pi-background-bash

Async/background bash for Pi: keep using the normal bash tool, but long-running commands stop blocking the agent.

pi-background-bash replaces Pi's bash execution with the PBB runner and adds two quality-of-life features:

• background: true starts a command in the background immediately.
• normal foreground commands automatically move to the background after 30 seconds.

As of v1, PBB-owned execution is the baseline: jobs are recorded with logs plus pid/pgid, and full output is available through pbb tail.

When a background command finishes, the extension injects a follow-up result into the session and wakes the agent.

Fork notice

This is a maintained fork of sshkeda/pi-background-bash with two fixes:

1. Installable out of the box. The upstream package depends on the private repository github:sshkeda/pi-context (returns 404), so pi install fails for everyone. The three functions it uses (piContext, truncateContextText, formatTruncationNotice) are now inlined in extensions/pi-context-utils.ts and the dependency is removed.
2. No stale-ctx crashes. The background-completion callbacks evaluated ctx.cwd lazily, after session teardown in headless one-shot mode, throwing This extension ctx is stale after session replacement or reload. cwd is now captured eagerly at job start.

Verified end-to-end (interactive + headless): background: true, automatic backgrounding after the configured threshold, detached pbb runner with full logs, follow-up injection into the session (custom_message entry with kind="background_bash_result"), and agent wake-up via triggerTurn.

Why

AI coding agents often need to run slow commands: test suites, builds, dev servers, downloads, deploys, benchmark loops, and watchers. Without background execution, the agent gets stuck waiting. With this extension, the agent can continue useful work and handle the command output when it arrives.

Install from this fork:

pi install git:github.com/mowenroot/pi-background-bash

Try without installing:

pi -e git:github.com/mowenroot/pi-background-bash

Upstream install (may fail due to the private pi-context dependency): pi install git:github.com/sshkeda/pi-background-bash

Local development:

git clone https://github.com/mowenroot/pi-background-bash.git
cd pi-background-bash
npm install
npm test
pi -e .

Usage

Run a command normally. If it is still running after 30 seconds, it automatically moves to the background:

bash({ command: "npm test" })

Start a command in the background immediately:

bash({ command: "npm test", background: true })

Add a timeout if you want Pi to kill the command after a fixed number of seconds:

bash({ command: "npm test", background: true, timeout: 120 })

Completion results arrive as Pi context messages:

<pi_context source="pi-background-bash" kind="background_bash_result" id="bg001" outcome="exit" exit_code="0">
...
</pi_context>

Commands run through the PBB-owned bash runner (bash -lc) so background jobs have recorded pid/pgid and can be killed as process groups. Verbose completion messages are truncated in-session with a pbb tail <job> --full hint; the full output is kept in the PBB log. See docs/pbb-runner.md for the v1 runner contract.

v1 migration

v1 is a hard migration to PBB-owned execution. The old native-runner compatibility path and PI_BACKGROUND_BASH_RUNNER switch are gone. If you depended on exact pre-v1 bash formatting, update callers to use pbb tail <job> --full for complete output and the recorded PBB job metadata for process control.

pbb CLI

This package also installs pbb, a small inspector for background bash jobs.

pbb self
pbb list
pbb status bg001
pbb tail bg001 -n 80
pbb kill bg001

pbb is designed for agents: output is wrapped in compact pi_context envelopes and always includes session/instance identity. Local job IDs are fixed-width strings such as bg001, bg002, and bg010 so listings sort chronologically. pbb uses pi-lane runtime identity env vars (PI_LANE_SESSION_KEY, PI_LANE_INSTANCE_ID, etc.) and defaults to the current live Pi instance, not every terminal attached to the same session.

Background job state is stored under:

~/.pi/pbb/sessions/{sessionKey}/instances/{instanceId}/
  identity.json
  jobs/{jobId}.json
  events.jsonl
  logs/{jobId}.log

pbb list and pbb status show owner liveness through the tracked pil CLI from pi-lane, so stale/disconnected owners are visible instead of silently confused with the current runtime. If tracked pi-lane/pil is missing or fails, pbb hard-fails instead of silently degrading liveness to unknown.

pbb kill writes a kill request into the owning instance mailbox. A live pi-background-bash runtime polls that mailbox and aborts the matching in-process job. Jobs record pid/pgid, so the runtime kills the full process group. If the owner is stale, pbb kill --stale --instance <id> <job> can signal the recorded process group explicitly.

Configuration

Default auto-background threshold: 30 seconds.

Configure the global threshold in ~/.pi-background-bash/config.json:

{
  "autoBackgroundAfterSeconds": 10
}

Disable automatic backgrounding while keeping background: true available:

{
  "autoBackgroundAfterSeconds": 0
}

You can also override the threshold for a single project with .pi/background-bash.json in that project. Project config wins over global config.

Agent prompt behavior

The extension updates the bash tool metadata exposed to models:

• the background boolean is part of the tool schema
• the tool description documents automatic backgrounding
• prompt snippets/guidelines teach the agent not to retry just to wait
• prompt guidelines teach the agent to use pbb list/status/tail for inspection
• background completion messages are described as final bash results

No global Pi prompt patch is required.

Security

This is a Pi extension. Like any Pi package, it runs with your local user permissions and can execute shell commands requested by the agent. Review the source before installing third-party extensions.

Development

npm install
npm run hooks:install
npm run typecheck
npm test

This repo uses Lefthook for local pre-commit checks. The test suite uses pi-mock to exercise the extension against a real Pi process.

License

MIT