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

DeepDrftManager/Components/Pages/Tracks/BatchUpload.razor

@@ -298,6 +298,29 @@
             return;
         }
 
+        // Pre-flight duplicate guard (primary block): the upload form creates new releases only, so a
+        // (title, artist) that already exists in the catalogue is refused BEFORE any bytes transfer —
+        // the admin is not surprised at the end of a long upload. The server backstops this on the
+        // create path, but checking here keeps the failure fast and visible. The values passed match
+        // exactly what the upload sends (untrimmed _albumName/_artist) so the pre-flight and the server
+        // agree on the match. A check failure (API unreachable) blocks rather than proceeding blind.
+        var duplicateCheck = await CmsTrackService.GetExistingReleaseAsync(_albumName, _artist);
+        if (!duplicateCheck.Success)
+        {
+            var checkError = duplicateCheck.Messages.FirstOrDefault()?.Message ?? "Unknown error";
+            _errorMessage = $"Could not verify the release name: {checkError}";
+            Snackbar.Add(_errorMessage, Severity.Error);
+            return;
+        }
+
+        if (duplicateCheck.Value is { } existing)
+        {
+            _errorMessage = $"A release titled '{existing.Title}' by {existing.Artist} already exists. "
+                + "The upload form creates new releases only — use the edit tools to change an existing one.";
+            Snackbar.Add(_errorMessage, Severity.Error);
+            return;
+        }
+
         // For single-track media (Session/Mix) the track name is derived from the Release Name —
         // no separate Track Name input is shown. Sync here so the stored name always matches.
         if (MediumRules.CardinalityOf(_medium).IsSingleTrack && _tracks.Count > 0)
@@ -327,6 +350,11 @@
             }
 
             int succeeded = 0, failed = 0;
+            // Within-batch attach: row 1 creates the release (no releaseId → CREATE path); once it
+            // succeeds we carry its ReleaseId into rows 2..N so they ATTACH to the just-created release
+            // rather than tripping the server's pre-existing-duplicate block. Only a multi-track Cut
+            // reaches row 2 (single-track media collapse to one row).
+            long? batchReleaseId = null;
             for (int i = 0; i < _tracks.Count; i++)
             {
                 var row = _tracks[i];
@@ -375,6 +403,7 @@
                         _releaseType,
                         trackNumber,
                         _medium,
+                        batchReleaseId,
                         progress);
 
                     if (!result.Success || result.Value is null)
@@ -387,6 +416,15 @@
                     }
                     else
                     {
+                        // Capture the release id created by the first successful row so subsequent rows
+                        // attach to it (the within-batch multi-track Cut path). Only set once — later
+                        // rows must not overwrite it. A null ReleaseId here (loose track) leaves it null,
+                        // which is correct: a release-less upload has no within-batch release to attach to.
+                        if (batchReleaseId is null && result.Value.ReleaseId is { } createdReleaseId)
+                        {
+                            batchReleaseId = createdReleaseId;
+                        }
+
                         // The upload endpoint does not accept an imagePath, so link the cover art with
                         // a follow-up metadata update — same two-step pattern BatchEdit uses.
                         if (_imagePath is { } imgPath)
@@ -487,7 +525,13 @@
             }
             else
             {
-                Snackbar.Add($"Uploaded {succeeded} track(s); {failed} failed — review errors below.", Severity.Warning);
+                // Surface the actual reason, not just counts — a server rejection (duplicate, cardinality)
+                // relays a human-readable message via row.ErrorMessage. Show the first failure's reason so
+                // the admin sees WHY without scanning the rows; the per-row errors remain as detail.
+                var firstError = _tracks.FirstOrDefault(t => t.Status == BatchRowStatus.Failed)?.ErrorMessage;
+                var reason = string.IsNullOrWhiteSpace(firstError) ? "review errors below" : firstError;
+                _errorMessage = succeeded == 0 ? reason : $"{succeeded} uploaded; {failed} failed: {reason}";
+                Snackbar.Add($"Uploaded {succeeded} track(s); {failed} failed — {reason}", Severity.Warning);
                 // Stay on page so the admin can see the failed rows.
             }
         }