docs(research): Phase 2 verification — floor renders, fix landed

User visually confirmed floors render in Holtburg Inn after the WB
TryGet<Setup> guard. Probe re-capture: 0 [wb-error] lines (was 385),
0 NULL_RESULT (was 55), Holtburg 123/123 cells complete (was 97/123).

Documents the nine pre-existing indoor bugs the user observed during
verification (see-through floor, indoor collision, stairs, walls,
clicking, indoor lighting artifacts, stabs-don't-react-to-atmospheric-
lighting, slope terrain lighting). All pre-existing; filed for follow-up
phases via docs/ISSUES.md.

Phase 2 complete.

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

docs/research/2026-05-19-indoor-cell-rendering-verification.md

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+# Indoor Cell Rendering — Phase 2 Verification
+
+**Date:** 2026-05-19
+**Outcome:** ✅ Floor renders in Holtburg Inn. User visually confirmed.
+**Predecessor:** [Phase 2 cause report](2026-05-19-indoor-cell-rendering-cause.md).
+
+---
+
+## Probe re-capture
+
+After applying the one-line WB fix at [`ObjectMeshManager.cs:1230`](../../references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/ObjectMeshManager.cs:1230):
+
+| Metric | Pre-fix | Post-fix |
+|---|---|---|
+| `[wb-error]` lines | 385 | **0** |
+| `[indoor-upload] NULL_RESULT` | 55 | **0** |
+| `[indoor-upload] FAILED` | 0 | 0 |
+| Total `[indoor-upload] requested` | — | 1157 |
+| Total `[indoor-upload] completed` | — | **1157** |
+| Holtburg (`0xA9B4`) requested | 123 | 123 |
+| Holtburg (`0xA9B4`) completed | 97 | **123** |
+| Holtburg (`0xA9B4`) missing | 26 | **0** |
+
+100% success rate on EnvCell uploads. Zero swallowed exceptions. Zero null returns.
+
+## Visual confirmation
+
+User walked into Holtburg Inn (and other nearby buildings whose cells were previously failing) and confirmed:
+
+> "Yes floors are rendering now inside houses."
+
+The previously-failing cells (`0xA9B40100`, `0xA9B40111`, `0xA9B40112`, `0xA9B40117`, `0xA9B4011B`, etc.) now upload successfully, the dispatcher finds their render data, and the floor / wall / ceiling geometry renders.
+
+## Regressions checked
+
+- Outdoor terrain still renders correctly. ✓
+- Outdoor scenery (trees, rocks, stabs) still render. ✓
+- NPCs, mobs, world entities still render. ✓
+- Build clean, no new warnings. ✓
+- No new test failures. ✓
+
+## Other observations during the walk
+
+The user reported **other indoor-related bugs** that are now observable because the floor is rendering. These are all **pre-existing** (not caused by this Phase 2 fix) but were hidden by the missing-floor bug. They are filed as separate issues for follow-up phases:
+
+1. See-through floor — other buildings visible "below" / "through" the rendered floor (depth/stab-culling).
+2. Spot lights on walls indoors (point-light positioning).
+3. Camera on 2nd floor goes very dark (per-cell ambient or trigger).
+4. Static building stabs don't react to atmospheric lighting changes (shader path).
+5. Some slope terrain lit incorrectly (terrain normal calculation).
+6. Collision "blocked by air" indoors (cell BSP misalignment).
+7. Walking up stairs broken (stair-step physics on EnvCell geometry).
+8. Pass through walls from outside→in (one-sided wall collision).
+9. Click selection penetrates walls (WorldPicker raycast not testing cell BSP).
+
+These nine items are tracked in `docs/ISSUES.md` with proposed phase groupings. None block Phase 2 closure.
+
+## Conclusion
+
+**Phase 2 of the indoor cell rendering fix is complete.** The single-root-cause exception was identified via the diagnostic chain shipped in Phase 1 + Phase 2, and resolved with a one-line guard at the WB call site that prevented blind `TryGet<Setup>` deserialization of GfxObj-typed stab ids.
+
+Total runtime for Phase 2: ~4 client launches.