Stream the waveform compute so large uploads no longer buffer the whole file (Wave 2 OOM)

DeepDrftContent/TrackContentService.cs

@@ -201,6 +201,45 @@ public class TrackContentService
         return await _fileDatabase.LoadResourceAsync<AudioBinary>(VaultConstants.Tracks, trackId);
     }
 
+    /// <summary>
+    /// Opens a read-only, seekable stream over a track's vault audio, or null if the entry has no
+    /// backing file. The caller owns the stream and must dispose it. Unlike <see cref="GetAudioBinaryAsync"/>
+    /// this never buffers the whole file — it is the source for the streaming waveform compute. Follows
+    /// the FileDatabase swallow-and-return-null contract.
+    /// </summary>
+    /// <param name="trackId">Track ID (EntryKey)</param>
+    public async Task<Stream?> OpenAudioStreamAsync(string trackId)
+    {
+        var vault = _fileDatabase.GetVault(VaultConstants.Tracks);
+        if (vault is null)
+        {
+            return null;
+        }
+
+        var media = await vault.GetEntryStreamAsync(trackId);
+        return media?.Stream;
+    }
+
+    /// <summary>
+    /// Reads a track's stored audio duration from the vault index metadata WITHOUT loading the audio
+    /// body — the cheap counterpart of <c>GetAudioBinaryAsync(...).Duration</c>. Returns null if the
+    /// entry is unknown or carries no audio metadata. The streaming high-res waveform path uses this to
+    /// derive the duration-based bucket count, matching the value the whole-buffer path read off
+    /// <see cref="AudioBinary.Duration"/> so the stored datum is byte-identical.
+    /// </summary>
+    /// <param name="trackId">Track ID (EntryKey)</param>
+    public async Task<double?> GetAudioDurationAsync(string trackId)
+    {
+        var vault = _fileDatabase.GetVault(VaultConstants.Tracks);
+        if (vault is null)
+        {
+            return null;
+        }
+
+        var metaData = await vault.GetEntryMetadata(trackId);
+        return metaData is AudioMetaData audio ? audio.Duration : null;
+    }
+
     /// <summary>
     /// Checks if FileDatabase is available and tracks vault exists
     /// </summary>