docs(p2): cellar corner-wedge pinned to step-up-onto-floor (retail cdb) + trace apparatus

Live retail cdb trace (tools/cdb/cellar-corner-escape.cdb) of the Holtburg
cottage cellar-top corner decodes the ground truth: retail escapes by
step_sphere_up->step_up (196x vs 38 near-misses), transitioning the contact
plane from the ramp (N.z=0.78) onto the flat cottage floor (N.z=1.0, 76
landings). acdream slides at the lip and never makes that ramp->floor
transition -> the intermittent cellar wedge.

So the remaining cellar bug is the #98-core step-up-onto-cottage-floor
(DoStepDown / step_sphere_down / find_walkable), which the shipped B1 (abbd761)
+ slide_sphere (0935a31) fixes got close to but didn't finish. Door still
blocks; generic step-up climbs; cellar went always-stuck -> works-mostly.

Next (handoff doc): instrument acdream's OWN corner path (does step_up fire at
the lip and fail to land on the cottage floor?) before porting the lip-climb --
no guessing (#98 saga rule).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/research/2026-06-04-p2-cellar-corner-stepup-handoff.md

@@ -0,0 +1,91 @@
+# P2 pickup — cellar-top corner wedge = step-up-onto-cottage-floor (retail cdb pinned)
+
+> **Canonical pickup, 2026-06-04.** Branch `claude/thirsty-goldberg-51bb9b` (do NOT
+> branch/worktree; do NOT push without asking; NEVER `git stash`/`gc`). PowerShell on
+> Windows; launch logs are UTF-16.
+
+## State both altitudes
+- **Milestone:** M1.5 — Indoor world feels right.
+- **Phase:** P2 (door / building-shell collision) of the verbatim spatial-pipeline port.
+- **Shipped this session (committed, branch HEAD `0935a31`):**
+  - `abbd761` — **B1 fix:** Path 5 (Contact) near-miss dispatch ported verbatim — gate
+    behind `num_sphere > 1`, head-first order, `neg_step_up` mapping (head→false/slide,
+    foot→true/step-up). Retail `transitional_insert`/`find_collisions` Contact branch
+    (`acclient_2013_pseudo_c.txt:323838-323881`, `set_neg_poly_hit` :323279). Fixed the
+    B1 grounded-step-up wedge (the handoff's "climb" localization was WRONG — proved via
+    `ITestOutputHelper` capture).
+  - `0935a31` — **slide_sphere fix:** head near-miss (`neg_step_up==0`) now calls the
+    faithful `CSphere::slide_sphere` (existing `SlideSphereInternal`) + continues the
+    insert loop, replacing the A6.P4 `Collided` shortcut (`transitional_insert`
+    pc:273350-273351).
+  - `f984e92` — docs (corrected the prior P2 handoff).
+- **Visual-verified 2026-06-04:** generic step-up climbs; **closed cottage door still
+  BLOCKS** (slides tangentially, no walkthrough — regression check passed); **cellar
+  ascent went from ALWAYS-stuck → WORKS-MOSTLY.**
+- **Remaining:** an **intermittent corner-wedge** at the cellar-top lip. Retail is
+  always smooth there (user-confirmed). So it's a real bug.
+
+## The cdb-pinned finding (retail ground truth)
+`tools/cdb/cellar-corner-escape.cdb` traced live retail at the cellar-top corner
+(decode: `parse_corner_log.py`; raw: `cellar-corner-retail.log`). Retail escapes the
+corner by **STEP-UP, not slide:**
+- `step_sphere_up`→`step_up` fired **196×** vs only **38 near-misses**. `step_up`
+  normals: +X wall ×78, **ceiling `(0,0,-1)` ×36**, +Y wall ×32, −X wall ×18, ramp
+  slope `(0,−0.62,0.78)` ×11, −Y wall ×10, floor `(0,0,1)` ×10. So retail step-ups
+  against EVERY grounded full-hit at the corner.
+- **Contact plane transitions ramp `N.z=0.78` (×63) → flat cottage floor `N.z=1.0`
+  (×76).** That's the escape: retail **climbs the lip off the ramp ONTO the cottage
+  floor.**
+- The user's "run in place against the ceiling (not stuck)" = `step_up` failing on the
+  ceiling normal `(0,0,-1)` → `step_up_slide` (transient; steer out).
+
+**Divergence pinned:** retail escapes by **stepping up onto the cottage floor**;
+acdream **slides at the lip and never makes the ramp→floor transition**. The slide
+itself (the `0935a31` fix) is correct + working; the gap is the **final lip-climb**.
+This is the **original #98 core** — `DoStepDown`/`step_sphere_down` finding + landing
+on the cottage floor — which B1+slide got close to but didn't finish.
+
+## Next step (evidence-first — #98 saga rule: do NOT guess)
+1. **Instrument acdream's OWN corner path.** The captures so far
+   (`cellar-up-capture*.jsonl`, `door-recheck-capture.jsonl`) have positions/normals but
+   NOT the path. Need to answer: at the cellar-top lip, does acdream's `step_sphere_up`→
+   `DoStepUp` FIRE and FAIL to land on the cottage floor (DoStepDown can't find
+   `N.z=1.0` within `StepUpHeight=0.6`), or does it not fire (the hit goes to the slide
+   path instead)? Relaunch acdream with `ProbeBuildingEnabled` (→ `[neg-poly-dispatch]`/
+   `[bsp-test]`) + `ACDREAM_DUMP_STEPUP=1` + `ProbeStepWalkEnabled` (→ `[step-walk]`),
+   reproduce the wedge, read the path. (xunit-swallow doesn't apply to the live app —
+   Console probes DO surface in the launch log.)
+2. **Compare to retail's 196 step_up / ramp→floor transition** and port the missing
+   lip-climb verbatim. Likely in `DoStepDown` (`TransitionTypes.cs:3074`) /
+   `BSPQuery.step_sphere_down` (:1206) / `find_walkable` (:693) — the cottage-floor
+   find+land. Retail anchors: `CTransition::step_up` pc:273099, `step_down` pc:272946,
+   `BSPTREE::step_sphere_down` pc:323665, `CObjCell::find_env_collisions` (the
+   walkable-refresh that overwrites the contact plane ramp→floor).
+3. **USER VISUAL GATE:** cellar ascent clean (no intermittent wedge); door still blocks;
+   generic step-up still climbs.
+
+## Apparatus (committed / available)
+- `tools/cdb/cellar-corner-escape.cdb` — retail corner trace (step_up/step_sphere_up/
+  neg_poly_hit/contact_plane counts + args; 30K threshold — TOO HIGH for these
+  lower-frequency BPs, lower to ~3000 next time so it auto-detaches in one wedge).
+- `parse_corner_log.py` — decodes the cdb log (hex→float, histograms).
+- Captures (UNCOMMITTED, in worktree root, ~32 MB each — do NOT commit):
+  `cellar-up-capture.jsonl` (v1, pre-slide-fix wedge), `cellar-up-capture-v2.jsonl`
+  (post-slide-fix: 96 hit-and-advanced slide frames), `door-recheck-capture.jsonl`,
+  `cellar-corner-retail.log` (the retail cdb trace).
+- `analyze_cellar.py` / `analyze_v2.py` — ad-hoc capture analyzers (capture-specific).
+
+## Test baseline
+Core 1310 pass / 4 fail / 1 skip. The 4 fails are pre-existing documents-the-bug /
+separate-issue: `DoorCollisionApparatusTests.Apparatus_Grounded_50cmOffCenter`
+(synthetic-test artifact — terrain=-1000, no queryable floor; NOT a real door-block
+failure — see `memory/project_p2_door_stepup_findings.md`), 2× `DoorBugTrajectoryReplay
+LiveCompare_*` (compare against captured-BUGGY-live positions; need re-baseline), and
+`BSPStepUpTests.D4` (airborne Path 6 sliding-normal persistence — separate). App 177 green.
+
+## Do NOT
+- Guess a step-up fix without acdream's corner path trace (the #98 saga burned 10+ guesses).
+- Flip `Apparatus_Grounded_50cmOffCenter` to `Assert.True(blocked)` — it blocks via a
+  synthetic-floor artifact, not a faithful door block.
+- Re-investigate B1 (the near-miss gate) or the slide_sphere head-near-miss path — both
+  shipped + verified.