Chat title generation

docs/api/rest.md

@@ -41,6 +41,25 @@ Content type:
 - Body: `{ "title"?: string }`
 - Response: `{ "chat": ChatSummary }`
 
+### `PATCH /v1/chats/:chatId`
+- Body: `{ "title": string }`
+- Response: `{ "chat": ChatSummary }`
+- Not found: `404 { "message": "chat not found" }`
+
+### `POST /v1/chats/title/suggest`
+- Body:
+```json
+{
+  "chatId": "chat-id",
+  "content": "user request text"
+}
+```
+- Response: `{ "chat": ChatSummary }`
+
+Behavior notes:
+- If the chat already has a non-empty title, server returns the existing chat unchanged.
+- Server always uses OpenAI `gpt-4.1-mini` to generate a one-line title (up to ~4 words), updates the chat title, and returns the updated chat.
+
 ### `DELETE /v1/chats/:chatId`
 - Response: `{ "deleted": true }`
 - Not found: `404 { "message": "chat not found" }`