add support for switching preferred model per chat session

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,