Keep long Pi sessions usable on OpenAI Codex models by replacing Pi's local summary request with Codex's provider-side RemoteCompactionV2 checkpoint when the current model supports the Codex Responses API.

Features

Uses the current openai-codex model for each compaction; it never silently changes the session model.
Sends only the history Pi is discarding, plus the previous Codex checkpoint, so the incoming/kept user message is not duplicated.
Persists Codex's opaque encrypted checkpoint and rehydrates it only for supported Codex requests.
Caps compaction input and response size and falls back to standard Pi compaction on failure.
Keeps a bounded readable transcript excerpt so switching models or providers remains usable.

The current Codex catalog includes models such as gpt-5.6-sol, gpt-5.6-terra, and gpt-5.6-luna. Capability detection follows the provider/API contract (openai-codex + openai-codex-responses) rather than a brittle model-name list.

Installation

pi install npm:pi-codex-compaction

For local development:

pi install /path/to/pi-mono/packages/pi-codex-compaction

Or load it for one run:

pi -e /path/to/pi-mono/packages/pi-codex-compaction

Behavior

When Pi starts compaction on a supported Codex model, the extension sends a streamed Responses request containing a compaction_trigger item and the remote_compaction_v2 beta feature. The returned opaque checkpoint is stored in the Pi compaction entry. Later supported Codex requests replace the textual compaction marker with the raw checkpoint; other providers/models receive the bounded textual fallback instead.

Compaction uses the model active when Pi triggers it. If a session switches from a larger to a smaller model, the remote request is bounded against the new model's context window and tool outputs are reduced before sending. If it still cannot fit, the extension leaves compaction to Pi's normal implementation.

If the remote request fails, is cancelled, or returns an unexpected response, Pi's standard compaction path runs. No configuration is required.

Development

npm install
npm run -w packages/pi-codex-compaction check
npm test -w packages/pi-codex-compaction
npm run -w packages/pi-codex-compaction pack:dry-run