fix: force task to be created with latest version (#19923)

Fixes https://github.com/coder/coder/issues/19744

site/src/pages/TasksPage/TaskPrompt.tsx

@@ -186,11 +186,12 @@ const CreateTaskForm: FC<CreateTaskFormProps> = ({ templates, onSuccess }) => {
 
 	const createTaskMutation = useMutation({
 		mutationFn: async ({ prompt }: CreateTaskMutationFnProps) =>
-			API.experimental.createTask(user.id, {
+			createTaskWithLatestTemplateVersion(
 				prompt,
-				template_version_id: selectedTemplate.active_version_id,
-				template_version_preset_id: selectedPresetId,
-			}),
+				user.id,
+				selectedTemplate.id,
+				selectedPresetId,
+			),
 		onSuccess: async (task) => {
 			await queryClient.invalidateQueries({ queryKey: ["tasks"] });
 			onSuccess(task);
@@ -427,3 +428,21 @@ function sortByDefault(a: Preset, b: Preset) {
 	// Otherwise, sort alphabetically by name
 	return a.Name.localeCompare(b.Name);
 }
+
+// TODO: Enforce task creation to always use the latest active template version.
+// During task creation, the active version might change between template load
+// and user action. Since handling this in the FE cannot guarantee correctness,
+// we should move the logic to the BE after the experimental phase.
+async function createTaskWithLatestTemplateVersion(
+	prompt: string,
+	userId: string,
+	templateId: string,
+	presetId: string | undefined,
+): Promise<Task> {
+	const template = await API.getTemplate(templateId);
+	return API.experimental.createTask(userId, {
+		prompt,
+		template_version_id: template.active_version_id,
+		template_version_preset_id: presetId,
+	});
+}

site/src/pages/TasksPage/TasksPage.stories.tsx

@@ -245,7 +245,12 @@ export const CreateTaskSuccessfully: Story = {
 		}),
 	},
 	beforeEach: () => {
+		const activeVersionId = `${MockTemplate.active_version_id}-latest`;
 		spyOn(API, "getTemplates").mockResolvedValue([MockTemplate]);
+		spyOn(API, "getTemplate").mockResolvedValue({
+			...MockTemplate,
+			active_version_id: activeVersionId,
+		});
 		spyOn(API.experimental, "getTasks")
 			.mockResolvedValueOnce(MockTasks)
 			.mockResolvedValue([MockNewTaskData, ...MockTasks]);
@@ -262,6 +267,17 @@ export const CreateTaskSuccessfully: Story = {
 			await userEvent.click(submitButton);
 		});
 
+		await step("Uses latest template version", () => {
+			expect(API.experimental.createTask).toHaveBeenCalledWith(
+				MockUserOwner.id,
+				{
+					prompt: MockNewTaskData.prompt,
+					template_version_id: `${MockTemplate.active_version_id}-latest`,
+					template_version_preset_id: undefined,
+				},
+			);
+		});
+
 		await step("Displays success message", async () => {
 			const body = within(canvasElement.ownerDocument.body);
 			const successMessage = await body.findByText(/task created/i);
@@ -281,6 +297,7 @@ export const CreateTaskError: Story = {
 	decorators: [withGlobalSnackbar],
 	beforeEach: () => {
 		spyOn(API, "getTemplates").mockResolvedValue([MockTemplate]);
+		spyOn(API, "getTemplate").mockResolvedValue(MockTemplate);
 		spyOn(API.experimental, "getTasks").mockResolvedValue(MockTasks);
 		spyOn(API.experimental, "createTask").mockRejectedValue(
 			mockApiError({