docs(expand): describe cancelling a long Expand Spacing search

docs/geometry/expand-spacing.md

@@ -4,4 +4,8 @@
 
 Every selected/selected and selected/nonselected pair has an operation-entry clearance floor, measured against material with cutouts subtracted. A later move may reuse slack opened by an earlier move, but it cannot reduce a pair below its own starting gap. Existing overlaps are accepted for attempted separation; a remaining overlap is reported as a violation, not a successful positive gap. Geometry whose material side is unresolved at sub-scale is conservatively reported as a violation when native extents intersect; that negative marker is not a measured penetration depth. An unchanged selected part already outside the work area also yields an edge violation and zero credited spacing. Temporarily blocked pairs are retried after another part moves, while a pass without positive movement stops the relaxation. An individual violation's `BlockedByEdge` flag is true only when the work-area edge is the first limiting cause; the desktop status currently displays a blocked-pair count, not those individual causes.
 
-Probes run on scratch poses. Each trial translation is clipped against blocking material along its entire straight path, including cutout walls and regenerated open cut-off paths; a remote cut-off does not pin an unrelated move. Entry floors for open cut-offs use nearest points on every native segment, not a program endpoint or a fictional closing chord. Open paths that strictly enter part material stay as violations even at zero target; boundary contact and paths wholly inside holes remain legal. An open path's broad box is not a blocker when its real segments miss the part. Initially overlapping convex line profiles and complete native disks can take a certified direct separating path, including a safe partial move when the plate edge prevents a full exit; unsupported or ambiguous overlap paths stay put and remain reported. Complete native disks use analytic clearance rather than interpreting a shallow arc overlap as a positive polygon gap. For other curved pairs, a polygon gap inside the combined 0.002-unit chord band is uncertain and conservatively reported as a violation rather than proof of clear material. When a part touches a cutout wall and the usual nearest-boundary direction makes no safe progress, the tool tries the opposite direction through the same checks. Tiny clamp keep-outs use tolerance-free material occupancy and a conservative native-bound motion limit when tolerant geometry cannot certify them. Cancellation before application leaves the live layout unchanged; `Separate` never changes it. The desktop command is synchronous and has no Cancel dialog or automatic save. A bounded search reports the spacing it found, not an optimum. See `docs/geometry/directional-slides.md` for directional contact behavior.
+Probes run on scratch poses. Each trial translation is clipped against blocking material along its entire straight path, including cutout walls and regenerated open cut-off paths; a remote cut-off does not pin an unrelated move. Entry floors for open cut-offs use nearest points on every native segment, not a program endpoint or a fictional closing chord. Open paths that strictly enter part material stay as violations even at zero target; boundary contact and paths wholly inside holes remain legal. An open path's broad box is not a blocker when its real segments miss the part. Initially overlapping convex line profiles and complete native disks can take a certified direct separating path, including a safe partial move when the plate edge prevents a full exit; unsupported or ambiguous overlap paths stay put and remain reported. Complete native disks use analytic clearance rather than interpreting a shallow arc overlap as a positive polygon gap. For other curved pairs, a polygon gap inside the combined 0.002-unit chord band is uncertain and conservatively reported as a violation rather than proof of clear material. When a part touches a cutout wall and the usual nearest-boundary direction makes no safe progress, the tool tries the opposite direction through the same checks. Tiny clamp keep-outs use tolerance-free material occupancy and a conservative native-bound motion limit when tolerant geometry cannot certify them. Cancellation before application leaves the live layout unchanged; `Separate` never changes it. A bounded search reports the spacing it found, not an optimum. See `docs/geometry/directional-slides.md` for directional contact behavior.
+
+## Cancelling a long search
+
+On a complex layout the search can run for minutes. The desktop command runs it on a worker thread; if it is still running after about 0.3 seconds, a small Expand Spacing window opens with an elapsed time and a Cancel button, and the rest of the application waits behind it. Cancel, Escape and the window's close box all request cancellation. The window then shows "Cancelling..." and stays open until the search stops at its next pair check, which took under 0.3 seconds on the real jobs measured. A cancelled search moves no part, and the status bar reads "Expand Spacing cancelled - no parts were moved". A search that finishes before the cancellation takes effect applies its result normally. The command does not save automatically.