Add Claude Code agent support alongside pi

[goyamegh]

Summary

Add first-class support for Anthropic's Claude Code as a selectable agent inside pi-web, alongside the existing pi agent. Today the drawer/composer assumes the pi agent's session model exclusively; running CC requires an external terminal and gives up the entire pi-web session UX.

Motivation

• Many of us already use Claude Code daily for the same kinds of tasks pi handles. Forcing a context switch to a terminal pane for CC defeats the purpose of pi-web's tab/drawer/marker/folder UX.
• CC's session files (~/.claude/...) follow a different layout than pi's (~/.pi/agent/sessions/...). A small adapter layer can normalise both into the existing SessionInfo shape so the drawer, marker buckets, pinned tabs, search, etc. all "just work".
• CC has its own user / project / plugin slash commands and skills. Surfacing those in the composer's slash-command palette is a natural extension once the agent is wired up.

Proposed scope

A first cut should include:

1. Agent abstraction in server.ts — extract a small interface (start session, stream events, list sessions, fork, rename, delete, send message) and have both pi and claude-code implement it. Pick the implementation per-tab from a UI selector or per-cwd default.
2. Claude Code adapter — wraps the CC CLI / SDK and translates its event stream into pi-web's existing agent_event envelope (text deltas, tool start/end, message_end, agent_end, errors, replay).
3. Session translator — read CC's on-disk session format and project it onto pi-web's SessionInfo (id, title, cwd, firstMessage, updatedAt, etc.) so the drawer renders CC sessions next to pi sessions, with the agent shown as a small badge / icon.
4. Open-anywhere session lookup — when a CC session is clicked, search across every cwd we know about (CC's per-project session dirs are not 1:1 with pi's). Cache the lookup so the common case stays cheap.
5. Slash-command bridge — surface CC's user / project / plugin commands and skills in the composer's slash-command palette, keyed off the active agent.
6. Tests — unit tests for the translator + adapter (event mapping, error paths), and Playwright e2e covering the end-to-end agent UI on a CC session (replay, tool turn, slash command).

Notes / context

• Locally I have a working prototype that does all of the above (feat(claude-code): add Claude Code agent alongside pi and follow-ups). Happy to clean it up and open a PR against main once the upstream direction is confirmed — wanted to file the issue first so the design choices (single adapter interface vs per-agent server modules; how to identify the active agent in SessionInfo; whether to ship a CC selector in the drawer footer or in settings) can be discussed before code review.
• Some adjacent papercuts surfaced while building this — see Drawer hides whole folders when filter is applied or sessions are empty #13 for the folder-visibility one.

Out of scope (for now)

• Bidirectional session migration between pi and CC.
• Cross-agent message replay (one CC turn replayed under pi, etc.).
• Renaming / re-homing CC sessions on disk.

Acceptance criteria

• An agent picker exists in pi-web (default = pi) and toggles which backend handles a tab's session.
• CC sessions appear in the drawer alongside pi sessions, with a clear visual distinction.
• Opening, replaying, and continuing a CC session works end-to-end inside pi-web.
• CC slash commands are listed in the composer palette when CC is the active agent.
• Unit + e2e tests cover the new agent adapter.