feat(catalog): add deadlock-retry helper for batched deletes

internal/catalog/folder_delete_test.go

@@ -0,0 +1,90 @@
+package catalog
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+// withFastDeadlockRetry shrinks retry timing/attempts for tests and restores
+// the originals on cleanup. Tests using it must not call t.Parallel().
+func withFastDeadlockRetry(t *testing.T, maxAttempts int) {
+	t.Helper()
+	oldMax, oldBackoff := deadlockMaxAttempts, deadlockBaseBackoff
+	deadlockMaxAttempts = maxAttempts
+	deadlockBaseBackoff = time.Millisecond
+	t.Cleanup(func() {
+		deadlockMaxAttempts = oldMax
+		deadlockBaseBackoff = oldBackoff
+	})
+}
+
+func TestRetryOnDeadlockRetriesThenSucceeds(t *testing.T) {
+	withFastDeadlockRetry(t, 5)
+	calls := 0
+	err := retryOnDeadlock(context.Background(), func() error {
+		calls++
+		if calls < 3 {
+			return &pgconn.PgError{Code: "40P01"}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("expected success, got %v", err)
+	}
+	if calls != 3 {
+		t.Fatalf("expected 3 calls, got %d", calls)
+	}
+}
+
+func TestRetryOnDeadlockReturnsNonRetryableImmediately(t *testing.T) {
+	withFastDeadlockRetry(t, 5)
+	sentinel := errors.New("boom")
+	calls := 0
+	err := retryOnDeadlock(context.Background(), func() error {
+		calls++
+		return sentinel
+	})
+	if !errors.Is(err, sentinel) {
+		t.Fatalf("expected sentinel, got %v", err)
+	}
+	if calls != 1 {
+		t.Fatalf("expected 1 call, got %d", calls)
+	}
+}
+
+func TestRetryOnDeadlockGivesUpAfterMaxAttempts(t *testing.T) {
+	withFastDeadlockRetry(t, 4)
+	calls := 0
+	err := retryOnDeadlock(context.Background(), func() error {
+		calls++
+		return &pgconn.PgError{Code: "40P01"}
+	})
+	var pgErr *pgconn.PgError
+	if !errors.As(err, &pgErr) || pgErr.Code != "40P01" {
+		t.Fatalf("expected 40P01 pg error, got %v", err)
+	}
+	if calls != 4 {
+		t.Fatalf("expected 4 calls, got %d", calls)
+	}
+}
+
+func TestRetryOnDeadlockStopsOnCanceledContext(t *testing.T) {
+	withFastDeadlockRetry(t, 5)
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	calls := 0
+	err := retryOnDeadlock(ctx, func() error {
+		calls++
+		return &pgconn.PgError{Code: "40P01"}
+	})
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("expected context.Canceled, got %v", err)
+	}
+	if calls != 1 {
+		t.Fatalf("expected 1 call before cancel, got %d", calls)
+	}
+}

internal/catalog/folder_repo.go

@@ -14,6 +14,40 @@ import (
 	"github.com/Silo-Server/silo-server/internal/models"
 )
 
+// Retry parameters for transient serialization/deadlock failures. They are
+// package vars (not consts) only so tests can shrink them; production code
+// never mutates them.
+var (
+	deadlockMaxAttempts = 5
+	deadlockBaseBackoff = 50 * time.Millisecond
+)
+
+// retryOnDeadlock runs op, retrying when Postgres reports a deadlock (40P01) or
+// serialization failure (40001), with exponential backoff. It returns
+// immediately for any other error, and honors context cancellation between
+// attempts.
+func retryOnDeadlock(ctx context.Context, op func() error) error {
+	backoff := deadlockBaseBackoff
+	for attempt := 1; ; attempt++ {
+		err := op()
+		if err == nil {
+			return nil
+		}
+		var pgErr *pgconn.PgError
+		if attempt < deadlockMaxAttempts && errors.As(err, &pgErr) &&
+			(pgErr.Code == "40P01" || pgErr.Code == "40001") {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-time.After(backoff):
+			}
+			backoff *= 2
+			continue
+		}
+		return err
+	}
+}
+
 // Sentinel errors for folder repository operations.
 var (
 	ErrFolderNotFound = errors.New("folder not found")