[contexto]: Exploration report for Pi Agent integration

[sm86]

Goal

Produce a written exploration report on what it would take to integrate Contexto with Pi Agent, before committing to build work. Sister ticket to #134 (Hermes), but discovery-only.

Why exploration first

We don't yet know whether Pi Agent's plugin / context surface maps cleanly onto our existing ContextoBackend + lifecycle hooks (afterTurn, compact, assemble, dispose), or whether it requires a different shape entirely (e.g. middleware, callback, sidecar). Building blind risks either an awkward adapter or a half-finished integration.

Deliverable

A short report (markdown, in docs/explorations/pi-agent.md or similar) covering:

1. Pi Agent plugin/extension surface — link the relevant docs; summarize the lifecycle and extension points.
2. Mapping to Contexto lifecycle — which Pi Agent hooks line up with afterTurn / compact / assemble / dispose; what's missing or differently shaped.
3. Compaction ownership — does Pi Agent own the context window (sliding-window analog) or always delegate?
4. Token-budget signals — does Pi Agent expose anything like tokenBudget / currentTokenCount / firstKeptEntryId?
5. Packaging — separate package (@ekai/contexto-pi) vs second entry in @ekai/contexto; what the install story looks like.
6. Recommendation — build now, build later, or don't build. With a one-paragraph justification.

Acceptance criteria

• Report committed to the repo and linked from this issue
• Recommendation is explicit (not "we could go either way")
• Follow-up build ticket opened if recommendation is "build"