Thin public wrapper over the existing retail-faithful
FindWalkableInternal (BSPNODE::find_walkable + BSPLEAF::find_walkable
port). Probes downward by probeDistance along up, returns the closest
walkable polygon the sphere would rest on plus the adjusted center.
Will replace Transition.TryFindIndoorWalkablePlane's linear first-match
scan (next commit). The wrapper is callable from any "stand here, find
my floor" use case; current intent is indoor walkable-plane synthesis.
4 unit tests covering: two-floors-foot-between (sphere overlapping lower
floor), only-upper-floor-foot-above (sphere overlapping upper floor),
no-walkable-in-probe-range (sphere out of overlap distance for all
polygons), steep-poly-rejected-by-WalkableAllowance. Note: find_walkable
requires sphere to overlap the polygon plane (|dist| <= radius);
the tests use geometry that exercises this correctly, unlike the spec's
illustrative values which assumed a "nearest below" scan.
Spec: docs/superpowers/specs/2026-05-19-indoor-walkable-plane-bsp-port-design.md
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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