Wire Opus end-to-end playback + Backfill-Opus action (Phase 18.5)

Player picks Opus when the browser can decode it and a sidecar exists (else lossless), injecting the sidecar before stream init; seek reuses the same format. Adds the Backfill-Opus bulk API endpoint + CMS action.

DeepDrftAPI/Controllers/TrackController.cs

@@ -269,6 +269,27 @@ public class TrackController : ControllerBase
         return Ok(new { updated = result.Value.Updated, skipped = result.Value.Skipped });
     }
 
+    // POST api/track/opus/backfill ([ApiKeyAuthorize], no body)
+    // Backfill-Opus (18.5, OQ4): enqueue a background Opus derive for every track lacking a complete Opus
+    // artifact (audio + sidecar). Mirrors the duration-backfill posture — enqueue-only and non-blocking, the
+    // transcodes run on the shared serial worker. Idempotent: a re-run only schedules tracks still missing
+    // Opus. Returns { enqueued, skipped }. Declared in the literal-route block (before "{trackId}") so the
+    // "opus/backfill" segment is never treated as a trackId; distinct shape from "{trackId}/opus" (per-track).
+    [ApiKeyAuthorize]
+    [HttpPost("opus/backfill")]
+    public async Task<ActionResult> BackfillOpus(CancellationToken cancellationToken)
+    {
+        var result = await _unifiedService.BackfillOpusAsync(cancellationToken);
+        if (!result.Success)
+        {
+            var error = result.Messages.FirstOrDefault()?.Message ?? "Unknown error";
+            _logger.LogError("BackfillOpus failed: {Error}", error);
+            return StatusCode(500, error);
+        }
+
+        return Ok(new { enqueued = result.Value.Enqueued, skipped = result.Value.Skipped });
+    }
+
     // POST api/track/upload: raw audio in (multipart/form-data) + metadata → persisted TrackDto out.
     // Accepts .wav, .mp3, and .flac. Used by the CMS upload flow on DeepDrftManager; that host
     // proxies the upload here so it never touches the vault disk path or SQL directly.
@@ -875,6 +896,32 @@ public class TrackController : ControllerBase
         return Ok();
     }
 
+    // POST api/track/{trackId}/opus ([ApiKeyAuthorize])
+    // Per-track Opus (re)derive trigger (18.5): schedule a single track's background transcode. Enqueue-only
+    // and non-blocking — the transcode runs on the shared serial worker; this returns as soon as it is
+    // scheduled. Re-runnable: overwrites any prior artifact in place. trackId is the EntryKey. 404 when the
+    // track id is unknown. The "opus" literal suffix keeps this distinct from the audio/waveform routes and
+    // from the parameterized PUT "{trackId}". Returns 202 Accepted — the work is queued, not done inline.
+    [ApiKeyAuthorize]
+    [HttpPost("{trackId}/opus")]
+    public async Task<ActionResult> GenerateOpus(string trackId, CancellationToken cancellationToken)
+    {
+        var result = await _unifiedService.EnqueueOpusAsync(trackId, cancellationToken);
+        if (result.Success)
+        {
+            return Accepted();
+        }
+
+        var error = result.Messages.FirstOrDefault()?.Message ?? "Unknown error";
+        if (string.Equals(error, UnifiedTrackService.TrackNotFoundMessage, StringComparison.Ordinal))
+        {
+            return NotFound();
+        }
+
+        _logger.LogError("GenerateOpus failed for {TrackId}: {Error}", trackId, error);
+        return StatusCode(500, error);
+    }
+
     [ApiKeyAuthorize]
     [HttpPut("{trackId}")]
     public async Task<ActionResult> PutTrack(string trackId, [FromBody] AudioBinaryDto track)