fix: bound task failures and release stalled workers

apps/admin_console/services/report_export.py

@@ -95,6 +95,11 @@ def failure_reason(directory: Path, status: str, recorded: str | None) -> str:
     state = read_json(directory / "status.json", {})
     if isinstance(state, dict) and state.get("error"):
         return redact(state["error"])
+    result = read_json(directory / "result.json", {})
+    if isinstance(result, dict) and result.get("status") == "failed":
+        reason = result.get("error") or result.get("explanation")
+        if reason:
+            return redact(reason)
     log_lines: list[str] = []
     for name in ("stdout.log", "stderr.log"):
         path = directory / name