pi-auto-compact

A minimal Pi extension that compacts the conversation before sending a prompt when the projected context (current usage plus the new input) crosses a configurable percentage of the current model's context window.

Compaction itself always reuses Pi's built-in ctx.compact() implementation. Pi's own automatic compaction is untouched — if enabled in Pi's settings, it still acts as the final safety net.

Install

pi install npm:pi-auto-compact

Or install directly from GitHub:

pi install git:github.com/Chasen-Liao/pi-auto-compact

Configuration

The default threshold is 78% used. Change it inside Pi with:

/compact-threshold 50

Values are 30–98; 99 is rejected because compaction itself needs headroom. This saves the setting atomically (merging into the existing file, so other keys survive). Show the current value:

/compact-threshold

Reset to the default 78%:

/compact-threshold reset

The threshold is calculated against the active model's context window, so the same percentage works across models with different window sizes. It is re-read before every prompt, so config changes apply without restarting the session.

Behavior

• Preflight trigger: when you submit a prompt while the agent is idle, the extension estimates current context + your input (using Pi's own token estimator). At or above the threshold, it compacts once before the prompt is sent, so long inputs never interrupt a running tool chain.
• Failure policy: if preflight compaction fails, the prompt is not sent (fail-closed; recall it from the editor history and resubmit) and an error is shown. Exception: "Nothing to compact" / "Already compacted" mean the context is already minimal, so the prompt is sent anyway.
• Status: the footer shows a warning when context is past the threshold (next prompt will compact) and while preflight compaction is running.
• Not preflighted: messages queued during an active run (steer/followUp), slash commands handled before the input event, and content injected later by /skill: or /template expansion — those remain covered by Pi's built-in compaction.
• Requires a known context window: if the active model doesn't report one (or usage is unknown, e.g. right after a compaction), the preflight is skipped and Pi's built-in compaction covers it.
• Session switches/reloads mid-compaction are detected; stale callbacks never touch the new session's status.

Development

npm install
npm run typecheck
npm test
pi -e .

npm test runs a mock smoke suite (test/smoke.ts, Node native TS type stripping) that covers threshold gating, failure classification, concurrency, session guarding, config persistence, and image-prompt projection.

License

MIT