feat(store): DeleteUpload removes a finished upload of the owner (#37)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/store/uploaded_transcripts.go

@@ -17,6 +17,10 @@ import (
 // nothing about whether someone else's upload exists (ADR-033).
 var ErrUploadNotFound = errors.New("store: uploaded transcript not found")
 
+// ErrUploadInProgress is returned by DeleteUpload for an upload that is still queued or
+// transcribing: the worker would write its result to a row that no longer exists.
+var ErrUploadInProgress = errors.New("store: uploaded transcript is still being processed")
+
 // Uploaded transcripts are PRIVATE per-user content, stored in their own
 // RLS-scoped table (migration 017) — never in the shared `transcripts` (ADR-021).
 // Every method goes through withUser, so row-level security confines it to the
@@ -103,6 +107,33 @@ func (s *Store) FailUpload(ctx context.Context, userID, id string, kind domain.U
 		string(kind))
 }
 
+// DeleteUpload removes one of the caller's finished (done or failed) uploads. An upload
+// still queued or transcribing is refused with ErrUploadInProgress and left untouched; one
+// that is not the caller's is ErrUploadNotFound, as for every other write (#37).
+func (s *Store) DeleteUpload(ctx context.Context, userID, id string) error {
+	return s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		ct, err := tx.Exec(ctx,
+			`DELETE FROM uploaded_transcripts
+			  WHERE id = $1 AND user_id = $2 AND status IN ('done', 'failed')`, id, userID)
+		if err != nil {
+			return fmt.Errorf("store: delete upload: %w", err)
+		}
+		if ct.RowsAffected() > 0 {
+			return nil
+		}
+		var exists bool
+		if err := tx.QueryRow(ctx,
+			`SELECT EXISTS (SELECT 1 FROM uploaded_transcripts WHERE id = $1 AND user_id = $2)`,
+			id, userID).Scan(&exists); err != nil {
+			return fmt.Errorf("store: delete upload: %w", err)
+		}
+		if exists {
+			return ErrUploadInProgress
+		}
+		return ErrUploadNotFound
+	})
+}
+
 // updateUpload runs one UPDATE keyed on ($1 = id, $2 = userID) plus extra args,
 // and maps "no row touched" to ErrUploadNotFound — which is what a write to another
 // user's upload looks like under RLS (the row is invisible, not forbidden).