#119 decisive probe: ACDREAM_DUMP_ENTITY one-shot entity dump (H-A/H-B/H-C discriminator)

The broken-state log (user-session-capture2.log) shows meshMissing=0 /
entSeen==entDrawn WHILE broken stairs are on screen - the staircase is
DRAWN WRONG, not missing. This probe discriminates the three live
hypotheses in ONE launch (handoff 2026-06-11 s4):

- HYDRATE dump (GameWindow.BuildInteriorEntitiesForStreaming): per-part
  placement-frame translations + dropped-part accounting at the MOMENT
  MeshRefs are constructed. H-A (SetupMesh.Flatten identity fallback /
  silent gfx-null part drops under degraded dat reads) shows here as
  zero translations or built<43.
- DRAW dump (WbDrawDispatcher, first tuple per entity): live MeshRefs
  translation summary + per-part loaded flags + Tier-1 classification
  cache state (batch count + RestPose translation summary), re-emitted
  compactly on signature change. H-B (partial/stale cached batch set)
  shows as correct translations + odd batch count.
- WALK-REJECT lines (rate-limited): attributes 'entity never reaches
  the draw loop' to the specific gate (visibleCellIds/frustum).
- Correct everything -> H-C (draw-side compose), instrument next.

Targets: ACDREAM_DUMP_ENTITY=0x020003F2,0x020005D8 (the 43-part spiral
staircase Setup + the wall barrels; H-A predicts the user's 'barrel' IS
the collapsed staircase). Probe is inert when the env var is unset.
Parser in RenderingDiagnostics (diagnostic-owner pattern) + 5 unit tests.

Suites: App 242+1skip / Core 1427+2skip / UI 420 / Net 294.

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

src/AcDream.Core/Rendering/RenderingDiagnostics.cs

@@ -373,6 +373,47 @@ public static class RenderingDiagnostics
     /// </summary>
     public static bool IsEnvCellId(ulong id) => (id & 0xFFFFu) >= 0x0100u;
 
+    /// <summary>
+    /// #119 tower-staircase decisive probe (2026-06-11). Comma-separated
+    /// Setup / GfxObj source ids (hex, optional 0x prefix) from
+    /// <c>ACDREAM_DUMP_ENTITY</c>. Any <c>WorldEntity</c> whose
+    /// <c>SourceGfxObjOrSetupId</c> is in this set emits:
+    /// (a) a <c>[dump-entity] HYDRATE</c> dump at MeshRef construction time
+    /// (<c>GameWindow.BuildInteriorEntitiesForStreaming</c>) — per-part
+    /// placement-frame translations + dropped-part accounting — discriminating
+    /// hydration-time corruption (H-A: SetupMesh.Flatten identity fallback /
+    /// silent gfx-null part drops under degraded dat reads);
+    /// (b) a <c>[dump-entity] DRAW</c> dump in <c>WbDrawDispatcher</c> at first
+    /// draw — live MeshRefs translations + Tier-1 classification cache state —
+    /// re-emitted compactly whenever that state changes (H-B: stale/partial
+    /// cached batch set); and
+    /// (c) rate-limited <c>[dump-entity] WALK-REJECT</c> lines when the
+    /// dispatcher's walk filters the entity out (absence-of-draw attribution).
+    /// Empty set = probe off; every call site early-outs on <c>Count == 0</c>.
+    /// </summary>
+    public static IReadOnlySet<uint> DumpEntitySourceIds { get; } =
+        ParseDumpEntityIds(Environment.GetEnvironmentVariable("ACDREAM_DUMP_ENTITY"));
+
+    /// <summary>
+    /// Parse the <c>ACDREAM_DUMP_ENTITY</c> value: comma-separated hex ids,
+    /// optional 0x prefix, whitespace tolerated, malformed segments ignored
+    /// (probes are forgiving — a typo'd segment must not take the launch down).
+    /// Internal for unit tests.
+    /// </summary>
+    internal static IReadOnlySet<uint> ParseDumpEntityIds(string? raw)
+    {
+        var set = new HashSet<uint>();
+        if (string.IsNullOrWhiteSpace(raw)) return set;
+        foreach (var seg in raw.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
+        {
+            var s = seg.StartsWith("0x", StringComparison.OrdinalIgnoreCase) ? seg[2..] : seg;
+            if (uint.TryParse(s, System.Globalization.NumberStyles.HexNumber,
+                    System.Globalization.CultureInfo.InvariantCulture, out var id))
+                set.Add(id);
+        }
+        return set;
+    }
+
     /// <summary>
     /// The top-level render branch: should this frame run the indoor (DrawInside) path?
     ///