[Obs AI Assistant] Fix passing of response language (#179064)

https://github.com/elastic/kibana/pull/178405 made some changes to how
the chat service passes data to the API, while doing this we missed to
pass along the `responseLanguage` setting, breaking the language
selection feature.

This PR just wires those up again and adds a test to catch this for the
future.

x-pack/plugins/observability_solution/observability_ai_assistant/public/service/complete.test.ts

@@ -98,6 +98,7 @@ describe('complete', () => {
         messages,
         persist: false,
         signal: new AbortController().signal,
+        responseLanguage: 'orcish',
         ...params,
       },
       requestCallback

x-pack/plugins/observability_solution/observability_ai_assistant/public/service/complete.ts

@@ -44,6 +44,7 @@ export function complete(
     messages: initialMessages,
     persist,
     signal,
+    responseLanguage,
   }: {
     client: Pick<ObservabilityAIAssistantChatService, 'chat' | 'complete'>;
     getScreenContexts: () => ObservabilityAIAssistantScreenContext[];
@@ -52,6 +53,7 @@ export function complete(
     messages: Message[];
     persist: boolean;
     signal: AbortSignal;
+    responseLanguage: string;
   },
   requestCallback: (
     params: ObservabilityAIAssistantAPIClientRequestParamsOf<'POST /internal/observability_ai_assistant/chat/complete'>
@@ -63,7 +65,14 @@ export function complete(
 
     const response$ = requestCallback({
       params: {
-        body: { connectorId, messages: initialMessages, persist, screenContexts, conversationId },
+        body: {
+          connectorId,
+          messages: initialMessages,
+          persist,
+          screenContexts,
+          conversationId,
+          responseLanguage,
+        },
       },
     }).pipe(
       filter(
@@ -134,6 +143,7 @@ export function complete(
               messages: initialMessages.concat(nextMessages),
               signal,
               persist,
+              responseLanguage,
             },
             requestCallback
           ).subscribe(subscriber);

x-pack/plugins/observability_solution/observability_ai_assistant/public/service/create_chat_service.test.ts

@@ -33,56 +33,55 @@ async function getConcatenatedMessage(
 }
 
 describe('createChatService', () => {
-  describe('chat', () => {
+  let service: ObservabilityAIAssistantChatService;
-    let service: ObservabilityAIAssistantChatService;
+  const clientSpy = jest.fn();
 
-    const clientSpy = jest.fn();
+  function respondWithChunks({ chunks, status = 200 }: { status?: number; chunks: string[] }) {
+    const response = {
+      response: {
+        status,
+        body: new ReadableStream({
+          start(controller) {
+            chunks.forEach((chunk) => {
+              controller.enqueue(new TextEncoder().encode(chunk));
+            });
+            controller.close();
+          },
+        }),
+      },
+    };
 
-    function respondWithChunks({ chunks, status = 200 }: { status?: number; chunks: string[] }) {
+    clientSpy.mockResolvedValueOnce(response);
-      const response = {
+  }
-        response: {
+
-          status,
+  beforeEach(async () => {
-          body: new ReadableStream({
+    clientSpy.mockImplementationOnce(async () => {
-            start(controller) {
+      return {
-              chunks.forEach((chunk) => {
+        functionDefinitions: [],
-                controller.enqueue(new TextEncoder().encode(chunk));
+        contextDefinitions: [],
-              });
-              controller.close();
-            },
-          }),
-        },
       };
+    });
+    service = await createChatService({
+      analytics: {
+        optIn: () => {},
+        reportEvent: () => {},
+        telemetryCounter$: new Observable(),
+      },
+      apiClient: clientSpy,
+      registrations: [],
+      signal: new AbortController().signal,
+    });
+  });
 
-      clientSpy.mockResolvedValueOnce(response);
+  afterEach(() => {
-    }
+    clientSpy.mockReset();
+  });
 
+  describe('chat', () => {
     function chat({ signal }: { signal: AbortSignal } = { signal: new AbortController().signal }) {
       return service.chat('my_test', { signal, messages: [], connectorId: '' });
     }
 
-    beforeEach(async () => {
-      clientSpy.mockImplementationOnce(async () => {
-        return {
-          functionDefinitions: [],
-          contextDefinitions: [],
-        };
-      });
-      service = await createChatService({
-        analytics: {
-          optIn: () => {},
-          reportEvent: () => {},
-          telemetryCounter$: new Observable(),
-        },
-        apiClient: clientSpy,
-        registrations: [],
-        signal: new AbortController().signal,
-      });
-    });
-
-    afterEach(() => {
-      clientSpy.mockReset();
-    });
-
     it('correctly parses a stream of JSON lines', async () => {
       const chunk1 =
         '{"id":"my-id","type":"chatCompletionChunk","message":{"content":"My"}}\n{"id":"my-id","type":"chatCompletionChunk","message":{"content":" new"}}';
@@ -230,4 +229,37 @@ describe('createChatService', () => {
       ).rejects.toEqual(expect.any(AbortError));
     });
   });
+
+  describe('complete', () => {
+    it("sends the user's preferred response language to the API", async () => {
+      respondWithChunks({
+        chunks: [
+          '{"id":"my-id","type":"chatCompletionChunk","message":{"content":"Some message"}}',
+        ],
+      });
+
+      const response$ = service.complete({
+        connectorId: '',
+        getScreenContexts: () => [],
+        messages: [],
+        persist: false,
+        signal: new AbortController().signal,
+        responseLanguage: 'orcish',
+      });
+
+      await getConcatenatedMessage(response$);
+
+      expect(clientSpy).toHaveBeenNthCalledWith(
+        2,
+        'POST /internal/observability_ai_assistant/chat/complete',
+        expect.objectContaining({
+          params: expect.objectContaining({
+            body: expect.objectContaining({
+              responseLanguage: 'orcish',
+            }),
+          }),
+        })
+      );
+    });
+  });
 });

x-pack/plugins/observability_solution/observability_ai_assistant/public/service/create_chat_service.ts

@@ -199,7 +199,15 @@ export async function createChatService({
         shareReplay()
       );
     },
-    complete({ getScreenContexts, connectorId, conversationId, messages, persist, signal }) {
+    complete({
+      getScreenContexts,
+      connectorId,
+      conversationId,
+      messages,
+      persist,
+      signal,
+      responseLanguage,
+    }) {
       return complete(
         {
           getScreenContexts,
@@ -209,6 +217,7 @@ export async function createChatService({
           persist,
           signal,
           client,
+          responseLanguage,
         },
         ({ params }) => {
           return from(