pi-babysit

A pi extension that runs any shell command under babysit-supervised sessions — one context-safe substrate for quick commands, background processes, and pi subagents. It retires both @mjakl/pi-processes (the process tool) and the old pi-subagent extension.

Install

pi install npm:@yusukeshib/pi-babysit

Then install the babysit binary (the extension does not auto-install it):

cargo install --git https://github.com/yusukeshib/babysit

or grab a prebuilt binary from the releases and put it on your PATH. If it's missing, every tool and the /babysit command fail with these instructions.

The model

Every session is a babysit worker owning a PTY, recording all output to a log, reachable from anywhere (~/.pi-babysit/<pi-session-id>/). Two kinds:

kind	started by	completion	on completion
process	babysit_run { command }	process exit	automatic notification message (triggerTurn) — the agent may end its turn after starting and is resumed on exit, same contract as the old process tool
subagent	babysit_run { profile: "subagent", task }	agent_end in the RPC event stream (process stays alive)	none — the agent polls babysit_check or blocks on babysit_wait; the idle session accepts follow-up tasks

The profile is a tool parameter, not a separate tool set: domain knowledge (RPC bookkeeping, per-task byte offsets, parked-turn detection, PTY-safe message delivery, spawn validation) lives in code, while the LLM sees one small generic surface.

Because sessions are real PTYs, the agent can also drive interactive programs (installers, wizards, REPLs): type with babysit_send (text or named keys) and read the rendered screen with babysit_check { screen: true } — a capability neither retired extension had.

Tools (LLM-callable)

Tool	What it does
babysit_run	Run any command (command, optional name/pty/timeout/idleTimeout/retryOnWorkerDeath) or start a subagent (profile: "subagent", task, optional agent/model/tools). Quick commands return inline; longer ones continue in the background
babysit_check	List all sessions, or inspect one: process → state + log tail (or screen: true for TUIs); subagent → live progress (turns, recent tool calls, partial answer)
babysit_send	Process: type text / press keys into the PTY. Subagent: steer mid-run, or send a follow-up task when idle (mode: auto/steer/task)
babysit_wait	Block until done: process exit (or expect: "regex" readiness marker), subagent task completion. Multi-wait: ids + mode: "any"|"all"
babysit_kill	Terminate a session (suppresses the exit notification)

A tool_call hook also blocks bash commands that background themselves (… &, nohup, setsid, disown) and points the agent at babysit_run (carried over from pi-processes' blockBackgroundCommands).

Commands (human)

Command	What it does
/babysit	Arrow-key picker over all sessions. Renders an inline snapshot (no tmux): running process → current rendered screen + recent output + a copy-paste babysit attach take-over hint (detach Ctrl-\ Ctrl-\); running **subagent** → read-only progress (RPC stdin stays untouchable); finished → summary. Re-run /babysit to refresh

A minimal widget above the editor shows live counts (N processes · M subagents working · K idle).

Logs without context flooding

babysit_run, babysit_wait, and automatic completion notifications always return lifecycle metadata and the absolute path to the complete output.log. When the complete output is at most 8 KB it is returned inline; larger output stays out of model context. Inspect large logs on demand with bounded shell commands such as:

tail -n 50 /path/to/output.log
rg -n 'FAIL|ERROR' /path/to/output.log

babysit_check { id, lines } remains available as a convenient bounded tail. Do not read a potentially large log file in full.

To enforce this policy, the extension blocks direct bash except for pwd, short Git status/branch checks, and head/tail/rg reads of .log files that are explicitly bounded to at most 100 lines. Broad searches, diffs, API calls, multiple commands, redirects, and shell wrappers are redirected to babysit_run. Set PI_BABYSIT_ALLOW_BASH=1 only as an emergency escape hatch to disable this gate.

External worker death

If endpoint security or another external actor kills the babysit supervisor, pi-babysit normalizes the stale running state to worker-dead, returns immediately instead of hanging, and explains that the command may have started. For commands known to be safe and idempotent, set retryOnWorkerDeath: true to retry once with a new session id. It is opt-in because blindly rerunning an arbitrary command can duplicate side effects.

How completion detection works

• Process: a 2.5s poller watches for running→exited transitions and injects one pi.sendMessage(…, { triggerTurn: true, deliverAs: "steer" }) per ended session (deduped via meta/<id>.json). babysit_kill and an exit already reported by babysit_wait suppress the notification.
• Subagent: babysit_wait blocks on babysit expect '"type":"agent_end"'. An agent_end whose last message is a parked toolResult — a babysit_run { command } result carrying the [notify-on-exit] marker (or the legacy process tool) — only means "turn parked awaiting a process-exit notification; pi resumes on its own", so the wait continues. Any other agent_end is real completion. Per-task byte offsets scope check/wait to the CURRENT task, which is what makes follow-up tasks work.

Subagents load self-reap.ts, which exits an idle finished subagent after a grace window (PI_BABYSIT_REAP_AFTER, default 120s) using the same parked-turn rule, so a subagent waiting on a long build is never false-killed.

Environment overrides

Var	Default	Purpose
PI_BABYSIT_DIR	~/.pi-babysit	babysit state root (namespaced per pi session)
PI_BABYSIT_BIN	pi	agent binary for subagents
PI_BABYSIT_CLI	babysit	babysit binary
PI_BABYSIT_VIEW_CMD	bundled format-stream.mjs	live-attach pretty printer for subagent JSONL ("" disables)
PI_BABYSIT_REAP_AFTER	120s	idle grace before a finished subagent self-exits (off/none/0 disables)

Requires babysit and pi on PATH. The extension does not auto-install babysit: if the binary is missing, every tool and the /babysit command fail with install instructions (cargo install --git https://github.com/yusukeshib/babysit or a prebuilt release), and a warning is shown at session start. Point $PI_BABYSIT_CLI at a custom binary path if needed.

(No tmux dependency — /babysit renders inline; take over a live process manually with the babysit attach command it shows.)