fix: harden workspace deletion cleanup

Move PostgreSQL sequence cleanup after the workspace deletion commits so auxiliary DDL failures cannot roll back valid deletions. Remove the unused transactional helper and pin the historical Zammad migration checksums to prevent accidental edits.

Author: Optic00

internal/database/zammad_schema_test.go

@@ -190,6 +190,28 @@ func TestZammadTicketLinkMetadataMigrationBackendParity(t *testing.T) {
 	}
 }
 
+func TestZammadCanonicalWorkspaceScopeMigrationChecksumStability(t *testing.T) {
+	var migration *Migration
+	for i := range Catalog {
+		if Catalog[i].Version == "20260901_zammad_canonical_workspace_scope" {
+			migration = &Catalog[i]
+			break
+		}
+	}
+	if migration == nil {
+		t.Fatal("Zammad canonical workspace scope migration is missing")
+	}
+
+	for driver, want := range map[string]string{
+		driverSQLite:   "164fb8cb79ee0f5705aa5891540576995bc030260effc89c75a6de470e45a33f",
+		driverPostgres: "4d1561e94cff763531c5c68a749f5f32bc3f3aa2feb2493ac7911d697bd450b4",
+	} {
+		if got := migration.checksum(driver); got != want {
+			t.Fatalf("historical %s migration checksum changed: got %s, want %s", driver, got, want)
+		}
+	}
+}
+
 func TestZammadTicketSyncLockOwnerMigrationBackendParity(t *testing.T) {
 	var migration *Migration
 	for i := range Catalog {

internal/repository/workspace_repository.go

@@ -730,14 +730,3 @@ func (r *WorkspaceRepository) DropItemSequence(workspaceID int64) error {
 	_, err := r.db.ExecWrite(fmt.Sprintf(`DROP SEQUENCE IF EXISTS %q`, seqName))
 	return err
 }
-
-// DropItemSequenceTx removes the per-workspace sequence inside the caller's
-// transaction. No-op on SQLite.
-func (r *WorkspaceRepository) DropItemSequenceTx(tx database.Tx, workspaceID int64) error {
-	if r.db.GetDriverName() != "postgres" {
-		return nil
-	}
-	seqName := fmt.Sprintf("workspace_%d_item_seq", workspaceID)
-	_, err := tx.ExecWrite(fmt.Sprintf(`DROP SEQUENCE IF EXISTS %q`, seqName))
-	return err
-}

internal/services/workspace_service.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"log/slog"
 	"strings"
 	"time"
 
@@ -376,14 +377,18 @@ func (s *WorkspaceService) Delete(id int) error {
 		if err := s.repo.DeleteTx(tx, id); err != nil {
 			return fmt.Errorf("delete workspace: %w", err)
 		}
-		if err := s.repo.DropItemSequenceTx(tx, int64(id)); err != nil {
-			return fmt.Errorf("drop workspace item sequence: %w", err)
-		}
 		return nil
 	}); err != nil {
 		return err
 	}
 
+	// The sequence is auxiliary cleanup. Run it after the workspace deletion
+	// commits so a failed DROP cannot roll back an otherwise valid deletion or
+	// leave a PostgreSQL transaction permanently aborted.
+	if err := s.repo.DropItemSequence(int64(id)); err != nil {
+		slog.Warn("failed to drop item sequence for workspace", "workspace_id", id, "error", err)
+	}
+
 	repository.InvalidateItemListCountCache(s.db, id)
 
 	return nil