feat(overlap): auto-recheck the active plate after layout edits settle

Nest windows now rerun the overlap check once the layout has been
unchanged for 0.5 s, instead of leaving 'Overlaps: not checked'. Edits
show 'Overlaps: check pending...'; drags are caught by the paint-time
pose stamp, collection edits by their events. The check waits while a
mouse button, modal dialog or fill is active, supersedes a running check
when the layout moves again, and does not retry a canceled or failed
layout until it changes. Rechecks use the incremental analyzer, so only
the moved parts' neighbors are recomputed.

Automatic results update only the canvas label (the status bar keeps the
last command's message) and keep Display > Off. Check Active Plate still
runs immediately. InvalidateOverlapCheck now also drops cached material.

docs/geometry/visual-overlap-check.md

@@ -33,10 +33,21 @@ and states how many distinct parts could not be checked. Pair counts are not
 fragment counts. This diagnostic checks shared material, not minimum spacing,
 plate edges, or cutting-path crossings.
 
-Edits clear the overlay and require another explicit check. Plate changes reset
-the check. Pan, zoom, selection, and display changes do not rerun geometry.
-Drawing-editor loading invalidates before loading, even if the dialog is later
-canceled. There is no automatic check during dragging or export.
+In a nest window the active plate is checked automatically. Any layout edit
+(add, remove, reorder, move, rotate, fill) clears the overlay and shows
+**Overlaps: check pending…**; once the layout has been unchanged for 0.5 s and no
+mouse button, modal dialog, or fill progress window is active, the check reruns.
+Automatic results appear only in the canvas label, so the status bar keeps the
+last command's message, and an automatic check keeps Display > Off rather than
+switching to Areas. Rechecks are incremental: drawing material is prepared once
+and reused, and pairs whose two parts have not moved reuse the previous result,
+so only the moved parts' neighbors are clipped again. Canceling a check is
+respected until the layout changes again, and a failed layout is not retried
+until it changes. Check Active Plate remains available and always runs at once.
+
+Plate changes reset the check. Pan, zoom, selection, and display changes do not
+rerun geometry. Drawing-editor loading invalidates before loading (dropping cached
+material), even if the dialog is later canceled. There is no check during export.
 
 ## Analysis API
 
@@ -185,7 +196,29 @@ metadata-only edits do not change material. In-place hole-program edits require
 the same explicit invalidation.
 
 `OverlapOverlayController` owns UI-thread captures, background analysis, request
-generations, cancellation, and the GDI display cache. It checks freshness before
+generations, cancellation, and the GDI display cache. `EditNestForm` enables its
+automatic recheck with `PlateView.SetOverlapAutoCheck(() => Nest.Units)`; other
+PlateView hosts (fill previews, pattern tiles) stay manual. The debounce decision
+is the Linux-testable `OverlapAutoCheckScheduler`: collection events and every
+paint's stamp comparison restart a WinForms timer, and the tick starts a check only
+if the stamp is unchanged since the last observation and no interaction is active.
+
+The controller passes one `OverlapMaterialCache` to
+`PlateOverlapAnalyzer.Capture(parts, cache)` and its last published report to
+`Analyze(snapshot, previous)`. The cache keeps each clean `Program`'s converted
+entities and prepared, validated material (weakly keyed by program reference; a
+changed code count or rotation is detected). Preparing material dominates
+first-check time for drawings with many holes. Incremental analysis reuses a pair
+only when both parts have the same cached source, bit-identical pose, and the same
+relative input order (clipping is operand-order sensitive), then renumbers it.
+`InvalidateOverlapCheck()` clears the cache and baseline, so in-place program
+editors must keep calling it before loading.
+
+Measured on 501 real PEP-converted plates with 2 to 384 parts, a from-scratch check
+takes median 1 ms, p99 368 ms and max 6.5 s (a 299-part plate); an incremental
+recheck after moving one part takes median 0.1 ms, p99 20 ms and max 35 ms. A
+comparison against uncached full analysis over 2505 edits (nudge, drag onto
+another part, move three, delete first, swap order) matched exactly. It checks freshness before
 publication and painting. Handle destruction/disposal cancels work and releases
 paths; old completions cannot replace a newer report. Snapshot conversion and
 clipping never run in paint or mouse-move handlers.
@@ -201,9 +234,10 @@ radii. Hover clears on edits, mode/request/view changes, leave, and teardown.
 Diagnostic details draw above action adorners and take precedence over the normal
 part-name tooltip only while visible.
 
-Next hardening: measure real-plate capture/analysis cost and cancellation latency
-before adding cached triangulations or background capture. Cancellation cannot
-interrupt the interior of an existing kernel operation.
+Next hardening: the first check of a plate with a hole-heavy drawing can still
+take seconds, and cancellation cannot interrupt the interior of material
+preparation or one kernel operation. Prepared per-part triangulations are not yet
+cached across requests.
 
 ## Verification
 
@@ -215,9 +249,14 @@ inputs, snapshot isolation, read-only output, cutting-program independence, and
 cancellation. Run:
 
 ```sh
-dotnet test OpenNest.Tests/OpenNest.Tests.csproj --filter 'FullyQualifiedName~PlateOverlapAnalyzerTests|FullyQualifiedName~OverlapReportStateTests|FullyQualifiedName~PolygonAreaMomentsTests|FullyQualifiedName~OverlapPairPresentationTests|FullyQualifiedName~OverlapHoverPagesTests'
+dotnet test OpenNest.Tests/OpenNest.Tests.csproj --filter 'FullyQualifiedName~PlateOverlapAnalyzerTests|FullyQualifiedName~OverlapReportStateTests|FullyQualifiedName~PolygonAreaMomentsTests|FullyQualifiedName~OverlapPairPresentationTests|FullyQualifiedName~OverlapHoverPagesTests|FullyQualifiedName~IncrementalOverlapAnalysisTests|FullyQualifiedName~OverlapAutoCheckSchedulerTests'
 ```
 
+`IncrementalOverlapAnalysisTests` compares incremental rechecks with uncached full
+analysis across moves, rotation, deletion, insertion, order swaps, renames and
+coincident duplicates, and covers pair reuse, issue renumbering, cache clearing and
+cancellation. `OverlapAutoCheckSchedulerTests` covers the quiet period, interaction
+waits, and the no-retry rule for canceled or failed layouts.
 `OverlapReportStateTests` verifies request supersession, exact pose/reference
 freshness, stale clearing, cancellation, and incomplete-versus-clear messaging.
 `PolygonAreaMomentsTests` covers analytic
@@ -227,7 +266,8 @@ formatting, sequence labels, coincident ordering, and zoom-independent DPI hit
 radii. `OverlapHoverPagesTests` proves bounded continuation pages retain every
 pair and long/Unicode name, with navigation bounds and explicit tiny-view failure.
 `OpenNest.WinForms.Tests/PlateOverlapOverlayTests.cs` adds STA worker/publication,
-menu/MDI, path-cache, uniform-fill pixel, and control-lifetime checks. Run those
+menu/MDI, path-cache, uniform-fill pixel, control-lifetime, and automatic-recheck
+(debounce, drag detection, busy wait, supersession, display/status) checks. Run those
 on Windows:
 
 ```sh
@@ -238,5 +278,6 @@ Linux can cross-build with `-p:EnableWindowsTargeting=true`, but that does not
 execute Windows tests or verify appearance, DPI, or interaction. On Windows,
 check partial overlap, containment, inside-hole placement, pan/zoom and quadrant
 alignment, stale clearing during edits/plate switches, converter cancellation,
+the pending label and automatic recheck after dragging a part onto another,
 crowded-marker PageUp/PageDown access to the last pair, and repeated
 check/toggle/close cycles without GDI/disposed-control errors.