fix(ai): keep equal-timestamp compression boundaries intact

中文：避免同秒消息跨摘要边界，防止已压缩内容重复回放或后续消息丢失。

English: Keep equal-timestamp messages on one boundary side so compressed content is not replayed and later messages remain visible.

packages/node-runtime/src/ai/compression/__tests__/compressor.test.ts

@@ -26,6 +26,25 @@ function cleanup(dir: string): void {
   }
 }
 
+function spreadMessageTimestamps(manager: AIChatManager, chatId: string): void {
+  const messages = manager.getMessages(chatId)
+  const baseTimestamp = Math.floor(Date.now() / 1000) - messages.length
+  messages.forEach((message, index) => {
+    manager.executeAiSQL(`UPDATE ai_message SET timestamp = ${baseTimestamp + index} WHERE id = '${message.id}'`)
+  })
+}
+
+function addMessageAt(
+  manager: AIChatManager,
+  chatId: string,
+  role: 'user' | 'assistant',
+  content: string,
+  timestamp: number
+): void {
+  const message = manager.addMessage(chatId, role, content)
+  manager.executeAiSQL(`UPDATE ai_message SET timestamp = ${timestamp} WHERE id = '${message.id}'`)
+}
+
 const CONFIG: CompressionConfig = {
   tokenThresholdPercent: 75,
   bufferSizePercent: 20,
@@ -74,10 +93,74 @@ function seedToolHeavyChat(manager: AIChatManager, withToolResults: boolean): st
   manager.addMessage(chat.id, 'assistant', 'more stats', undefined, undefined, [toolBlock('query_b', result2)])
   manager.addMessage(chat.id, 'user', 'thanks')
   manager.addMessage(chat.id, 'assistant', 'you are welcome')
+  spreadMessageTimestamps(manager, chat.id)
   return chat.id
 }
 
 describe('checkAndCompress tool result token accounting', () => {
+  it('keeps equal-timestamp messages on the buffer side of the compression boundary', async () => {
+    const dir = createTempDir()
+    const manager = createManager(dir)
+    try {
+      const baseTimestamp = 2_000_000_000
+      const chat = manager.createAIChat('session-1', 'Compression boundary', 'general_cn')
+      for (let index = 0; index < 4; index++) {
+        addMessageAt(
+          manager,
+          chat.id,
+          index % 2 === 0 ? 'user' : 'assistant',
+          `old-${index} ${'old '.repeat(150)}`,
+          baseTimestamp + index
+        )
+      }
+      addMessageAt(manager, chat.id, 'user', `BOUNDARY_USER ${'user '.repeat(180)}`, baseTimestamp + 10)
+      addMessageAt(manager, chat.id, 'assistant', `BOUNDARY_ASSISTANT ${'assistant '.repeat(60)}`, baseTimestamp + 10)
+
+      const adapter: CompressionLlmAdapter = {
+        contextWindow: 1000,
+        compress: async (prompt: string) =>
+          prompt.includes('BOUNDARY_USER') ? 'SUMMARY_CONTAINS_BOUNDARY_USER' : 'SUMMARY_SAFE',
+      }
+
+      const result = await checkAndCompress(chat.id, CONFIG, 'system', adapter, manager)
+
+      assert.equal(result.compressed, true)
+      assert.deepEqual(
+        manager.getHistoryForAgent(chat.id).map((message) => message.content.split(' ')[0]),
+        ['SUMMARY_SAFE', 'BOUNDARY_USER', 'BOUNDARY_ASSISTANT']
+      )
+
+      const largeChat = manager.createAIChat('session-1', 'Large compression boundary', 'general_cn')
+      for (let index = 0; index < 4; index++) {
+        addMessageAt(
+          manager,
+          largeChat.id,
+          index % 2 === 0 ? 'user' : 'assistant',
+          `old-${index} ${'old '.repeat(180)}`,
+          baseTimestamp + index
+        )
+      }
+      addMessageAt(manager, largeChat.id, 'assistant', `LATEST_ASSISTANT ${'latest '.repeat(260)}`, baseTimestamp + 10)
+      const largeResult = await checkAndCompress(
+        largeChat.id,
+        CONFIG,
+        'system',
+        createAdapter({ prompt: null }),
+        manager
+      )
+      addMessageAt(manager, largeChat.id, 'user', 'NEXT_USER', baseTimestamp + 10)
+
+      assert.equal(largeResult.compressed, true)
+      assert.deepEqual(
+        manager.getHistoryForAgent(largeChat.id).map((message) => message.content.split(' ')[0]),
+        ['COMPRESSED', 'LATEST_ASSISTANT', 'NEXT_USER']
+      )
+    } finally {
+      manager.close()
+      cleanup(dir)
+    }
+  })
+
   it('counts replayed tool results toward the compression threshold', async () => {
     const dir = createTempDir()
     const manager = createManager(dir)
@@ -141,6 +224,7 @@ describe('checkAndCompress tool result token accounting', () => {
       ])
       manager.addMessage(chat.id, 'user', 'thanks')
       manager.addMessage(chat.id, 'assistant', 'you are welcome')
+      spreadMessageTimestamps(manager, chat.id)
 
       const captured: { prompt: string | null } = { prompt: null }
       const result = await checkAndCompress(chat.id, CONFIG, 'system', createAdapter(captured), manager)
@@ -177,6 +261,7 @@ describe('checkAndCompress tool result token accounting', () => {
       ])
       manager.addMessage(chat.id, 'user', 'continue')
       manager.addMessage(chat.id, 'assistant', 'done')
+      spreadMessageTimestamps(manager, chat.id)
 
       const captured: { prompt: string | null } = { prompt: null }
       const result = await checkAndCompress(chat.id, CONFIG, 'system', createAdapter(captured), manager)

packages/node-runtime/src/ai/compression/compressor.ts

@@ -274,6 +274,12 @@ function splitMessagesForCompression<T extends CompressibleMessage>(
     }
   }
 
+  // Summary boundaries have second precision, so equal-timestamp messages must stay together.
+  if (splitIndex > 0) {
+    const boundaryTimestamp = messages[Math.min(splitIndex, messages.length - 1)]!.timestamp
+    while (splitIndex > 0 && messages[splitIndex - 1]!.timestamp === boundaryTimestamp) splitIndex--
+  }
+
   return {
     bufferMessages: messages.slice(splitIndex),
     messagesToCompress: messages.slice(0, splitIndex),