fix(editor): scope slab room paint to the clicked slab's level

[Aymericr]

Room-scope paint on a slab spreads to slabs on other levels. In a two-storey building — where stacked floors share a footprint by definition — painting a ground-floor slab also repaints the slab directly above it.

Found while reviewing #554; this one is on main today and unrelated to that PR.

Cause

resolvePaintScopeTargets gates on space.levelId in every wall path — resolveWallPaintSpace (paint-scope.ts:169), connectedExteriorBoundaries (:205), wallTargetsForBoundaries (:276). The slab path gated on nothing: it picked the first space whose polygon contains the slab's centroid, then fanned out to every slab whose centroid falls in that polygon, regardless of level.

Since space polygons are per-level footprints and storeys stack, both lookups match the wrong level as readily as the right one.

Fix

Gate both the space lookup and the fan-out on the clicked slab's level, using node.parentId ?? resolveLevelId(...) — the same definition of level membership space-detection uses (space-detection.ts:1532 filters a level's slabs by node.parentId === levelId).

Why no test caught it

The existing slab() fixture built nodes without parentId:

function slab(id: string, polygon: Array<[number, number]>): SlabNode {
  return { id, type: 'slab', polygon } as unknown as SlabNode
}

So the level dimension was invisible to the whole slab suite. Real slabs always carry a parent — packages/nodes/src/slab/tool.tsx:72 calls createNode(slab, levelId), and reconciliation creates them with { node, parentId: levelId }. The fixture now takes a level (defaulting to 'l1', so existing cases are unaffected).

Added slab room stops at the level boundary: two slabs with identical polygons on l1 and l2, one space per level. Verified it fails against unpatched paint-scope.ts (["ground:surface", "upstairs:surface"]) and passes with it.

Only wall and slab declare capabilities.paint.roomScope, and walls were already correct — so this was the only affected kind.

Gates

check 1600 files clean · check-types 9/9 · test 12/12, paint-scope 27 pass

🤖 Generated with Claude Code

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Note

Low Risk
Localized fix to paint target resolution with a regression test; no auth, data, or API surface changes.

Overview
Room-scope slab painting no longer bleeds onto slabs on other storeys when floors share the same footprint.

resolvePaintScopeTargets now resolves the clicked slab’s level (parentId ?? resolveLevelId) and uses it for both the space polygon lookup and the fan-out to other slabs—matching how wall room paint already gates on levelId.

Tests: the slab() helper sets parentId (default l1), and slab room stops at the level boundary asserts stacked l1/l2 slabs with identical polygons only paint the ground slab.

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