fix(runner): extract last assistant message, not first, from snapshot

GRPCMessageWriter used next() to find the first assistant message in
MESSAGES_SNAPSHOT, which in multi-turn runs is a tool-call-only message
with content=None. The real final response is in the last assistant
message. Iterate to find the last one with actual content.

Remove the fragile UI-side enrichMessages workaround that tried to
extract last_assistant_message from nearby hook:Stop system events.
Replace with simple filterEmptyMessages that drops empty assistant
records (which should no longer occur with the runner fix).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jsell-rh

components/ambient-ui/src/components/__tests__/chat-messages.test.ts

@@ -3,8 +3,7 @@ import type { DomainSessionMessage } from '@/domain/types'
 import {
   tryParseToolPayload,
   tryParseToolResult,
-  extractLastAssistantMessage,
-  enrichMessages,
+  filterEmptyMessages,
   groupChatItems,
   buildChatItems,
 } from '../chat-messages'
@@ -111,95 +110,35 @@ describe('tryParseToolResult', () => {
   })
 })
 
-// ---- extractLastAssistantMessage ----
+// ---- filterEmptyMessages ----
 
-describe('extractLastAssistantMessage', () => {
-  it('extracts last_assistant_message from a system event payload', () => {
-    const payload = JSON.stringify({
-      value: { last_assistant_message: 'Hello from the assistant' },
-    })
-    expect(extractLastAssistantMessage(payload)).toBe('Hello from the assistant')
-  })
-
-  it('returns null when last_assistant_message is missing', () => {
-    const payload = JSON.stringify({ value: { other_field: 'x' } })
-    expect(extractLastAssistantMessage(payload)).toBeNull()
-  })
-
-  it('returns null when last_assistant_message is whitespace-only', () => {
-    const payload = JSON.stringify({ value: { last_assistant_message: '   ' } })
-    expect(extractLastAssistantMessage(payload)).toBeNull()
-  })
-
-  it('returns null when value is not an object', () => {
-    const payload = JSON.stringify({ value: 'string-value' })
-    expect(extractLastAssistantMessage(payload)).toBeNull()
-  })
-
-  it('returns null for invalid JSON', () => {
-    expect(extractLastAssistantMessage('not json')).toBeNull()
-  })
-
-  it('returns null for a JSON array', () => {
-    expect(extractLastAssistantMessage('[1]')).toBeNull()
-  })
-})
-
-// ---- enrichMessages ----
-
-describe('enrichMessages', () => {
-  it('enriches empty assistant messages from a preceding system event', () => {
-    const messages = [
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({
-          value: { last_assistant_message: 'Extracted text' },
-        }),
-      }),
-      makeMsg({ eventType: 'assistant', payload: '' }),
-    ]
-
-    const result = enrichMessages(messages)
-    expect(result).toHaveLength(2)
-    // The system event passes through
-    expect(result[0].eventType).toBe('system')
-    // The assistant message is enriched
-    expect(result[1].eventType).toBe('assistant')
-    expect(result[1].payload).toBe('Extracted text')
-  })
-
-  it('drops empty assistant messages with no nearby system event', () => {
+describe('filterEmptyMessages', () => {
+  it('drops empty assistant messages', () => {
     const messages = [
       makeMsg({ eventType: 'user', payload: 'hello' }),
       makeMsg({ eventType: 'assistant', payload: '' }),
     ]
 
-    const result = enrichMessages(messages)
+    const result = filterEmptyMessages(messages)
     expect(result).toHaveLength(1)
     expect(result[0].eventType).toBe('user')
   })
 
-  it('drops empty assistant messages when system event lacks last_assistant_message', () => {
+  it('drops whitespace-only assistant messages', () => {
     const messages = [
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({ value: { some_other: 'data' } }),
-      }),
-      makeMsg({ eventType: 'assistant', payload: '' }),
+      makeMsg({ eventType: 'assistant', payload: '   ' }),
     ]
 
-    const result = enrichMessages(messages)
-    // System passes through, empty assistant is dropped
-    expect(result).toHaveLength(1)
-    expect(result[0].eventType).toBe('system')
+    const result = filterEmptyMessages(messages)
+    expect(result).toHaveLength(0)
   })
 
-  it('passes through non-empty assistant messages unchanged', () => {
+  it('passes through non-empty assistant messages', () => {
     const messages = [
       makeMsg({ eventType: 'assistant', payload: 'I have content' }),
     ]
 
-    const result = enrichMessages(messages)
+    const result = filterEmptyMessages(messages)
     expect(result).toHaveLength(1)
     expect(result[0].payload).toBe('I have content')
   })
@@ -211,49 +150,10 @@ describe('enrichMessages', () => {
       makeMsg({ eventType: 'lifecycle', payload: 'started' }),
     ]
 
-    const result = enrichMessages(messages)
+    const result = filterEmptyMessages(messages)
     expect(result).toHaveLength(3)
     expect(result.map(m => m.eventType)).toEqual(['user', 'tool_use', 'lifecycle'])
   })
-
-  it('looks back up to 3 positions for a system event', () => {
-    const messages = [
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({
-          value: { last_assistant_message: 'Found it' },
-        }),
-      }),
-      makeMsg({ eventType: 'user', payload: 'filler1' }),
-      makeMsg({ eventType: 'user', payload: 'filler2' }),
-      makeMsg({ eventType: 'assistant', payload: '' }),
-    ]
-
-    const result = enrichMessages(messages)
-    const assistant = result.find(m => m.eventType === 'assistant')
-    expect(assistant).toBeDefined()
-    expect(assistant!.payload).toBe('Found it')
-  })
-
-  it('does not look back more than 3 positions', () => {
-    const messages = [
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({
-          value: { last_assistant_message: 'Too far' },
-        }),
-      }),
-      makeMsg({ eventType: 'user', payload: 'a' }),
-      makeMsg({ eventType: 'user', payload: 'b' }),
-      makeMsg({ eventType: 'user', payload: 'c' }),
-      makeMsg({ eventType: 'assistant', payload: '' }),
-    ]
-
-    const result = enrichMessages(messages)
-    // The empty assistant should be dropped since system event is 4 positions back
-    const assistant = result.find(m => m.eventType === 'assistant')
-    expect(assistant).toBeUndefined()
-  })
 })
 
 // ---- groupChatItems ----
@@ -371,12 +271,7 @@ describe('buildChatItems', () => {
     const messages = [
       makeMsg({ eventType: 'user', payload: 'Fix the bug' }),
       makeMsg({ eventType: 'lifecycle', payload: 'session_started' }),
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({
-          value: { last_assistant_message: 'I will fix the bug.' },
-        }),
-      }),
+      makeMsg({ eventType: 'system', payload: '{}' }),
       makeMsg({ eventType: 'assistant', payload: '' }),
       makeMsg({
         eventType: 'tool_use',
@@ -391,31 +286,25 @@ describe('buildChatItems', () => {
 
     const items = buildChatItems(messages)
 
-    // lifecycle and system events are filtered out
+    // lifecycle, system, and empty assistant are filtered out
     const kinds = items.map(i => i.kind)
-    expect(kinds).toEqual(['message', 'message', 'tool_call', 'message'])
+    expect(kinds).toEqual(['message', 'tool_call', 'message'])
 
     // First message is the user message
     if (items[0].kind === 'message') {
       expect(items[0].message.eventType).toBe('user')
       expect(items[0].message.payload).toBe('Fix the bug')
     }
 
-    // Second message is the enriched assistant
-    if (items[1].kind === 'message') {
-      expect(items[1].message.eventType).toBe('assistant')
-      expect(items[1].message.payload).toBe('I will fix the bug.')
-    }
-
     // Tool call is grouped
-    if (items[2].kind === 'tool_call') {
-      expect(items[2].group.toolResult).not.toBeNull()
+    if (items[1].kind === 'tool_call') {
+      expect(items[1].group.toolResult).not.toBeNull()
     }
 
-    // Final assistant message
-    if (items[3].kind === 'message') {
-      expect(items[3].message.eventType).toBe('assistant')
-      expect(items[3].message.payload).toBe('Done fixing.')
+    // Final assistant message (with content)
+    if (items[2].kind === 'message') {
+      expect(items[2].message.eventType).toBe('assistant')
+      expect(items[2].message.payload).toBe('Done fixing.')
     }
   })
 
@@ -433,23 +322,13 @@ describe('buildChatItems', () => {
     }
   })
 
-  it('includes enriched empty assistant messages derived from system events', () => {
+  it('drops empty assistant messages', () => {
     const messages = [
-      makeMsg({
-        eventType: 'system',
-        payload: JSON.stringify({
-          value: { last_assistant_message: 'Enriched reply' },
-        }),
-      }),
       makeMsg({ eventType: 'assistant', payload: '' }),
     ]
 
     const items = buildChatItems(messages)
-    expect(items).toHaveLength(1)
-    if (items[0].kind === 'message') {
-      expect(items[0].message.eventType).toBe('assistant')
-      expect(items[0].message.payload).toBe('Enriched reply')
-    }
+    expect(items).toHaveLength(0)
   })
 
   it('returns empty array when given no messages', () => {

components/ambient-ui/src/components/chat-messages.tsx

@@ -88,46 +88,12 @@ export function tryFormatJson(payload: string): string {
   }
 }
 
-// ---- Message Enrichment ----
+// ---- Message Filtering ----
 
-export function extractLastAssistantMessage(payload: string): string | null {
-  try {
-    const parsed: unknown = JSON.parse(payload)
-    if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) return null
-    const obj = parsed as Record<string, unknown>
-    if (typeof obj.value !== 'object' || obj.value === null) return null
-    const value = obj.value as Record<string, unknown>
-    if (typeof value.last_assistant_message === 'string' && value.last_assistant_message.trim()) {
-      return value.last_assistant_message
-    }
-    return null
-  } catch {
-    return null
-  }
-}
-
-export function enrichMessages(messages: DomainSessionMessage[]): DomainSessionMessage[] {
-  const enriched: DomainSessionMessage[] = []
-  for (let i = 0; i < messages.length; i++) {
-    const msg = messages[i]
-    if (msg.eventType === 'assistant' && !msg.payload.trim()) {
-      for (let j = i - 1; j >= Math.max(0, i - 3); j--) {
-        if (messages[j].eventType === 'system') {
-          const extracted = extractLastAssistantMessage(messages[j].payload)
-          if (extracted) {
-            enriched.push({ ...msg, payload: extracted })
-            break
-          }
-        }
-      }
-      // Empty assistant messages with no extractable text are dropped — the
-      // runner sometimes pushes an empty "assistant" record alongside a system
-      // event that contains the actual response in last_assistant_message.
-      continue
-    }
-    enriched.push(msg)
-  }
-  return enriched
+export function filterEmptyMessages(messages: DomainSessionMessage[]): DomainSessionMessage[] {
+  return messages.filter(
+    (msg) => !(msg.eventType === 'assistant' && !msg.payload.trim()),
+  )
 }
 
 // ---- Tool Call Grouping ----
@@ -474,7 +440,7 @@ export function ChatItemsList({
 
 /** Filter and group raw messages into chat items */
 export function buildChatItems(messages: DomainSessionMessage[]): ChatItem[] {
-  const enriched = enrichMessages(messages)
-  const chatOnly = enriched.filter(m => CHAT_EVENT_TYPES.has(m.eventType))
+  const filtered = filterEmptyMessages(messages)
+  const chatOnly = filtered.filter(m => CHAT_EVENT_TYPES.has(m.eventType))
   return groupChatItems(chatOnly)
 }