docs(handoff): indoor follow-up brief + fresh-session kickoff prompt

After Phase 1+2 (indoor cell rendering — missing floors fixed),
9 follow-up issues (#78-#86 in docs/ISSUES.md) need their own
phases. This handoff doc gives the next session everything it needs
to start cold: probe infrastructure status, issue cluster groupings,
suggested phase order, and the verification approach that worked
for Phase 1+2.

Companion prompt file is a self-contained kickoff that can be pasted
into a fresh Claude Code session to start work on the cluster.

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

docs/research/2026-05-19-indoor-followup-prompt.md

@@ -0,0 +1,65 @@
+# Indoor follow-up — fresh-session kickoff prompt
+
+Copy the block below into a fresh Claude Code session in this repo. The model
+will load CLAUDE.md automatically and find the handoff doc + filed issues
+on its own.
+
+---
+
+```
+Pick up the indoor-walking follow-up work for acdream. The starting point:
+
+1. Read docs/research/2026-05-19-indoor-followup-handoff.md — that's the
+   session-start brief.
+
+2. Read docs/ISSUES.md issues #78 through #86 — these are the 9 bugs the
+   user observed once floors started rendering at Holtburg Inn. They are
+   ALL pre-existing (not caused by Phase 1+2 which just made indoor floors
+   visible).
+
+3. Use the existing [indoor-*] probe infrastructure shipped in Phase 1
+   (toggleable via ACDREAM_PROBE_INDOOR_ALL=1 + DebugPanel checkboxes).
+   WbMeshAdapter also injects a real ConsoleErrorLogger now, so any
+   silently-caught WB exception will appear as [wb-error] lines in the
+   log automatically.
+
+4. The recommended approach per the handoff:
+   - START with Cluster A (cell-BSP / portal-cull cluster — issues #78,
+     #84, #85, #86). These share a likely root cause and have the biggest
+     gameplay impact.
+   - Don't try to fix all 9 at once. Pick the cluster, pick one issue
+     within it, brainstorm via superpowers:brainstorming, and proceed
+     phase-by-phase.
+
+5. CLAUDE.md's rules apply:
+   - No workarounds; fix root causes.
+   - Use superpowers skills for major work (brainstorming → writing-plans
+     → subagent-driven-development → finishing-a-development-branch).
+   - Drive autonomously — Claude picks what to work on next; user
+     reviews. Don't ask "what should I work on?" between phases.
+   - Visual verification by the user is the acceptance test for any
+     rendering / collision / lighting fix.
+
+6. Phase 1+2 took 4 client launches total. Your work should be similar
+   if you preserve the diagnostic-driven approach: probe → capture →
+   diagnose → fix → verify.
+
+State the milestone and current cluster in the first action you take.
+Then begin by reading the handoff doc.
+```
+
+---
+
+## Quick reference for the helper
+
+If the new session asks "which phase should I do first?":
+
+- **Cluster A (cell-BSP/portal)** — #78 see-through floor + #84 blocked-by-air + #85 pass-through-walls + #86 click-through-walls. Hypothesis: cell BSP is cached but not consulted correctly by the movement resolver / picker, AND outdoor stabs aren't stencil-culled when player is in a sealed cell.
+- **Cluster B (lighting plumbing)** — #79 + #80 + #81 + (maybe #82). Less urgent.
+- **Standalone #83 stairs** — physics work on EnvCell stair geometry. Smaller scope.
+
+## Quick reference for the user
+
+To start the new session: open a fresh Claude Code in the acdream repo and paste the boxed prompt above. Or just say:
+
+> "Read `docs/research/2026-05-19-indoor-followup-handoff.md` and start on the indoor-walking follow-up work."