Wraps the existing `Err(e)` arm with a `cli.json` branch:
- `--json`: stderr ndjson `error.v1` via wire_error_v1
- non-`--json`: legacy `error: <msg>` text path (unchanged)
exit_code() unchanged — RefusalSignal/NoHitSignal/DoctorUnhealthy
still drive 1/1/3.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>