fix(audio): bound decoded-wave and AL-buffer caches (2026-07-24 audit review)

Two audit-verified caches grew monotonically for process lifetime, which is
fatal for the 30-bot long-uptime headless-fleet goal:

- DatSoundCache._waves (Core) memoized every decoded PCM WaveData forever
  in a bare ConcurrentDictionary — no LRU, no byte budget.
- OpenAlAudioEngine._bufferByWaveId (App) retained a native OpenAL buffer
  copy of the same PCM per wave id until engine disposal — a second,
  independent unbounded cache.

DatSoundCache now bounds payload residency with a 32 MiB byte-budget LRU
(decoded PCM waves run ~100-500 KB each, so this holds a comfortable
working set). Missing/unsupported-format waves are memoized separately in
an unbounded-but-cheap negative-result set (bounded by the finite Wave dat
id space) so they can never compete with or get evicted alongside payload
entries. Concurrent first-touch decodes of the same wave id are deduped
via a shared Lazy<T> so racing callers don't pay for WaveDecoder.Decode
twice. AcDream.Core cannot reference AcDream.Content (code-structure rule
2), so the LRU is a local reimplementation mirroring
BoundedDatObjectCache/DecodedTextureCache's shape rather than a shared
dependency.

OpenAlAudioEngine._bufferByWaveId now bounds native buffer residency with
a 48 MiB byte-budget LRU (AlBufferBudgetTracker), evicting least-recently-
used buffers once oversized. alDeleteBuffers fails on a buffer still
attached to a source, so eviction queries live AL per-source state
(GetSourceInteger.Buffer) rather than tracking a second, easily-stale
copy — several call sites (Play3DWave, PlayUiWave) set a source's buffer
directly. The buffer EnsureBuffer just created is explicitly protected
from its own eviction pass, since the caller hasn't attached it to a
source yet at that point. Evicted waves simply replay through
DatSoundCache -> EnsureBuffer on next use, identical to a first play.

Verified before implementing: AudioHookSink is the only GetWave caller
(single per-frame render-thread path per AnimationHookRouter's own
threading doc), and PcmBytes is read only at DatSoundCache.Admit (byte
accounting) and EnsureBuffer's first-upload branch — confirmed dead after
AL upload on the steady-state replay path, so bounding either cache
independently is correctness-safe; a cold replay after both evict simply
falls back to a full re-decode + re-upload, identical to a first play.

AlBufferBudgetTracker's eviction/budget decision is extracted as pure
logic (no AL dependency) specifically so it's unit-testable: the existing
OpenAlResourceLifetimeTests fake exposes a null AL, which short-circuits
every native buffer call before it runs, so the engine's actual AL wiring
isn't testable headless.

Tests: 9 new DatSoundCacheTests (Core.Tests) covering eviction order, byte
accounting, negative-result memoization, oversize-single-entry handling,
and concurrent-access smoke tests; 10 new AlBufferBudgetTrackerTests
(App.Tests) covering the pure LRU/budget/protection logic. Full suite:
3214/2 skip (Core.Tests), 3471/3 skip (App.Tests) plus one pre-existing,
unrelated failure (LandblockBuildOriginTests.FarLoad_..., reproduces
identically with these changes stashed out — landblock streaming, not
audio).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit 76c880d35bcf30b50e3f7b4cb8635dc9ab9e3ec7)

tests/AcDream.Core.Tests/Audio/DatSoundCacheTests.cs

@@ -0,0 +1,237 @@
+using System.Collections.Concurrent;
+using AcDream.Core.Audio;
+using AcDream.Core.Content;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Lib.IO;
+using System.Diagnostics.CodeAnalysis;
+using Xunit;
+
+namespace AcDream.Core.Tests.Audio;
+
+/// <summary>
+/// Covers the payload-LRU eviction added to bound <c>DatSoundCache</c>'s
+/// decoded-wave residency (verified-unbounded audit, 2026-07-24): eviction
+/// order, byte accounting, negative-result (missing/unsupported) handling,
+/// and a concurrency smoke test.
+/// </summary>
+public sealed class DatSoundCacheTests
+{
+    [Fact]
+    public void GetWave_DecodesAndReturnsPcmWave()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(1, MakePcmWave(1, dataBytes: 100));
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        WaveData? wave = cache.GetWave(1);
+
+        Assert.NotNull(wave);
+        Assert.Equal(100, wave!.PcmBytes.Length);
+        Assert.Equal(1, cache.CachedWaveCount);
+        Assert.Equal(100, cache.ResidentWaveBytes);
+    }
+
+    [Fact]
+    public void GetWave_MissingWave_ReturnsNullAndMemoizesNegativeWithoutRepeatedLookup()
+    {
+        var dats = new FakeDatObjectSource(); // no wave registered for id 7
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        Assert.Null(cache.GetWave(7));
+        Assert.Null(cache.GetWave(7));
+        Assert.Null(cache.GetWave(7));
+
+        // The negative-result memo short-circuits GetWave before it ever
+        // reaches the dat lookup a second time.
+        Assert.Equal(1, dats.GetCallCount(7));
+        Assert.Equal(0, cache.CachedWaveCount);
+        Assert.Equal(0, cache.ResidentWaveBytes);
+    }
+
+    [Fact]
+    public void GetWave_UnsupportedFormat_ReturnsNullAndDoesNotConsumeByteBudget()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(2, MakeMp3Wave(2)); // WaveDecoder.Decode returns null for MP3
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        Assert.Null(cache.GetWave(2));
+        Assert.Equal(0, cache.CachedWaveCount);
+        Assert.Equal(0, cache.ResidentWaveBytes);
+
+        // Second call hits the negative memo, not a fresh decode of the dat entry.
+        Assert.Null(cache.GetWave(2));
+        Assert.Equal(1, dats.GetCallCount(2));
+    }
+
+    [Fact]
+    public void GetWave_CacheHit_ReturnsSameInstanceWithoutRedecoding()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(1, MakePcmWave(1, dataBytes: 100));
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        WaveData? first = cache.GetWave(1);
+        WaveData? second = cache.GetWave(1);
+
+        Assert.Same(first, second);
+        Assert.Equal(1, dats.GetCallCount(1));
+    }
+
+    [Fact]
+    public void GetWave_EvictsLeastRecentlyUsedWhenOverBudget()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(1, MakePcmWave(1, dataBytes: 150)); // A
+        dats.AddWave(2, MakePcmWave(2, dataBytes: 150)); // B
+        dats.AddWave(3, MakePcmWave(3, dataBytes: 150)); // C
+        var cache = new DatSoundCache(dats, maxWaveBytes: 300);
+
+        WaveData? a1 = cache.GetWave(1);
+        WaveData? b1 = cache.GetWave(2);
+        Assert.Equal(2, cache.CachedWaveCount);
+        Assert.Equal(300, cache.ResidentWaveBytes); // exactly at budget, no eviction yet
+
+        // Touch A so B becomes the least-recently-used entry.
+        Assert.Same(a1, cache.GetWave(1));
+
+        // Admitting C (150) would push residency to 450 > 300 — B must go.
+        WaveData? c1 = cache.GetWave(3);
+        Assert.Equal(2, cache.CachedWaveCount);
+        Assert.Equal(300, cache.ResidentWaveBytes);
+
+        // A and C are still resident (no re-decode); B was evicted (re-decodes on next use).
+        Assert.Same(a1, cache.GetWave(1));
+        Assert.Equal(1, dats.GetCallCount(1));
+        Assert.Same(c1, cache.GetWave(3));
+        Assert.Equal(1, dats.GetCallCount(3));
+
+        WaveData? b2 = cache.GetWave(2);
+        Assert.NotNull(b2);
+        Assert.NotSame(b1, b2); // evicted entries decode fresh on next request
+        Assert.Equal(2, dats.GetCallCount(2));
+    }
+
+    [Fact]
+    public void GetWave_OversizeSingleWave_IsServedButNotRetained()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(9, MakePcmWave(9, dataBytes: 500));
+        var cache = new DatSoundCache(dats, maxWaveBytes: 100); // budget smaller than the wave itself
+
+        WaveData? first = cache.GetWave(9);
+        Assert.NotNull(first);
+        Assert.Equal(0, cache.CachedWaveCount);
+        Assert.Equal(0, cache.ResidentWaveBytes);
+
+        WaveData? second = cache.GetWave(9);
+        Assert.NotNull(second);
+        Assert.NotSame(first, second); // not retained, so this re-decoded
+        Assert.Equal(2, dats.GetCallCount(9));
+    }
+
+    [Fact]
+    public void GetWave_ConcurrentSameId_PublishesOneCanonicalWaveAndDecodesOnce()
+    {
+        var dats = new FakeDatObjectSource();
+        dats.AddWave(1, MakePcmWave(1, dataBytes: 1000));
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        var results = new ConcurrentBag<WaveData?>();
+        Parallel.For(0, 200, _ => results.Add(cache.GetWave(1)));
+
+        WaveData?[] all = results.ToArray();
+        Assert.All(all, Assert.NotNull);
+        WaveData canonical = all[0]!;
+        Assert.All(all, value => Assert.Same(canonical, value));
+        Assert.Equal(1, dats.GetCallCount(1));
+    }
+
+    [Fact]
+    public void GetWave_ConcurrentMissingId_NeverThrowsAndAllReturnNull()
+    {
+        var dats = new FakeDatObjectSource(); // id 5 never registered
+        var cache = new DatSoundCache(dats, maxWaveBytes: 10_000);
+
+        var results = new ConcurrentBag<WaveData?>();
+        Parallel.For(0, 200, _ => results.Add(cache.GetWave(5)));
+
+        Assert.All(results, Assert.Null);
+        Assert.Equal(0, cache.CachedWaveCount);
+    }
+
+    // ── Test fixtures ────────────────────────────────────────────────────
+
+    private static byte[] MakePcmHeader(ushort channels = 1, uint rate = 22050, ushort bits = 16)
+    {
+        byte[] h = new byte[18];
+        h[0] = 0x01; h[1] = 0x00;                    // fmtTag PCM
+        h[2] = (byte)channels; h[3] = (byte)(channels >> 8);
+        h[4] = (byte)rate;     h[5] = (byte)(rate >> 8);
+        h[6] = (byte)(rate >> 16); h[7] = (byte)(rate >> 24);
+        uint avg = rate * channels * (uint)(bits / 8);
+        h[8]  = (byte)avg;       h[9]  = (byte)(avg >> 8);
+        h[10] = (byte)(avg >> 16); h[11] = (byte)(avg >> 24);
+        ushort blockAlign = (ushort)(channels * (bits / 8));
+        h[12] = (byte)blockAlign; h[13] = (byte)(blockAlign >> 8);
+        h[14] = (byte)bits;       h[15] = (byte)(bits >> 8);
+        return h;
+    }
+
+    private static Wave MakePcmWave(uint id, int dataBytes) => new()
+    {
+        Id = id,
+        Header = MakePcmHeader(),
+        Data = new byte[dataBytes],
+    };
+
+    private static Wave MakeMp3Wave(uint id) => new()
+    {
+        Id = id,
+        Header = new byte[18] { 0x55, 0x00, 0x02, 0x00, 0x44, 0xAC, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
+        Data = new byte[1024],
+    };
+
+    private sealed class FakeDatObjectSource : IDatObjectSource
+    {
+        private readonly Dictionary<uint, Wave> _waves = new();
+        private readonly Dictionary<uint, int> _callCounts = new();
+        private readonly object _gate = new();
+
+        public void AddWave(uint id, Wave wave) => _waves[id] = wave;
+
+        public int GetCallCount(uint id)
+        {
+            lock (_gate)
+                return _callCounts.TryGetValue(id, out int count) ? count : 0;
+        }
+
+        [return: MaybeNull]
+        public T Get<T>(uint fileId) where T : IDBObj
+        {
+            if (typeof(T) == typeof(Wave))
+            {
+                lock (_gate)
+                {
+                    _callCounts.TryGetValue(fileId, out int count);
+                    _callCounts[fileId] = count + 1;
+                }
+
+                return _waves.TryGetValue(fileId, out var wave) ? (T)(object)wave : default;
+            }
+            return default;
+        }
+
+        public bool TryGet<T>(uint fileId, [MaybeNullWhen(false)] out T value) where T : IDBObj
+        {
+            T? result = Get<T>(fileId);
+            if (result is null)
+            {
+                value = default!;
+                return false;
+            }
+            value = result;
+            return true;
+        }
+    }
+}