fix(ai): preserve last-used model during app session

apps/desktop/src/components/editor/AiAssistant.vue

@@ -1614,10 +1614,6 @@ async function deleteConversation(id: string) {
 function startNewChat() {
   clearMessages();
   showConversationList.value = false;
-  const defaultConfig = settings.aiConfigs.find((c) => c.isDefault) || settings.aiConfigs[0];
-  if (defaultConfig) {
-    settings.updateActiveModel({ configId: defaultConfig.id, modelId: defaultConfig.model });
-  }
 }
 
 onMounted(async () => {

apps/desktop/src/stores/__tests__/settingsStore.spec.ts

@@ -1,5 +1,7 @@
-import { describe, expect, it } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
 import { normalizeDesktopSettings, normalizeEditorSettings } from "@/stores/settingsStore";
+import { createPinia, setActivePinia } from "pinia";
+import type { AiConfigItem } from "@/types/ai";
 
 describe("normalizeEditorSettings", () => {
   it("enables automatic table aliases by default", () => {
@@ -162,3 +164,134 @@ describe("normalizeEditorSettings - tabLayout", () => {
     expect(normalizeEditorSettings({ tabLayout: 123 } as any).tabLayout).toBe("scroll");
   });
 });
+
+// --- Helpers for Pinia store tests ---
+
+function makeTestConfig(overrides: Partial<AiConfigItem> & { id: string }): AiConfigItem {
+  return {
+    provider: "openai",
+    apiKey: "",
+    authMethod: "api-key",
+    endpoint: "https://api.openai.com/v1/chat/completions",
+    model: "gpt-4o-mini",
+    apiStyle: "completions",
+    name: overrides.id,
+    ...overrides,
+  } as AiConfigItem;
+}
+
+// --- activeModel lifecycle tests ---
+
+describe("settingsStore activeModel lifecycle", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    setActivePinia(createPinia());
+  });
+
+  it("updateActiveModel persists the model and does not change any config isDefault", async () => {
+    vi.doMock("@/lib/backend/api", () => ({
+      loadAiConfigs: vi.fn().mockResolvedValue([]),
+      loadAiConfig: vi.fn().mockResolvedValue(null),
+      loadAiProviderConfigs: vi.fn().mockResolvedValue(null),
+    }));
+
+    const { useSettingsStore } = await import("@/stores/settingsStore");
+    const store = useSettingsStore();
+
+    store.aiConfigs = [makeTestConfig({ id: "c1", model: "model-a", isDefault: true }), makeTestConfig({ id: "c2", model: "model-b", isDefault: false })];
+    store.isAiConfigLoaded = true;
+
+    store.updateActiveModel({ configId: "c1", modelId: "model-a" });
+    expect(store.activeModel).toEqual({ configId: "c1", modelId: "model-a" });
+
+    store.updateActiveModel({ configId: "c2", modelId: "model-b" });
+    expect(store.activeModel).toEqual({ configId: "c2", modelId: "model-b" });
+
+    // 核心保障：不改变任何配置的 isDefault
+    expect(store.aiConfigs[0].isDefault).toBe(true);
+    expect(store.aiConfigs[1].isDefault).toBe(false);
+  });
+
+  it("setDefaultAiConfig(id) on success points activeModel to the new default config", async () => {
+    const setDefaultAiConfig = vi.fn().mockResolvedValue(undefined);
+
+    vi.doMock("@/lib/backend/api", () => ({
+      loadAiConfigs: vi.fn().mockResolvedValue([]),
+      loadAiConfig: vi.fn().mockResolvedValue(null),
+      loadAiProviderConfigs: vi.fn().mockResolvedValue(null),
+      setDefaultAiConfig,
+    }));
+
+    const { useSettingsStore } = await import("@/stores/settingsStore");
+    const store = useSettingsStore();
+
+    store.aiConfigs = [makeTestConfig({ id: "c1", model: "model-a", isDefault: true }), makeTestConfig({ id: "c2", model: "model-b", isDefault: false })];
+    store.isAiConfigLoaded = true;
+
+    // 先手动切到非默认的配置
+    store.updateActiveModel({ configId: "c2", modelId: "model-b" });
+    expect(store.activeModel).toEqual({ configId: "c2", modelId: "model-b" });
+
+    await store.setDefaultAiConfig("c2");
+
+    expect(setDefaultAiConfig).toHaveBeenCalledWith("c2");
+    expect(store.aiConfigs[0].isDefault).toBe(false);
+    expect(store.aiConfigs[1].isDefault).toBe(true);
+    expect(store.activeModel).toEqual({ configId: "c2", modelId: "model-b" });
+  });
+
+  it("setDefaultAiConfig does not mutate state when backend call fails", async () => {
+    const error = new Error("backend error");
+    const setDefaultAiConfig = vi.fn().mockRejectedValue(error);
+
+    vi.doMock("@/lib/backend/api", () => ({
+      loadAiConfigs: vi.fn().mockResolvedValue([]),
+      loadAiConfig: vi.fn().mockResolvedValue(null),
+      loadAiProviderConfigs: vi.fn().mockResolvedValue(null),
+      setDefaultAiConfig,
+    }));
+
+    const { useSettingsStore } = await import("@/stores/settingsStore");
+    const store = useSettingsStore();
+
+    store.aiConfigs = [makeTestConfig({ id: "c1", model: "model-a", isDefault: true }), makeTestConfig({ id: "c2", model: "model-b", isDefault: false })];
+    store.isAiConfigLoaded = true;
+    store.updateActiveModel({ configId: "c1", modelId: "model-a" });
+
+    await expect(store.setDefaultAiConfig("c2")).rejects.toThrow("backend error");
+
+    // isDefault 不变
+    expect(store.aiConfigs[0].isDefault).toBe(true);
+    expect(store.aiConfigs[1].isDefault).toBe(false);
+    // activeModel 不变
+    expect(store.activeModel).toEqual({ configId: "c1", modelId: "model-a" });
+  });
+
+  it("reloadAiConfigs sets activeModel to null when config list is empty", async () => {
+    vi.doMock("@/lib/backend/api", () => ({
+      loadAiConfigs: vi.fn().mockResolvedValue([]),
+      loadAiConfig: vi.fn().mockResolvedValue(null),
+      loadAiProviderConfigs: vi.fn().mockResolvedValue(null),
+    }));
+
+    const { useSettingsStore } = await import("@/stores/settingsStore");
+    const store = useSettingsStore();
+    store.isAiConfigLoaded = false;
+    await store.reloadAiConfigs();
+    expect(store.activeModel).toBeNull();
+  });
+
+  it("reloadAiConfigs points activeModel to isDefault config, not first in list", async () => {
+    const configs = [makeTestConfig({ id: "c1", model: "model-a", isDefault: false }), makeTestConfig({ id: "c2", model: "model-b", isDefault: true }), makeTestConfig({ id: "c3", model: "model-c", isDefault: false })];
+
+    vi.doMock("@/lib/backend/api", () => ({
+      loadAiConfigs: vi.fn().mockResolvedValue(configs),
+    }));
+
+    const { useSettingsStore } = await import("@/stores/settingsStore");
+    const store = useSettingsStore();
+    store.isAiConfigLoaded = false;
+    await store.reloadAiConfigs();
+    expect(store.activeModel).toEqual({ configId: "c2", modelId: "model-b" });
+  });
+});

apps/desktop/src/stores/settingsStore.ts

@@ -944,7 +944,8 @@ export const useSettingsStore = defineStore("settings", () => {
       await migrateToMultiConfig();
     }
 
-    // 同步活跃状态到默认配置
+    // 重置 activeModel 到默认配置是有意行为——activeModel 是本次运行 (run-scoped) 的末次使用选择，
+    // 应用启动和配置同步下载 (reloadAiConfigs) 两条路径均需丢弃会话内手动切换的模型、回到默认。
     const defaultConfig = aiConfigs.value.find((c) => c.isDefault) || aiConfigs.value[0];
     if (defaultConfig) {
       activeModel.value = { configId: defaultConfig.id, modelId: defaultConfig.model };
@@ -956,14 +957,7 @@ export const useSettingsStore = defineStore("settings", () => {
   async function reloadAiConfigs(): Promise<void> {
     isAiConfigLoaded.value = false;
     await initAiConfigs();
-    // If the active config was deleted, fall back to the default
-    if (activeModel.value && !aiConfigs.value.find((c) => c.id === activeModel.value!.configId)) {
-      if (aiConfigs.value.length > 0) {
-        activeModel.value = { configId: aiConfigs.value[0].id, modelId: aiConfigs.value[0].model };
-      } else {
-        activeModel.value = null;
-      }
-    }
+    if (aiConfigs.value.length === 0) activeModel.value = null;
   }
 
   async function migrateToMultiConfig(): Promise<void> {
@@ -1029,6 +1023,11 @@ export const useSettingsStore = defineStore("settings", () => {
     aiConfigs.value.forEach((c) => {
       c.isDefault = c.id === id;
     });
+    const config = aiConfigs.value.find((c) => c.id === id);
+    if (config) {
+      // 修改默认配置时丢弃用户手动选择的模型，回到新默认——放在 await 之后确保后端持久化成功才执行
+      activeModel.value = { configId: config.id, modelId: config.model };
+    }
   }
 
   function updateActiveModel(model: { configId: string; modelId: string }) {