Block duplicate-release uploads by (title, artist): pre-flight check + server 409 backstop, with within-batch Cut attach via releaseId

DeepDrftManager/Services/ICmsTrackService.cs

@@ -25,6 +25,10 @@ public interface ICmsTrackService
     /// sets Content-Length and is the denominator for <paramref name="progress"/>, which reports cumulative
     /// bytes pushed to the wire. Each progress tick also resets the idle/heartbeat upload timeout, so a
     /// stalled connection aborts without a fixed total-duration cap.
+    /// <paramref name="releaseId"/> distinguishes the two rows of a within-batch multi-track Cut: null on
+    /// the first row (CREATE — the server rejects a pre-existing (title, artist) as a duplicate) and the
+    /// id returned by that first row on rows 2..N (ATTACH — the server skips the duplicate check and adds
+    /// the track to the release the batch just created).
     /// </summary>
     Task<ResultContainer<TrackDto>> UploadTrackAsync(
         Stream wavStream,
@@ -42,9 +46,20 @@ public interface ICmsTrackService
         ReleaseType releaseType,
         int trackNumber,
         ReleaseMedium medium = ReleaseMedium.Cut,
+        long? releaseId = null,
         IProgress<long>? progress = null,
         CancellationToken ct = default);
 
+    /// <summary>
+    /// Upload-form pre-flight: returns the existing release whose exact (title, artist) matches, or null
+    /// when none exists. Backs the duplicate block the form runs BEFORE transferring bytes, so the admin
+    /// is not surprised at the end of a long upload. A 404 from the API is the not-found (null) case, not
+    /// a failure. The match semantics are the API's <c>GetReleaseByTitleAndArtist</c> — the same read the
+    /// server backstop uses — so the pre-flight and the backstop agree.
+    /// </summary>
+    Task<ResultContainer<ReleaseDto?>> GetExistingReleaseAsync(
+        string title, string artist, CancellationToken ct = default);
+
     /// <summary>
     /// Delete a track via the Content API, which removes the SQL row then the vault entry.
     /// Maps a 404 to a "Track not found." failure.