Show AI log assistant with fallback message fields (#243437)

The AI assistant on log messages was only showing if the field was
`message` and not falling back if `exception.message` or oher fields are
used.

| before | after |
| --- | --- |
| <img width="1042" height="1710" alt="Image"
src="https://github.com/user-attachments/assets/995891c2-d145-42ae-9f30-2e43585a47de"
/>| <img width="1066" height="1734" alt="CleanShot 2025-11-18 at 22 52
30@2x"
src="https://github.com/user-attachments/assets/9fe8fc87-7704-4e8e-b35d-8e7e4fe72579"
/> |

Fixes #243436

Author: smith

x-pack/platform/plugins/shared/logs_shared/public/components/log_ai_assistant/log_ai_assistant.test.tsx

@@ -0,0 +1,43 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import type { Message } from '@kbn/observability-ai-assistant-plugin/common';
+import { observabilityAIAssistantPluginMock } from '@kbn/observability-ai-assistant-plugin/public/mock';
+import { render } from '@testing-library/react';
+import React from 'react';
+import { LogAIAssistant } from './log_ai_assistant';
+
+const observabilityAIAssistant = observabilityAIAssistantPluginMock.createStartContract();
+jest
+  .spyOn(observabilityAIAssistant, 'getContextualInsightMessages')
+  .mockReturnValue([{ message: { content: 'hello' } } as Message]);
+
+describe('LogAIAssistant', () => {
+  describe('when a message field is present', () => {
+    it('shows the assistant panel', () => {
+      const doc = { fields: [{ field: 'message', value: ['hello'] }] };
+
+      const elements = render(
+        <LogAIAssistant doc={doc} observabilityAIAssistant={observabilityAIAssistant} />
+      );
+
+      expect(elements.container.getElementsByClassName('euiFlexGroup').length).toBe(1);
+    });
+  });
+
+  describe('when an alternate message field is present', () => {
+    it('shows the assistant panel', () => {
+      const doc = { fields: [{ field: 'exception.message', value: ['hello'] }] };
+
+      const elements = render(
+        <LogAIAssistant doc={doc} observabilityAIAssistant={observabilityAIAssistant} />
+      );
+
+      expect(elements.container.getElementsByClassName('euiFlexGroup').length).toBe(1);
+    });
+  });
+});

x-pack/platform/plugins/shared/logs_shared/public/components/log_ai_assistant/log_ai_assistant.tsx

@@ -7,6 +7,7 @@
 
 import React, { useMemo } from 'react';
 import { EuiFlexGroup, EuiFlexItem } from '@elastic/eui';
+import { type LogDocumentOverview, getMessageFieldWithFallbacks } from '@kbn/discover-utils';
 import type {
   Message,
   ObservabilityAIAssistantPublicStart,
@@ -35,7 +36,7 @@ export const LogAIAssistant = ({
       return undefined;
     }
 
-    const message = doc.fields.find((field) => field.field === 'message')?.value[0];
+    const message = getMessageFieldWithFallbacks(doc as unknown as LogDocumentOverview);
 
     if (!message) {
       return undefined;