* fix(cli): exit non-zero when a headless run ends in an LLM error fallback
LLMErrorHandlingMiddleware turns provider failures (e.g. an expired
credential returning 401) into an AIMessage flagged
`deerflow_error_fallback` instead of raising. The Gateway run status and
the subagent executor already treat that flag as a failure. #5963 gave
`deerflow --print` / `--json` an error boundary for raised exceptions,
but a flagged fallback never raises, so both modes still printed the
fallback text and exited 0.
Both headless modes now follow #5963's failure contract when the run's
final AI message carries the flag: `--print` keeps the fallback text on
stdout and adds an `Error:` line on stderr; `--json` appends the terminal
`{"type": "error"}` record. Both exit 1.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
* refactor(cli): share final-answer accumulation with the embedded client
* docs: scope headless accumulator guidance to TUI
---------
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>