fix(sessions): Surface failed agent prompt sends to the user

apps/code/src/renderer/desktop-services.ts

@@ -152,8 +152,8 @@ container
   .toConstantValue(new RendererHedgehogModeHost());
 container
   .bind<AgentPromptSender>(AGENT_PROMPT_SENDER)
-  .toConstantValue((taskId, prompt) => {
-    void resolveService<SessionService>(SESSION_SERVICE).sendPrompt(
+  .toConstantValue(async (taskId, prompt) => {
+    await resolveService<SessionService>(SESSION_SERVICE).sendPrompt(
       taskId,
       prompt,
     );

packages/ui/src/features/sessions/agentPromptSender.ts

@@ -3,6 +3,6 @@ import type { ContentBlock } from "@agentclientprotocol/sdk";
 export type AgentPromptSender = (
   taskId: string,
   prompt: string | ContentBlock[],
-) => void;
+) => Promise<void>;
 
 export const AGENT_PROMPT_SENDER = Symbol.for("posthog.ui.AgentPromptSender");

packages/ui/src/features/sessions/sendPromptToAgent.test.ts

@@ -0,0 +1,113 @@
+import { toast } from "@posthog/ui/primitives/toast";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { DEFAULT_TAB_IDS } from "../panels/panelConstants";
+import { AGENT_PROMPT_SENDER } from "./agentPromptSender";
+import { sendPromptToAgent } from "./sendPromptToAgent";
+
+const { mockSender, reviewState, panelState, findTabInTree } = vi.hoisted(
+  () => ({
+    mockSender: vi.fn(),
+    reviewState: {
+      mode: "split" as "split" | "expanded",
+      setReviewMode: vi.fn(),
+    },
+    panelState: {
+      taskLayouts: {} as Record<string, { panelTree: unknown }>,
+      setActiveTab: vi.fn(),
+    },
+    findTabInTree: vi.fn(),
+  }),
+);
+
+vi.mock("@posthog/ui/primitives/toast", () => ({
+  toast: { error: vi.fn(), info: vi.fn(), success: vi.fn() },
+}));
+
+vi.mock("@posthog/di/container", () => ({
+  resolveService: (token: unknown) => {
+    if (token === AGENT_PROMPT_SENDER) return mockSender;
+    throw new Error(`resolveService: unmocked token ${String(token)}`);
+  },
+}));
+
+vi.mock("../code-review/reviewNavigationStore", () => ({
+  useReviewNavigationStore: {
+    getState: () => ({
+      getReviewMode: () => reviewState.mode,
+      setReviewMode: reviewState.setReviewMode,
+    }),
+  },
+}));
+
+vi.mock("../panels/panelLayoutStore", () => ({
+  usePanelLayoutStore: {
+    getState: () => ({
+      taskLayouts: panelState.taskLayouts,
+      setActiveTab: panelState.setActiveTab,
+    }),
+  },
+}));
+
+vi.mock("../panels/panelTree", () => ({ findTabInTree }));
+
+describe("sendPromptToAgent", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    reviewState.mode = "split";
+    panelState.taskLayouts = {};
+    findTabInTree.mockReturnValue({ panelId: "panel-logs" });
+  });
+
+  it.each([
+    [
+      new Error("Agent server is not reachable"),
+      "Agent server is not reachable",
+    ],
+    ["boom", "Failed to send your message to the agent. Please try again."],
+  ])(
+    "surfaces a rejected send as an error toast (%#)",
+    async (rejection, expectedMessage) => {
+      mockSender.mockRejectedValueOnce(rejection);
+
+      sendPromptToAgent("task-1", "hello");
+
+      await vi.waitFor(() =>
+        expect(toast.error).toHaveBeenCalledWith(expectedMessage),
+      );
+    },
+  );
+
+  it("does not toast when the send resolves", async () => {
+    mockSender.mockResolvedValueOnce(undefined);
+
+    sendPromptToAgent("task-1", "hello");
+
+    // Await the exact promise the sender returned rather than guessing how many
+    // microtasks the catch chain takes to settle.
+    await mockSender.mock.results[0]?.value;
+    expect(toast.error).not.toHaveBeenCalled();
+  });
+
+  // The send is fire-and-forget, so the panel/review side effects must run
+  // regardless of whether it ultimately resolves or rejects.
+  it.each([
+    ["resolves", () => mockSender.mockResolvedValueOnce(undefined)],
+    ["rejects", () => mockSender.mockRejectedValueOnce(new Error("nope"))],
+  ])(
+    "collapses review and switches to the logs tab when the send %s",
+    (_label, primeSender) => {
+      primeSender();
+      reviewState.mode = "expanded";
+      panelState.taskLayouts = { "task-1": { panelTree: {} } };
+
+      sendPromptToAgent("task-1", "hello");
+
+      expect(reviewState.setReviewMode).toHaveBeenCalledWith("task-1", "split");
+      expect(panelState.setActiveTab).toHaveBeenCalledWith(
+        "task-1",
+        "panel-logs",
+        DEFAULT_TAB_IDS.LOGS,
+      );
+    },
+  );
+});

packages/ui/src/features/sessions/sendPromptToAgent.ts

@@ -1,5 +1,6 @@
 import type { ContentBlock } from "@agentclientprotocol/sdk";
 import { resolveService } from "@posthog/di/container";
+import { toast } from "@posthog/ui/primitives/toast";
 import { useReviewNavigationStore } from "../code-review/reviewNavigationStore";
 import { DEFAULT_TAB_IDS } from "../panels/panelConstants";
 import { usePanelLayoutStore } from "../panels/panelLayoutStore";
@@ -17,7 +18,19 @@ export function sendPromptToAgent(
   taskId: string,
   prompt: string | ContentBlock[],
 ): void {
-  resolveService<AgentPromptSender>(AGENT_PROMPT_SENDER)(taskId, prompt);
+  // Button/review/skill-initiated prompts are fire-and-forget, but a rejected
+  // send (auth failure, sandbox unreachable, agent process died) must still be
+  // surfaced, or the turn just shows "Generated in Xs" with no reply.
+  void resolveService<AgentPromptSender>(AGENT_PROMPT_SENDER)(
+    taskId,
+    prompt,
+  ).catch((error: unknown) => {
+    toast.error(
+      error instanceof Error
+        ? error.message
+        : "Failed to send your message to the agent. Please try again.",
+    );
+  });
 
   const { getReviewMode, setReviewMode } = useReviewNavigationStore.getState();
   if (getReviewMode(taskId) === "expanded") {