diff --git a/packages/agent/src/adapters/claude/claude-agent.wake-up.test.ts b/packages/agent/src/adapters/claude/claude-agent.wake-up.test.ts
new file mode 100644
index 0000000000..dfa6e307a5
--- /dev/null
+++ b/packages/agent/src/adapters/claude/claude-agent.wake-up.test.ts
@@ -0,0 +1,317 @@
+import type { AgentSideConnection } from "@agentclientprotocol/sdk";
+import type {
+  SDKMessage,
+  SDKUserMessage,
+} from "@anthropic-ai/claude-agent-sdk";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { POSTHOG_NOTIFICATIONS } from "../../acp-extensions";
+import { createMockQuery, type MockQuery } from "../../test/mocks/claude-sdk";
+import { Pushable } from "../../utils/streams";
+
+vi.mock("@anthropic-ai/claude-agent-sdk", () => ({
+  query: vi.fn(),
+}));
+
+vi.mock("./mcp/tool-metadata", () => ({
+  fetchMcpToolMetadata: vi.fn().mockResolvedValue(undefined),
+  getConnectedMcpServerNames: vi.fn().mockReturnValue([]),
+  getCachedMcpTools: vi.fn().mockReturnValue([]),
+  clearMcpToolMetadataCache: vi.fn(),
+  setMcpToolApprovalStates: vi.fn(),
+  isMcpToolReadOnly: vi.fn().mockReturnValue(false),
+  getMcpToolMetadata: vi.fn().mockReturnValue(undefined),
+  getMcpToolApprovalState: vi.fn().mockReturnValue(undefined),
+}));
+
+const { ClaudeAcpAgent } = await import("./claude-agent");
+type Agent = InstanceType<typeof ClaudeAcpAgent>;
+
+interface ClientMocks {
+  sessionUpdate: ReturnType<typeof vi.fn>;
+  extNotification: ReturnType<typeof vi.fn>;
+}
+
+function makeAgent(): { agent: Agent; client: ClientMocks } {
+  const client: ClientMocks = {
+    sessionUpdate: vi.fn().mockResolvedValue(undefined),
+    extNotification: vi.fn().mockResolvedValue(undefined),
+  };
+  const agent = new ClaudeAcpAgent(client as unknown as AgentSideConnection);
+  return { agent, client };
+}
+
+function installFakeSession(
+  agent: Agent,
+  sessionId: string,
+): { query: MockQuery; input: Pushable<SDKUserMessage> } {
+  const query = createMockQuery();
+  const input = new Pushable<SDKUserMessage>();
+  const abortController = new AbortController();
+
+  const session = {
+    query,
+    queryOptions: { sessionId, cwd: "/tmp/repo", abortController },
+    buildInProcessMcpServers: () => ({}),
+    localToolsServerNames: [] as string[],
+    input,
+    cancelled: false,
+    interruptReason: undefined,
+    settingsManager: { dispose: vi.fn(), getRepoRoot: () => "/tmp/repo" },
+    permissionMode: "default" as const,
+    abortController,
+    accumulatedUsage: {
+      inputTokens: 0,
+      outputTokens: 0,
+      cachedReadTokens: 0,
+      cachedWriteTokens: 0,
+    },
+    sessionResources: new Set(),
+    configOptions: [],
+    turnQueue: [],
+    activeTurn: null,
+    pendingOrphanResults: 0,
+    queryGeneration: 0,
+    cwd: "/tmp/repo",
+    notificationHistory: [] as unknown[],
+    taskRunId: "run-1",
+    lastContextWindowSize: 200_000,
+    modelId: "claude-sonnet-4-6",
+    taskState: new Map(),
+  };
+
+  (agent as unknown as { session: typeof session }).session = session;
+  (agent as unknown as { sessionId: string }).sessionId = sessionId;
+
+  return { query, input };
+}
+
+function tick(): Promise<void> {
+  return new Promise((resolve) => setImmediate(resolve));
+}
+
+async function send(query: MockQuery, message: unknown): Promise<void> {
+  query._mockHelpers.sendMessage(message as SDKMessage);
+  await tick();
+}
+
+// Replays the prompt's own user message back through the query so the consumer
+// activates its Turn before the terminal result arrives.
+async function echoUserMessage(
+  query: MockQuery,
+  input: Pushable<SDKUserMessage>,
+): Promise<void> {
+  const { value: pushed } = await input[Symbol.asyncIterator]().next();
+  await send(query, pushed);
+}
+
+function messageStart(sessionId: string, apiId: string) {
+  return {
+    type: "stream_event",
+    parent_tool_use_id: null,
+    session_id: sessionId,
+    uuid: `start-${apiId}`,
+    event: { type: "message_start", message: { id: apiId, usage: {} } },
+  };
+}
+
+function textDelta(sessionId: string, text: string) {
+  return {
+    type: "stream_event",
+    parent_tool_use_id: null,
+    session_id: sessionId,
+    uuid: `delta-${text}`,
+    event: {
+      type: "content_block_delta",
+      index: 0,
+      delta: { type: "text_delta", text },
+    },
+  };
+}
+
+function assistantMessage(sessionId: string, apiId: string, text: string) {
+  return {
+    type: "assistant",
+    parent_tool_use_id: null,
+    session_id: sessionId,
+    uuid: `assistant-${apiId}`,
+    message: {
+      id: apiId,
+      role: "assistant",
+      content: [{ type: "text", text }],
+    },
+  };
+}
+
+function resultSuccess(sessionId: string, uuid: string) {
+  return {
+    type: "result",
+    subtype: "success",
+    session_id: sessionId,
+    uuid,
+    result: "",
+    is_error: false,
+    usage: {},
+    modelUsage: {},
+  };
+}
+
+function taskNotificationResult(sessionId: string, uuid: string) {
+  return {
+    ...resultSuccess(sessionId, uuid),
+    origin: { kind: "task-notification" },
+  };
+}
+
+function taskNotification(sessionId: string) {
+  return {
+    type: "system",
+    subtype: "task_notification",
+    session_id: sessionId,
+    uuid: "task-note-1",
+    task_id: "task-1",
+    status: "completed",
+    output_file: "/tmp/task-1.out",
+    summary: "Background command completed",
+  };
+}
+
+function messageChunkTexts(
+  calls: ClientMocks["sessionUpdate"]["mock"]["calls"],
+): string[] {
+  return calls
+    .map(
+      ([call]) =>
+        (
+          call as {
+            update?: { sessionUpdate?: string; content?: { text?: string } };
+          }
+        ).update,
+    )
+    .filter((update) => update?.sessionUpdate === "agent_message_chunk")
+    .map((update) => update?.content?.text ?? "");
+}
+
+async function runTurn(
+  agent: Agent,
+  client: ClientMocks,
+  query: MockQuery,
+  input: Pushable<SDKUserMessage>,
+  sessionId: string,
+  text: string,
+): Promise<void> {
+  const promptPromise = agent.prompt({
+    sessionId,
+    prompt: [{ type: "text", text: "hi" }],
+  });
+  await tick();
+  await echoUserMessage(query, input);
+  await send(query, assistantMessage(sessionId, `msg-${text}`, text));
+  await send(query, resultSuccess(sessionId, `result-${text}`));
+  const result = await promptPromise;
+  expect(result.stopReason).toBe("end_turn");
+  expect(messageChunkTexts(client.sessionUpdate.mock.calls)).toContain(text);
+}
+
+// Regression coverage for #1919: a backgrounded task (Bash run_in_background /
+// Monitor) wakes the agent AFTER its turn settled, and the SDK emits that
+// follow-up turn with no prompt() call in flight. The session-lifetime
+// consumer must forward those messages live, not leave them queued until the
+// next user prompt.
+describe("ClaudeAcpAgent — background wake-ups between turns", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("forwards agent messages produced after the turn settled", async () => {
+    const { agent, client } = makeAgent();
+    const sessionId = "s-wake";
+    const { query, input } = installFakeSession(agent, sessionId);
+
+    await runTurn(agent, client, query, input, sessionId, "waiting for task");
+
+    // The turn is over; the background task completes and wakes the agent.
+    await send(query, taskNotification(sessionId));
+    await send(
+      query,
+      assistantMessage(sessionId, "msg-wake", "the test succeeded"),
+    );
+
+    expect(client.extNotification).toHaveBeenCalledWith(
+      POSTHOG_NOTIFICATIONS.TASK_NOTIFICATION,
+      expect.objectContaining({ sessionId, taskId: "task-1" }),
+    );
+    expect(messageChunkTexts(client.sessionUpdate.mock.calls)).toContain(
+      "the test succeeded",
+    );
+  });
+
+  it("streams wake-up deltas live and drops the assembled duplicate", async () => {
+    const { agent, client } = makeAgent();
+    const sessionId = "s-wake-stream";
+    const { query, input } = installFakeSession(agent, sessionId);
+
+    await runTurn(agent, client, query, input, sessionId, "waiting");
+
+    await send(query, messageStart(sessionId, "msg-wake"));
+    await send(query, textDelta(sessionId, "woke up"));
+    await send(query, assistantMessage(sessionId, "msg-wake", "woke up"));
+
+    const texts = messageChunkTexts(client.sessionUpdate.mock.calls);
+    expect(texts.filter((text) => text === "woke up")).toHaveLength(1);
+  });
+
+  it("keeps a task-notification result from settling the next queued turn", async () => {
+    const { agent, client } = makeAgent();
+    const sessionId = "s-wake-result";
+    const { query, input } = installFakeSession(agent, sessionId);
+
+    await runTurn(agent, client, query, input, sessionId, "waiting");
+
+    // A second prompt is queued but not yet echoed when the wake-up turn's
+    // terminal result arrives. That result is background work: it must not
+    // resolve the queued turn.
+    const promptPromise = agent.prompt({
+      sessionId,
+      prompt: [{ type: "text", text: "follow-up" }],
+    });
+    await tick();
+    await send(
+      query,
+      assistantMessage(sessionId, "msg-wake", "the test succeeded"),
+    );
+    await send(query, taskNotificationResult(sessionId, "wake-result"));
+
+    let settled = false;
+    void promptPromise.then(() => {
+      settled = true;
+    });
+    await tick();
+    expect(settled).toBe(false);
+
+    await echoUserMessage(query, input);
+    await send(query, assistantMessage(sessionId, "msg-2", "done"));
+    await send(query, resultSuccess(sessionId, "result-2"));
+
+    const result = await promptPromise;
+    expect(result.stopReason).toBe("end_turn");
+    const texts = messageChunkTexts(client.sessionUpdate.mock.calls);
+    expect(texts).toContain("the test succeeded");
+    expect(texts).toContain("done");
+  });
+
+  it("runs a normal turn after wake-up output", async () => {
+    const { agent, client } = makeAgent();
+    const sessionId = "s-wake-next";
+    const { query, input } = installFakeSession(agent, sessionId);
+
+    await runTurn(agent, client, query, input, sessionId, "waiting");
+
+    await send(query, assistantMessage(sessionId, "msg-wake", "woke up"));
+    await send(query, taskNotificationResult(sessionId, "wake-result"));
+
+    await runTurn(agent, client, query, input, sessionId, "next answer");
+    expect(messageChunkTexts(client.sessionUpdate.mock.calls)).toContain(
+      "woke up",
+    );
+  });
+});