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/FileDatabase/Services/MediaVault.cs

@@ -56,6 +56,37 @@ public abstract class MediaVault : VaultIndexDirectory
         await FileUtils.PutFileAsync(mediaPath, buffer);
     }
 
+    /// <summary>
+    /// Streams an entry's bytes into the vault without ever materializing the whole file in memory:
+    /// records the supplied <paramref name="metaData"/> in the index, then invokes
+    /// <paramref name="writeContent"/> to emit bytes directly to the backing <see cref="FileStream"/>.
+    /// The metadata is supplied by the caller (there is no in-memory <see cref="FileBinary"/> to infer
+    /// it from) — the store path (upload / replace-audio) sources its bytes from a staging file, not a
+    /// buffer. Returns the number of bytes written, for the caller to log.
+    ///
+    /// Index-then-file ordering matches <see cref="AddEntryAsync"/>; a mid-write failure therefore
+    /// leaves an index entry over a partial/missing file, the same exposure the buffered path has on
+    /// an I/O fault. The caller treats a thrown exception as a failed register.
+    /// </summary>
+    public async Task<long> AddEntryStreamingAsync(
+        string entryId,
+        MetaData metaData,
+        Func<Stream, CancellationToken, Task> writeContent,
+        CancellationToken cancellationToken = default)
+    {
+        var mediaPath = GetMediaPathFromEntryKey(entryId, metaData.Extension);
+
+        await AddToIndexAsync(entryId, metaData);
+
+        await using var fileStream = new FileStream(
+            mediaPath, FileMode.Create, FileAccess.Write, FileShare.None,
+            bufferSize: 81920, useAsync: true);
+        await writeContent(fileStream, cancellationToken);
+        await fileStream.FlushAsync(cancellationToken);
+
+        return fileStream.Length;
+    }
+
     /// <summary>
     /// Retrieves an entry from the vault (MediaVaultType inferred from T)
     /// </summary>