docs: indoor walkable-plane BSP port partial-ship handoff

Foundation work (6 commits ff548b9..f845b22) landed but visual
verification 2026-05-19 FAILED to fix the user-reported indoor bugs.
Documenting the deeper diagnosis + the next phase target without
reverting the foundation work.

What landed (kept):
- BSPQuery.FindWalkableInternal gained ref ushort hitPolyId (Task 1).
- New public BSPQuery.FindWalkableSphere wrapper over the existing
  retail-faithful walkable finder (Task 2).
- Transition.TryFindIndoorWalkablePlane refactored through it,
  PointInPolygonXY deleted (Task 3).
- [indoor-walkable] runtime-toggleable probe (Task 4).
- 5 new tests + 9 updated existing tests, all green; build clean.

What didn't fix: cellar descent FAIL, 2nd-floor walking FAIL
(intermittent falling-stuck), single-floor cottage REGRESSION (was
stable, now intermittent falling-stuck), phantom collisions PERSIST.

Probe evidence: 1443 MISS / 2 HIT over 1445 calls. Smoking gun:
foot-sphere-tangent-to-floor case fails PolygonHitsSpherePrecise's
|dist| > radius - epsilon check by ~0.0002. The BSP walker is
correct; the caller (TryFindIndoorWalkablePlane) is misusing it.

Root cause (deeper than originally diagnosed): TryFindIndoorWalkablePlane
exists only as a Phase 2 commit eb0f772 stop-gap. Retail doesn't
synthesize a ContactPlane per frame — retail RETAINS the previous
frame's plane when the BSP says no collision. Retail's find_walkable
only runs inside step_sphere_down (a sweep), never as a standing-still
query.

Next phase target: port retail's ContactPlane retention so the
resolver retains state across frames. Likely eliminates the per-frame
TryFindIndoorWalkablePlane call entirely. Foundation work (BSP walker
+ probe + tests) remains useful regardless.

ISSUES #83 remains OPEN with the deeper diagnosis.
Roadmap header updated to reflect partial-ship status.
Handoff at docs/research/2026-05-19-indoor-walkable-plane-bsp-port-shipped-handoff.md.

Spec: docs/superpowers/specs/2026-05-19-indoor-walkable-plane-bsp-port-design.md
Plan: docs/superpowers/plans/2026-05-19-indoor-walkable-plane-bsp-port.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/plans/2026-04-11-roadmap.md

@@ -1,6 +1,6 @@
 # acdream — strategic roadmap
 
-**Status:** Living document. Updated 2026-05-19. **Between phases.** **Since the last header update:** Indoor cell rendering Phase 1 (diagnostics) + Phase 2 (fix) shipped — root cause was a one-line WB bug at `ObjectMeshManager.cs:1223` (blind `TryGet<Setup>` on GfxObj-prefixed stab ids threw `ArgumentOutOfRangeException` which WB's outer catch silently swallowed, causing 26/123 Holtburg cells to fail upload). Identified via diagnostic chain (5 `[indoor-*]` probes + a `ContinueWith` exception surfacer + a `ConsoleErrorLogger` injected into WB), fixed with a Setup-prefix guard. User visually confirmed floors render. Surfaced 9 pre-existing indoor bugs filed in `docs/ISSUES.md`. **Earlier:** C.1.5b shipped (issue #56 per-part transforms for multi-emitter PES + `EntityScriptActivator` extended to dat-hydrated EnvCell statics & exterior stabs — portal swirl, inn fireplace flames, cottage chimney smoke, spell-cast particles all match retail). post-A.5 polish completed (#52 lifestone, #54 JobKind, #53 Tier 1 cache); N.6 slice 1 shipped (gpu_us fix + radius=12 perf baseline, conclusion CPU dominates GPU 30–50×); C.1.5a shipped (portal PES wiring; surfaced #56 → resolved in C.1.5b).
+**Status:** Living document. Updated 2026-05-19. **Between phases.** **Since the last header update:** Indoor walkable-plane BSP port FOUNDATION shipped (6 commits, `ff548b9` → `f845b22`) but visual verification failed — cellar descent, 2nd-floor walking, single-floor cottage regressions all confirm the shipped fix doesn't address the user-reported indoor bugs. Root cause now diagnosed as deeper than originally thought: `TryFindIndoorWalkablePlane` exists as a Phase 2 stop-gap that retail doesn't have an analog for. Retail retains ContactPlane state across frames; we re-synthesize per frame. Foundation work (BSP walker + probe + tests) remains useful; next phase needs to port retail's ContactPlane retention mechanism and likely eliminate `TryFindIndoorWalkablePlane` entirely. Handoff: [`docs/research/2026-05-19-indoor-walkable-plane-bsp-port-shipped-handoff.md`](../research/2026-05-19-indoor-walkable-plane-bsp-port-shipped-handoff.md). ISSUES #83 remains OPEN with deeper diagnosis. **Earlier:** Indoor cell rendering Phase 1 (diagnostics) + Phase 2 (fix) shipped — root cause was a one-line WB bug at `ObjectMeshManager.cs:1223` (blind `TryGet<Setup>` on GfxObj-prefixed stab ids threw `ArgumentOutOfRangeException` which WB's outer catch silently swallowed, causing 26/123 Holtburg cells to fail upload). Identified via diagnostic chain (5 `[indoor-*]` probes + a `ContinueWith` exception surfacer + a `ConsoleErrorLogger` injected into WB), fixed with a Setup-prefix guard. User visually confirmed floors render. Surfaced 9 pre-existing indoor bugs filed in `docs/ISSUES.md`. **Earlier:** C.1.5b shipped (issue #56 per-part transforms for multi-emitter PES + `EntityScriptActivator` extended to dat-hydrated EnvCell statics & exterior stabs — portal swirl, inn fireplace flames, cottage chimney smoke, spell-cast particles all match retail). post-A.5 polish completed (#52 lifestone, #54 JobKind, #53 Tier 1 cache); N.6 slice 1 shipped (gpu_us fix + radius=12 perf baseline, conclusion CPU dominates GPU 30–50×); C.1.5a shipped (portal PES wiring; surfaced #56 → resolved in C.1.5b).
 **Purpose:** One source of truth for where the project is and where it's going. Every observed defect or missing feature has a named phase that owns it; when something looks wrong in-game, look here to find the phase that'll address it. Implementation details live in per-phase specs under `docs/superpowers/specs/`, not in this file.
 
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