docs: the cathedral seven-report synthesis + adjudicated FW4 plan

Files the independent review corpus (fable/opus/external + audit,
DAT-format, F418 DAT-geometry, retail decomp reconstruction) and the
synthesis that adjudicates their disagreements: retail roots INTERIOR
at the posed terrace defect pose with a ONE-CELL flood and ov=1 (the
free captures rooted outdoor - both were real); the falls are outdoor
landblock emitters 0xCF418000-13; the "thin seam bands" claim is
DAT-refuted (full-size exits; the seam is a coincident double
exit-to-outside plane at y=48); clear+seals live inside retail''s ov>0
block with a one-frame seal latch. Carries the instrument-first plan
(falls-owner trace, depth checkpoints, pose conformance) and the
decomp-pinned repair sequence toward FW4''s single-owner goal.

Also sweeps in the probe scaffolding slice 5''s path-limited add had
missed (RenderingDiagnostics field + the launch-options row wording).

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

src/AcDream.Core/Rendering/RenderingDiagnostics.cs

@@ -189,6 +189,14 @@ public static class RenderingDiagnostics
     /// Written only while the probe is on.</summary>
     public static string WalkRootPhase = "";
 
+    /// <summary>Companion scratch for <see cref="ProbeWalkRootEnabled"/>
+    /// (throwaway, same investigation): true on the frames (~every 90th)
+    /// where the walk's PView logs its per-portal seen/in-view/clip
+    /// decisions as <c>[walk-portal]</c> lines — pins WHY an exit view
+    /// collapses at a given camera pose. Set by the renderer before
+    /// Collect; read by WalkPView.</summary>
+    public static bool WalkPortalProbeThisFrame;
+
     /// <summary>
     /// Bounded-propagation port apparatus (2026-06-08). When true, PortalVisibilityBuilder.Build emits
     /// one [portal-churn] summary line per call: per-cell pop count (re-pops = churn), total re-enqueues,