diff --git a/__tests__/api/agent-server-adapter.test.ts b/__tests__/api/agent-server-adapter.test.ts
index 017f589dd9..e0169e25a8 100644
--- a/__tests__/api/agent-server-adapter.test.ts
+++ b/__tests__/api/agent-server-adapter.test.ts
@@ -1,5 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { CANVAS_UI_CLIENT_TOOL_NAME } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_TOOL_NAME } from "#/constants/child-conversation";
 
 import {
   ACP_SERVER_TAG_KEY,
@@ -677,13 +678,12 @@ describe("buildStartConversationRequest", () => {
     });
   });
 
-  describe("canvas_ui client tool injection", () => {
+  describe("client tool injection", () => {
     it("sends canvas_ui as a client-defined JSON tool", () => {
       const payload = buildStartConversationRequest({
         settings: DEFAULT_SETTINGS,
       });
 
-      expect(payload.client_tools).toHaveLength(1);
       expect(payload.client_tools[0]).toMatchObject({
         name: CANVAS_UI_CLIENT_TOOL_NAME,
         parameters: {
@@ -761,6 +761,7 @@ describe("buildStartConversationRequest", () => {
 
       expect(payload.client_tools.map((tool) => tool.name)).toEqual([
         CANVAS_UI_CLIENT_TOOL_NAME,
+        LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
       ]);
     });
 
@@ -773,6 +774,7 @@ describe("buildStartConversationRequest", () => {
       expect(payload.conversation_id).toBe("legacy-conversation-id");
       expect(payload.client_tools.map((tool) => tool.name)).toEqual([
         CANVAS_UI_CLIENT_TOOL_NAME,
+        LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
       ]);
     });
 
diff --git a/__tests__/api/agent-server-conversation-service.test.ts b/__tests__/api/agent-server-conversation-service.test.ts
index f1d958c7a9..78b6457ba3 100644
--- a/__tests__/api/agent-server-conversation-service.test.ts
+++ b/__tests__/api/agent-server-conversation-service.test.ts
@@ -463,6 +463,40 @@ describe("AgentServerConversationService", () => {
       expect(payload.workspace.working_dir).toBe("/Users/jane/projects/foo");
       expect(payload.worktree).toBe(true);
     });
+
+    it("links a local conversation to its parent", async () => {
+      mockGetSettings.mockResolvedValue({
+        agent_settings: { llm: { model: "gpt-4o" } },
+        conversation_settings: {},
+      });
+      mockGetSettingsForConversation.mockResolvedValue({
+        agentSettings: { llm: { model: "gpt-4o" } },
+        conversationSettings: {},
+        secretsEncrypted: true,
+      });
+      mockHttpPost.mockResolvedValue({
+        data: {
+          id: "ignored-server-id",
+          created_at: "2024-01-01",
+          updated_at: "2024-01-01",
+        },
+      });
+
+      await AgentServerConversationService.createConversation(
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        "/Users/jane/projects/foo",
+        "new_worktree",
+        "parent-conversation-id",
+      );
+
+      const [payloadCall] = mockHttpPost.mock.calls;
+      expect(payloadCall[1]).toMatchObject({
+        parent_conversation_id: "parent-conversation-id",
+      });
+    });
   });
 
   describe("downloadConversation local branch", () => {
diff --git a/__tests__/api/cloud-conversation-service.test.ts b/__tests__/api/cloud-conversation-service.test.ts
index 4248b23e0d..44ad6b2ce4 100644
--- a/__tests__/api/cloud-conversation-service.test.ts
+++ b/__tests__/api/cloud-conversation-service.test.ts
@@ -9,6 +9,7 @@ import { setStoredConversationMetadata } from "#/api/conversation-metadata-store
 import {
   batchGetCloudConversations,
   createCloudAppConversation,
+  pickCloudBackendForLaunch,
   searchCloudConversations,
 } from "#/api/cloud/conversation-service.api";
 import { AGENT_CANVAS_CLIENT_HEADERS } from "#/api/client-source";
@@ -64,6 +65,52 @@ describe("cloud conversation-service overlay", () => {
     );
   });
 
+  it("starts a Cloud conversation on a registered backend while a local one is active", async () => {
+    const localBackend: Backend = {
+      id: "local-1",
+      kind: "local",
+      host: "http://localhost:8000",
+      apiKey: "local-key",
+      name: "Local",
+    };
+    setRegisteredBackends([localBackend, cloudBackend]);
+    setActiveSelection({ backendId: localBackend.id, orgId: null });
+    mockCallCloudProxy.mockResolvedValueOnce({ id: "start-task" });
+
+    await createCloudAppConversation(
+      {
+        initial_message: null,
+        selected_repository: null,
+        selected_branch: null,
+        git_provider: null,
+        parent_conversation_id: null,
+      },
+      pickCloudBackendForLaunch()!,
+    );
+
+    expect(mockCallCloudProxy).toHaveBeenCalledWith(
+      expect.objectContaining({
+        backend: cloudBackend,
+        path: "/api/v1/app-conversations",
+        headers: AGENT_CANVAS_CLIENT_HEADERS,
+      }),
+    );
+  });
+
+  it("has no cloud backend to launch on when only local backends are registered", () => {
+    const localBackend: Backend = {
+      id: "local-1",
+      kind: "local",
+      host: "http://localhost:8000",
+      apiKey: "local-key",
+      name: "Local",
+    };
+    setRegisteredBackends([localBackend]);
+    setActiveSelection({ backendId: localBackend.id, orgId: null });
+
+    expect(pickCloudBackendForLaunch()).toBeNull();
+  });
+
   it("overlays locally-stored repo selection onto batchGetCloudConversations results when the server returns nulls", async () => {
     setStoredConversationMetadata("conv-1", {
       selected_repository: "octocat/hello-world",
diff --git a/__tests__/components/conversation-events/chat/event-content-helpers/should-render-event.test.ts b/__tests__/components/conversation-events/chat/event-content-helpers/should-render-event.test.ts
index 7e5b00b7bf..9920ec6f3b 100644
--- a/__tests__/components/conversation-events/chat/event-content-helpers/should-render-event.test.ts
+++ b/__tests__/components/conversation-events/chat/event-content-helpers/should-render-event.test.ts
@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import { shouldRenderEvent } from "#/components/conversation-events/chat/event-content-helpers/should-render-event";
+import { CHILD_CONVERSATION_RESULT_PREFIX } from "#/constants/child-conversation";
 import {
   createPlanningFileEditorActionEvent,
   createOtherActionEvent,
@@ -277,4 +278,14 @@ describe("shouldRenderEvent - /goal loop re-prompts", () => {
     ).toBe(true);
     expect(shouldRenderEvent(makeUserMessage("hello"))).toBe(true);
   });
+
+  it("hides the child-conversation launch result the frontend posts back", () => {
+    expect(
+      shouldRenderEvent(
+        makeUserMessage(
+          `${CHILD_CONVERSATION_RESULT_PREFIX}{"status":"launched","target":"local"}`,
+        ),
+      ),
+    ).toBe(false);
+  });
 });
diff --git a/__tests__/components/conversation-events/get-event-content.test.tsx b/__tests__/components/conversation-events/get-event-content.test.tsx
index 44eefa10ae..44dc346359 100644
--- a/__tests__/components/conversation-events/get-event-content.test.tsx
+++ b/__tests__/components/conversation-events/get-event-content.test.tsx
@@ -4,6 +4,10 @@ import {
   CANVAS_UI_CLIENT_ACTION_KIND,
   CANVAS_UI_CLIENT_TOOL_NAME,
 } from "#/constants/canvas-ui";
+import {
+  LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "#/constants/child-conversation";
 import { getEventContent } from "#/components/conversation-events/chat";
 import {
   ActionEvent,
@@ -392,4 +396,59 @@ describe("getEventContent", () => {
       "UI command 'open_tab' dispatched to the Agent Canvas frontend.",
     );
   });
+
+  // Without the explicit mapping the default branch would surface the SDK's
+  // generated discriminator ("CLIENTACTION_LAUNCH_CHILD_CONVERSATION") to users.
+  it("titles the launch-child-conversation tool call and its acknowledgement", () => {
+    const launchAction: ActionEvent = {
+      id: "action-launch",
+      timestamp: new Date().toISOString(),
+      source: "agent",
+      thought: [],
+      thinking_blocks: [],
+      action: {
+        kind: LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+        target: "local",
+        task: "Add a regression test for the parser",
+      },
+      tool_name: LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+      tool_call_id: "tool-launch",
+      tool_call: {
+        id: "tool-launch",
+        type: "function",
+        function: {
+          name: LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+          arguments: '{"target":"local","task":"Add a regression test"}',
+        },
+      },
+      llm_response_id: "response-launch",
+      security_risk: SecurityRisk.LOW,
+      summary: "",
+    };
+    const launchObservation: ObservationEvent = {
+      id: "obs-launch",
+      timestamp: new Date().toISOString(),
+      source: "environment",
+      tool_name: LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+      tool_call_id: "tool-launch",
+      action_id: "action-launch",
+      observation: {
+        kind: "ClientToolObservation",
+        content: [{ type: "text", text: "Tool call dispatched to client." }],
+        is_error: false,
+      },
+    };
+
+    render(<span>{getEventContent(launchAction).title}</span>);
+    expect(
+      screen.getByText("ACTION_MESSAGE$LAUNCH_CHILD_CONVERSATION"),
+    ).toBeInTheDocument();
+
+    render(
+      <span>{getEventContent(launchObservation, launchAction).title}</span>,
+    );
+    expect(
+      screen.getByText("OBSERVATION_MESSAGE$LAUNCH_CHILD_CONVERSATION"),
+    ).toBeInTheDocument();
+  });
 });
diff --git a/__tests__/services/child-conversation-launch.test.ts b/__tests__/services/child-conversation-launch.test.ts
new file mode 100644
index 0000000000..88d12c225f
--- /dev/null
+++ b/__tests__/services/child-conversation-launch.test.ts
@@ -0,0 +1,573 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import {
+  CHILD_CONVERSATION_RESULT_PREFIX,
+  LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "#/constants/child-conversation";
+import { setStoredConversationMetadata } from "#/api/conversation-metadata-store";
+import { useGoalStore } from "#/stores/goal-store";
+import type { LaunchChildConversationAction } from "#/types/agent-server/core";
+import { isLaunchChildConversationActionEvent } from "#/types/agent-server/type-guards";
+import {
+  handleLaunchChildConversationAction,
+  type LaunchChildConversationResult,
+} from "#/services/child-conversation-launch";
+
+const {
+  mockCreateConversation,
+  mockResolveWorkingDir,
+  mockSendMessage,
+  mockUpdateTitle,
+  mockCreateCloudAppConversation,
+  mockGetCloudStartTask,
+  mockPickCloudBackend,
+  mockGetCachedAgentServerVersion,
+} = vi.hoisted(() => ({
+  mockCreateConversation: vi.fn(),
+  mockResolveWorkingDir: vi.fn(),
+  mockSendMessage: vi.fn(),
+  mockUpdateTitle: vi.fn(),
+  mockCreateCloudAppConversation: vi.fn(),
+  mockGetCloudStartTask: vi.fn(),
+  mockPickCloudBackend: vi.fn(),
+  mockGetCachedAgentServerVersion: vi.fn(),
+}));
+
+vi.mock(
+  "#/api/conversation-service/agent-server-conversation-service.api",
+  () => ({
+    default: {
+      createConversation: mockCreateConversation,
+      resolveConversationWorkingDir: mockResolveWorkingDir,
+      sendMessage: mockSendMessage,
+      updateConversationTitle: mockUpdateTitle,
+    },
+  }),
+);
+
+vi.mock("#/api/cloud/conversation-service.api", () => ({
+  createCloudAppConversation: mockCreateCloudAppConversation,
+  getCloudAppConversationStartTask: mockGetCloudStartTask,
+  pickCloudBackendForLaunch: mockPickCloudBackend,
+}));
+
+vi.mock("#/api/agent-server-compatibility", () => ({
+  getCachedAgentServerVersion: mockGetCachedAgentServerVersion,
+  compareAgentServerVersions: (actual: string, required: string) => {
+    const parse = (v: string) => v.split(".").map(Number);
+    const [a, b] = [parse(actual), parse(required)];
+    for (let i = 0; i < 3; i += 1) {
+      if (a[i] > b[i]) return 1;
+      if (a[i] < b[i]) return -1;
+    }
+    return 0;
+  },
+}));
+
+vi.mock("#/utils/custom-toast-handlers", () => ({
+  displayErrorToast: vi.fn(),
+  displaySuccessToastWithLink: vi.fn(),
+}));
+
+const PARENT_ID = "parent-conversation-id";
+
+function action(
+  overrides: Partial<LaunchChildConversationAction>,
+): LaunchChildConversationAction {
+  return {
+    kind: LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+    target: "local",
+    task: "Add a regression test for the parser",
+    ...overrides,
+  } as LaunchChildConversationAction;
+}
+
+/** Read back the JSON payload the service posted into the parent conversation. */
+function reportedResult(): LaunchChildConversationResult {
+  const [, message] = mockSendMessage.mock.calls.at(-1) as [
+    string,
+    { content: { text: string }[] },
+  ];
+  return JSON.parse(
+    message.content[0].text.slice(CHILD_CONVERSATION_RESULT_PREFIX.length),
+  );
+}
+
+let toolCall = 0;
+const nextToolCallId = () => {
+  toolCall += 1;
+  return `tool-call-${toolCall}`;
+};
+
+/** The repo fields the parent's metadata hands down to its children. */
+const PARENT_REPO_METADATA = {
+  selected_repository: "octocat/hello-world",
+  selected_branch: "main",
+  git_provider: null,
+};
+
+/**
+ * Give the parent a repository/workspace, which is what marks its workspace as
+ * able to host a worktree. Without stored metadata the parent is a scratch
+ * directory and the worktree is skipped.
+ */
+function seedWorktreeCapableParent() {
+  setStoredConversationMetadata(PARENT_ID, {
+    ...PARENT_REPO_METADATA,
+    selected_workspace: "/Users/jane/projects/foo",
+  });
+}
+
+describe("handleLaunchChildConversationAction", () => {
+  beforeEach(() => {
+    window.localStorage.clear();
+    useGoalStore.setState({ statusByConversation: {} });
+    vi.clearAllMocks();
+    mockResolveWorkingDir.mockResolvedValue("/Users/jane/projects/foo");
+    mockCreateConversation.mockResolvedValue({
+      id: "start-task-id",
+      app_conversation_id: "child-id",
+      status: "READY",
+    });
+    mockUpdateTitle.mockResolvedValue(undefined);
+    mockSendMessage.mockResolvedValue(undefined);
+    mockGetCachedAgentServerVersion.mockReturnValue("1.37.1");
+  });
+
+  describe("parameter validation", () => {
+    // `enum` is advertised to the LLM but dropped when the agent-server builds
+    // the action model, so these values arrive intact and must be caught here.
+    it.each([
+      [
+        "an unknown target",
+        { target: "clould" },
+        '`target` must be exactly "local" or "cloud"',
+      ],
+      [
+        "an unknown isolation",
+        { isolation: "worktre" },
+        '`isolation` must be exactly "worktree" or "shared"',
+      ],
+      [
+        "a repository on a local target",
+        { target: "local", repository: "octocat/hello-world" },
+        "A local child always runs in this conversation's workspace",
+      ],
+      [
+        "an isolation on a cloud target",
+        { target: "cloud", isolation: "worktree" },
+        "Cloud children always run in their own isolated sandbox",
+      ],
+      [
+        "a branch without a repository",
+        { target: "cloud", branch: "main" },
+        'Pass `repository` as "owner/repo" alongside `branch`',
+      ],
+      [
+        "an empty task",
+        { task: "   " },
+        "`task` must be a self-contained brief",
+      ],
+    ])(
+      "rejects %s with corrective guidance and launches nothing",
+      async (_label, overrides, guidance) => {
+        await handleLaunchChildConversationAction(
+          action(overrides),
+          PARENT_ID,
+          nextToolCallId(),
+        );
+
+        const result = reportedResult();
+        expect(result.status).toBe("error");
+        expect(result.status === "error" && result.guidance).toContain(
+          guidance,
+        );
+        expect(mockCreateConversation).not.toHaveBeenCalled();
+        expect(mockCreateCloudAppConversation).not.toHaveBeenCalled();
+      },
+    );
+  });
+
+  describe("local target", () => {
+    // The agent server rejects a parent in a different workspace, so the child
+    // has to request the parent's own directory and isolate via the worktree.
+    it("launches into the parent's workspace as a linked, isolated child", async () => {
+      seedWorktreeCapableParent();
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledWith(
+        "Add a regression test for the parser",
+        undefined,
+        undefined,
+        PARENT_REPO_METADATA,
+        "/Users/jane/projects/foo",
+        "new_worktree",
+        PARENT_ID,
+      );
+    });
+
+    it("reports the child's id, url and status back to the agent", async () => {
+      seedWorktreeCapableParent();
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(reportedResult()).toMatchObject({
+        status: "launched",
+        target: "local",
+        conversation_id: "child-id",
+        url: "http://localhost:3000/conversations/child-id",
+        initial_status: "READY",
+        workspace: "/Users/jane/projects/foo",
+        isolation: "worktree",
+        parent_link: true,
+      });
+    });
+
+    // Local start requests carry no title field — only `autotitle` — so an
+    // explicit title has to be applied as a follow-up rename.
+    it("renames the child when a title is given", async () => {
+      await handleLaunchChildConversationAction(
+        action({ title: "Parser tests" }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockUpdateTitle).toHaveBeenCalledWith("child-id", "Parser tests");
+    });
+
+    it("runs a shared-isolation child in the parent's directory itself", async () => {
+      await handleLaunchChildConversationAction(
+        action({ isolation: "shared" }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledWith(
+        expect.anything(),
+        undefined,
+        undefined,
+        null,
+        "/Users/jane/projects/foo",
+        "local_repo",
+        PARENT_ID,
+      );
+    });
+
+    // `parent_conversation_id` landed in agent-server 1.37.1; older servers
+    // drop it silently, so the agent must not be told the link exists.
+    it("reports that an older agent server did not persist the parent link", async () => {
+      mockGetCachedAgentServerVersion.mockReturnValue("1.37.0");
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      const result = reportedResult();
+      expect(result).toMatchObject({ status: "launched", parent_link: false });
+      expect(result.status === "launched" && result.parent_link_note).toContain(
+        "1.37.1",
+      );
+    });
+
+    it("turns a failed launch into corrective guidance", async () => {
+      mockCreateConversation.mockRejectedValue(new Error("boom"));
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(reportedResult()).toMatchObject({
+        status: "error",
+        error: "boom",
+      });
+    });
+
+    // A conversation started without a repository runs in a scratch directory
+    // that is `git init`-ed but never committed to. `git worktree add` cannot
+    // branch from an unborn HEAD, and the agent-server raises that as a 500
+    // that used to take the whole launch down.
+    it("skips the worktree when the parent workspace cannot host one", async () => {
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledTimes(1);
+      expect(mockCreateConversation).toHaveBeenCalledWith(
+        expect.anything(),
+        undefined,
+        undefined,
+        null,
+        "/Users/jane/projects/foo",
+        "local_repo",
+        PARENT_ID,
+      );
+
+      const result = reportedResult();
+      expect(result).toMatchObject({ status: "launched", isolation: "shared" });
+      expect(result.status === "launched" && result.isolation_note).toContain(
+        "no commits",
+      );
+    });
+
+    // The metadata check cannot see the workspace's git state, so a worktree
+    // that fails anyway must not lose the launch.
+    it("falls back to a shared child when the worktree cannot be created", async () => {
+      seedWorktreeCapableParent();
+      mockCreateConversation.mockRejectedValueOnce(
+        new Error("fatal: not a valid object name: 'HEAD'"),
+      );
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledTimes(2);
+      expect(mockCreateConversation).toHaveBeenLastCalledWith(
+        expect.anything(),
+        undefined,
+        undefined,
+        PARENT_REPO_METADATA,
+        "/Users/jane/projects/foo",
+        "local_repo",
+        PARENT_ID,
+      );
+
+      const result = reportedResult();
+      expect(result).toMatchObject({
+        status: "launched",
+        conversation_id: "child-id",
+        isolation: "shared",
+      });
+      // The agent promised the user an isolated child, so it has to learn that
+      // this one shares the parent's directory after all.
+      expect(result.status === "launched" && result.isolation_note).toContain(
+        "not a valid object name",
+      );
+    });
+
+    // Both attempts failing means the worktree was not the problem, so the
+    // agent gets the original error rather than the fallback's.
+    it("reports the original failure when the shared fallback also fails", async () => {
+      seedWorktreeCapableParent();
+      mockCreateConversation
+        .mockRejectedValueOnce(new Error("worktree boom"))
+        .mockRejectedValueOnce(new Error("fallback boom"));
+
+      await handleLaunchChildConversationAction(
+        action({}),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledTimes(2);
+      expect(reportedResult()).toMatchObject({
+        status: "error",
+        error: "worktree boom",
+      });
+    });
+
+    it("does not retry a child that never asked for a worktree", async () => {
+      mockCreateConversation.mockRejectedValue(new Error("boom"));
+
+      await handleLaunchChildConversationAction(
+        action({ isolation: "shared" }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateConversation).toHaveBeenCalledTimes(1);
+      expect(reportedResult()).toMatchObject({
+        status: "error",
+        error: "boom",
+      });
+    });
+  });
+
+  describe("cloud target", () => {
+    const cloudBackend = {
+      id: "cloud-1",
+      kind: "cloud" as const,
+      host: "https://app.all-hands.dev",
+      apiKey: "secret",
+      name: "Cloud",
+    };
+
+    beforeEach(() => {
+      mockPickCloudBackend.mockReturnValue(cloudBackend);
+    });
+
+    it("starts the child on the connected cloud backend without a dangling parent link", async () => {
+      mockCreateCloudAppConversation.mockResolvedValue({
+        id: "start-task-id",
+        app_conversation_id: "cloud-child-id",
+        status: "READY",
+      });
+
+      await handleLaunchChildConversationAction(
+        action({
+          target: "cloud",
+          repository: "octocat/hello-world",
+          branch: "main",
+        }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(mockCreateCloudAppConversation).toHaveBeenCalledWith(
+        expect.objectContaining({
+          selected_repository: "octocat/hello-world",
+          selected_branch: "main",
+          // The parent lives on the local agent server, so Cloud has no
+          // conversation to link the child to — and a dangling id would hide
+          // the child from the Cloud conversation list.
+          parent_conversation_id: null,
+        }),
+        cloudBackend,
+      );
+    });
+
+    // Cloud provisions the sandbox asynchronously and only fills in
+    // `app_conversation_id` at READY, so reporting the first response would
+    // hand the agent a result with no conversation to open.
+    it("waits for the sandbox to expose the conversation id before reporting", async () => {
+      mockCreateCloudAppConversation.mockResolvedValue({
+        id: "start-task-id",
+        app_conversation_id: null,
+        status: "WORKING",
+      });
+      mockGetCloudStartTask.mockResolvedValue({
+        id: "start-task-id",
+        app_conversation_id: "cloud-child-id",
+        status: "READY",
+      });
+
+      await handleLaunchChildConversationAction(
+        action({ target: "cloud" }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      expect(reportedResult()).toMatchObject({
+        status: "launched",
+        target: "cloud",
+        conversation_id: "cloud-child-id",
+        url: "https://app.all-hands.dev/conversations/cloud-child-id",
+        initial_status: "READY",
+        parent_link: false,
+      });
+    });
+
+    it("guides the agent back to local when no cloud backend is connected", async () => {
+      mockPickCloudBackend.mockReturnValueOnce(null);
+
+      await handleLaunchChildConversationAction(
+        action({ target: "cloud" }),
+        PARENT_ID,
+        nextToolCallId(),
+      );
+
+      const result = reportedResult();
+      expect(result.status).toBe("error");
+      expect(result.status === "error" && result.guidance).toContain(
+        'target="local"',
+      );
+      expect(mockCreateCloudAppConversation).not.toHaveBeenCalled();
+    });
+  });
+
+  // A replayed ActionEvent (socket reconnect, or a REST/WebSocket race after a
+  // reload) must not start a second — on Cloud, billable — conversation.
+  it("ignores a replayed tool call", async () => {
+    const toolCallId = nextToolCallId();
+
+    await handleLaunchChildConversationAction(
+      action({}),
+      PARENT_ID,
+      toolCallId,
+    );
+    await handleLaunchChildConversationAction(
+      action({}),
+      PARENT_ID,
+      toolCallId,
+    );
+
+    expect(mockCreateConversation).toHaveBeenCalledTimes(1);
+    expect(mockSendMessage).toHaveBeenCalledTimes(1);
+  });
+
+  // The agent server cancels an active /goal loop on any inbound message, so
+  // the result stays in the toast rather than ending the user's loop.
+  it("does not post the result while a goal loop is running", async () => {
+    useGoalStore.setState({
+      statusByConversation: {
+        [PARENT_ID]: {
+          active: true,
+          status: "running",
+          iteration: 1,
+          max_iterations: 5,
+          objective: "ship it",
+          verdict: null,
+        },
+      },
+    });
+
+    await handleLaunchChildConversationAction(
+      action({}),
+      PARENT_ID,
+      nextToolCallId(),
+    );
+
+    expect(mockCreateConversation).toHaveBeenCalledTimes(1);
+    expect(mockSendMessage).not.toHaveBeenCalled();
+  });
+});
+
+describe("isLaunchChildConversationActionEvent", () => {
+  const makeActionEvent = (toolName: string) =>
+    ({
+      id: "evt-1",
+      timestamp: "2026-07-26T00:00:00Z",
+      source: "agent",
+      action: {
+        kind: LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+        target: "local",
+        task: "do the thing",
+      },
+      tool_name: toolName,
+      tool_call_id: "call-1",
+    }) as never;
+
+  it("returns true for an ActionEvent from the launch tool", () => {
+    expect(
+      isLaunchChildConversationActionEvent(
+        makeActionEvent(LAUNCH_CHILD_CONVERSATION_TOOL_NAME),
+      ),
+    ).toBe(true);
+  });
+
+  it("returns false when tool_name belongs to a different tool", () => {
+    expect(
+      isLaunchChildConversationActionEvent(
+        makeActionEvent("canvas_ui_control"),
+      ),
+    ).toBe(false);
+  });
+});
diff --git a/__tests__/tools/launch-child-conversation-tool.test.ts b/__tests__/tools/launch-child-conversation-tool.test.ts
new file mode 100644
index 0000000000..74fcc0d52d
--- /dev/null
+++ b/__tests__/tools/launch-child-conversation-tool.test.ts
@@ -0,0 +1,51 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+  LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "#/api/launch-child-conversation-client-tool";
+
+describe("launch_child_conversation client tool", () => {
+  it("exports the semantic tool name and generated action kind", () => {
+    expect(LAUNCH_CHILD_CONVERSATION_TOOL_NAME).toBe(
+      "launch_child_conversation",
+    );
+    expect(LAUNCH_CHILD_CONVERSATION_ACTION_KIND).toBe(
+      "ClientAction_launch_child_conversation",
+    );
+    expect(LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL.name).toBe(
+      LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+    );
+  });
+
+  it("pins the validated parameter schema", () => {
+    expect(LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL.parameters).toMatchObject({
+      type: "object",
+      // Misspelled parameter names must fail server-side (the SDK builds a
+      // pydantic model with extra="forbid") instead of launching a child with
+      // silently dropped arguments.
+      additionalProperties: false,
+      properties: {
+        target: { enum: ["local", "cloud"] },
+        isolation: { enum: ["worktree", "shared"] },
+      },
+      required: ["target", "task"],
+    });
+  });
+
+  it("is annotated as a non-idempotent, outward-reaching tool", () => {
+    expect(LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL.annotations).toEqual({
+      readOnlyHint: false,
+      destructiveHint: false,
+      idempotentHint: false,
+      openWorldHint: true,
+    });
+  });
+
+  it("tells the agent the result arrives as a follow-up message", () => {
+    expect(LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL.description).toContain(
+      "[child-conversation]",
+    );
+  });
+});
diff --git a/src/api/agent-server-adapter.test.ts b/src/api/agent-server-adapter.test.ts
index d78a9b62b7..bfa5b3920a 100644
--- a/src/api/agent-server-adapter.test.ts
+++ b/src/api/agent-server-adapter.test.ts
@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 import { CANVAS_UI_CLIENT_TOOL_NAME } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_TOOL_NAME } from "#/constants/child-conversation";
 import { DEFAULT_SETTINGS } from "#/services/settings";
 import type { Settings } from "#/types/settings";
 import { buildStartConversationRequest } from "./agent-server-adapter";
@@ -190,6 +191,7 @@ describe("buildStartConversationRequest — agentProfileId path", () => {
     expect(payload.agent_settings).toBeUndefined();
     expect(payload.client_tools.map((tool) => tool.name)).toEqual([
       CANVAS_UI_CLIENT_TOOL_NAME,
+      LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
     ]);
   });
 
diff --git a/src/api/agent-server-adapter.ts b/src/api/agent-server-adapter.ts
index cdc6b97044..4ea06e28a4 100644
--- a/src/api/agent-server-adapter.ts
+++ b/src/api/agent-server-adapter.ts
@@ -38,6 +38,10 @@ import {
   LEGACY_CANVAS_UI_TOOL_NAME,
   type ClientToolSpec,
 } from "./canvas-ui-client-tool";
+import {
+  LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "./launch-child-conversation-client-tool";
 
 export interface DirectConversationInfo {
   id: string;
@@ -933,6 +937,7 @@ type StartConversationPayload = Record<string, unknown> & {
   worktree: boolean;
   secrets_encrypted?: true;
   conversation_id?: string;
+  parent_conversation_id?: string;
   secrets?: Record<string, LookupSecret>;
   tags?: Record<string, string>;
   client_tools: ClientToolSpec[];
@@ -945,6 +950,11 @@ export interface StartConversationOptions {
   conversationInstructions?: string;
   plugins?: PluginSpec[];
   conversationId?: string;
+  // Links the new conversation to an existing one as its child. The
+  // agent-server requires the parent to exist and to share this
+  // conversation's requested `workspace.working_dir` (software-agent-sdk
+  // #4188, agent-server >= 1.37.1); older servers ignore the field.
+  parentConversationId?: string;
   workingDir?: string;
   worktree?: boolean;
   encryptedAgentSettings?: Record<string, SettingsValue>;
@@ -1020,8 +1030,15 @@ export function buildStartConversationRequest(
       ? { agent_profile_id: options.agentProfileId }
       : { agent_settings: agentSettings }),
     workspace: conversationSettings.workspace,
+    // The agent-server caches each client tool's schema per tool *name* for the
+    // life of the process and rejects a re-registration with a different schema
+    // (`ClientToolSchemaConflictError`). Editing either schema below therefore
+    // requires restarting a long-running dev agent-server before new
+    // conversations can start.
     client_tools:
-      launchAgentKind === "openhands" ? [CANVAS_UI_CLIENT_TOOL] : [],
+      launchAgentKind === "openhands"
+        ? [CANVAS_UI_CLIENT_TOOL, LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL]
+        : [],
     confirmation_policy:
       getConversationConfirmationPolicy(conversationSettings),
     max_iterations:
@@ -1060,6 +1077,10 @@ export function buildStartConversationRequest(
     payload.conversation_id = options.conversationId;
   }
 
+  if (options.parentConversationId) {
+    payload.parent_conversation_id = options.parentConversationId;
+  }
+
   const securityAnalyzer =
     getConversationSecurityAnalyzer(conversationSettings);
   if (securityAnalyzer) {
@@ -1085,6 +1106,7 @@ export function buildStartConversationRequest(
   };
   delete toolModuleQualnames[LEGACY_CANVAS_UI_TOOL_NAME];
   delete toolModuleQualnames[CANVAS_UI_CLIENT_TOOL_NAME];
+  delete toolModuleQualnames[LAUNCH_CHILD_CONVERSATION_TOOL_NAME];
   if (Object.keys(toolModuleQualnames).length > 0) {
     payload.tool_module_qualnames = toolModuleQualnames;
   }
@@ -1150,6 +1172,7 @@ export async function buildStartConversationRequestWithEncryptedSettings(options
   conversationInstructions?: string;
   plugins?: PluginSpec[];
   conversationId?: string;
+  parentConversationId?: string;
   workingDir?: string;
   worktree?: boolean;
   agentProfileId?: string;
diff --git a/src/api/cloud/conversation-service.api.ts b/src/api/cloud/conversation-service.api.ts
index f5e5f29d65..74dfc53e32 100644
--- a/src/api/cloud/conversation-service.api.ts
+++ b/src/api/cloud/conversation-service.api.ts
@@ -1,4 +1,7 @@
-import { getActiveBackend } from "../backend-registry/active-store";
+import {
+  getActiveBackend,
+  getRegisteredBackends,
+} from "../backend-registry/active-store";
 import type { Backend } from "../backend-registry/types";
 import { getStoredConversationMetadata } from "../conversation-metadata-store";
 import type {
@@ -51,6 +54,31 @@ function getActiveCloudBackend(): Backend {
   return active;
 }
 
+/**
+ * Resolve the cloud backend a Cloud conversation should be launched against
+ * when the active backend may not be a cloud one. Cloud conversations cannot
+ * register client tools, so the typed launch action always runs from a local
+ * parent and has to reach a registered-but-inactive cloud backend.
+ *
+ * Prefers the active backend when it is already cloud, then the first
+ * registered cloud backend that carries credentials. Returns `null` when the
+ * user has no cloud backend connected, so callers can give the agent
+ * corrective guidance instead of failing opaquely.
+ *
+ * Note: `createCloudClient` only sends `X-Org-Id` for the *active* backend, so
+ * a conversation launched against an inactive backend lands in the API key's
+ * own organization.
+ */
+export function pickCloudBackendForLaunch(): Backend | null {
+  const active = getActiveBackend().backend;
+  if (active.kind === "cloud") return active;
+  return (
+    getRegisteredBackends().find(
+      (backend) => backend.kind === "cloud" && !!backend.apiKey,
+    ) ?? null
+  );
+}
+
 /**
  * Search the cloud app-conversations list. Mirrors the local
  * `AgentServerConversationService.searchConversations` interface but calls
@@ -120,8 +148,11 @@ export async function batchGetCloudConversations(
  */
 export async function createCloudAppConversation(
   request: AppConversationStartRequest,
+  // Defaults to the active backend. The typed launch action passes an explicit
+  // backend because it always runs from a *local* parent conversation.
+  backendOverride?: Backend,
 ): Promise<AppConversationStartTask> {
-  const backend = getActiveCloudBackend();
+  const backend = backendOverride ?? getActiveCloudBackend();
   const data = await callCloudProxy<AppConversationStartTask>({
     backend,
     method: "POST",
@@ -250,8 +281,9 @@ export async function readCloudConversationFile(
  */
 export async function getCloudAppConversationStartTask(
   taskId: string,
+  backendOverride?: Backend,
 ): Promise<AppConversationStartTask | null> {
-  const backend = getActiveCloudBackend();
+  const backend = backendOverride ?? getActiveCloudBackend();
   const params = new URLSearchParams();
   params.set("ids", taskId);
   const data = await callCloudProxy<(AppConversationStartTask | null)[]>({
diff --git a/src/api/conversation-service/agent-server-conversation-service.api.ts b/src/api/conversation-service/agent-server-conversation-service.api.ts
index 9c86b87081..999da8f1a0 100644
--- a/src/api/conversation-service/agent-server-conversation-service.api.ts
+++ b/src/api/conversation-service/agent-server-conversation-service.api.ts
@@ -439,6 +439,11 @@ class AgentServerConversationService {
       conversationInstructions,
       plugins,
       conversationId,
+      // The agent-server rejects a parent in a different workspace, so callers
+      // launching a child must pass the parent's own `working_dir` as
+      // `workingDirOverride` (see `resolveConversationWorkingDir`). Servers
+      // older than 1.37.1 ignore the field and create an unlinked conversation.
+      parentConversationId,
       workingDir,
       worktree: resolvedWorkspaceMode === "new_worktree",
       agentProfileId,
diff --git a/src/api/launch-child-conversation-client-tool.ts b/src/api/launch-child-conversation-client-tool.ts
new file mode 100644
index 0000000000..17ca180111
--- /dev/null
+++ b/src/api/launch-child-conversation-client-tool.ts
@@ -0,0 +1,112 @@
+import {
+  CHILD_CONVERSATION_ISOLATIONS,
+  CHILD_CONVERSATION_RESULT_PREFIX,
+  CHILD_CONVERSATION_TARGETS,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "#/constants/child-conversation";
+import type { ClientToolSpec } from "./canvas-ui-client-tool";
+
+export {
+  LAUNCH_CHILD_CONVERSATION_ACTION_KIND,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+} from "#/constants/child-conversation";
+
+const LAUNCH_CHILD_CONVERSATION_DESCRIPTION = `Start a NEW, independent conversation to work on a well-scoped task in parallel with this one, without the user having to run any CLI command. The new conversation is recorded as a child of this one.
+
+The child runs on its own. It does not block you, you do not see its output,
+and it cannot see this conversation's history — everything it needs must be in
+the task brief.
+
+Choosing target:
+
+* target="local" — runs on the same machine, in this conversation's workspace.
+  Fast, no repository clone, no sandbox provisioning. Use this by default when
+  the work is on code that is already checked out here.
+
+* target="cloud" — runs on OpenHands Cloud in its own isolated sandbox, from a
+  git repository. Use this when the work should not touch the user's machine or
+  when it needs a repository that is not checked out locally. Requires the user
+  to have an OpenHands Cloud backend connected in Agent Canvas; if none is
+  connected you will be told so and should fall back to target="local".
+
+Writing the task brief:
+
+* Put everything the child needs in "task": the goal, the relevant file paths,
+  the constraints, the expected deliverable, and how it should report back.
+* Keep each child's scope independent of its siblings so parallel children do
+  not fight over the same files.
+* One call per delegated task. Do NOT call this tool twice for the same task.
+
+Parameter rules (a call that breaks one of these launches nothing and comes
+back with corrective guidance):
+
+* "repository" and "branch" apply to target="cloud" only. A local child always
+  inherits this conversation's workspace, so do not pass them with
+  target="local".
+* "isolation" applies to target="local" only. Cloud sandboxes are always
+  isolated, so do not pass it with target="cloud".
+* isolation="worktree" (the default) gives the child its own git worktree and
+  branch, cut from the repository's default branch — it will NOT see this
+  conversation's uncommitted or committed work. isolation="shared" puts the
+  child in this conversation's exact directory; only choose it when the child
+  genuinely must see work in progress, and expect the two agents to conflict.
+
+What comes back: this tool is acknowledged immediately, before the conversation
+exists. The real outcome arrives moments later as a follow-up message starting
+with "${CHILD_CONVERSATION_RESULT_PREFIX.trim()}" that carries the child's
+conversation id, URL, target and initial status — or an error with guidance.
+Wait for it, then tell the user what you launched and give them the URL. If it
+reports an error, fix the parameters and call this tool again.`;
+
+export const LAUNCH_CHILD_CONVERSATION_CLIENT_TOOL: ClientToolSpec = {
+  name: LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+  description: LAUNCH_CHILD_CONVERSATION_DESCRIPTION,
+  parameters: {
+    type: "object",
+    additionalProperties: false,
+    properties: {
+      target: {
+        type: "string",
+        enum: [...CHILD_CONVERSATION_TARGETS],
+        description:
+          "Where the child runs. 'local' reuses this machine and this conversation's workspace; 'cloud' runs in an isolated OpenHands Cloud sandbox.",
+      },
+      task: {
+        type: "string",
+        description:
+          "Self-contained task brief, sent as the child's first message. The child cannot see this conversation, so state the goal, constraints, expected output and handoff criteria.",
+      },
+      title: {
+        type: "string",
+        description:
+          "Optional short title for the child conversation. Omit to let it title itself from the task.",
+      },
+      repository: {
+        type: "string",
+        description:
+          "target='cloud' only. Repository to clone into the sandbox, as 'owner/repo'. Defaults to this conversation's repository when it has one.",
+      },
+      branch: {
+        type: "string",
+        description:
+          "target='cloud' only, and only together with 'repository'. Defaults to the repository's default branch.",
+      },
+      isolation: {
+        type: "string",
+        enum: [...CHILD_CONVERSATION_ISOLATIONS],
+        description:
+          "target='local' only. 'worktree' (default) gives the child its own git worktree and branch; 'shared' runs it in this conversation's exact directory.",
+      },
+    },
+    required: ["target", "task"],
+  },
+  annotations: {
+    // Launching a conversation writes real state and is not repeatable, so the
+    // agent is asked to predict a security risk before every call.
+    readOnlyHint: false,
+    destructiveHint: false,
+    idempotentHint: false,
+    // The cloud target reaches OpenHands Cloud.
+    openWorldHint: true,
+  },
+};
diff --git a/src/components/conversation-events/chat/event-content-helpers/get-action-event-title.ts b/src/components/conversation-events/chat/event-content-helpers/get-action-event-title.ts
index 9e49321606..95d68e0e57 100644
--- a/src/components/conversation-events/chat/event-content-helpers/get-action-event-title.ts
+++ b/src/components/conversation-events/chat/event-content-helpers/get-action-event-title.ts
@@ -1,4 +1,5 @@
 import { CANVAS_UI_CLIENT_ACTION_KIND } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_ACTION_KIND } from "#/constants/child-conversation";
 import type { ActionEvent } from "#/types/agent-server/core";
 
 export type EventTitleDescriptor =
@@ -131,6 +132,12 @@ export const getActionEventTitleDescriptor = (
     case "CanvasUIAction":
     case CANVAS_UI_CLIENT_ACTION_KIND:
       return { kind: "text", text: "CANVASUI" };
+    case LAUNCH_CHILD_CONVERSATION_ACTION_KIND:
+      return {
+        kind: "translation",
+        key: "ACTION_MESSAGE$LAUNCH_CHILD_CONVERSATION",
+        values: {},
+      };
     default:
       return {
         kind: "text",
diff --git a/src/components/conversation-events/chat/event-content-helpers/get-event-content.tsx b/src/components/conversation-events/chat/event-content-helpers/get-event-content.tsx
index e8dd3d840d..e05afb92ee 100644
--- a/src/components/conversation-events/chat/event-content-helpers/get-event-content.tsx
+++ b/src/components/conversation-events/chat/event-content-helpers/get-event-content.tsx
@@ -1,6 +1,7 @@
 import { Trans } from "react-i18next";
 import React from "react";
 import { CANVAS_UI_CLIENT_TOOL_NAME } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_TOOL_NAME } from "#/constants/child-conversation";
 import {
   OpenHandsEvent,
   ObservationEvent,
@@ -222,6 +223,10 @@ const getObservationEventTitle = (
         observationKey = "OBSERVATION_MESSAGE$CANVAS_UI";
         break;
       }
+      if (event.tool_name === LAUNCH_CHILD_CONVERSATION_TOOL_NAME) {
+        observationKey = "OBSERVATION_MESSAGE$LAUNCH_CHILD_CONVERSATION";
+        break;
+      }
       return observationType.replace("Observation", "").toUpperCase();
     case "SwitchLLMObservation":
       observationKey = event.observation.is_error
diff --git a/src/components/conversation-events/chat/event-content-helpers/should-render-event.ts b/src/components/conversation-events/chat/event-content-helpers/should-render-event.ts
index f3001db297..5e8005b361 100644
--- a/src/components/conversation-events/chat/event-content-helpers/should-render-event.ts
+++ b/src/components/conversation-events/chat/event-content-helpers/should-render-event.ts
@@ -1,3 +1,4 @@
+import { CHILD_CONVERSATION_RESULT_PREFIX } from "#/constants/child-conversation";
 import { MessageEvent, OpenHandsEvent } from "#/types/agent-server/core";
 import {
   isActionEvent,
@@ -24,18 +25,31 @@ const GOAL_REPROMPT_PREFIXES = [
   "Resuming a goal that was paused or interrupted.",
 ];
 
-const isGoalLoopReprompt = (event: MessageEvent): boolean => {
-  if (event.llm_message?.role !== "user") return false;
+const userMessageText = (event: MessageEvent): string | null => {
+  if (event.llm_message?.role !== "user") return null;
   const content = event.llm_message.content;
-  const text = Array.isArray(content)
+  return Array.isArray(content)
     ? content
         .filter((c) => c.type === "text")
         .map((c) => c.text)
         .join("\n")
     : "";
+};
+
+const isGoalLoopReprompt = (event: MessageEvent): boolean => {
+  const text = userMessageText(event);
+  if (text === null) return false;
   return GOAL_REPROMPT_PREFIXES.some((prefix) => text.startsWith(prefix));
 };
 
+// The frontend posts the outcome of a `launch_child_conversation` call back as
+// a `user` message because client tools have no result channel (see
+// `services/child-conversation-launch.ts`). It is a JSON payload addressed to
+// the agent, which reports the child's id and link in its own reply, so the
+// raw message does not belong in the chat.
+const isChildConversationResult = (event: MessageEvent): boolean =>
+  userMessageText(event)?.startsWith(CHILD_CONVERSATION_RESULT_PREFIX) ?? false;
+
 export const shouldRenderEvent = (event: OpenHandsEvent) => {
   if (isConversationStateUpdateEvent(event)) {
     // A finished `/goal` loop renders inline so it settles into the
@@ -90,9 +104,11 @@ export const shouldRenderEvent = (event: OpenHandsEvent) => {
 
   // Render message events (user and assistant messages), except the goal loop's
   // injected re-prompts — the judge feedback they carry is shown in the goal
-  // banner, so otherwise they leak into the chat as fake user turns.
+  // banner, so otherwise they leak into the chat as fake user turns — and the
+  // child-conversation launch results, which are machine payloads the agent
+  // relays in its own reply.
   if (isMessageEvent(event)) {
-    return !isGoalLoopReprompt(event);
+    return !isGoalLoopReprompt(event) && !isChildConversationResult(event);
   }
 
   // Render agent error events
diff --git a/src/constants/child-conversation.ts b/src/constants/child-conversation.ts
new file mode 100644
index 0000000000..2cbb4eb062
--- /dev/null
+++ b/src/constants/child-conversation.ts
@@ -0,0 +1,37 @@
+export const LAUNCH_CHILD_CONVERSATION_TOOL_NAME = "launch_child_conversation";
+
+/**
+ * Action discriminator generated by the SDK for the client-defined launch tool
+ * (`ClientAction_<tool-name>`). Keep the SDK naming convention contained here
+ * instead of repeating its generated class name throughout the frontend.
+ */
+export const LAUNCH_CHILD_CONVERSATION_ACTION_KIND =
+  `ClientAction_${LAUNCH_CHILD_CONVERSATION_TOOL_NAME}` as const;
+
+/**
+ * Prefix of the machine-generated message the frontend posts back into the
+ * parent conversation after a launch. Client tools are acknowledged by the
+ * agent-server before the browser has done any work, so this message is the
+ * only way to hand the agent the child's id, URL and status — or corrective
+ * guidance when the call was malformed. The chat hides it (see
+ * `should-render-event.ts`) because the agent relays the same information in
+ * its own reply.
+ */
+export const CHILD_CONVERSATION_RESULT_PREFIX = "[child-conversation] ";
+
+export const CHILD_CONVERSATION_TARGETS = ["local", "cloud"] as const;
+export type ChildConversationTarget =
+  (typeof CHILD_CONVERSATION_TARGETS)[number];
+
+export const CHILD_CONVERSATION_ISOLATIONS = ["worktree", "shared"] as const;
+export type ChildConversationIsolation =
+  (typeof CHILD_CONVERSATION_ISOLATIONS)[number];
+
+/**
+ * `parent_conversation_id` on the local start-conversation request landed in
+ * software-agent-sdk#4188. Older agent-servers accept the request and drop the
+ * field (the pydantic model ignores extras), so the launch still succeeds — we
+ * just tell the agent the relationship was not persisted instead of letting it
+ * believe in a link that does not exist.
+ */
+export const MIN_AGENT_SERVER_VERSION_FOR_PARENT_LINK = "1.37.1";
diff --git a/src/contexts/conversation-websocket-context.tsx b/src/contexts/conversation-websocket-context.tsx
index f21aa89ccd..d1e984dd30 100644
--- a/src/contexts/conversation-websocket-context.tsx
+++ b/src/contexts/conversation-websocket-context.tsx
@@ -38,8 +38,10 @@ import {
   isBrowserNavigateActionEvent,
   isSwitchLLMObservationEvent,
   isCanvasUIActionEvent,
+  isLaunchChildConversationActionEvent,
 } from "#/types/agent-server/type-guards";
 import { handleCanvasUIAction } from "#/services/canvas-ui";
+import { handleLaunchChildConversationAction } from "#/services/child-conversation-launch";
 import { ConversationStateUpdateEventStats } from "#/types/agent-server/core/events/conversation-state-event";
 import type {
   ConversationErrorEvent,
@@ -644,6 +646,17 @@ export function ConversationWebSocketProvider({
           if (isCanvasUIActionEvent(event)) {
             handleCanvasUIAction(event.action, conversationId ?? null);
           }
+
+          // Same client-tool pattern, but the work is a network call: launch
+          // the requested child conversation and post the outcome back so the
+          // agent learns the id the server-side acknowledgement can't carry.
+          if (conversationId && isLaunchChildConversationActionEvent(event)) {
+            void handleLaunchChildConversationAction(
+              event.action,
+              conversationId,
+              event.tool_call_id,
+            );
+          }
         }
       } catch (error) {
         console.warn("Failed to parse WebSocket message as JSON:", error);
diff --git a/src/i18n/translation.json b/src/i18n/translation.json
index 6c7eb8f938..78b7004d0f 100644
--- a/src/i18n/translation.json
+++ b/src/i18n/translation.json
@@ -37364,5 +37364,107 @@
     "de": "Nach Updates suchen",
     "uk": "Перевірити наявність оновлень",
     "ca": "Comprova si hi ha actualitzacions"
+  },
+  "CHILD_CONVERSATION$LAUNCHED_LOCAL": {
+    "en": "Launched a local child conversation",
+    "ja": "ローカルの子会話を開始しました",
+    "zh-CN": "已启动本地子会话",
+    "zh-TW": "已啟動本機子對話",
+    "ko-KR": "로컬 하위 대화를 시작했습니다",
+    "no": "Startet en lokal undersamtale",
+    "ar": "تم إطلاق محادثة فرعية محلية",
+    "de": "Lokale untergeordnete Unterhaltung gestartet",
+    "fr": "Conversation enfant locale lancée",
+    "it": "Conversazione figlia locale avviata",
+    "pt": "Conversa filha local iniciada",
+    "es": "Se inició una conversación hija local",
+    "tr": "Yerel alt sohbet başlatıldı",
+    "uk": "Запущено локальну дочірню розмову",
+    "ca": "S'ha iniciat una conversa filla local"
+  },
+  "CHILD_CONVERSATION$LAUNCHED_CLOUD": {
+    "en": "Launched a Cloud child conversation",
+    "ja": "クラウドの子会話を開始しました",
+    "zh-CN": "已启动云端子会话",
+    "zh-TW": "已啟動雲端子對話",
+    "ko-KR": "클라우드 하위 대화를 시작했습니다",
+    "no": "Startet en Cloud-undersamtale",
+    "ar": "تم إطلاق محادثة فرعية على السحابة",
+    "de": "Untergeordnete Cloud-Unterhaltung gestartet",
+    "fr": "Conversation enfant Cloud lancée",
+    "it": "Conversazione figlia Cloud avviata",
+    "pt": "Conversa filha na Cloud iniciada",
+    "es": "Se inició una conversación hija en la nube",
+    "tr": "Cloud alt sohbeti başlatıldı",
+    "uk": "Запущено хмарну дочірню розмову",
+    "ca": "S'ha iniciat una conversa filla al núvol"
+  },
+  "CHILD_CONVERSATION$OPEN": {
+    "en": "Open",
+    "ja": "開く",
+    "zh-CN": "打开",
+    "zh-TW": "開啟",
+    "ko-KR": "열기",
+    "no": "Åpne",
+    "ar": "فتح",
+    "de": "Öffnen",
+    "fr": "Ouvrir",
+    "it": "Apri",
+    "pt": "Abrir",
+    "es": "Abrir",
+    "tr": "Aç",
+    "uk": "Відкрити",
+    "ca": "Obre"
+  },
+  "CHILD_CONVERSATION$LAUNCH_FAILED": {
+    "en": "Could not launch the child conversation: {{error}}",
+    "ja": "子会話を開始できませんでした: {{error}}",
+    "zh-CN": "无法启动子会话：{{error}}",
+    "zh-TW": "無法啟動子對話：{{error}}",
+    "ko-KR": "하위 대화를 시작할 수 없습니다: {{error}}",
+    "no": "Kunne ikke starte undersamtalen: {{error}}",
+    "ar": "تعذّر إطلاق المحادثة الفرعية: {{error}}",
+    "de": "Untergeordnete Unterhaltung konnte nicht gestartet werden: {{error}}",
+    "fr": "Impossible de lancer la conversation enfant : {{error}}",
+    "it": "Impossibile avviare la conversazione figlia: {{error}}",
+    "pt": "Não foi possível iniciar a conversa filha: {{error}}",
+    "es": "No se pudo iniciar la conversación hija: {{error}}",
+    "tr": "Alt sohbet başlatılamadı: {{error}}",
+    "uk": "Не вдалося запустити дочірню розмову: {{error}}",
+    "ca": "No s'ha pogut iniciar la conversa filla: {{error}}"
+  },
+  "ACTION_MESSAGE$LAUNCH_CHILD_CONVERSATION": {
+    "en": "Launching a child conversation",
+    "ja": "子会話を開始しています",
+    "zh-CN": "正在启动子会话",
+    "zh-TW": "正在啟動子對話",
+    "ko-KR": "하위 대화를 시작하는 중",
+    "no": "Starter en undersamtale",
+    "ar": "جارٍ إطلاق محادثة فرعية",
+    "de": "Untergeordnete Unterhaltung wird gestartet",
+    "fr": "Lancement d'une conversation enfant",
+    "it": "Avvio di una conversazione figlia",
+    "pt": "Iniciando uma conversa filha",
+    "es": "Iniciando una conversación hija",
+    "tr": "Alt sohbet başlatılıyor",
+    "uk": "Запуск дочірньої розмови",
+    "ca": "S'està iniciant una conversa filla"
+  },
+  "OBSERVATION_MESSAGE$LAUNCH_CHILD_CONVERSATION": {
+    "en": "Requested a child conversation",
+    "ja": "子会話をリクエストしました",
+    "zh-CN": "已请求子会话",
+    "zh-TW": "已請求子對話",
+    "ko-KR": "하위 대화를 요청했습니다",
+    "no": "Ba om en undersamtale",
+    "ar": "تم طلب محادثة فرعية",
+    "de": "Untergeordnete Unterhaltung angefordert",
+    "fr": "Conversation enfant demandée",
+    "it": "Conversazione figlia richiesta",
+    "pt": "Conversa filha solicitada",
+    "es": "Se solicitó una conversación hija",
+    "tr": "Alt sohbet istendi",
+    "uk": "Запитано дочірню розмову",
+    "ca": "S'ha sol·licitat una conversa filla"
   }
 }
diff --git a/src/services/child-conversation-launch.ts b/src/services/child-conversation-launch.ts
new file mode 100644
index 0000000000..c4d0a06824
--- /dev/null
+++ b/src/services/child-conversation-launch.ts
@@ -0,0 +1,538 @@
+import i18n from "#/i18n";
+import { I18nKey } from "#/i18n/declaration";
+import {
+  compareAgentServerVersions,
+  getCachedAgentServerVersion,
+} from "#/api/agent-server-compatibility";
+import {
+  createCloudAppConversation,
+  getCloudAppConversationStartTask,
+  pickCloudBackendForLaunch,
+} from "#/api/cloud/conversation-service.api";
+import type { Backend } from "#/api/backend-registry/types";
+import {
+  getStoredConversationMetadata,
+  type ConversationMetadata,
+} from "#/api/conversation-metadata-store";
+import AgentServerConversationService from "#/api/conversation-service/agent-server-conversation-service.api";
+import type { AppConversationStartTask } from "#/api/conversation-service/agent-server-conversation-service.types";
+import {
+  CHILD_CONVERSATION_ISOLATIONS,
+  CHILD_CONVERSATION_RESULT_PREFIX,
+  CHILD_CONVERSATION_TARGETS,
+  LAUNCH_CHILD_CONVERSATION_TOOL_NAME,
+  MIN_AGENT_SERVER_VERSION_FOR_PARENT_LINK,
+  type ChildConversationIsolation,
+  type ChildConversationTarget,
+} from "#/constants/child-conversation";
+import { useGoalStore } from "#/stores/goal-store";
+import type { LaunchChildConversationAction } from "#/types/agent-server/core";
+import { buildAgentCanvasPath } from "#/utils/base-path";
+import {
+  displayErrorToast,
+  displaySuccessToastWithLink,
+} from "#/utils/custom-toast-handlers";
+
+/** Cadence and ceiling for waiting on a Cloud sandbox to expose its id. */
+const CLOUD_START_POLL_INTERVAL_MS = 3_000;
+const CLOUD_START_POLL_TIMEOUT_MS = 180_000;
+
+const LEDGER_STORAGE_KEY_PREFIX = "openhands-child-conversation-launches:";
+
+interface LaunchSuccess {
+  status: "launched";
+  target: ChildConversationTarget;
+  conversation_id: string | null;
+  url: string | null;
+  initial_status: string;
+  title: string | null;
+  /** Local only: the directory the child inherited from this conversation. */
+  workspace?: string;
+  /** Local only: which isolation mode was actually applied. */
+  isolation?: ChildConversationIsolation;
+  /**
+   * Present when the applied isolation is not the one that was asked for,
+   * explaining why and what it means for the child.
+   */
+  isolation_note?: string;
+  /** Cloud only: poll this if `conversation_id` is still null. */
+  start_task_id?: string;
+  /** Cloud only: which connected Cloud backend the child was launched on. */
+  backend?: string;
+  /** Whether the parent/child link was persisted server-side. */
+  parent_link: boolean;
+  /** Present when `parent_link` is false, explaining why. */
+  parent_link_note?: string;
+}
+
+interface LaunchFailure {
+  status: "error";
+  error: string;
+  guidance: string;
+}
+
+export type LaunchChildConversationResult = LaunchSuccess | LaunchFailure;
+
+interface ValidatedParams {
+  target: ChildConversationTarget;
+  task: string;
+  title: string | null;
+  repository: string | null;
+  branch: string | null;
+  isolation: ChildConversationIsolation;
+}
+
+const failure = (error: string, guidance: string): LaunchFailure => ({
+  status: "error",
+  error,
+  guidance,
+});
+
+const quoted = (values: readonly string[]) =>
+  values.map((value) => `"${value}"`).join(" or ");
+
+const blankToNull = (value: string | null | undefined) => {
+  const trimmed = value?.trim();
+  return trimmed ? trimmed : null;
+};
+
+/**
+ * Validate what the agent-server cannot.
+ *
+ * The tool's JSON Schema is turned into a pydantic model with `extra="forbid"`,
+ * so unknown/misspelled parameter names, missing required parameters and wrong
+ * types already fail server-side with a corrective message. `enum` is the gap:
+ * the SDK advertises it to the LLM but drops it when building the model, so a
+ * misspelled `target` reaches us intact and must be rejected here. The
+ * cross-target rules (cloud-only / local-only parameters) are ours to enforce
+ * too, since a schema cannot express them.
+ */
+function validateLaunchParams(
+  action: LaunchChildConversationAction,
+):
+  | { ok: true; params: ValidatedParams }
+  | { ok: false; failure: LaunchFailure } {
+  const target = action.target as ChildConversationTarget;
+  if (!CHILD_CONVERSATION_TARGETS.includes(target)) {
+    return {
+      ok: false,
+      failure: failure(
+        `Unknown target ${JSON.stringify(action.target)}.`,
+        `\`target\` must be exactly ${quoted(CHILD_CONVERSATION_TARGETS)}. Nothing was launched — call ${LAUNCH_CHILD_CONVERSATION_TOOL_NAME} again with a valid target.`,
+      ),
+    };
+  }
+
+  const task = blankToNull(action.task);
+  if (!task) {
+    return {
+      ok: false,
+      failure: failure(
+        "`task` is empty.",
+        "`task` must be a self-contained brief: the child conversation cannot see this one, so state the goal, constraints and expected output.",
+      ),
+    };
+  }
+
+  const repository = blankToNull(action.repository);
+  const branch = blankToNull(action.branch);
+  const isolation = blankToNull(
+    action.isolation,
+  ) as ChildConversationIsolation | null;
+
+  if (target === "local" && (repository || branch)) {
+    return {
+      ok: false,
+      failure: failure(
+        '`repository`/`branch` were passed with target="local".',
+        'A local child always runs in this conversation\'s workspace. Drop `repository` and `branch`, or use target="cloud" to run against a repository in a Cloud sandbox.',
+      ),
+    };
+  }
+
+  if (target === "cloud" && isolation) {
+    return {
+      ok: false,
+      failure: failure(
+        '`isolation` was passed with target="cloud".',
+        'Cloud children always run in their own isolated sandbox. Drop `isolation`, or use target="local" to choose between "worktree" and "shared".',
+      ),
+    };
+  }
+
+  if (branch && !repository) {
+    return {
+      ok: false,
+      failure: failure(
+        "`branch` was passed without `repository`.",
+        'Pass `repository` as "owner/repo" alongside `branch`, or drop `branch` to use the repository\'s default branch.',
+      ),
+    };
+  }
+
+  if (isolation && !CHILD_CONVERSATION_ISOLATIONS.includes(isolation)) {
+    return {
+      ok: false,
+      failure: failure(
+        `Unknown isolation ${JSON.stringify(action.isolation)}.`,
+        `\`isolation\` must be exactly ${quoted(CHILD_CONVERSATION_ISOLATIONS)}. Nothing was launched — call ${LAUNCH_CHILD_CONVERSATION_TOOL_NAME} again with a valid isolation.`,
+      ),
+    };
+  }
+
+  return {
+    ok: true,
+    params: {
+      target,
+      task,
+      title: blankToNull(action.title),
+      repository,
+      branch,
+      isolation: isolation ?? "worktree",
+    },
+  };
+}
+
+/**
+ * Remember which tool calls have already been acted on.
+ *
+ * Unlike the Canvas UI tool, a launch is not idempotent: replaying its
+ * ActionEvent (a socket reconnect that falls back to `resend_mode: "all"`, or a
+ * REST/WebSocket race after a reload) would start a second — on Cloud, billable
+ * — conversation. Claim the tool call before any network work so a replay that
+ * arrives mid-flight is dropped too.
+ */
+function claimToolCall(parentConversationId: string, toolCallId: string) {
+  const key = `${LEDGER_STORAGE_KEY_PREFIX}${parentConversationId}`;
+  let handled: string[] = [];
+  try {
+    const raw = window.localStorage.getItem(key);
+    const parsed: unknown = raw ? JSON.parse(raw) : null;
+    if (Array.isArray(parsed)) {
+      handled = parsed.filter((id): id is string => typeof id === "string");
+    }
+  } catch {
+    // A corrupt ledger must not block the launch; start a fresh one.
+  }
+
+  if (handled.includes(toolCallId)) return false;
+
+  try {
+    window.localStorage.setItem(key, JSON.stringify([...handled, toolCallId]));
+  } catch {
+    // Storage full or unavailable — proceed, accepting replay risk over never
+    // launching at all.
+  }
+  return true;
+}
+
+function absoluteCanvasUrl(path: string) {
+  const canvasPath = buildAgentCanvasPath(path);
+  if (typeof window === "undefined") return canvasPath;
+  return new URL(canvasPath, window.location.origin).toString();
+}
+
+/**
+ * `parent_conversation_id` on the local start request landed in agent-server
+ * 1.37.1. Older servers ignore unknown fields, so the child is created without
+ * the link — report that rather than letting the agent assume a relationship
+ * that does not exist.
+ */
+function localParentLinkNote(): string | null {
+  const version = getCachedAgentServerVersion();
+  if (!version) return null;
+  const comparison = compareAgentServerVersions(
+    version,
+    MIN_AGENT_SERVER_VERSION_FOR_PARENT_LINK,
+  );
+  if (comparison === null || comparison >= 0) return null;
+  return `Agent server ${version} does not persist parent/child conversation links (needs ${MIN_AGENT_SERVER_VERSION_FOR_PARENT_LINK}); the child was created but is not linked to this conversation.`;
+}
+
+/**
+ * Whether the parent's workspace can host a git worktree.
+ *
+ * A conversation started without a repository or an attached workspace runs in
+ * a scratch directory that is `git init`-ed but never committed to. `git
+ * worktree add` cannot branch from an unborn HEAD, and the agent-server raises
+ * the resulting error straight out of its start-conversation handler as a 500,
+ * so asking for a worktree there fails the whole launch. Conversation metadata
+ * is only persisted when a repository or an explicit workspace was chosen (see
+ * `createConversation`), so its absence pinpoints exactly those scratch
+ * workspaces. Anything else is attempted and falls back on failure, because the
+ * frontend cannot inspect the workspace's git state directly.
+ */
+const parentSupportsWorktree = (
+  metadata: ConversationMetadata | null,
+): boolean => !!(metadata?.selected_repository || metadata?.selected_workspace);
+
+const SHARED_FALLBACK_CONSEQUENCE =
+  "The child was launched in this conversation's directory instead, so it can see work in progress here and the two agents may conflict over the same files.";
+
+async function launchLocalChild(
+  params: ValidatedParams,
+  parentConversationId: string,
+): Promise<LaunchChildConversationResult> {
+  // The agent-server rejects a parent whose workspace differs from the child's,
+  // so the child requests the parent's own directory. `worktree` then carves an
+  // isolated worktree out of it, which is what keeps siblings from colliding.
+  const workspace =
+    await AgentServerConversationService.resolveConversationWorkingDir(
+      parentConversationId,
+    );
+  const parentMetadata = getStoredConversationMetadata(parentConversationId);
+
+  const createChild = (isolation: ChildConversationIsolation) =>
+    AgentServerConversationService.createConversation(
+      params.task,
+      undefined,
+      undefined,
+      parentMetadata
+        ? {
+            selected_repository: parentMetadata.selected_repository,
+            selected_branch: parentMetadata.selected_branch,
+            git_provider: parentMetadata.git_provider,
+          }
+        : null,
+      workspace,
+      isolation === "shared" ? "local_repo" : "new_worktree",
+      parentConversationId,
+    );
+
+  let isolation = params.isolation;
+  let isolationNote: string | null = null;
+
+  if (isolation === "worktree" && !parentSupportsWorktree(parentMetadata)) {
+    isolation = "shared";
+    isolationNote = `This conversation's workspace is a scratch directory with no commits, which git cannot cut a worktree from. ${SHARED_FALLBACK_CONSEQUENCE}`;
+  }
+
+  let startTask;
+  try {
+    startTask = await createChild(isolation);
+  } catch (worktreeError) {
+    if (isolation !== "worktree") throw worktreeError;
+    // Creating the worktree is the one part of a local launch that can fail on
+    // an otherwise healthy workspace, so retry without it rather than losing
+    // the launch. Anything else fails both attempts and is reported as-is.
+    try {
+      startTask = await createChild("shared");
+    } catch {
+      throw worktreeError;
+    }
+    isolation = "shared";
+    isolationNote = `Creating a git worktree in this conversation's workspace failed (${worktreeError instanceof Error ? worktreeError.message : String(worktreeError)}). ${SHARED_FALLBACK_CONSEQUENCE}`;
+  }
+
+  const conversationId = startTask.app_conversation_id ?? startTask.id;
+
+  if (params.title) {
+    // Local start requests carry no title — only `autotitle`. Best effort: a
+    // failed rename must not fail the launch.
+    await AgentServerConversationService.updateConversationTitle(
+      conversationId,
+      params.title,
+    ).catch(() => undefined);
+  }
+
+  const parentLinkNote = localParentLinkNote();
+  return {
+    status: "launched",
+    target: "local",
+    conversation_id: conversationId,
+    url: absoluteCanvasUrl(`/conversations/${conversationId}`),
+    initial_status: startTask.status,
+    title: params.title,
+    workspace,
+    isolation,
+    ...(isolationNote ? { isolation_note: isolationNote } : {}),
+    parent_link: !parentLinkNote,
+    ...(parentLinkNote ? { parent_link_note: parentLinkNote } : {}),
+  };
+}
+
+const delay = (ms: number) =>
+  new Promise((resolve) => {
+    setTimeout(resolve, ms);
+  });
+
+/**
+ * Wait for the Cloud start task to expose its conversation id.
+ *
+ * The Cloud API provisions a sandbox asynchronously and only fills in
+ * `app_conversation_id` once the task reaches READY, so without this the agent
+ * would get a result with no conversation to open. Bounded: on timeout the
+ * caller reports the still-provisioning task instead of hanging.
+ */
+async function waitForCloudConversationId(
+  task: AppConversationStartTask,
+  backend: Backend,
+): Promise<AppConversationStartTask> {
+  const deadline = Date.now() + CLOUD_START_POLL_TIMEOUT_MS;
+  let latest = task;
+  while (!latest.app_conversation_id && latest.status !== "ERROR") {
+    if (Date.now() >= deadline) break;
+
+    await delay(CLOUD_START_POLL_INTERVAL_MS);
+
+    const next = await getCloudAppConversationStartTask(
+      latest.id,
+      backend,
+    ).catch(() => null);
+    if (!next) break;
+    latest = next;
+  }
+  return latest;
+}
+
+async function launchCloudChild(
+  params: ValidatedParams,
+  parentConversationId: string,
+): Promise<LaunchChildConversationResult> {
+  const backend = pickCloudBackendForLaunch();
+  if (!backend) {
+    return failure(
+      "No OpenHands Cloud backend is connected in Agent Canvas.",
+      'Ask the user to connect OpenHands Cloud from the backend picker, then call this tool again — or relaunch now with target="local".',
+    );
+  }
+
+  const parentMetadata = getStoredConversationMetadata(parentConversationId);
+  const startTask = await createCloudAppConversation(
+    {
+      initial_message: {
+        role: "user",
+        content: [{ type: "text", text: params.task }],
+      },
+      title: params.title,
+      // Fall back to this conversation's repository so a bare `target: "cloud"`
+      // call still lands the child on the code the user is working on. The
+      // provider only travels with the inherited repository — it may not apply
+      // to one the agent named itself.
+      selected_repository:
+        params.repository ?? parentMetadata?.selected_repository ?? null,
+      selected_branch: params.branch ?? null,
+      git_provider: params.repository
+        ? null
+        : (parentMetadata?.git_provider ?? null),
+      // The parent runs on the local agent-server, so its id means nothing to
+      // Cloud. Sending it would only hide the child from the Cloud
+      // conversation list, which filters out anything with a parent.
+      parent_conversation_id: null,
+    },
+    backend,
+  );
+
+  const settled = await waitForCloudConversationId(startTask, backend);
+  if (settled.status === "ERROR") {
+    return failure(
+      settled.detail || "The Cloud conversation failed to start.",
+      'The Cloud sandbox could not be provisioned. Report this to the user; you can retry, or fall back to target="local".',
+    );
+  }
+
+  const conversationId = settled.app_conversation_id;
+  return {
+    status: "launched",
+    target: "cloud",
+    conversation_id: conversationId,
+    url: conversationId
+      ? `${backend.host.replace(/\/$/, "")}/conversations/${conversationId}`
+      : null,
+    initial_status: settled.status,
+    title: params.title,
+    start_task_id: settled.id,
+    backend: backend.name,
+    // Cloud children of a local parent carry no server-side link; see above.
+    parent_link: false,
+    parent_link_note:
+      "This conversation runs on the local agent server, so OpenHands Cloud has no parent to link the child to.",
+  };
+}
+
+/**
+ * Hand the outcome back to the agent and the user.
+ *
+ * Client tools are acknowledged by the agent-server before the browser does any
+ * work, so a message is the only way to give the agent the child's id or tell
+ * it how to fix a malformed call. `sendMessage` runs the agent, which is what
+ * makes it relay the result to the user in its next turn.
+ */
+async function reportLaunchResult(
+  parentConversationId: string,
+  result: LaunchChildConversationResult,
+) {
+  if (result.status === "error") {
+    displayErrorToast(
+      i18n.t(I18nKey.CHILD_CONVERSATION$LAUNCH_FAILED, {
+        error: result.error,
+      }),
+    );
+  } else if (result.url) {
+    displaySuccessToastWithLink(
+      i18n.t(
+        result.target === "cloud"
+          ? I18nKey.CHILD_CONVERSATION$LAUNCHED_CLOUD
+          : I18nKey.CHILD_CONVERSATION$LAUNCHED_LOCAL,
+      ),
+      i18n.t(I18nKey.CHILD_CONVERSATION$OPEN),
+      result.url,
+    );
+  }
+
+  // The agent-server cancels an active `/goal` loop on any inbound message, so
+  // a launch must not silently end one. The toast above still tells the user
+  // what happened.
+  const goalStatus =
+    useGoalStore.getState().statusByConversation[parentConversationId];
+  if (goalStatus?.active) return;
+
+  await AgentServerConversationService.sendMessage(parentConversationId, {
+    role: "user",
+    content: [
+      {
+        type: "text",
+        text: `${CHILD_CONVERSATION_RESULT_PREFIX}${JSON.stringify(result)}`,
+      },
+    ],
+  });
+}
+
+/**
+ * Execute a `launch_child_conversation` tool call.
+ *
+ * Never rejects: every failure is turned into corrective guidance for the
+ * agent, because the agent-server has already told it the call succeeded.
+ */
+export async function handleLaunchChildConversationAction(
+  action: LaunchChildConversationAction,
+  parentConversationId: string,
+  toolCallId: string,
+): Promise<void> {
+  if (!claimToolCall(parentConversationId, toolCallId)) return;
+
+  const validation = validateLaunchParams(action);
+  let result: LaunchChildConversationResult;
+  if (!validation.ok) {
+    result = validation.failure;
+  } else {
+    try {
+      result =
+        validation.params.target === "cloud"
+          ? await launchCloudChild(validation.params, parentConversationId)
+          : await launchLocalChild(validation.params, parentConversationId);
+    } catch (error) {
+      result = failure(
+        error instanceof Error ? error.message : String(error),
+        "The launch request failed. Report the error to the user; retry only if the cause looks transient.",
+      );
+    }
+  }
+
+  await reportLaunchResult(parentConversationId, result).catch((error) => {
+    console.warn(
+      `[${LAUNCH_CHILD_CONVERSATION_TOOL_NAME}] Failed to report the launch result:`,
+      error,
+    );
+  });
+}
diff --git a/src/types/agent-server/core/base/action.ts b/src/types/agent-server/core/base/action.ts
index a316bf584c..60a502db03 100644
--- a/src/types/agent-server/core/base/action.ts
+++ b/src/types/agent-server/core/base/action.ts
@@ -1,4 +1,5 @@
 import { CANVAS_UI_CLIENT_ACTION_KIND } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_ACTION_KIND } from "#/constants/child-conversation";
 import { ActionBase } from "./base";
 import { TaskItem } from "./common";
 
@@ -321,6 +322,24 @@ export interface CanvasUIAction extends ActionBase<
   tab?: string | null;
 }
 
+/**
+ * Request to launch a child conversation, emitted over the existing WebSocket
+ * and intercepted by handleLaunchChildConversationAction. The agent-server
+ * validates the parameter *names* and types against the tool schema but not
+ * `enum` values, so the fields stay loosely typed here and the dispatcher
+ * narrows them (returning corrective guidance on a mismatch).
+ */
+export interface LaunchChildConversationAction extends ActionBase<
+  typeof LAUNCH_CHILD_CONVERSATION_ACTION_KIND
+> {
+  target: string;
+  task: string;
+  title?: string | null;
+  repository?: string | null;
+  branch?: string | null;
+  isolation?: string | null;
+}
+
 export type Action =
   | MCPToolAction
   | FinishAction
@@ -346,4 +365,5 @@ export type Action =
   | InvokeSkillAction
   | TaskAction
   | SwitchLLMAction
-  | CanvasUIAction;
+  | CanvasUIAction
+  | LaunchChildConversationAction;
diff --git a/src/types/agent-server/core/base/base.ts b/src/types/agent-server/core/base/base.ts
index 891e105851..31eea2470b 100644
--- a/src/types/agent-server/core/base/base.ts
+++ b/src/types/agent-server/core/base/base.ts
@@ -1,4 +1,5 @@
 import { CANVAS_UI_CLIENT_ACTION_KIND } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_ACTION_KIND } from "#/constants/child-conversation";
 
 type EventType =
   | "MCPTool"
@@ -37,7 +38,8 @@ type ActionEventType =
   | "GrepAction"
   // The `task` tool delegating work to a spawned subagent.
   | "TaskAction"
-  | typeof CANVAS_UI_CLIENT_ACTION_KIND;
+  | typeof CANVAS_UI_CLIENT_ACTION_KIND
+  | typeof LAUNCH_CHILD_CONVERSATION_ACTION_KIND;
 type ObservationEventType =
   | `${ObservationOnlyType}Observation`
   | `${EventType}Observation`
diff --git a/src/types/agent-server/type-guards.ts b/src/types/agent-server/type-guards.ts
index 542a9da400..65504665ba 100644
--- a/src/types/agent-server/type-guards.ts
+++ b/src/types/agent-server/type-guards.ts
@@ -2,6 +2,7 @@ import {
   CANVAS_UI_CLIENT_TOOL_NAME,
   LEGACY_CANVAS_UI_TOOL_NAME,
 } from "#/constants/canvas-ui";
+import { LAUNCH_CHILD_CONVERSATION_TOOL_NAME } from "#/constants/child-conversation";
 
 import {
   OpenHandsEvent,
@@ -16,6 +17,7 @@ import {
   BrowserNavigateAction,
   SwitchLLMObservation,
   CanvasUIAction,
+  LaunchChildConversationAction,
 } from "./core";
 import { AgentErrorEvent } from "./core/events/observation-event";
 import { MessageEvent } from "./core/events/message-event";
@@ -184,6 +186,18 @@ export const isCanvasUIActionEvent = (
   (event.tool_name === LEGACY_CANVAS_UI_TOOL_NAME ||
     event.tool_name === CANVAS_UI_CLIENT_TOOL_NAME);
 
+/**
+ * Type guard for launch-child-conversation tool ActionEvents.
+ *
+ * Discriminates on tool_name, like `isCanvasUIActionEvent`, so the
+ * SDK-generated action kind stays contained in the constants module.
+ */
+export const isLaunchChildConversationActionEvent = (
+  event: OpenHandsEvent,
+): event is ActionEvent<LaunchChildConversationAction> =>
+  isActionEvent(event) &&
+  event.tool_name === LAUNCH_CHILD_CONVERSATION_TOOL_NAME;
+
 /**
  * Type guard function to check if an event is a system prompt event
  */