add support for switching preferred model per chat session

public/script.js

@@ -368,6 +368,20 @@ async function saveGenerationSettings() {
     setNotice("Generation settings saved.", "success");
 }
 
+async function saveSelectedModel() {
+    if (!activeChatId || !modelSelect.value) return;
+    const chatId = activeChatId;
+    const selectedModel = modelSelect.value;
+    const res = await put(`/chats/${chatId}/model`, {model: selectedModel});
+    if (res.error || !res.chat) return setNotice(res.error || "Unable to switch models.", "error");
+    const chat = getChatById(chatId);
+    if (chat) Object.assign(chat, res.chat);
+    if (chatId === activeChatId && modelSelect.value === selectedModel) {
+        renderModelSection();
+        setNotice(`Model switched to ${modelSelect.selectedOptions[0]?.textContent || selectedModel}.`, "success");
+    }
+}
+
 function resizeComposerInput() {
     msgInput.style.height = "auto";
     const nextHeight = Math.min(Math.max(msgInput.scrollHeight, 46), 96);
@@ -1978,6 +1992,7 @@ if (importWorkspaceFileInput) importWorkspaceFileInput.addEventListener("change"
 chatSearchInput.addEventListener("input", () => { void loadChatSessions(); });
 modelSelect.addEventListener("change", () => {
     renderModelSection();
+    void saveSelectedModel();
 });
 saveGenerationSettingsBtn.addEventListener("click", () => { void saveGenerationSettings(); });
 roleplayNewPersonaBtn.addEventListener("click", () => openPersonaForm(null, "assistant"));

src/db/repositories.js

@@ -163,6 +163,7 @@ export function createRepositories(db, config) {
             SET preferred_model = ?, temperature = ?, context_length = ?, response_length = ?, system_instruction = ?, updated_at = CURRENT_TIMESTAMP
             WHERE id = ? AND username = ?
         `),
+        updateChatPreferredModel: db.prepare("UPDATE chat_sessions SET preferred_model = ?, updated_at = CURRENT_TIMESTAMP WHERE id = ? AND username = ?"),
         updateChatActiveLeaf: db.prepare("UPDATE chat_sessions SET active_leaf_message_id = ?, updated_at = CURRENT_TIMESTAMP WHERE id = ? AND username = ?"),
         updateChatBranchSource: db.prepare("UPDATE chat_sessions SET source_chat_id = ?, branched_from_message_id = ?, updated_at = CURRENT_TIMESTAMP WHERE id = ? AND username = ?"),
         setChatActiveLeafById: db.prepare("UPDATE chat_sessions SET active_leaf_message_id = ?, updated_at = CURRENT_TIMESTAMP WHERE id = ?"),
@@ -1027,6 +1028,7 @@ export function createRepositories(db, config) {
             chatId,
             username
         ),
+        updateChatPreferredModel: (chatId, username, model) => statements.updateChatPreferredModel.run(model || null, chatId, username),
         updateChatMessage: (chatId, messageId, content) => statements.updateChatMessage.run(content, messageId, chatId),
         updateChatMessageRetryState: (chatId, messageId, payload) => statements.updateChatMessageWithRetryState.run(
             payload.content,

src/routes/chats.js

@@ -91,6 +91,13 @@ const generationSettingsValidator = (body) => {
     }};
 };
 
+const preferredModelValidator = (body) => {
+    const model = String(body?.model || "").trim();
+    if (!model) return {error: "Model is required"};
+    if (model.length > 200) return {error: "Model must be 200 characters or fewer"};
+    return {value: {model}};
+};
+
 export function createChatsRouter({repositories, chatService, modelService, config, chatRateLimiters}) {
     const router = express.Router();
     router.use(requireLogin);
@@ -180,6 +187,13 @@ export function createChatsRouter({repositories, chatService, modelService, conf
         return res.json({chat: repositories.getChat(chatId, req.session.user)});
     });
 
+    router.put("/chats/:id/model", validateBody(preferredModelValidator), (req, res) => {
+        const chatId = Number(req.params.id);
+        if (!repositories.getChat(chatId, req.session.user)) return res.status(404).json({error: "Chat not found"});
+        repositories.updateChatPreferredModel(chatId, req.session.user, req.validatedBody.model);
+        return res.json({chat: repositories.getChat(chatId, req.session.user)});
+    });
+
     router.post("/chats/:id/branches/:messageId/activate", (req, res) => {
         const result = chatService.activateBranch({
             user: req.session.user,

src/services/chatService.js

@@ -65,7 +65,7 @@ export function createChatService(repositories, modelService, config) {
     };
 
     const getGenerationSettings = (session, requestedModel) => ({
-        model: session.preferred_model || requestedModel || "mistral:latest",
+        model: requestedModel || session.preferred_model || "mistral:latest",
         generation: {
             temperature: session.temperature ?? undefined,
             contextLength: session.context_length ?? undefined,

test/app.test.js

@@ -434,11 +434,17 @@ test("conversation branches, edit-resend, and generation settings work", async (
         body: {preferredModel: "preferred:model", temperature: 0.4, contextLength: 4096, responseLength: 300, systemInstruction: "Be exact."},
         jar
     });
-    await request(server.baseUrl, "/chat", {method: "POST", body: {chatId, message: "first", model: "ignored:model"}, jar});
-    assert.equal(calls[0].model, "preferred:model");
+    await request(server.baseUrl, "/chat", {method: "POST", body: {chatId, message: "first", model: "selected:model"}, jar});
+    assert.equal(calls[0].model, "selected:model");
     assert.deepEqual(calls[0].options.generation, {temperature: 0.4, contextLength: 4096, responseLength: 300});
     assert.match(calls[0].messages[0].content, /Be exact/);
 
+    const switchedModel = await request(server.baseUrl, `/chats/${chatId}/model`, {
+        method: "PUT", body: {model: "selected:model"}, jar
+    });
+    assert.equal(switchedModel.status, 200);
+    assert.equal(switchedModel.json.chat.preferred_model, "selected:model");
+
     await request(server.baseUrl, "/chat", {method: "POST", body: {chatId, message: "second", model: "ignored:model"}, jar});
     const original = await request(server.baseUrl, `/chats/${chatId}/messages`, {jar});
     const firstAssistant = original.json.messages[1];
@@ -470,7 +476,7 @@ test("conversation branches, edit-resend, and generation settings work", async (
     assert.equal(branched.json.chat.branched_from_message_id, firstAssistant.id);
     assert.match(branched.json.chat.title, /\(branch\)$/);
     assert.deepEqual(branched.json.messages.map((message) => message.content), ["first", "reply-1"]);
-    assert.equal(branched.json.chat.preferred_model, "preferred:model");
+    assert.equal(branched.json.chat.preferred_model, "selected:model");
     assert.equal(branched.json.chat.temperature, 0.4);
 
     const edited = await request(server.baseUrl, `/chats/${chatId}/messages/${active.json.messages[0].id}/edit-resend`, {