feat: Introduce optional session ID for helix app

packages/backend/src/apps/helix/actions/new-chat/index.js

@@ -13,11 +13,20 @@ export default defineAction({
       description: 'Prompt to start the chat with.',
       variables: true,
     },
+    {
+      label: 'Session ID',
+      key: 'sessionId',
+      type: 'string',
+      required: false,
+      description:
+        'ID of the chat session to continue. Leave empty to start a new chat.',
+      variables: true,
+    },
   ],
 
   async run($) {
     const response = await $.http.post('/api/v1/sessions/chat', {
-      session_id: '',
+      session_id: $.step.parameters.sessionId,
       messages: [
         {
           role: 'user',