Merge cms-track-replace-gating into dev

Replace track audio in CMS edit form + gate last-track delete.

DeepDrftAPI/Services/UnifiedTrackService.cs

@@ -166,6 +166,55 @@ public class UnifiedTrackService
         return saveResult;
     }
 
+    /// <summary>
+    /// Replace an existing track's audio in place: look up the SQL row, swap only the vault bytes
+    /// keyed by its EntryKey, then regenerate both waveform datums from the new audio. Track id,
+    /// EntryKey, release membership, track number, and all metadata are preserved — nothing in SQL
+    /// is written. The waveform regen is best-effort (a missing datum renders as a flat seekbar /
+    /// blank visualizer downstream), so a datum failure is logged and swallowed rather than failing
+    /// the replace. No release-cardinality cascade applies: the track count is unchanged, so the
+    /// single-track-Mix case stays intact.
+    /// </summary>
+    public async Task<Result> ReplaceAudioAsync(long trackId, string tempFilePath, CancellationToken ct)
+    {
+        var lookup = await _sqlTrackService.GetById(trackId);
+        if (!lookup.Success)
+        {
+            var error = lookup.Messages.FirstOrDefault()?.Message ?? "unknown error";
+            _logger.LogError("ReplaceAudioAsync: GetById failed for track {TrackId}: {Error}", trackId, error);
+            return Result.CreateFailResult("Failed to load track.");
+        }
+
+        if (lookup.Value is null)
+        {
+            return Result.CreateFailResult(TrackNotFoundMessage);
+        }
+
+        var entryKey = lookup.Value.EntryKey;
+
+        var newAudio = await _contentTrackContentService.ReplaceTrackAudioAsync(entryKey, tempFilePath);
+        if (newAudio is null)
+        {
+            _logger.LogWarning("ReplaceAudioAsync: content swap returned null for track {TrackId} ({EntryKey})", trackId, entryKey);
+            return Result.CreateFailResult("Failed to process and store the replacement audio.");
+        }
+
+        // The old waveform no longer matches the new bytes. Regenerate both datums in place; keyed
+        // by the same EntryKey, the re-run overwrites the stale data (proven re-runnable). The
+        // freshly stored buffer is the authoritative source — no re-read of the vault needed.
+        try
+        {
+            await _waveformProfileService.ComputeAndStoreAsync(newAudio.Buffer, entryKey);
+            await _waveformProfileService.ComputeAndStoreHighResAsync(newAudio.Buffer, entryKey, newAudio.Duration);
+        }
+        catch (Exception ex) when (ex is not OperationCanceledException)
+        {
+            _logger.LogError(ex, "ReplaceAudioAsync: waveform regen failed for {EntryKey}; replace unaffected.", entryKey);
+        }
+
+        return Result.CreatePassResult();
+    }
+
     // Compute and store both waveform datums for a freshly uploaded track: the fixed 512-bucket profile
     // the player-bar seeker consumes, and the duration-derived high-res datum the lava visualizer
     // consumes (phase-12 §5 — every track now carries one, computed at upload). Both source the same