diag(render): composite-warmup stall probe for the session-3 tunnel hang

The 2026-07-29 Coldeve session 3 stuck the player in the portal tunnel
forever: generation 2 (Town Network, 0x00070156) published render but
composites/collision never became ready, and the reveal latch correctly
held the tunnel. The composite warmup queue in WbDrawDispatcher has
exactly two permanent-stall shapes - a GfxObj id that never resolves
(silent load failure, e.g. custom-server content absent from the baked
pak) or an upload budget that never reopens - and they are
indistinguishable from the reveal log alone.

ACDREAM_PROBE_REVEAL=1 (NetDiagnostics.ProbeReveal) now emits one
[composite-warmup] STALL line per second while warmup blocks a reveal:
pending count, queue depth, scan state, upload-budget gate, and the
first four pending GfxObj ids. Zero cost when off.

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

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -228,6 +229,50 @@ public sealed partial class WbDrawDispatcher : IDisposable
             + (_compositeWarmupScanComplete ? 0 : entities.Count - _compositeWarmupScanIndex);
         CompositeTexturesReady = _compositeWarmupScanComplete
             && _compositeWarmupQueue.Count == 0;
+        if (!CompositeTexturesReady
+            && AcDream.Core.Net.NetDiagnostics.ProbeReveal)
+        {
+            ProbeRevealWarmupStall();
+        }
+    }
+
+    // #260 probe: while composite warmup blocks a reveal, name the stall once
+    // per second. The two permanent-stall shapes — a GfxObj id that never
+    // resolves (silent load failure, e.g. custom-server content missing from
+    // the baked pak) versus an upload budget that never reopens — are
+    // otherwise indistinguishable from the reveal log's composites=False.
+    private long _probeWarmupLastEmitTs;
+
+    private void ProbeRevealWarmupStall()
+    {
+        long now = Stopwatch.GetTimestamp();
+        if (_probeWarmupLastEmitTs != 0
+            && now - _probeWarmupLastEmitTs < Stopwatch.Frequency)
+        {
+            return;
+        }
+        _probeWarmupLastEmitTs = now;
+
+        var pendingIds = new System.Text.StringBuilder();
+        int listed = 0;
+        foreach (WorldEntity entity in _compositeWarmupQueue)
+        {
+            if (listed >= 4)
+                break;
+            ulong gfxObjId = entity.MeshRefs.Count > 0
+                ? entity.MeshRefs[0].GfxObjId
+                : 0;
+            if (listed > 0)
+                pendingIds.Append(',');
+            pendingIds.Append($"0x{gfxObjId:X8}");
+            listed++;
+        }
+        Console.WriteLine(
+            $"[composite-warmup] STALL pending={LastCompositeWarmupPendingCount}"
+            + $" queue={_compositeWarmupQueue.Count}"
+            + $" scanComplete={_compositeWarmupScanComplete}"
+            + $" uploadOpen={_textures.CanStartCompositeUpload}"
+            + $" firstPending=[{pendingIds}]");
     }
 
     internal static bool RequiresCompositeWarmupRebuild(

src/AcDream.Core.Net/NetDiagnostics.cs

@@ -33,4 +33,16 @@ public static class NetDiagnostics
     /// </summary>
     public static bool ProbeNet { get; set; } =
         Environment.GetEnvironmentVariable("ACDREAM_PROBE_NET") == "1";
+
+    /// <summary>
+    /// <c>ACDREAM_PROBE_REVEAL=1</c> — #260 reveal-stall probe: while a
+    /// reveal destination's composite warmup is incomplete, emit one
+    /// <c>[composite-warmup]</c> line per second naming the pending queue
+    /// depth, scan state, upload-budget gate, and the first few unresolved
+    /// GfxObj ids. The two permanent-stall shapes (a mesh id that never
+    /// resolves vs. an upload budget that never reopens) are otherwise
+    /// indistinguishable and invisible.
+    /// </summary>
+    public static bool ProbeReveal { get; set; } =
+        Environment.GetEnvironmentVariable("ACDREAM_PROBE_REVEAL") == "1";
 }