diff --git a/packages/opencode/src/acp/event.ts b/packages/opencode/src/acp/event.ts
index 7d05fa6ee58..dec34b8b662 100644
--- a/packages/opencode/src/acp/event.ts
+++ b/packages/opencode/src/acp/event.ts
@@ -40,7 +40,10 @@ export class Subscription {
   private readonly abort = new AbortController()
   private readonly shellSnapshots = new Map<string, string>()
   private readonly toolStarts = new Set<string>()
+  private readonly connectionWaiters = new Set<() => void>()
+  private readonly idleWaiters = new Map<string, Set<ReturnType<typeof signal>>>()
   private readonly permission: ACPPermission.Handler
+  private connected = false
   private started = false
 
   constructor(
@@ -63,10 +66,35 @@ export class Subscription {
 
   stop() {
     this.abort.abort()
+    this.disconnected()
+    for (const resolve of this.connectionWaiters) resolve()
+    this.connectionWaiters.clear()
+  }
+
+  async runUntilIdle<A>(sessionId: string, request: () => Promise<A>) {
+    await this.waitUntilConnected()
+    const waiter = signal()
+    const waiters = this.idleWaiters.get(sessionId) ?? new Set()
+    waiters.add(waiter)
+    this.idleWaiters.set(sessionId, waiters)
+
+    try {
+      // Idle is queued after the turn's events, and this subscription awaits each update in order.
+      void waiter.promise.catch(() => {})
+      const response = await request()
+      await waiter.promise
+      return response
+    } finally {
+      waiters.delete(waiter)
+      if (waiters.size === 0) this.idleWaiters.delete(sessionId)
+    }
   }
 
   async handle(event: Event) {
     switch (event.type) {
+      case "session.status":
+        if (event.properties.status.type === "idle") this.idle(event.properties.sessionID)
+        return
       case "permission.asked":
         this.permission.handle(event)
         return
@@ -115,19 +143,51 @@ export class Subscription {
 
   private async run() {
     while (!this.abort.signal.aborted) {
-      const events = (await this.input.sdk.global.event({
-        signal: this.abort.signal,
-      })) as GlobalEventStream
-
-      for await (const event of events.stream) {
-        if (this.abort.signal.aborted) return
-        if (!event.payload) continue
-        await this.handle(event.payload).catch(() => {})
-      }
+      await this.consume().catch(() => {})
+      this.disconnected()
       if (!this.abort.signal.aborted) await new Promise((resolve) => setTimeout(resolve, 1000))
     }
   }
 
+  private async consume() {
+    const events = (await this.input.sdk.global.event({
+      signal: this.abort.signal,
+    })) as GlobalEventStream
+    this.connected = true
+    for (const resolve of this.connectionWaiters) resolve()
+    this.connectionWaiters.clear()
+
+    for await (const event of events.stream) {
+      if (this.abort.signal.aborted) return
+      if (!event.payload) continue
+      await this.handle(event.payload).catch(() => {})
+    }
+  }
+
+  private async waitUntilConnected() {
+    while (!this.connected) {
+      if (this.abort.signal.aborted) throw new Error("ACP event subscription stopped")
+      await new Promise<void>((resolve) => this.connectionWaiters.add(resolve))
+    }
+  }
+
+  private disconnected() {
+    if (!this.connected) return
+    this.connected = false
+    const error = new Error("ACP event stream disconnected")
+    for (const waiters of this.idleWaiters.values()) {
+      for (const waiter of waiters) waiter.reject(error)
+    }
+    this.idleWaiters.clear()
+  }
+
+  private idle(sessionId: string) {
+    const waiters = this.idleWaiters.get(sessionId)
+    if (!waiters) return
+    this.idleWaiters.delete(sessionId)
+    for (const waiter of waiters) waiter.resolve()
+  }
+
   private async handlePartUpdated(event: EventMessagePartUpdated) {
     const part = event.properties.part
     const sessionId = part.sessionID || event.properties.sessionID
@@ -339,4 +399,23 @@ export class Subscription {
   }
 }
 
+function signal() {
+  const state: {
+    resolve: () => void
+    reject: (reason?: unknown) => void
+  } = {
+    resolve: () => {},
+    reject: () => {},
+  }
+  const promise = new Promise<void>((resolve, reject) => {
+    state.resolve = resolve
+    state.reject = reject
+  })
+  return {
+    promise,
+    resolve: () => state.resolve(),
+    reject: (reason?: unknown) => state.reject(reason),
+  }
+}
+
 export * as ACPEvent from "./event"
diff --git a/packages/opencode/src/acp/service.ts b/packages/opencode/src/acp/service.ts
index 7257efa7658..fe295918978 100644
--- a/packages/opencode/src/acp/service.ts
+++ b/packages/opencode/src/acp/service.ts
@@ -88,6 +88,8 @@ export function make(input: {
     ? ACPEvent.start({ sdk: input.sdk, connection: input.connection, session })
     : undefined
   if (events) input.eventSubscription?.(events)
+  const runUntilIdle = <A>(sessionId: string, fn: () => Promise<A>) =>
+    events ? events.runUntilIdle(sessionId, fn) : fn()
 
   const initialize = Effect.fn("ACP.initialize")(function* (params: InitializeRequest) {
     const started = performance.now()
@@ -504,19 +506,21 @@ export function make(input: {
       if (!command) {
         const response = yield* request(
           () =>
-            input.sdk.session.prompt(
-              {
-                sessionID: current.id,
-                model: {
-                  providerID: selected.providerID,
-                  modelID: selected.modelID,
+            runUntilIdle(current.id, () =>
+              input.sdk.session.prompt(
+                {
+                  sessionID: current.id,
+                  model: {
+                    providerID: selected.providerID,
+                    modelID: selected.modelID,
+                  },
+                  ...(variant ? { variant } : {}),
+                  parts,
+                  ...(modeId ? { agent: modeId } : {}),
+                  directory: current.cwd,
                 },
-                ...(variant ? { variant } : {}),
-                parts,
-                ...(modeId ? { agent: modeId } : {}),
-                directory: current.cwd,
-              },
-              { throwOnError: true },
+                { throwOnError: true },
+              ),
             ),
           "session",
         )
@@ -528,17 +532,19 @@ export function make(input: {
       if (known) {
         const response = yield* request(
           () =>
-            input.sdk.session.command(
-              {
-                sessionID: current.id,
-                command: known.name,
-                arguments: command.args,
-                model: `${selected.providerID}/${selected.modelID}`,
-                ...(variant ? { variant } : {}),
-                ...(modeId ? { agent: modeId } : {}),
-                directory: current.cwd,
-              },
-              { throwOnError: true },
+            runUntilIdle(current.id, () =>
+              input.sdk.session.command(
+                {
+                  sessionID: current.id,
+                  command: known.name,
+                  arguments: command.args,
+                  model: `${selected.providerID}/${selected.modelID}`,
+                  ...(variant ? { variant } : {}),
+                  ...(modeId ? { agent: modeId } : {}),
+                  directory: current.cwd,
+                },
+                { throwOnError: true },
+              ),
             ),
           "session",
         )
@@ -549,14 +555,16 @@ export function make(input: {
       if (command.name === "compact") {
         yield* request(
           () =>
-            input.sdk.session.summarize(
-              {
-                sessionID: current.id,
-                directory: current.cwd,
-                providerID: selected.providerID,
-                modelID: selected.modelID,
-              },
-              { throwOnError: true },
+            runUntilIdle(current.id, () =>
+              input.sdk.session.summarize(
+                {
+                  sessionID: current.id,
+                  directory: current.cwd,
+                  providerID: selected.providerID,
+                  modelID: selected.modelID,
+                },
+                { throwOnError: true },
+              ),
             ),
           "session",
         )
diff --git a/packages/opencode/test/acp/service-session.test.ts b/packages/opencode/test/acp/service-session.test.ts
index 8dd25492c09..d784709dbb2 100644
--- a/packages/opencode/test/acp/service-session.test.ts
+++ b/packages/opencode/test/acp/service-session.test.ts
@@ -10,7 +10,7 @@ import type {
   SessionConfigSelectOption,
   SetSessionConfigOptionResponse,
 } from "@agentclientprotocol/sdk"
-import type { AssistantMessage, OpencodeClient } from "@opencode-ai/sdk/v2"
+import type { AssistantMessage, Event, OpencodeClient } from "@opencode-ai/sdk/v2"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { ModelV2 } from "@opencode-ai/core/model"
 import { Effect } from "effect"
@@ -24,6 +24,54 @@ const modelID = ModelV2.ID.make("test-model")
 const configuredModelID = ModelV2.ID.make("configured-model")
 const secondModelID = ModelV2.ID.make("second-model")
 
+function createEventStream() {
+  const queue: Event[] = []
+  const waiters: Array<(event: Event | undefined) => void> = []
+  const push = (event: Event) => {
+    const waiter = waiters.shift()
+    if (waiter) return waiter(event)
+    queue.push(event)
+  }
+  const stream = async function* (signal?: AbortSignal) {
+    while (!signal?.aborted) {
+      const event = queue.shift()
+      if (event) {
+        yield { payload: event }
+        continue
+      }
+      const next = await new Promise<Event | undefined>((resolve) => {
+        waiters.push(resolve)
+        signal?.addEventListener("abort", () => resolve(undefined), { once: true })
+      })
+      if (!next) return
+      yield { payload: next }
+    }
+  }
+  return { push, stream }
+}
+
+function idleEvent(sessionID: string): Event {
+  return {
+    id: `evt_idle_${sessionID}`,
+    type: "session.status",
+    properties: {
+      sessionID,
+      status: { type: "idle" },
+    },
+  }
+}
+
+function deferred<A>() {
+  const state: { resolve?: (value: A) => void } = {}
+  const promise = new Promise<A>((resolve) => {
+    state.resolve = resolve
+  })
+  return {
+    promise,
+    resolve: (value: A) => state.resolve?.(value),
+  }
+}
+
 const provider: Provider.Info = {
   id: providerID,
   name: "Test",
@@ -147,6 +195,7 @@ describe("ACP service sessions", () => {
     options?: {
       abort?: (input: { sessionID: string }) => Promise<{ data: boolean }>
       prompt?: (input: unknown) => Promise<{ data: { info: ReturnType<typeof assistantInfo> } }>
+      sessionUpdate?: (update: SessionNotification) => Promise<void>
     },
   ) => {
     const updates: SessionNotification[] = []
@@ -157,6 +206,7 @@ describe("ACP service sessions", () => {
     const commands: unknown[] = []
     const summarizes: unknown[] = []
     const usageUpdates: string[] = []
+    const events = createEventStream()
     const sessions = Array.from({ length: 102 }, (_, index) => ({
       id: `ses_${index + 1}`,
       directory: index % 2 === 0 ? "/workspace" : "/other",
@@ -164,6 +214,9 @@ describe("ACP service sessions", () => {
       time: { created: index + 1, updated: index + 1 },
     }))
     const sdk = {
+      global: {
+        event: (input?: { signal?: AbortSignal }) => Promise.resolve({ stream: events.stream(input?.signal) }),
+      },
       config: {
         providers: () => Promise.resolve({ data: { providers: [provider], default: { test: modelID } } }),
         get: () => Promise.resolve({ data: {} }),
@@ -196,11 +249,9 @@ describe("ACP service sessions", () => {
             data: input.directory ? sessions.filter((session) => session.directory === input.directory) : sessions,
           }),
         messages: () => Promise.resolve({ data: messages }),
-        prompt:
-          options?.prompt ??
-          ((input: unknown) => {
-            prompts.push(input)
-            return Promise.resolve({
+        prompt: async (input: { sessionID: string }) => {
+          const response = await (options?.prompt?.(input) ??
+            Promise.resolve({
               data: {
                 info: assistantInfo({
                   input: 100,
@@ -209,10 +260,14 @@ describe("ACP service sessions", () => {
                   cache: { read: 11, write: 13 },
                 }),
               },
-            })
-          }),
-        command: (input: unknown) => {
+            }))
+          prompts.push(input)
+          events.push(idleEvent(input.sessionID))
+          return response
+        },
+        command: (input: { sessionID: string }) => {
           commands.push(input)
+          events.push(idleEvent(input.sessionID))
           return Promise.resolve({
             data: {
               info: assistantInfo({
@@ -224,8 +279,9 @@ describe("ACP service sessions", () => {
             },
           })
         },
-        summarize: (input: unknown) => {
+        summarize: (input: { sessionID: string }) => {
           summarizes.push(input)
+          events.push(idleEvent(input.sessionID))
           return Promise.resolve({ data: true })
         },
         abort:
@@ -249,7 +305,7 @@ describe("ACP service sessions", () => {
     const connection = {
       sessionUpdate: (update: SessionNotification) => {
         updates.push(update)
-        return Promise.resolve()
+        return options?.sessionUpdate?.(update) ?? Promise.resolve()
       },
     } as Pick<AgentSideConnection, "sessionUpdate">
     const usage = UsageService.Service.of({
@@ -273,6 +329,7 @@ describe("ACP service sessions", () => {
       commands,
       summarizes,
       usageUpdates,
+      events,
     }
   }
 
@@ -1018,6 +1075,75 @@ describe("ACP service sessions", () => {
     expect(usageUpdates).toEqual([session.sessionId])
   })
 
+  it("waits for queued session updates before returning end_turn", async () => {
+    const called = deferred<void>()
+    const response = deferred<{ data: { info: ReturnType<typeof assistantInfo> } }>()
+    const update = deferred<void>()
+    const release = deferred<void>()
+    const order: string[] = []
+    const fixture = makeService([], {
+      prompt: () => {
+        called.resolve(undefined)
+        return response.promise
+      },
+      sessionUpdate: (notification) => {
+        if (notification.update.sessionUpdate !== "agent_thought_chunk") return Promise.resolve()
+        update.resolve(undefined)
+        return release.promise.then(() => {
+          order.push("update")
+        })
+      },
+    })
+    const session = await Effect.runPromise(fixture.service.newSession({ cwd: "/workspace", mcpServers: [] }))
+    const result = Effect.runPromise(
+      fixture.service.prompt({ sessionId: session.sessionId, prompt: [{ type: "text", text: "hello" }] }),
+    ).then((value) => {
+      order.push("response")
+      return value
+    })
+
+    await called.promise
+    fixture.events.push({
+      id: "evt_part",
+      type: "message.part.updated",
+      properties: {
+        sessionID: session.sessionId,
+        time: Date.now(),
+        part: {
+          id: "part_reasoning",
+          sessionID: session.sessionId,
+          messageID: "msg_assistant",
+          type: "reasoning",
+          text: "",
+          time: { start: Date.now() },
+        },
+      },
+    })
+    fixture.events.push({
+      id: "evt_delta",
+      type: "message.part.delta",
+      properties: {
+        sessionID: session.sessionId,
+        messageID: "msg_assistant",
+        partID: "part_reasoning",
+        field: "text",
+        delta: "thinking",
+      },
+    })
+    response.resolve({
+      data: {
+        info: assistantInfo({ input: 1, output: 1, reasoning: 1, cache: { read: 0, write: 0 } }),
+      },
+    })
+
+    await update.promise
+    expect(order).toEqual([])
+
+    release.resolve(undefined)
+    expect((await result).stopReason).toBe("end_turn")
+    expect(order).toEqual(["update", "response"])
+  })
+
   it("maps assistant prompt errors to request errors instead of end turn", async () => {
     const { service } = makeService([], {
       prompt: () =>