The bundle command group's _fail() helper is documented as printing 'to stderr', and the module contract is 'human logs go to stderr/console' while --json 'emits machine-readable data on stdout'. But it called console.print(), and the shared console writes to STDOUT, so every bundle error (every command routes through _fail) landed on stdout -- corrupting the JSON stream that --json consumers parse.
Add a stderr-bound err_console to _console.py (its documented role as the single Console source) and use it in _fail. stdout now carries only the JSON payload.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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