# plan-acp-agent

The coding agent as an ACP server with **session modes** composed — the live composition of the [plan-mode Agent Note](../../.agents/notes/implemented/feature/2026-07-07-plan-mode.md).

## What it demonstrates

`session/new` advertises the mode picker (`default` / `plan`) plus the sandbox-mode and approval config options — two independent axes on one session, the composition this example exists to demonstrate. Plan mode adds the plan guidance section and the `exit_plan_mode` tool and touches nothing else: the sandbox keeps whatever mode its own knob says (workspace-write here by default), escalation prompts work in plan exactly as in default, and switching either axis never disturbs the other, in any order. A user who wants a hard read-only floor while planning flips the sandbox-mode option to read-only alongside the mode picker. There is deliberately no per-mode tool list either: `write`/`edit`/`bash` stay present in plan and the section's guidance is what defers changes to after the review (the effects-based generalization is the RFC's deferred item). A blocking decision goes to the user through `ask_user_question`. The model leaves by presenting its plan through `exit_plan_mode`: the plan markdown renders as the tool's call card, the review question arrives as an elicitation form (approve / keep planning, free text welcome), and a keep-planning answer returns the feedback to the model verbatim.

## Run

```sh
pnpm run demo:plan-acp   # needs DEEPSEEK_API_KEY (repo-root .env works)
```

Drive it from Zed or any ACP client; the mode picker appears on the session beside the sandbox/approval selects. Switching back to `default` (or an approved `exit_plan_mode`) drops the plan section and the exit tool on the next step; the sandbox and approval knobs stay exactly where the user left them.

## Tests

`pnpm run test:snapshot` replays three scenarios keyless (the recorded bash re-executes for real under the host's sandbox runner — Seatbelt on macOS, bwrap on Linux CI). `modes-advertise` (authored): the `modes` advertisement and both config options on `session/new`, both `session/set_mode` round-trips with their optimistic `current_mode_update`, and the loud rejection of an unknown mode id, as committed wire bytes. `plan-mode` (recorded, the header pin): the full arc — setMode(plan), the plan-shaped initial header (full toolset + exit tool + section), a real `cat` run inside plan (under the sandbox's own workspace-write default — the mode does not change it), the plan presented via `exit_plan_mode`, a scripted elicitation approve, the boundary-flushed `mode/set` back with a complete changed `request/header`, then a real edit mid-turn. `plan-mode-reject` (recorded): the keep-planning branch, whose corrective `isError` carries the reviewer's free-text feedback verbatim and leaves the session in plan mode. The sandbox-denial marker stays pinned at the unit tier (`packages/bash/tool-bash/tests` — a recorded denial's stderr would be the backend's dialect and replay only where it was recorded).