints`):
-  `Route_EndpointBoxes_AreExcludedFromObstacles` confirms the connector reaches the endpoints' boundary
-  anchors even though both boxes appear in the box list.
+- **Endpoint boxes as ordinary obstacles** (`Rendering-Layout-ConnectorRouter-ExcludesEndpoints`):
+  `Route_EndpointBoxes_ReachBoundaryAnchorsViaApproachStub` confirms the connector still reaches the
+  endpoints' boundary anchors even though both boxes are treated as obstacles, and
+  `Route_NineParallelEdgesIntoCompartmentBox_DoNotCrossTargetInterior` confirms a batch of parallel
+  connectors converging on one box face never cuts through that box's (or the source box's) interior,
+  reproducing a previously reported defect.
 - **Styling carried** (`Rendering-Layout-ConnectorRouter-CarriesStyling`):
   `Route_Connection_CarriesRequestedStyling` confirms the requested target marker, line style, and
   label flow onto the produced line while the source end stays unmarked.
@@ -94,7 +97,8 @@ level rather than introducing a new `ConnectorRouter`-level responsibility:
 - **`Rendering-Layout-ConnectorRouter-AvoidsObstacles`**:
   Route_ObstacleBetweenEndpoints_RoutesAroundInterior
 - **`Rendering-Layout-ConnectorRouter-ExcludesEndpoints`**:
-  Route_EndpointBoxes_AreExcludedFromObstacles
+  Route_EndpointBoxes_ReachBoundaryAnchorsViaApproachStub,
+  Route_NineParallelEdgesIntoCompartmentBox_DoNotCrossTargetInterior
 - **`Rendering-Layout-ConnectorRouter-CarriesStyling`**:
   Route_Connection_CarriesRequestedStyling
 - **`Rendering-Layout-ConnectorRouter-BatchOrder`**:

src/DemaConsulting.Rendering.Abstractions/BoxMetrics.cs

@@ -26,6 +26,25 @@ public static double FolderTabHeight(Theme theme)
         return theme.FontSizeBody + 2.0 * theme.LabelPadding;
     }
 
+    /// <summary>
+    /// Computes the size of the folded-corner cutout drawn at the top-right of a
+    /// <see cref="BoxShape.Note"/> box: a fraction of the box's shorter side
+    /// (<see cref="NotationMetrics.NoteFoldFraction"/>), capped at
+    /// <see cref="NotationMetrics.NoteFoldMaxSize"/>. The same value is the horizontal inset from
+    /// the right edge and the vertical inset from the top edge, since the fold cutout is a
+    /// right-angle triangle. Both renderers, and anything reasoning about how close a horizontal
+    /// divider may safely approach a Note box's top edge, must call this so the fold's drawn
+    /// geometry and any content clearance never disagree.
+    /// </summary>
+    /// <param name="box">The Note-shaped box whose fold size is resolved.</param>
+    /// <returns>The fold size in logical pixels.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="box"/> is <see langword="null"/>.</exception>
+    public static double NoteFoldSize(LayoutBox box)
+    {
+        ArgumentNullException.ThrowIfNull(box);
+        return Math.Min(Math.Min(box.Width, box.Height) * NotationMetrics.NoteFoldFraction, NotationMetrics.NoteFoldMaxSize);
+    }
+
     /// <summary>
     /// Computes the height of the title area of a box: the vertical space reserved at the top
     /// for the optional keyword line and the bold name line.

src/DemaConsulting.Rendering.Abstractions/DemaConsulting.Rendering.Abstractions.csproj

@@ -39,6 +39,7 @@
 
     <!-- Polyfill Configuration -->
     <PolyArgumentExceptions>true</PolyArgumentExceptions>
+    <PolyUseEmbeddedAttribute>true</PolyUseEmbeddedAttribute>
 
     <!-- SBOM Configuration -->
     <GenerateSBOM>true</GenerateSBOM>
@@ -74,6 +75,8 @@
 
   <ItemGroup>
     <InternalsVisibleTo Include="DemaConsulting.Rendering.Abstractions.Tests" />
+    <InternalsVisibleTo Include="DemaConsulting.Rendering.Layout" />
+    <InternalsVisibleTo Include="DemaConsulting.Rendering.Layout.Tests" />
   </ItemGroup>
 
   <ItemGroup>