babysit

name	babysit
description	Run long-running tasks under babysit — supervised background runner with cgroup-enforced memory/CPU caps and observability-stall kill. Use BEFORE any long-running task (>2 min), compute-intensive jobs (e.g. builds/benchmarks/renders/training), background work, or when the user says "run in background", "use babysit". This skill defines guardrails and the mandatory workflow, not just a how-to.
allowed-tools	["Bash(babysit:*)","Read"]
hooks	{"PreToolUse":[{"matcher":"Bash","hooks":[{"type":"command","command":"bash ${CLAUDE_SKILL_DIR-$HOME/.claude/skills/babysit}/hooks/no-sleep-babysit.sh","timeout":5}]}]}
compatibilty	Claude Code

babysit — Supervised Background Task Runner

!command -v babysit || (mkdir -p "$HOME/.local/bin" && install -m755 "${CLAUDE_SKILL_DIR}/scripts/babysit.py" "$HOME/.local/bin/babysit" && echo "babysit installed to ~/.local/bin") || echo "babysit installation failed, consider use self-contained scripts/babysit.py" # auto-install CLI tool on skill load !command -v babysit && (babysit ping 2>&1 || babysit daemon-start 2>&1 || echo "babysit daemon failed to start") # auto-start daemon on skill load

When to Use

• Non-interactive long-running tasks expected to run for >2 minutes
• Compute-intensive tasks: per-task cgroup caps (mem ≤40%, cpu ≤90%) prevent runaway resource use
• Long-running tasks that must survive the Claude session: daemon runs detached under user systemd

When NOT to Use

• Short tasks (<2 minutes): run in Bash directly
• Interactive commands: use /tmux instead
• IO-bound polling loops: babysit's scheduler does not help
• Lightweight (low CPU + low memory) tasks fine to die with Claude: Bash run_in_background: true

Hard Guardrail — Don't Bypass

/babysit is the cost guardrail for compute-intensive work on this host — not an optional tool. If a task is heavy (CPU-bound, memory-bound, multi-process), it MUST run under babysit so the cgroup caps and observability watchdog can stop runaway cost. Anti-patterns:

• Routing heavy work through built-in run_in_background: true to dodge the queue → no one monitors footprint; the host can thrash and lock the user out of SSH.
• Inflating --estimated_mem_bytes / --estimated_cpu_cores to pass the soft-deny gate while you don't actually need the headroom → starves other tasks and defeats fair-scheduling.
• Auto-backgrounded long Bash commands (e.g. tools that fork into daemons): if they're heavy, kill and re-launch under babysit run.

When your task hits the resource cap, the first reflex is NOT to raise the limit. It is to:

1. Audit the script — profile, drop unused intermediates, rolling / partial read, subsampling, reduce space / time complexity, optimize nested loops, lower batch size / n_jobs / parallelism.
2. Re-run footprint-optimized; confirm the demand is genuinely unavoidable.
3. Only then raise estimates and babysit wait_for_capacity for moderation.

Workflow

0. Smoke test

Before launching heavy work, smoke test on small scale for correctness and performance whenever appliable. Only proceed full-scale after the program is verified working and effcient in time and space.

1. Enqueue

babysit run \
  --name="<unique-name>" \
  --command="uv run python -u path/to/script.py" \
  --estimated_time="10m" \
  --estimated_mem_bytes="4G" \
  --estimated_cpu_cores=4

Provide best-effort estimates for time, peak memory, and peak CPU cores — by extrapolation of smoke test (if linear complexity appliable) plus prior live experience (if any). Never over-estimate without clue (starves other tasks). You'll get a runaway_risk notification when any actual exceeds its estimate. Pick estimation wisely.

The call is non-blocking: returns immediately with queued: <name>. The daemon dispatches as soon as system has capacity.

Required: --name (unique), --command (single shell string). Optional: --estimated_time (default 10m), --kill_timeout (default 2× estimated), --observability_interval (default 5m), --mem_pct_limit (default 40), --cpu_pct_limit (default 90), --estimated_mem_bytes (default 4G), --estimated_cpu_cores (default 4), --cwd (default current shell cwd).

Override the defaults to match your workload — under system memory/CPU pressure the daemon kills estimate-exceeders before within-estimate tasks, so accurate predictions protect long-running work. Hard kill fires at 2× sustained (daemon, graceful) or 3× instant via cgroup OOM. If the pressure is caused by an external (non-babysit) process — when the sum of all managed tasks' usage is smaller than the excess over threshold — the daemon logs and skips the kill rather than punishing its own tasks for someone else's load.

If capacity is tight, babysit run may soft-deny with capacity_exceeded (exit 2, JSON on stderr) — run the babysit wait_for_capacity --mem_bytes=… --cpu_cores=… (blocks until room exists) to wait for room, reduce estimates, or pass --force to override.

2. Wait for completion (background)

babysit wait --name="<unique-name>"

Run with run_in_background: true and attach Monitor for runaway risk notifications. You get:

• a mid-flight {"event":"runaway_risk","dim":"elapsed|mem|cpu", ...} JSON line on stderr the first time an actual exceeds its declared estimate (elapsed > estimated_time, mem > estimated_mem_bytes, or cpu_cores > estimated_cpu_cores) — inspect the log and decide whether to keep waiting or babysit kill. Daemon hard-kills for mem/cpu at 2× sustained for the monitor tolerance window; elapsed hard-kills at --kill_timeout (default 2× estimated_time).
• a terminal-status JSON object on stdout plus a <task-notification> when the task reaches a terminal state (exit 0 only on completed; exit 1 for everything else — failed, killed, unknown). For a kill, kill_reason + kill_hint fields at the top of the JSON tell you what to fix.

Do not poll with babysit status in a sleep loop — the daemon already knows; subscribe instead of polling.

3. Check log / progress at any time

babysit log --tail=15 --name="<unique-name>"
babysit log --follow --name="<unique-name>"   # stream; use with run_in_background: true

4. List / kill / adjust

babysit list                           # running/pending + terminal ended within 24h; --all for full history
babysit status --name="<name>"         # one task, JSON
babysit kill --name="<name>"           # SIGTERM, then scope-stop fallback
babysit adjust --name="<name>" --estimated_mem_bytes=32G  # retune estimated peak memory

The Observability Contract

babysit kills tasks that go silent for longer than observability_interval (default 5m). Your command MUST print at least one line every 5 minutes. Use:

• PYTHONUNBUFFERED=1 (or python -u) to defeat block-buffering
• Periodic progress markers with real signal: [3/42] ETA ~3m loss=1.2e-4
• LightGBM / native C++ stdout under pipes: write a custom Python callback with flush=True — lgb.log_evaluation is silent under non-tty stdout
• Generic keep-alives (Keep-alive, heartbeat, dots) defeat the purpose; emit progress, not noise

Conversation Example

Start training in the background. ``` Bash(command: "babysit run --name=train-maker-200t --command='PYTHONUNBUFFERED=1 uv run python -u src/train_maker_twohead.py' --estimated_time=2h", run_in_background: false) Bash(command: "babysit wait --name=train-maker-200t", run_in_background: true) ``` Training enqueued; will notify on completion. [STOP AND WAIT] ~2h later: <task-notification>Background command "babysit wait ..." completed (exit code 0)</task-notification> [`babysit log --tail=40 --name=train-maker-200t` to inspect final metrics] Training complete. Sharpe 2.74, AR 20.55%.

Pitfalls

babysit status showing completed does NOT guarantee success

Exit code 0 ≠ success when the inner runner swallows errors. A just <recipe> whose inner step fails with exit 1 may still return 0 to babysit. Always verify expected output files exist before chaining downstream tasks.

Bash-wrapper double-quoting

--command is passed to bash -c internally. Do NOT nest a bash -c '...' inside:

# WRONG — bash -c sees only "VAR=1"
babysit run --name=x --command="bash -c 'VAR=1 uv run python -u s.py'"

# RIGHT
babysit run --name=x --command="VAR=1 uv run python -u s.py"

Unbuffered Python under uv

uv run -u is rejected (-u flag goes to uv, not python). Use either:

PYTHONUNBUFFERED=1 uv run python script.py
uv run python -u script.py

Native C++ stdout is unaffected by PYTHONUNBUFFERED

LightGBM, XGBoost, sklearn's joblib workers, etc. write to stdout from C/C++ and ignore Python's buffering. Under babysit's pipe stdout, the native iter-loggers appear silent and the observability watchdog will kill the task. Wrap with a Python callback that reads metrics and prints with flush=True.

babysit ping failure means daemon is down

If commands return babysit daemon not running, run babysit daemon-start. One-time setup per host: loginctl enable-linger $USER so the daemon survives logout.

Names must be unique across active tasks

babysit run rejects a name that matches an existing non-terminal task. Pick descriptive names (maker-cv-200t-2026-05-19), or babysit kill the prior one first.

Skill Files

• references/babysit.md — full babysit spec (CLI flags, daemon config, resource rules)
• hooks/no-sleep-babysit.sh — blocks sleep N && babysit log/status anti-pattern
• scripts/babysit.py — self-contained babysit implementation (installed to ~/.local/bin)