A hidden tmux client: tmux attach running on a PTY pair the app owns.
From tmux’s perspective this is a normal terminal, so attach triggers a
full repaint, PTY resize drives window size (window-size latest), and
keyboard bytes written to the master are real terminal input.
Data-driven agent-harness registry — harness definitions are DATA, not
code (spec: field-notes-design.md §V “Backend (registry, not enum)”).
Four known harnesses ship as compiled-in default specs; [harnesses.*]
config entries override (whole-spec replace) or extend the registry, so
adding a future harness requires zero Rust changes.
File-based inbox for orchestrator↔worker messaging (opt-in, see
config::InboxMessagingConfig). One file per message under
{dir}/{session_id}.inbox/ — same shape as hooks::append_work_request’s
{dir}/{session_id}.requests/, and for the same reason: every writer
stays single-owner, so nothing here ever read-modify-writes a file
another process could be touching concurrently.
Orchestrator↔worker message delivery, gated by the opt-in file-based
inbox toggle (config::InboxMessagingConfig, default off). Shared by
both callers that inject a message into a session: the ninox send CLI
and Engine::send_to_session (poller reactions).