docs(handoff): A6.P3 #98 — full-session handoff doc + CLAUDE.md/ISSUES.md updates

Adds the canonical pickup document
docs/research/2026-05-23-a6-p3-issue98-harness-handoff.md with:
- TL;DR + session arc (10 commits chronological)
- What the trajectory replay harness IS (committed apparatus)
- Bug 1 status: #98 cellar-up freeze (unfixed, 6 fix shapes failed)
- Bug 2 status: airborne-at-tick-1 (new, 6 hypotheses tested, root
  cause not isolated)
- Exclusion list: DO NOT retry any of the 6+6 dead ends
- Apparatus inventory: probes, tests, fixtures, cdb captures
- Recommended next move: side-by-side comparison harness against
  live PlayerMovementController state (evidence-first instead of
  speculation-first)
- Alternative moves: pivot to other M1.5 issues or M2 prep
- Self-contained pickup prompt at the bottom of the handoff doc

Updates CLAUDE.md's "Current A6 phase" block to point at the new
handoff doc as the canonical resume artifact.

Updates ISSUES.md's #98 entry with the late-day extension findings,
the 6-hypothesis exclusion list, and a pointer to the handoff doc.

Test baseline maintained at 1172 + 8 pre-existing failures.

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

CLAUDE.md

@@ -764,8 +764,14 @@ divergence (low confidence).** Full divergence reading +
 fix-plan pickup prompt at
 [`docs/research/2026-05-23-a6-p3-issue98-replay-comparison.md`](docs/research/2026-05-23-a6-p3-issue98-replay-comparison.md).
 Current A6 phase:
-**A6.P3 — PAUSED 2026-05-23 evening after two days of work.** The
-session shipped further apparatus + first failed fix attempt + revert:
+**A6.P3 — PAUSED 2026-05-23 (full day). Trajectory replay harness shipped
+but BLOCKED on a new bug surfaced during commissioning.** Read
+[`docs/research/2026-05-23-a6-p3-issue98-harness-handoff.md`](docs/research/2026-05-23-a6-p3-issue98-harness-handoff.md)
+as the canonical pickup document — it has the chronological commit list,
+the apparatus inventory, the exclusion list (do-not-retry), and three
+concrete next-session options ranked by recommendation.
+
+The session shipped further apparatus + first failed fix attempt + revert:
 `8a232a3` (`[step-walk-adjust]` probe inside `Transition.AdjustOffset`
 revealing branch tokens and per-call zGain), `8daf7e7` (findings note
 at [`docs/research/2026-05-23-a6-stepwalkadjust-findings.md`](docs/research/2026-05-23-a6-stepwalkadjust-findings.md)
@@ -787,8 +793,23 @@ research on `CEnvCell::find_env_collisions` → `BSPTREE::find_collisions`
 indoor CP-setting chain (prior research worked on the outdoor
 `CLandCell` path; indoor was never fully traced). Session-end ISSUES.md
 entry has the full reading and pickup prompt. **NO further #98 fix
-attempts until apparatus or research has converged — five+ failed
+attempts until apparatus or research has converged — six+ failed
 attempts in the saga is the signal.**
+
+**Late-day extension (2026-05-23 PM):** trajectory replay harness shipped
+(commits `4c9290c` → `5c6bdbe`). Mechanics work — runs 200 ticks in <100 ms.
+Five tests pass. NEW finding: the cellar ramp polygon is in a GfxObj
+(static building piece), not the cell's PhysicsPolygons. Harness now
+includes `RegisterStairRampGfxObj` for synthetic stair construction
+and `AttachSyntheticBsp` to wrap hydrated cells (which have BSP=null)
+with a one-leaf BSP that exposes the indoor BSP collision path.
+**NEW BLOCKER:** even with full apparatus, sphere goes airborne at
+tick 1 with `hit=(0,1,0)` (a +Y wall normal matching no registered
+geometry). 6 hypotheses tested via the harness, none isolated root cause.
+Per systematic-debugging skill's "question architecture" rule, stop and
+reflect. Next session: build a side-by-side comparison harness that
+captures live PlayerMovementController state and diffs against the
+test harness — evidence-first instead of speculation-first.
 Findings doc:
 [`docs/research/2026-05-21-a6-cdb-capture-findings.md`](docs/research/2026-05-21-a6-cdb-capture-findings.md).
 Original demo scenario (Holtburg Sewer end-to-end) is unreachable: sewer