Both backends now return the same command-line state (prompt, running,
keywords, accept, buffer, history, historyExpanded). cmdline.input echoes
a refused line to the history and `output` and also reports it in `error`
on both sides. Headless app.open without a path answers "missing path"
like the app instead of reaching OPEN. Documented in control-protocol.md.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
