feat(acp): ACP bridge — drive the coding agent from an editor over JSON-RPC stdio

Implements the RFC 010 MVP: a new `@deepseek-ai/dsh-acp` package bridges the
harness agent to the Agent Client Protocol (JSON-RPC 2.0 over newline-delimited
stdio), so Zed and other ACP editors can drive the coding agent — streaming
render, tool-call display, and resumable sessions via `session/load`.

- packages/acp: AgentSideConnection wiring; initialize/newSession/loadSession/
  prompt/cancel; a total TurnEndReason→StopReason codec; settle-once with a
  fallback chain (agent/turn-end → logged turn/end → idle); single-session
  guard; cwd-must-equal-launch-dir validation; load replays from the persisted
  event log (assistant/chunk→agent_message_chunk, tool/call/result→tool_call*).
- agent: add Agent.whenIdle() quiescence signal to the interface; LoopAgent
  implements it (resolves on the first running→idle/disposed transition). The
  bridge awaits it on disposal so teardown reaches quiescence, not just abort.
- examples: extract the shared provider/tool core into examples/base.yml;
  coding-agent nest-includes it; new examples/acp-agent serves the agent over
  ACP with JSONL persistence and no stdout logger (stdout is the protocol).
- Permission gate deferred (TODO(rfc010-permission-gate)): tools run with the
  executor's full authority; only the Agent→sessionId ownership seam is laid
  down. Cancel is best-effort for a not-yet-started queued turn
  (TODO(rfc010-cancel-prestep)). RFC 010 stays `proposed`.
- Docs: package README + Zed snippet; client-driver cookbook section; root and
  packages layout/commands; RFC 010 implementation-status note.

48 bridge tests + whenIdle coverage; 100% per-file coverage; e2e boots the
example as a subprocess and verifies a written file on disk (key-gated, with a
no-key stdout-purity check).

examples/acp-agent/README.md

@@ -0,0 +1,35 @@
+# acp-agent example
+
+The DeepSeek Harness coding agent exposed as an **Agent Client Protocol (ACP)** server over JSON-RPC stdio — drive it from Zed or any other ACP client.
+
+```sh
+yarn demo:acp          # needs DEEPSEEK_API_KEY (repo-root .env or env)
+```
+
+This boots `@deepseek-ai/dsh-acp` over the shared provider/tool core (`../base.yml`), with `agent-loop` configured with **no pre-created agents** (ACP `session/new` creates them on demand) and JSONL session persistence (so `session/load` works).
+
+## stdout is the protocol
+
+This example loads **no stdout logger** — `stdout` carries the JSON-RPC frames, and any other write corrupts them. Do not add `@cordisjs/plugin-logger-console` or a stdio UI here. Use a stderr exporter if you need logs.
+
+## Zed configuration
+
+Add to your Zed `settings.json` under `agent_servers`:
+
+```json
+{
+  "agent_servers": {
+    "DeepSeek Harness": {
+      "command": "yarn",
+      "args": ["demo:acp"],
+      "env": { "DEEPSEEK_API_KEY": "sk-…" }
+    }
+  }
+}
+```
+
+Run from the repo root (the MVP requires the server's launch directory to be the workspace — see the `cwd` note in `packages/acp`).
+
+## MVP limitations
+
+The bridge is the RFC 010 MVP: single session per connection (RFC 011 lifts this), text-only prompts, `cwd` must equal the launch directory, and the tool-permission gate is deferred (`TODO(rfc010-permission-gate)` — tools run with the executor's full authority). See `packages/acp/README.md` for the full contract.