feat(phys L.2d slice 1): BSP-hit diagnostic probe + plan-of-record correction

Adds ACDREAM_PROBE_BUILDING — a read-only per-shadow-entry probe that
captures full BSP collision evidence whenever TransitionTypes.FindObjCollisions
attributes a hit (via the existing L.2a slice 3 chain). One multi-line
[resolve-bldg] entry per attributed hit: partIdx, hasPhys, bspR vs
vAabbR, world-space entOrigin_lb, and the actual hit polygon's vertices
in both object-local and world space.

Paired with a one-time [entity-source] line at every ShadowObjects.Register
call site in GameWindow so entityId from a probe line is greppable to its
WorldEntity source within a single log file.

Plumbing: BSPQuery writes the resolved hit polygon to a new
PhysicsDiagnostics.LastBspHitPoly side-channel at the 5 SetCollisionNormal
sites in Paths 5/6 + CollideWithPt. TransitionTypes clears that field
before each shadow-entry dispatch and reads it back at the L.2a slice 3
attribution site to emit the probe line.

Spec component 4 originally described an out ResolvedPolygon? parameter
on BSPQuery.FindCollisions; the static side-channel achieves the same
observable behavior without plumbing through BSPQuery's recursive private
methods. Deviation noted in PhysicsDiagnostics.LastBspHitPoly's XML doc.

Reframes the plan-of-record's L.2d sub-direction paragraph: the 2026-05-12
handoff proposed porting CBuildingObj + per-cell walkability, but ACE
BuildingObj.cs:39-52 + named-retail acclient_2013_pseudo_c.txt:701260
show find_building_collisions is one BSP test on Parts[0]. Per-cell
walkability belongs to L.2e, not L.2d. L.2d slice 1 is the diagnostic;
slice 2 is the actual fix scoped from slice 1's evidence (one of three
hypotheses: wrong BSP loaded / over-registered parts / BSPQuery flaw).

Tests: 2 synthetic unit tests in PhysicsDiagnosticsTests.cs pin the
static API contract that the BSPQuery → side-channel → TransitionTypes
emission chain depends on. The multi-line line format itself is verified
by acceptance criterion 2 (live Holtburg-doorway capture) — covering it
here would require a heavy PhysicsEngine + Transition fixture for a
diagnostic-only emission.

Verified: dotnet build green; the 2 new tests pass; the 8 pre-existing
test failures listed in the L.2a handoff (MotionInterpreter GetMaxSpeed_*,
PositionManager.ComputeOffset_BothActive_Combined,
PlayerMovementController.Update_ForwardInput_*, Dispatcher.W_held_*,
BSPStepUpTests.{D4,C3}) remain failing — none introduced by this slice.

Spec: docs/superpowers/specs/2026-05-13-l2d-cbuildingobj-collision-design.md
Conformance anchors:
- acclient_2013_pseudo_c.txt:701260 (CBuildingObj::find_building_collisions)
- acclient_2013_pseudo_c.txt:323725 (BSPTREE::find_collisions)
- ACE references/ACE/Source/ACE.Server/Physics/Common/BuildingObj.cs:39-52

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

docs/plans/2026-04-29-movement-collision-conformance.md

@@ -169,21 +169,29 @@ fallback.
 - Audit `Setup.Radius` and cylinder fallback behavior against retail before
   relying on them for conformance.
 
-Current sub-direction (2026-05-12, evidence-driven by L.2a slice 2 + 3):
+Current sub-direction (revised 2026-05-13 in slice 1 design spec):
 The "I can't walk through doorways" symptom at Holtburg is **NOT a door-
-state-toggle issue**. The `[resolve]` probe captured 140 hit=yes lines
-at the doorway with `obj=0xA9B47900` (126 hits) — a landblock-baked
-static in the `0xLLLLxxxx` range, i.e. the **building itself**, not a
-door entity (no `0xCC0Cxxxx`-range hits). The building's baked collision
-mesh is treated as one solid block; the doorway gap that's visible in
-the rendered mesh isn't represented in the collision data we consume.
+state-toggle issue** — the `[resolve]` probe captured 140 hit=yes lines
+at the doorway with `obj=0xA9B47900` (126 hits), one specific BSP shadow
+entry. The 2026-05-12 handoff initially proposed porting `CBuildingObj` +
+**per-cell walkability** as the fix, but reading
+[ACE BuildingObj.cs:39-52](../../references/ACE/Source/ACE.Server/Physics/Common/BuildingObj.cs)
+and named-retail
+[acclient_2013_pseudo_c.txt:701260](../research/named-retail/acclient_2013_pseudo_c.txt)
+shows that's **not how retail solves doorways**. `find_building_collisions`
+is just one BSP test on `PartArray.Parts[0]`. The doorway gap lives
+inside that part's physics BSP itself. Per-cell walkability
+(`CCellStruct::point_in_cell`, `sphere_intersects_cell`,
+`box_intersects_cell`, `CObjCell::find_cell_list`) is how the resolver
+selects **which cells** to iterate, not how it decides whether a wall
+has a hole — that work belongs to **L.2e**, not L.2d.
 
-L.2d slice 1's scope is therefore the `CBuildingObj` + per-cell
-walkability port (interpretation 2 of the handoff). The named retail
-anchors `CCellStruct::point_in_cell`, `CCellStruct::sphere_intersects_cell`,
-`CCellStruct::box_intersects_cell`, `CBuildingObj::find_building_collisions`
-are the entry points. Spec to be written at
-`docs/superpowers/specs/2026-05-13-l2d-cbuildingobj-collision-design.md`.
+L.2d slice 1 is therefore a **read-only BSP-hit diagnostic** that
+captures full collision evidence per `[resolve]` `hit=yes` line.
+Distinguishes three hypotheses (wrong BSP loaded / over-registered
+parts / BSPQuery flaw) from a single Holtburg-doorway capture; slice
+2 is the right-sized fix scoped from slice 1's evidence. Design spec:
+[docs/superpowers/specs/2026-05-13-l2d-cbuildingobj-collision-design.md](../superpowers/specs/2026-05-13-l2d-cbuildingobj-collision-design.md).
 Handoff: [docs/research/2026-05-12-l2a-shipped-l2d-handoff.md](../research/2026-05-12-l2a-shipped-l2d-handoff.md).
 
 ### L.2e - Cell Ownership: Outdoor Seams, CELLARRAY, cell_bsp