Function filterTrailingThinkingFromLastAssistant

src/utils/messages.ts:4781–4828

* Filter trailing thinking blocks from the last message if it's an assistant message. * The API doesn't allow assistant messages to end with thinking/redacted_thinking blocks.

(
  messages: (UserMessage | AssistantMessage)[],
)

 * The API doesn't allow assistant messages to end with thinking/redacted_thinking blocks.
 */
function filterTrailingThinkingFromLastAssistant(
  messages: (UserMessage | AssistantMessage)[],
): (UserMessage | AssistantMessage)[] {
  const lastMessage = messages.at(-1)
  if (!lastMessage || lastMessage.type !== 'assistant') {
    // Last message is not assistant, nothing to filter
    return messages
  }

  const content = lastMessage.message.content
  const lastBlock = content.at(-1)
  if (!lastBlock || !isThinkingBlock(lastBlock)) {
    return messages
  }

  // Find last non-thinking block
  let lastValidIndex = content.length - 1
  while (lastValidIndex >= 0) {
    const block = content[lastValidIndex]
    if (!block || !isThinkingBlock(block)) {
      break
    }
    lastValidIndex--
  }

  logEvent('tengu_filtered_trailing_thinking_block', {
    messageUUID:
      lastMessage.uuid as AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
    blocksRemoved: content.length - lastValidIndex - 1,
    remainingBlocks: lastValidIndex + 1,
  })

  // Insert placeholder if all blocks were thinking
  const filteredContent =
    lastValidIndex < 0
      ? [{ type: 'text' as const, text: '[No message content]', citations: [] }]
      : content.slice(0, lastValidIndex + 1)

  const result = [...messages]
  result[messages.length - 1] = {
    ...lastMessage,
    message: {
      ...lastMessage.message,
      content: filteredContent,
    },
  }
  return result
}

/**
 * Check if an assistant message has only whitespace-only text content blocks.