fix: don't switch LLM profile before the conversation UUID exists (avoids 422) (#14900)

frontend/__tests__/components/features/chat/switch-profile-button.test.tsx

@@ -13,6 +13,7 @@ import type { LlmProfileSummary } from "#/api/settings-service/profiles-service.
 const mockUseLlmProfiles = vi.hoisted(() => vi.fn());
 const mockUseActiveConversation = vi.hoisted(() => vi.fn());
 const mockSwitchAndLog = vi.hoisted(() => vi.fn());
+const mockConversationId = vi.hoisted(() => ({ value: "conv-1" }));
 const mockModelStore = vi.hoisted(() => ({
   activeProfileByConversation: {} as Record<string, string>,
 }));
@@ -34,7 +35,7 @@ vi.mock("#/hooks/mutation/use-switch-llm-profile-and-log", () => ({
 }));
 
 vi.mock("#/hooks/use-conversation-id", () => ({
-  useConversationId: () => ({ conversationId: "conv-1" }),
+  useConversationId: () => ({ conversationId: mockConversationId.value }),
 }));
 
 vi.mock("#/stores/model-store", () => ({
@@ -102,6 +103,7 @@ const setupHooks = (
 describe("SwitchProfileButton", () => {
   beforeEach(() => {
     mockSwitchAndLog.mockReset();
+    mockConversationId.value = "conv-1";
   });
 
   afterEach(() => {
@@ -205,6 +207,13 @@ describe("SwitchProfileButton", () => {
     expect(mockSwitchAndLog).toHaveBeenCalledWith("conv-1", "default");
   });
 
+  it("is disabled while the conversation id is still the `task-` placeholder", () => {
+    mockConversationId.value = "task-abc-123";
+    setupHooks({ conversationModel: "openai/gpt-5" });
+    renderButton();
+    expect(screen.getByTestId("switch-profile-button")).toBeDisabled();
+  });
+
   it("does not call switchAndLog when the already-active profile is selected", async () => {
     const user = userEvent.setup();
     setupHooks({ conversationModel: "openai/gpt-5" }); // gpt-5 is active

frontend/__tests__/hooks/mutation/use-switch-llm-profile-and-log.test.ts

@@ -52,6 +52,17 @@ describe("useSwitchLlmProfileAndLog", () => {
     );
   });
 
+  it("no-ops for a `task-` placeholder id (no call, no error toast) during startup", async () => {
+    const { result } = renderTestHook();
+    act(() => result.current.switchAndLog("task-abc-123", "gpt-5"));
+    // Give any pending mutation a tick to fire (it shouldn't).
+    await new Promise((r) => {
+      setTimeout(r, 0);
+    });
+    expect(mockSwitchProfile).not.toHaveBeenCalled();
+    expect(mockDisplayErrorToast).not.toHaveBeenCalled();
+  });
+
   it("records a switch entry on success, anchored to the latest rendered v1 event", async () => {
     useEventStore.setState({
       events: [],

frontend/src/components/features/chat/switch-profile-button.tsx

@@ -25,6 +25,10 @@ export function SwitchProfileButton() {
   const profiles = data?.profiles ?? [];
   const conversationModel = conversation?.llm_model ?? null;
 
+  // Still starting: the id is the placeholder `task-<uuid>`, not the real
+  // conversation UUID yet, so a switch can't be persisted (would 422).
+  const isStarting = conversationId.startsWith("task-");
+
   // Resolve the active profile, most-authoritative source first:
   //   1. A switch the user made this session (recorded by name, so it's exact
   //      even when several profiles share a model string, e.g. SaaS managed
@@ -77,7 +81,7 @@ export function SwitchProfileButton() {
       <button
         type="button"
         onClick={handleClick}
-        disabled={isPending}
+        disabled={isPending || isStarting}
         data-testid="switch-profile-button"
         title={activeProfileModel ?? undefined}
         aria-haspopup="menu"

frontend/src/hooks/mutation/use-switch-llm-profile-and-log.ts

@@ -17,6 +17,11 @@ export function useSwitchLlmProfileAndLog() {
   // Stable identity so the /model interceptor's outer useCallback doesn't bust each render.
   const switchAndLog = useCallback(
     (conversationId: string, profileName: string) => {
+      // During chat startup the id is the placeholder `task-<uuid>` (the real
+      // conversation UUID doesn't exist yet); the switch endpoint types its
+      // path param as a UUID and would 422. No-op until the UUID is live.
+      if (conversationId.startsWith("task-")) return;
+
       const last = getRenderedV1Events(useEventStore.getState().uiEvents).at(
         -1,
       );