perf(content): close prepared asset cutover

src/AcDream.Content/DatCollectionAdapter.cs

@@ -5,14 +5,15 @@ using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Threading;
 
 namespace AcDream.Content;
 
 /// <summary>
 /// THE <see cref="DatCollection"/> → <see cref="IDatReaderWriter"/> adapter,
-/// shared by all three consumers: ObjectMeshManager (AcDream.App, via
-/// WbMeshAdapter), acdream-bake (AcDream.Bake.BakeRunner), and the pak
-/// equivalence suite (AcDream.Content.Tests). MP1b's review found the
+/// shared by runtime DAT-backed gameplay/content access,
+/// acdream-bake (AcDream.Bake.BakeRunner), and the pak equivalence suite
+/// (AcDream.Content.Tests). MP1b's review found the
 /// original App-internal copy had silently forked into three near-identical
 /// versions — drift between them is exactly what the live-vs-pak equivalence
 /// suite CANNOT detect (both sides would drift together only if they share
@@ -218,6 +219,7 @@ public sealed class DatDatabaseWrapper : IDatDatabase {
     // cache itself documents why estimated bytes are not a hard heap bound.
     private readonly BoundedDatObjectCache _cache = new();
     private readonly object _databaseLock = new();
+    private int _malformedRecordDiagnosticEmitted;
 
     public DatDatabaseWrapper(DatDatabase db) {
         ArgumentNullException.ThrowIfNull(db);
@@ -241,6 +243,7 @@ public sealed class DatDatabaseWrapper : IDatDatabase {
             return true;
         }
 
+        bool existingRecordFailed;
         lock (_databaseLock) {
             // A different reader may have populated the cache while this
             // caller waited for the serialized DatDatabase read path.
@@ -253,17 +256,25 @@ public sealed class DatDatabaseWrapper : IDatDatabase {
                 return true;
             }
 
-            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix):
-            // a miss for an id whose BTree entry EXISTS is always an anomaly —
-            // either Unpack returned false or the lookup flickered transiently.
-            // Legit not-found probes (e.g. Portal→HighRes fallback) stay silent.
-            // Kept through the MP1b unification — the tripwire now covers the
-            // bake tool and the equivalence suite too, not just the client.
-            if (_db.Tree.TryGetFile(fileId, out _)) {
-                Console.WriteLine(
-                    $"[dat-miss] {typeof(T).Name} 0x{fileId:X8} entry EXISTS but TryGet failed " +
-                    $"(thread={Environment.CurrentManagedThreadId})");
-            }
+            // A miss for an id whose BTree entry exists is a typed-access
+            // anomaly (wrong requested type, malformed content, or an unpacker
+            // failure). Capture only the fact while serialized DAT access is
+            // held; diagnostics must never perform console I/O under this
+            // shared lock.
+            existingRecordFailed = _db.Tree.TryGetFile(fileId, out _);
+        }
+
+        // One actionable report per database keeps a repeatedly requested
+        // malformed record from becoming another exception/logging-style hot
+        // path. Missing keys stay silent.
+        if (existingRecordFailed
+            && Interlocked.Exchange(
+                ref _malformedRecordDiagnosticEmitted,
+                1) == 0)
+        {
+            Console.Error.WriteLine(
+                $"[dat-miss] {typeof(T).Name} 0x{fileId:X8} entry EXISTS but TryGet failed " +
+                $"(thread={Environment.CurrentManagedThreadId}; further reports suppressed)");
         }
 
         return false;