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/tests/acp.e2e.ts

@@ -0,0 +1,142 @@
+import { spawn, type ChildProcessWithoutNullStreams } from 'node:child_process'
+import { Readable, Writable } from 'node:stream'
+import { mkdtemp, rm, readFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { afterEach, describe, expect, it } from 'vitest'
+import {
+  ClientSideConnection,
+  ndJsonStream,
+  PROTOCOL_VERSION,
+  type Agent as AcpAgent,
+  type Client,
+  type RequestPermissionRequest,
+  type RequestPermissionResponse,
+  type SessionNotification,
+} from '@agentclientprotocol/sdk'
+
+/**
+ * End-to-end: boot examples/acp-agent as a real subprocess speaking ACP over
+ * its stdio, drive it with a real ClientSideConnection, send a real prompt, and
+ * verify the WORLD (a file the agent wrote), not the agent's self-report. Owns
+ * and disposes the subprocess in afterEach. Key-gated.
+ *
+ * Also asserts stdout purity (only framed JSON-RPC on stdout) — that one runs
+ * WITHOUT a key, since it only needs the server to boot and answer initialize.
+ */
+
+const startScript = fileURLToPath(new URL('../start.ts', import.meta.url))
+// Resolve tsx's loader to an ABSOLUTE path: the subprocess runs with cwd set to
+// a temp workdir (the MVP requires session cwd === process.cwd()), where a bare
+// `--import tsx` would not resolve from node_modules. import.meta.resolve gives
+// the worktree's tsx regardless of the child's cwd.
+const tsxLoader = fileURLToPath(import.meta.resolve('tsx'))
+
+interface Spawned {
+  child: ChildProcessWithoutNullStreams
+  client: ClientSideConnection
+  updates: SessionNotification['update'][]
+  stderr: string[]
+}
+
+function spawnAcpAgent(cwd: string): Spawned {
+  const child = spawn(
+    process.execPath,
+    ['--import', tsxLoader, startScript],
+    { cwd, env: { ...process.env }, stdio: ['pipe', 'pipe', 'pipe'] },
+  )
+  const stderr: string[] = []
+  child.stderr.setEncoding('utf8')
+  child.stderr.on('data', (chunk: string) => stderr.push(chunk))
+
+  const updates: SessionNotification['update'][] = []
+  const stream = ndJsonStream(
+    Writable.toWeb(child.stdin) as WritableStream<Uint8Array>,
+    Readable.toWeb(child.stdout) as ReadableStream<Uint8Array>,
+  )
+  const makeClient = (_agent: AcpAgent): Client => ({
+    sessionUpdate(params: SessionNotification): Promise<void> {
+      updates.push(params.update)
+      return Promise.resolve()
+    },
+    requestPermission(_params: RequestPermissionRequest): Promise<RequestPermissionResponse> {
+      // Permission gate is deferred (TODO(rfc010-permission-gate)); the bridge
+      // never requests permission yet, so just allow if it ever does.
+      return Promise.resolve({ outcome: { outcome: 'cancelled' } })
+    },
+  })
+  const client = new ClientSideConnection(makeClient, stream)
+  return { child, client, updates, stderr }
+}
+
+let spawned: Spawned | undefined
+let workdir: string | undefined
+
+afterEach(async () => {
+  if (spawned) {
+    spawned.child.kill('SIGKILL')
+    spawned = undefined
+  }
+  if (workdir !== undefined) await rm(workdir, { recursive: true, force: true })
+  workdir = undefined
+})
+
+describe('acp-agent stdout purity (no key required)', () => {
+  it('emits only framed JSON-RPC on stdout', async () => {
+    workdir = await mkdtemp(join(tmpdir(), 'acp-e2e-'))
+    // Collect raw stdout bytes directly (bypass the SDK framing) to inspect.
+    // A dummy key lets the deepseek adapter APPLY (it only checks the key is
+    // present at boot, not valid — the key is used only on a real model call,
+    // which this purity test never triggers). So this runs WITHOUT real creds.
+    const child = spawn(process.execPath, ['--import', tsxLoader, startScript], {
+      cwd: workdir,
+      env: { ...process.env, DEEPSEEK_API_KEY: process.env.DEEPSEEK_API_KEY ?? 'sk-dummy-for-boot' },
+      stdio: ['pipe', 'pipe', 'pipe'],
+    })
+    const out: string[] = []
+    child.stdout.setEncoding('utf8')
+    child.stdout.on('data', (c: string) => out.push(c))
+
+    // Send a single initialize request as a newline-delimited JSON-RPC frame.
+    const req = JSON.stringify({ jsonrpc: '2.0', id: 1, method: 'initialize', params: { protocolVersion: PROTOCOL_VERSION, clientCapabilities: {} } })
+    child.stdin.write(req + '\n')
+
+    // Give it a moment to boot + reply, then inspect stdout.
+    await new Promise(r => setTimeout(r, 4000))
+    child.kill('SIGKILL')
+
+    const lines = out.join('').split('\n').filter(l => l.trim().length > 0)
+    expect(lines.length).toBeGreaterThan(0)
+    for (const line of lines) {
+      // Every stdout line MUST parse as JSON (a JSON-RPC frame). A non-JSON
+      // line means a logger/print leaked onto the protocol channel.
+      expect(() => JSON.parse(line) as unknown).not.toThrow()
+    }
+  }, 30_000)
+})
+
+describe.skipIf(!process.env.DEEPSEEK_API_KEY)('acp-agent e2e: real prompt over ACP', () => {
+  it('runs a real turn and the agent writes the requested file (verified on disk)', async () => {
+    workdir = await mkdtemp(join(tmpdir(), 'acp-e2e-'))
+    spawned = spawnAcpAgent(workdir)
+    const { client, updates } = spawned
+
+    await client.initialize({ protocolVersion: PROTOCOL_VERSION, clientCapabilities: {} })
+    // The MVP requires cwd === the server's launch dir (its cwd is `workdir`).
+    const { sessionId } = await client.newSession({ cwd: workdir, mcpServers: [] })
+
+    const res = await client.prompt({
+      sessionId,
+      prompt: [{ type: 'text', text: 'Use the bash tool to write the exact text ACP_OK into a file named proof.txt in the current directory. Then stop.' }],
+    })
+    expect(['end_turn', 'max_tokens']).toContain(res.stopReason)
+
+    // Verify the WORLD, not the agent's self-report: read the file from disk.
+    const proof = await readFile(join(workdir, 'proof.txt'), 'utf8')
+    expect(proof).toContain('ACP_OK')
+
+    // And the client saw tool-call activity stream through.
+    expect(updates.some(u => u.sessionUpdate === 'tool_call')).toBe(true)
+  }, 180_000)
+})