diff --git a/backend/src/workspace-maintenance.ts b/backend/src/workspace-maintenance.ts
index e506eeaa..bb66d8b3 100644
--- a/backend/src/workspace-maintenance.ts
+++ b/backend/src/workspace-maintenance.ts
@@ -41,8 +41,10 @@ function boundedJson(result: WorkspaceOperationResult): string {
   return encoded;
 }
 
-function sanitizeStderr(_error: unknown): string {
-  return "workspace maintenance failed\n";
+function sanitizeStderr(error: unknown): string {
+  const detail = error instanceof Error ? error.message : String(error);
+  const safe = detail.replace(/[\r\n]+/g, " ").slice(0, 512);
+  return safe.length > 0 ? `workspace maintenance failed: ${safe}\n` : "workspace maintenance failed\n";
 }
 
 function parseRequest(command: string, stdin: string): Record<string, unknown> {