diff --git a/backend/src/workspace-maintenance.ts b/backend/src/workspace-maintenance.ts
index 7a94171d..4dce11c4 100644
--- a/backend/src/workspace-maintenance.ts
+++ b/backend/src/workspace-maintenance.ts
@@ -135,7 +135,12 @@ export async function runWorkspaceMaintenanceCli(
       try { return JSON.parse(io.stdin).workspaceId ?? ""; } catch { return ""; }
     })());
     io.writeStdout(boundedJson(result));
-    io.writeStderr(sanitizeStderr(error));
+    if (process.env.P2_CHILD_DEBUG === "1") {
+      const detail = String((error as Error).message ?? "").replace(/[\r\n]+/g, " ").slice(0, 2048);
+      io.writeStderr(`workspace maintenance failed: ${detail}\n`);
+    } else {
+      io.writeStderr(sanitizeStderr(error));
+    }
     const message = String((error as Error).message ?? "");
     const requestError = error instanceof SyntaxError
       || message === "invalid request"