Background Agent .output file is 0 bytes on Windows without Developer Mode, while the launch result calls it "the full subagent JSONL transcript" (still in 2.1.282; follows #55263)

Claude Code 2.1.282, Windows 11 Home (build 26200), Windows Developer Mode off.

Steps

1. Start a subagent with the Agent tool and run_in_background: true.
2. Read the launch result. It names .../tasks/<id>.output as "the full subagent JSONL transcript".
3. When the agent finishes, tasks/<id>.output is a plain 0-byte file, not a symlink. subagents/agent-<id>.jsonl in the session folder holds the full transcript (hundreds of KB).

Expected

Either the output file reads as the transcript (a hardlink or copy when a symlink cannot be made), or the launch text says the file may be empty and names the transcript path.

Notes

#55263 found the cause: symlink creation fails without Developer Mode, and the CLI falls back to an empty file. That issue was auto-closed as stale and is now locked. We see the same on 2.1.282, across two sessions and every background child in them. The final report still reaches the parent, so the harm is to anything that follows the launch text to the file.