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.

DeepDrftContent/Processors/Mp3AudioProcessor.cs

@@ -25,7 +25,13 @@ public class Mp3AudioProcessor
     private const double FallbackDuration = 180.0;
     private const int FallbackBitrate = 320;
 
-    public async Task<AudioBinary?> ProcessMp3FileAsync(string filePath)
+    // Metadata lives in the leading ID3v2 tag plus the first MPEG frame. Cap the header read so a
+    // large MP3 is not pulled into memory whole just to read it; a tag larger than this (very large
+    // embedded art) simply falls back to the CBR/default estimate, never an OOM. The body is stored
+    // by streaming the original file, not from this window.
+    private const long HeaderCap = 8 * 1024 * 1024;
+
+    public async Task<ProcessedAudio?> ProcessMp3FileAsync(string filePath, CancellationToken cancellationToken = default)
     {
         if (!File.Exists(filePath))
         {
@@ -37,24 +43,21 @@ public class Mp3AudioProcessor
             throw new ArgumentException("File must be an MP3 file", nameof(filePath));
         }
 
-        var buffer = await File.ReadAllBytesAsync(filePath);
-        var meta = ExtractMp3Metadata(buffer);
+        var fileLength = new FileInfo(filePath).Length;
+        var window = await AudioStoreStream.ReadPrefixAsync(filePath, HeaderCap, cancellationToken);
+        var meta = ExtractMp3Metadata(window, fileLength);
 
-        var parameters = new AudioBinaryParams(
-            Buffer: buffer,
-            Size: buffer.Length,
-            Extension: ".mp3",
-            Duration: meta.Duration,
-            Bitrate: meta.Bitrate);
-
-        return new AudioBinary(parameters);
+        // MP3 is stored unmodified — passthrough the original bytes via a streamed disk-to-disk copy.
+        return ProcessedAudio.Passthrough(filePath, ".mp3", meta.Duration, meta.Bitrate, fileLength);
     }
 
     /// <summary>
     /// Parses the first valid MPEG frame (after any ID3v2 tag) and any Xing/VBRI tag inside it.
     /// On any parse failure, logs a warning and returns synthetic defaults — never throws.
+    /// <paramref name="fileLength"/> is the true file size (the header window may be shorter), used
+    /// for the CBR duration estimate.
     /// </summary>
-    private static Mp3Metadata ExtractMp3Metadata(byte[] buffer)
+    private static Mp3Metadata ExtractMp3Metadata(byte[] buffer, long fileLength)
     {
         try
         {
@@ -65,7 +68,7 @@ public class Mp3AudioProcessor
             }
 
             var header = DecodeFrameHeader(buffer, frameStart);
-            var duration = ComputeDuration(buffer, frameStart, header);
+            var duration = ComputeDuration(buffer, frameStart, header, fileLength);
 
             return new Mp3Metadata { Duration = duration, Bitrate = header.BitrateKbps };
         }
@@ -202,7 +205,7 @@ public class Mp3AudioProcessor
     /// Computes duration from a Xing/Info or VBRI tag (accurate for VBR) when present; otherwise
     /// falls back to the CBR estimate fileSize / (bitrate_kbps * 125). Guards divide-by-zero.
     /// </summary>
-    private static double ComputeDuration(byte[] buffer, int frameStart, FrameHeader header)
+    private static double ComputeDuration(byte[] buffer, int frameStart, FrameHeader header, long fileLength)
     {
         var xingFrames = ReadXingFrameCount(buffer, frameStart, header);
         if (xingFrames > 0 && header.SampleRate > 0)
@@ -216,10 +219,10 @@ public class Mp3AudioProcessor
             return (double)vbriFrames * header.SamplesPerFrame / header.SampleRate;
         }
 
-        // CBR fallback: bitrate_kbps * 1000 / 8 bytes per second = bitrate_kbps * 125.
-        // Exclude the ID3v2 tag bytes (everything before frameStart) from the estimate.
+        // CBR fallback: bitrate_kbps * 1000 / 8 bytes per second = bitrate_kbps * 125. Uses the true
+        // file length (not the bounded header window), excluding the ID3v2 tag bytes before frameStart.
         var bytesPerSecond = header.BitrateKbps * 125;
-        return bytesPerSecond > 0 ? (double)(buffer.Length - frameStart) / bytesPerSecond : FallbackDuration;
+        return bytesPerSecond > 0 ? (double)(fileLength - frameStart) / bytesPerSecond : FallbackDuration;
     }
 
     /// <summary>