Respect board outline in obstacle indexing

[0hmX]

Motivation

• The board outline (cutout) was not consistently respected because board-void rectangles were not always present in the per-layer obstacle RBush indexes.
• When solver snapshots are rehydrated or an obstacle index is provided externally, the board mask might be missing and free-space seeds can appear inside cutouts.
• The intent is to ensure the board-outline mask is treated as obstacles so seeding and expansion honor the outline.

Description

• Add a helper ensureBoardVoidRectsInObstacleIndex to inject board void XYRects into obstacleIndexByLayer (RBush) arrays without duplicating entries.
• Call this helper from RectDiffSeedingSolver during setup and from RectDiffExpansionSolver when preparing obstacle indexes so both phases consistently include the board mask.
• Keep the helper and call sites type-safe by operating on Array<RBush<RTreeRect>> and using rectToTree/sameTreeRect to dedupe.

Testing

• Ran type-checking with bunx tsc --noEmit which completed successfully with no errors.
• Ran the test suite with bun test and all automated tests passed (11 pass, 1 skip, 0 fail), including tests/board-outline.test.ts which verifies the outline behavior.
• The changes were committed with message Ensure board void rects in obstacle index.

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Codex Task

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Project	Deployment	Review	Updated (UTC)
rectdiff	Ready	Preview, Comment	Dec 24, 2025 8:37pm