fix(geometry): resolve blocking contacts across directional slide paths

docs/geometry/directional-slides.md

@@ -0,0 +1,37 @@
+# Directional slides and repeated pushes
+
+## Behavior contract
+
+For initially non-overlapping closed material boundaries, a directional slide stops at the first contact that blocks forward motion. Leaving an existing contact or sliding along a straight shared edge is legal. Skipping a contact must not skip the rest of that obstacle: a later hook or the opposite wall of a hole still stops the slide. Distances retain the existing `Tolerance.Epsilon` snapping and `double.MaxValue` no-hit convention; supplied vector directions are unit vectors.
+
+`SpatialQuery.DirectionalDistance` overloads and CPU best-fit batches use the same event sources and contact resolver. Events carry both contact points in their initial world frames, rather than only a snapped distance. The classifier uses closed-loop material sectors, native-curve containment for hole depth, and the curvature of the supporting boundary at a tangential contact. A full-circle arc has no physical corner at its seam. Raw ray helpers remain first-touch primitives, not material-aware slide queries.
+
+Open/incomplete chains and ambiguous contacts conservatively block. This is not an overlap-repair operation or a general replacement for layout validation. Caller-provided contact topology must represent the same boundaries and offsets as the query. Prepared geometry must not be mutated; prepare a classifier before sharing it between parallel queries. Edge-array queries still sort their arrays, and recover loop order from private copies before classifying contacts.
+
+## Callers
+
+- PlateView uses `SelectionManager.PushSelected` → `Compactor.Push`. The zero-spacing nudge-and-discard workaround is removed. Cutout contours on stationary obstacles are retained, and the plate entry's existing-overlap filter accounts for holes rather than relying solely on `Part.Intersects` (which compares outer perimeters).
+- Linear fill inherits the shared native-entity query unchanged. Extents fill passes complete boundary loops instead of direction-filtered fragments.
+- CPU best-fit batches prepare contact topology once and use all vertices plus curve/line interior and curve/curve tangency events. The old leading-half vertex filter cannot establish the next blocker after a skipped touch.
+- GPU kernels retain nearest-hit reduction and return unsnapped contact witnesses. The shared CPU classifier accepts a blocking witness or replays the full query after a nonblocking witness, preserving tied/later blockers. Both batch APIs honor active buffer lengths and refresh mutated/reused segment arrays. The GPU distance adapter sends only exact cardinal directions to the axis-only slide interface; arbitrary directions and native curves use the shared CPU path.
+
+## Regression coverage
+
+`SlideContactTests` exercises cardinal line, translated line, reused edge-array, arbitrary-vector, native-entity, and both CPU batch paths. Cases include winding reversal, nonzero origins, rotated hooks, holes, separating circles, positive-distance grazing followed by a blocker, full-circle arc seams, concave/straight junctions, thin rings, and circle/line interior contact.
+
+`CompactorTests` covers the reported sequence (push left with spacing, then right/up/down), genuine zero-distance blocking, zero/nonzero-spacing later hooks, and inside-hole pushes through both direct and plate entry points. Physical spacing is measured from raw outlines rather than the inflated contours used by the solver.
+
+Verification commands:
+
+```sh
+dotnet test OpenNest.Tests/OpenNest.Tests.csproj --filter 'FullyQualifiedName~SlideContactTests|FullyQualifiedName~CurveContactDistanceTests|FullyQualifiedName~CompactorTests'
+dotnet test OpenNest.Tests/OpenNest.Tests.csproj
+dotnet test OpenNest.Engine.Tests/OpenNest.Engine.Tests.csproj
+dotnet test OpenNest.IO.Tests/OpenNest.IO.Tests.csproj
+```
+
+The isolated repair tree (excluding other sessions' fill-performance and spacing-expander work) passed 130 targeted cases and the full Debug suites: main 1758 passed / 21 skipped, engine 300 passed, IO 41 passed. The main Release suite passed 1728 / 21 skipped. Skips are not counted as passes. The 142 `GpuSlideContactTests` also pass in a net8 harness linking the production GPU class and test source, using ILGPU 1.5.1's CPU accelerator (not a mocked distance solver). The Windows desktop/test project cross-build passes in Release. Neither physical GPU execution nor Windows UI interaction was runtime-verified on Linux.
+
+## Remaining hardening
+
+This repair does not change saved best-fit cache versioning, add a clearance acceptance gate to every fill entry, repair existing overlapping layouts, or claim the earlier real-DXF/grid-validator discrepancies in [pair-spacing checks](pair-spacing.md) are resolved. That document's measured candidate counts describe its earlier tree; removing CPU projection filtering and adding interior curve/line contacts does not substitute for rerunning its corpus. General `Part.Intersects` hole semantics remain unchanged outside Compactor. Profile the new classification path before attempting optimizations; retain the first-blocking-contact regressions.

docs/geometry/pair-spacing.md

@@ -4,7 +4,7 @@
 
 CPU best-fit slides and shared directional-distance queries now check both external and internal curve tangency. A convex offset corner inside a concave slot contacts at the difference of the radii, not their sum. Both forward ray/circle roots must be checked: the nearer root can be outside an arc's angular span while the farther root is the first actual contact. Tangent-point directions differ for internal contact, including when the moving curve is the larger one.
 
-`SpatialQuery.CurveTangencyDistance` shares this calculation between the two callers. It assumes a unit direction, nonnegative radii and world-frame centers. An optional arc supplies only angular limits; null represents a full circle. This helper supplements the existing vertex/line phases rather than replacing them. Equal-radius coincident curves have no isolated internal tangent and remain the vertex phases' responsibility; zero-radius curves are points. No spacing tolerances or acceptance policies were changed.
+The raw `SpatialQuery.CurveTangencyDistance` helper and shared slide events implement this calculation. The subsequent [directional-slide repair](directional-slides.md) routes both callers through material-aware contact events; the measurements below describe the earlier native-tangency repair. It assumes a unit direction, nonnegative radii and world-frame centers. An optional arc supplies only angular limits; null represents a full circle. This helper supplements the existing vertex/line phases rather than replacing them. Equal-radius coincident curves have no isolated internal tangent and remain the vertex phases' responsibility; zero-radius curves are points. No spacing tolerances or acceptance policies were changed.
 
 ### Reproduced U-shaped part