feat(cli): register acp command

packages/cli/src/commands/commands.ts

@@ -34,6 +34,7 @@ export const Commands = Spec.make(typeof OPENCODE_CLI_NAME === "string" ? OPENCO
     ),
   },
   commands: [
+    Spec.make("acp", { description: "Start an Agent Client Protocol server" }),
     Spec.make("api", {
       description: "Make a request to the running server",
       params: {

packages/cli/src/commands/handlers/acp.ts

@@ -0,0 +1,36 @@
+import { AgentSideConnection, ndJsonStream } from "@agentclientprotocol/sdk"
+import { OpenCode } from "@opencode-ai/client/promise"
+import { Service } from "@opencode-ai/client/effect/service"
+import { Effect } from "effect"
+import { ACP } from "../../acp/agent"
+import { Commands } from "../commands"
+import { Runtime } from "../../framework/runtime"
+import { Standalone } from "../../services/standalone"
+
+export default Runtime.handler(
+  Commands.commands.acp,
+  Effect.fn("cli.acp")(function* () {
+    process.env.OPENCODE_CLIENT = "acp"
+    const endpoint = yield* Standalone.start()
+    const client = OpenCode.make({ baseUrl: endpoint.url, headers: Service.headers(endpoint) })
+    const input = new WritableStream<Uint8Array>({
+      write: (chunk) =>
+        new Promise<void>((resolve, reject) => {
+          process.stdout.write(chunk, (error) => (error ? reject(error) : resolve()))
+        }),
+    })
+    const output = new ReadableStream<Uint8Array>({
+      start(controller) {
+        process.stdin.on("data", (chunk: Buffer) => controller.enqueue(new Uint8Array(chunk)))
+        process.stdin.on("end", () => controller.close())
+        process.stdin.on("error", (error) => controller.error(error))
+      },
+    })
+    const stream = ndJsonStream(input, output)
+    const connection = new AgentSideConnection((connection) => ACP.create(client, connection), stream)
+    process.stdin.resume()
+    yield* Effect.promise(() => connection.closed)
+    // EOF owns this stdio process; exiting also closes the private server's lease pipe.
+    yield* Effect.sync(() => process.exit(0))
+  }),
+)

packages/cli/src/index.ts

@@ -15,6 +15,7 @@ import { Npm } from "@opencode-ai/core/npm"
 
 const Handlers = Runtime.handlers(Commands, {
   $: () => import("./commands/handlers/default"),
+  acp: () => import("./commands/handlers/acp"),
   api: () => import("./commands/handlers/api"),
   auth: {
     connect: () => import("./commands/handlers/auth/connect"),

packages/cli/test/acp/command.test.ts

@@ -0,0 +1,101 @@
+import { afterEach, describe, expect, test } from "bun:test"
+import path from "node:path"
+
+type Message = { readonly id?: number; readonly result?: unknown; readonly error?: unknown }
+const children: Bun.Subprocess[] = []
+
+afterEach(async () => {
+  await Promise.all(
+    children.splice(0).map(async (child) => {
+      child.kill("SIGKILL")
+      await child.exited
+    }),
+  )
+})
+
+describe("acp command", () => {
+  test("is registered", async () => {
+    const result = await cli(["--help"])
+    expect(result.exitCode).toBe(0)
+    expect(result.stdout).toContain("acp        Start an Agent Client Protocol server")
+  })
+
+  test("initializes over ndjson and exits on stdin eof", async () => {
+    const child = spawn()
+    const stderr = new Response(child.stderr).text()
+    child.stdin.write(
+      new TextEncoder().encode(
+        JSON.stringify({
+          jsonrpc: "2.0",
+          id: 1,
+          method: "initialize",
+          params: {
+            protocolVersion: 1,
+            clientCapabilities: {},
+            clientInfo: { name: "test", version: "1.0.0" },
+          },
+        }) + "\n",
+      ),
+    )
+    child.stdin.flush()
+    const response = await readMessage(child.stdout)
+    expect(response.id).toBe(1)
+    expect(response.error).toBeUndefined()
+    expect(response.result).toMatchObject({
+      protocolVersion: 1,
+      agentCapabilities: { loadSession: true },
+      agentInfo: { name: "OpenCode" },
+    })
+
+    child.stdin.end()
+    const exitCode = await child.exited
+    const errorOutput = await stderr
+    if (exitCode !== 0) throw new Error(`ACP exited with ${exitCode}: ${errorOutput}`)
+    children.splice(children.indexOf(child), 1)
+  }, 30_000)
+})
+
+function spawn() {
+  const child = Bun.spawn([process.execPath, "run", "src/index.ts", "acp"], {
+    cwd: path.join(import.meta.dir, "../.."),
+    stdin: "pipe",
+    stdout: "pipe",
+    stderr: "pipe",
+  })
+  children.push(child)
+  return child
+}
+
+async function readMessage(stream: ReadableStream<Uint8Array>) {
+  const reader = stream.getReader()
+  const decoder = new TextDecoder()
+  let output = ""
+  while (true) {
+    const result = await Promise.race([
+      reader.read(),
+      Bun.sleep(20_000).then(() => {
+        throw new Error("timed out waiting for ACP response")
+      }),
+    ])
+    if (result.done) throw new Error(`ACP exited before responding: ${output}`)
+    output += decoder.decode(result.value, { stream: true })
+    const newline = output.indexOf("\n")
+    if (newline === -1) continue
+    reader.releaseLock()
+    return JSON.parse(output.slice(0, newline)) as Message
+  }
+}
+
+async function cli(args: string[]) {
+  const child = Bun.spawn([process.execPath, "run", "src/index.ts", ...args], {
+    cwd: path.join(import.meta.dir, "../.."),
+    stdout: "pipe",
+    stderr: "pipe",
+  })
+  const [stdout, stderr, exitCode] = await Promise.all([
+    new Response(child.stdout).text(),
+    new Response(child.stderr).text(),
+    child.exited,
+  ])
+  return { stdout, stderr, exitCode }
+}