Added PermanentError type, IsPermanent() helper. Permanent errors are logged and not retried

backend/internal/notifications/notifier.go

@@ -1,6 +1,10 @@
 package notifications
 
-import "context"
+import (
+	"context"
+	"errors"
+	"net/http"
+)
 
 // AlertMetadata holds context about the alert being sent.
 type AlertMetadata struct {
@@ -13,3 +17,22 @@ type AlertMetadata struct {
 type Notifier interface {
 	Send(ctx context.Context, message string, meta AlertMetadata) error
 }
+
+// PermanentError wraps errors that should not be retried (e.g. 401, 403, 404).
+type PermanentError struct{ Err error }
+
+func (e *PermanentError) Error() string { return e.Err.Error() }
+func (e *PermanentError) Unwrap() error { return e.Err }
+
+func IsPermanent(err error) bool {
+	var p *PermanentError
+	return errors.As(err, &p)
+}
+
+func isPermanentStatusCode(code int) bool {
+	return code == http.StatusUnauthorized ||
+		code == http.StatusForbidden ||
+		code == http.StatusNotFound ||
+		code == http.StatusMethodNotAllowed ||
+		code == http.StatusGone
+}