feat(physics): S2 chunk 3 - one flood per registration feeds collision rows and render entries

ShadowObjectRegistry computes the CELLARRAY once per registration under
Contract A (cylsphere route from the Setup's collision cylspheres, else the
bbox route over the whole visual part array) and derives BOTH products from
it: the collision rows (_entityToCells/_cells, CShadowObj per cell via
add_shadows_to_cells @0x00514ae0) and the per-part render entries
(AddPartsShadow @0x00517e40). The second, independent collision flood is
gone. A caller that supplies no part array floods from its collision shapes
exactly as before, so every legacy expectation holds byte-for-byte.

The staged SetPosition pipeline now carries the retail part array, cell
array, route, and entries through TryCaptureOwnerState/InstallOwnerState
and publishes them beside the collision cell replacements, honoring the
keep-when-empty rule (SetPositionInternal num_cells gate, pc:283540) for
both products together; two new tests pin a cross-cell move and the
keep-when-empty case. Behavior change, retail-exact: an object with
decorative non-BSP parts now has its collision shapes registered in every
cell those parts reach (pinned by a two-cell fixture); all-BSP objects are
unchanged. Movement paths still take collision cells from the transition
and recompute the retail product separately; chunk 4 unifies them on the
transition's array as retail does. No particle emitter reaches this registry.

Gates (implementer's isolated worktree at identical content): Release
build 0/0; Core 4,961/4,961; App hermetic 6,760/6,760; collision/InstalledDat
fixtures 63/63; Runtime 1,884/1,884; Content 213/213.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture/worldbuilder-inventory.md

@@ -177,27 +177,35 @@ draws its complete constructed shell. Portal polygons are not GPU mesh clips;
 pixel occlusion comes from the ordered walk and depth buffer.
 
 **Retail static render-shadow cell membership (2026-08-31; ownership moved
-to `ShadowObjectRegistry` by Campaign OVERHAUL S2 chunk 2).** Indoor statics
-are not rendered solely from their authored parent EnvCell. Retail's
-`CEnvCell::init_static_objects` creates a `CPhysicsObj` for every static,
-then `calc_cross_cells_static` + `CPartArray::AddPartsShadow` places every
-visual part in each crossed cell's `shadow_part_list`, including decorative
-GfxObjs that have no collision BSP. `ShadowObjectRegistry` owns this product
-as a retained per-entity retail CELLARRAY (`TryGetRetailCellArray`) plus
-per-cell part entries (`GetRetailPartEntriesInCell`), computed once at the
-SAME registration transaction as the collision flood
-(`RegisterMultiPart`/`Register`'s optional `partArray:` parameter) — not
-rebuilt per frame. `WalkProductionWorldData`'s indoor and outdoor static
-sweeps BORROW that array whole per record; they no longer recompute
-membership from each MeshRef's prepared visual AABB (the deleted
-`ResolveStaticRenderCells` / `ShadowObjectRegistry.ComputeStaticRenderCells`
-pair). The retail CELLARRAY remains distinct from `ShadowObjectRegistry`'s
-own collision rows (`GetOwnerCells`/`_entityToCells`) — the two retail lists
-share transit math but have different membership (collision cutover to the
-same CELLARRAY is S2 chunk 3) — until then, a record whose registry entry has
-no retail array yet (a streaming-window race between the static-projection
-journal and the physics publisher) falls back to its authored parent cell
-alone, counted by `WalkProductionWorldData.UnregisteredStaticRenderFallbackCount`.
+to `ShadowObjectRegistry` by Campaign OVERHAUL S2 chunk 2; collision cutover
+by S2 chunk 3, 2026-09-02).** Indoor statics are not rendered solely from
+their authored parent EnvCell. Retail's `CEnvCell::init_static_objects`
+creates a `CPhysicsObj` for every static, then `calc_cross_cells_static` +
+`CPartArray::AddPartsShadow` places every visual part in each crossed cell's
+`shadow_part_list`, including decorative GfxObjs that have no collision BSP —
+one CELLARRAY flood feeds BOTH the collision `shadow_object_list` and the
+render `shadow_part_list` (Contract B). `ShadowObjectRegistry` now mirrors
+this exactly: `RegisterMultiPart`/`Register`'s optional `partArray:`
+parameter, when supplied (every production call site since chunk 1b), drives
+ONE Contract A flood (`ComputeContractACellArray`) whose result becomes BOTH
+`GetOwnerCells`/`_entityToCells`/`_cells` (collision) and the retained
+per-entity retail CELLARRAY (`TryGetRetailCellArray`) plus per-cell part
+entries (`GetRetailPartEntriesInCell`) — not two independent floods, and not
+rebuilt per frame. A caller that supplies no part array (only test/legacy
+call sites remain) keeps the pre-chunk-3 collision-only dispatch untouched.
+`WalkProductionWorldData`'s indoor and outdoor static sweeps BORROW the
+retail array whole per record; they no longer recompute membership from each
+MeshRef's prepared visual AABB (the deleted `ResolveStaticRenderCells` /
+`ShadowObjectRegistry.ComputeStaticRenderCells` pair). A structural
+consequence: an object mixing a colliding BSP part with a decorative
+non-BSP part now gets a collision row for its BSP part in every cell the
+combined CELLARRAY reaches, including cells the BSP part alone would not
+have crossed — membership is decided by the whole-part-array flood, not per
+part; the BSP polygon test still decides actual contact at query time. A
+record whose registry entry has no retail array yet (a streaming-window race
+between the static-projection journal and the physics publisher) falls back
+to its authored parent cell alone, counted by
+`WalkProductionWorldData.UnregisteredStaticRenderFallbackCount`.
 A primitive-only Setup may reuse its already-authored cylsphere collision
 cell set; BSP-bearing and pure-visual statics use the all-visual-part box
 walk. The Facility Hub stair Setup `0x02000623` is the installed-DAT