feat(agent): persist assistant model preference

src/app/settings/assistant-actions.ts

@@ -9,6 +9,7 @@ import {
   MAX_ASSISTANT_NAME_LENGTH,
   MAX_ASSISTANT_SYSTEM_PROMPT_LENGTH,
 } from "@/lib/assistant-config";
+import { isValidLlmModelId, listLlmModels } from "@/lib/llm/models";
 import { users } from "@/modules/_core/schema";
 import { getCurrentSession } from "@/lib/session";
 
@@ -50,6 +51,25 @@ export async function setAssistantSystemPrompt(prompt: string | null): Promise<v
   revalidateAssistantSurfaces();
 }
 
+export async function setAssistantModel(model: string | null): Promise<void> {
+  const { user } = await getCurrentSession();
+  const normalized = model?.trim() || null;
+
+  if (normalized !== null && !isValidLlmModelId(normalized)) {
+    throw new Error("Invalid assistant model");
+  }
+
+  const available = await listLlmModels();
+  const requested = normalized === available.fallbackModel ? null : normalized;
+
+  if (requested !== null && !available.models.some((option) => option.id === requested)) {
+    throw new Error("Invalid assistant model");
+  }
+
+  await db.update(users).set({ assistantModel: requested }).where(eq(users.id, user.id));
+  revalidateAssistantSurfaces();
+}
+
 export async function resetAssistantName(): Promise<void> {
   await setAssistantName(DEFAULT_ASSISTANT_NAME);
 }