Fix

x-pack/packages/kbn-langchain/server/language_models/chat_vertex/chat_vertex.test.ts

@@ -54,8 +54,10 @@ const mockStreamExecute = jest.fn().mockImplementation(() => {
   };
 });
 
+const systemInstruction = 'Answer the following questions truthfully and as best you can.';
+
 const callMessages = [
-  new SystemMessage('Answer the following questions truthfully and as best you can.'),
+  new SystemMessage(systemInstruction),
   new HumanMessage('Question: Do you know my name?\n\n'),
 ] as unknown as BaseMessage[];
 
@@ -196,4 +198,29 @@ describe('ActionsClientChatVertexAI', () => {
       expect(handleLLMNewToken).toHaveBeenCalledWith('token3');
     });
   });
+
+  describe('message formatting', () => {
+    it('Properly sorts out the system role', async () => {
+      const actionsClientChatVertexAI = new ActionsClientChatVertexAI(defaultArgs);
+
+      await actionsClientChatVertexAI._generate(callMessages, callOptions, callRunManager);
+      const params = actionsClient.execute.mock.calls[0][0].params.subActionParams;
+      console.log(actionsClient.execute.mock.calls[0][0].params.subActionParams);
+      expect(params.messages.length).toEqual(1);
+      expect(params.messages[0].parts.length).toEqual(1);
+      expect(params.systemInstruction).toEqual(systemInstruction);
+    });
+    it('Handles 2 messages in a row from the same role', async () => {
+      const actionsClientChatVertexAI = new ActionsClientChatVertexAI(defaultArgs);
+
+      await actionsClientChatVertexAI._generate(
+        [...callMessages, new HumanMessage('Oh boy, another')],
+        callOptions,
+        callRunManager
+      );
+      const messages = actionsClient.execute.mock.calls[0][0].params.subActionParams.messages;
+      expect(messages.length).toEqual(1);
+      expect(messages[0].parts.length).toEqual(2);
+    });
+  });
 });

x-pack/packages/kbn-langchain/server/language_models/chat_vertex/connection.ts

@@ -39,6 +39,22 @@ export class ActionsClientChatConnection<Auth> extends ChatConnection<Auth> {
     this.caller = caller;
     this.#model = fields.model;
     this.temperature = fields.temperature ?? 0;
+    const nativeFormatData = this.formatData.bind(this);
+    this.formatData = async (data, options) => {
+      const result = await nativeFormatData(data, options);
+      if (result?.contents.length) {
+        // ensure there are not 2 messages in a row from the same role,
+        // if there are combine them
+        result.contents = result.contents.reduce((acc, currentEntry) => {
+          if (currentEntry.role === acc[acc.length - 1]?.role) {
+            acc[acc.length - 1].parts = acc[acc.length - 1].parts.concat(currentEntry.parts);
+            return acc;
+          }
+          return [...acc, currentEntry];
+        }, []);
+      }
+      return result;
+    };
   }
 
   async _request(