fix(api): stream audio store path to eliminate whole-file buffering (OOM)

Processors now emit a ProcessedAudio plan with a streamed writer instead of a whole-file AudioBinary; vault writes stream via RegisterResourceStreamingAsync. Header parsing is bounded. Wave 2 (waveform/Opus) still re-reads the full file by design.

DeepDrftTests/TrackReplaceAudioTests.cs

@@ -68,9 +68,9 @@ public class TrackReplaceAudioTests
         var originalDuration = before!.Duration;
 
         var replacement = await WriteWavAsync(BuildMinimalPcmWav(6.0), ".wav");
-        var newAudio = await content.ReplaceTrackAudioAsync(entryKey, replacement);
+        var newDuration = await content.ReplaceTrackAudioAsync(entryKey, replacement);
 
-        Assert.That(newAudio, Is.Not.Null, "Replace should return the freshly stored audio");
+        Assert.That(newDuration, Is.Not.Null, "Replace should return the freshly stored audio's duration");
 
         var after = await content.GetAudioBinaryAsync(entryKey);
         Assert.Multiple(() =>
@@ -78,8 +78,8 @@ public class TrackReplaceAudioTests
             Assert.That(after, Is.Not.Null, "The track must remain retrievable under the same EntryKey");
             Assert.That(after!.Duration, Is.GreaterThan(originalDuration),
                 "The retrieved audio must reflect the longer replacement, not the original");
-            Assert.That(newAudio!.Duration, Is.EqualTo(after.Duration),
-                "The returned binary must match what is stored under the key");
+            Assert.That(newDuration!.Value, Is.EqualTo(after.Duration),
+                "The returned duration must match what is stored under the key");
         });
     }
 
@@ -101,9 +101,9 @@ public class TrackReplaceAudioTests
         Assert.That(wavFilesBefore, Is.Not.Empty, "Sanity: the original .wav backing file exists");
 
         var replacement = await WriteFlacAsync();
-        var newAudio = await content.ReplaceTrackAudioAsync(entryKey, replacement);
+        var newDuration = await content.ReplaceTrackAudioAsync(entryKey, replacement);
 
-        Assert.That(newAudio, Is.Not.Null);
+        Assert.That(newDuration, Is.Not.Null);
         Assert.Multiple(() =>
         {
             Assert.That(Directory.GetFiles(vaultDir, "*.wav"), Is.Empty,
@@ -135,12 +135,15 @@ public class TrackReplaceAudioTests
         Assert.That(staleHighRes, Is.Not.Null);
 
         var replacement = await WriteWavAsync(BuildMinimalPcmWav(20.0), ".wav");
-        var newAudio = await content.ReplaceTrackAudioAsync(entryKey, replacement);
-        Assert.That(newAudio, Is.Not.Null);
+        var newDuration = await content.ReplaceTrackAudioAsync(entryKey, replacement);
+        Assert.That(newDuration, Is.Not.Null);
 
-        // Regen step (mirrors the orchestrator).
-        Assert.That(await waveforms.ComputeAndStoreAsync(newAudio!.Buffer, entryKey), Is.True);
-        Assert.That(await waveforms.ComputeAndStoreHighResAsync(newAudio.Buffer, entryKey, newAudio.Duration), Is.True);
+        // Regen step (mirrors the orchestrator, which re-reads the freshly stored audio from the vault
+        // rather than consuming an in-memory buffer the streamed store no longer hands back).
+        var newStored = await content.GetAudioBinaryAsync(entryKey);
+        Assert.That(newStored, Is.Not.Null);
+        Assert.That(await waveforms.ComputeAndStoreAsync(newStored!.Buffer, entryKey), Is.True);
+        Assert.That(await waveforms.ComputeAndStoreHighResAsync(newStored.Buffer, entryKey, newStored.Duration), Is.True);
 
         var freshHighRes = await waveforms.GetProfileAsync(entryKey, VaultConstants.TrackWaveforms);
         var freshProfile = await waveforms.GetProfileAsync(entryKey);