probe(render): cathedral Phase I instrumentation

Implements the synthesis plan''s Phase I (instrument-first, no rendering
edits): the [falls] watch printing EVERY particle submission carrying a
real falls owner (the outdoor landblock emitters 0xCF418000-13 the six
fix rounds never traced) with route + phase; [falls-adm] admission
verdicts for F418 emitters at the retail ShouldDrawParticles port
(owner, cell, distance, in-set, eligibility); the continuous
[walk-root] line now separating the TRUE root flood
(InteriorFloodCells) from the visited union (root + look-ins - the
conflation the review corpus indicted) and printing the walk''s own
exit-view count; [walk-cam] replayable camera dumps; and the restored
[walk-portal] per-portal side/clip decisions. All under the existing
ACDREAM_PROBE_WALK_ROOT flag; the depth-checkpoint readback is
deferred until these answers narrow the question (mid-pass Vulkan
depth reads need render-pass splitting).

Hermetic 6,762/0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/launch-options.md

@@ -315,7 +315,7 @@ issue is closed, the strip was missed; delete both.
 | `ACDREAM_PROBE_CHILD_CELL` | c4 route 7 | `=1` | gates one `[child-cell]` line per Runtime committed-child canonical-cell write in `RuntimeLiveEntitySessionController`, `RuntimeEntityObjectLifetime`, `RuntimeEntityDirectory` (parent/child guid, old/new cell, cause tag) | print-only | `PhysicsDiagnostics.ProbeChildCellEnabled` |
 | `ACDREAM_PROBE_CLIPROUTE` | "throwaway apparatus — strip once §4 ships" | `=1` | print-on-change `[clip-route]` / `[clip-route-disp]` / `[clip-route-scis]` lines: outside-slice clip routing, region-SSBO bytes, terrain-UBO head, actual GL/RHI scissor state | print-only | `RenderingDiagnostics.ProbeClipRouteEnabled` |
 | `ACDREAM_PROBE_WALK_SHADOW` | Campaign FW3.2b-2 flip apparatus — dies with the flip commit | `=1` | runs the PRODUCTION retail frame walk per frame in SHADOW (no draws change) and prints one `[walk-shadow]` line per frame whose visited cell/building sets diverge from the old visibility path (the I5 dual-shadow pattern applied to the FW3 static cutover) | print-only; adds the per-frame CPU cost of the shadow walk while set | `RenderingDiagnostics.ProbeWalkShadowEnabled` |
-| `ACDREAM_PROBE_WALK_ROOT` | FW3 visual-gate apparatus (stairwell-transition + cathedral-falls defects) — dies with those fixes | `=1` | after every interior/outdoor root flip, prints 8 `[walk-root]` lines (one per frame): viewer cell, root cell, camera-cell resolution, slice count, eye position, and the walk's visited cell list; also prints `[walk-part]` lines at every particle submission route (route name, owner ids, pre/post-depth-clear phase), `[walk-alpha]` lines at every retail alpha-queue drain, `[walk-dyn]` lines with each dynamic's outside-stage/viewcone verdicts (~every 120th product frame), and `[walk-portal]` lines with the walk PView's per-portal side/clip decisions (~every 90th frame) — together they pin which crossing frames root wrong, flood short, submit particles after the interior depth clear, or collapse an exit view at the portal walk | print-only; chatty near particle-heavy scenes while set | `RenderingDiagnostics.ProbeWalkRootEnabled` |
+| `ACDREAM_PROBE_WALK_ROOT` | the cathedral Phase I instrumentation (synthesis doc `docs/research/2026-08-30-cathedral-synthesis.md`) — dies with that investigation | `=1` | prints `[walk-root]` rooting lines every ~30th frame AND for 8 frames after each interior/outdoor root flip (viewer/root cell, camera-cell resolution, slice count, the walk's OWN exit-view count, the TRUE root flood separated from the visited union, eye + forward); `[walk-cam]` replayable camera dumps (eye, viewport, full view-projection) every ~300 frames and at flips; `[falls]` lines on EVERY particle submission carrying a real falls owner (0xCF418000-13) with route + phase; `[falls-adm]` admission verdicts for F418 emitters (~every 120th ApplyRetailView); plus the earlier family — `[walk-part]` per-route submissions, `[walk-alpha]` drains, `[walk-dyn]` outside-stage verdicts (~120th product frame), `[walk-portal]` per-portal side/clip decisions (~90th frame) | print-only; chatty near particle-heavy scenes while set | `RenderingDiagnostics.ProbeWalkRootEnabled` |
 | `ACDREAM_PROBE_CONTACT_PLANE` | spike-only, 2026-05-20 | `=1` | gates one `[cp-write]` line per write to `CollisionInfo.ContactPlane*`/`LastKnownContactPlane*` fields (field, old→new, caller method via stack walk, source line); only logs on actual value changes | print-only, but performs a stack walk to identify the caller method when firing — real CPU cost per write while on (not just a string format); suppresses no-op writes to bound volume | `PhysicsDiagnostics.ProbeContactPlaneEnabled` |
 | `ACDREAM_PROBE_ENT` | #138 | `="1"` | Traces the persistent player entity across teleport streaming churn: presence in the render draw-set flat view vs. survival of the dynamics cull, to distinguish "missing from draw set" vs "present but culled" | print-only, "Observation-only — emits no behavior change" (doc comment). `LogPlayerDynOnChange` dedupes by transition to avoid per-frame spam. Marked STRIP-once-root-caused (like the dense-town FPS apparatus). | `EntityVanishProbe.Enabled` (`EntityVanishProbe.cs:23-24`), issue #138-B |
 | `ACDREAM_PROBE_FLAP` | "throwaway apparatus — strip once the flap mechanism is confirmed" | `=1` | EVERY FRAME (unthrottled, not change-gated) while the camera root is indoor: `[flap]` from `PortalVisibilityBuilder.Build` (portal side-test/traverse/cull/projection) + paired `[flap-cam]` from `PhysicsCameraCollisionProbe`/`[flap-sweep]` (FindCameraCell resolution, eye positions) | print-only, but unthrottled per-frame `StringBuilder` allocation + `Console.WriteLine` on multiple call sites while indoor — heavy log volume/allocation under sustained indoor play; does not alter rendered output | `RenderingDiagnostics.ProbeFlapEnabled` |