revert /reply to previous behavior (replacing session history) when full conversation provided (#6058)

ui/desktop/openapi.json

@@ -2715,15 +2715,16 @@
       "ChatRequest": {
         "type": "object",
         "required": [
-          "messages",
+          "user_message",
           "session_id"
         ],
         "properties": {
-          "messages": {
+          "conversation_so_far": {
             "type": "array",
             "items": {
               "$ref": "#/components/schemas/Message"
-            }
+            },
+            "nullable": true
           },
           "recipe_name": {
             "type": "string",
@@ -2735,6 +2736,9 @@
           },
           "session_id": {
             "type": "string"
+          },
+          "user_message": {
+            "$ref": "#/components/schemas/Message"
           }
         }
       },

ui/desktop/src/api/types.gen.ts

@@ -59,10 +59,11 @@ export type CallToolResponse = {
 };
 
 export type ChatRequest = {
-    messages: Array<Message>;
+    conversation_so_far?: Array<Message> | null;
     recipe_name?: string | null;
     recipe_version?: string | null;
     session_id: string;
+    user_message: Message;
 };
 
 export type CheckProviderRequest = {

ui/desktop/src/hooks/useChatStream.ts

@@ -292,12 +292,13 @@ export function useChatStream({
         window.dispatchEvent(new CustomEvent('session-created'));
       }
 
-      // Build message list: add new message if provided, otherwise continue with existing
+      const newMessage = hasNewMessage
+        ? createUserMessage(userMessage)
+        : messagesRef.current[messagesRef.current.length - 1];
       const currentMessages = hasNewMessage
-        ? [...messagesRef.current, createUserMessage(userMessage)]
+        ? [...messagesRef.current, newMessage]
         : [...messagesRef.current];
 
-      // Update UI with new message before streaming
       if (hasNewMessage) {
         updateMessages(currentMessages);
       }
@@ -310,7 +311,7 @@ export function useChatStream({
         const { stream } = await reply({
           body: {
             session_id: sessionId,
-            messages: currentMessages,
+            user_message: newMessage,
           },
           throwOnError: true,
           signal: abortControllerRef.current.signal,
@@ -356,7 +357,7 @@ export function useChatStream({
         const { stream } = await reply({
           body: {
             session_id: sessionId,
-            messages: currentMessages,
+            user_message: responseMessage,
           },
           throwOnError: true,
           signal: abortControllerRef.current.signal,