Function ensureNonEmptyAssistantContent

src/utils/messages.ts:4933–4977

* Ensure all non-final assistant messages have non-empty content. * * The API requires "all messages must have non-empty content except for the * optional final assistant message". This can happen when the model returns * an empty content array. * * For non-final assistant messages with empty

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

 * Note: Whitespace-only text content is handled separately by filterWhitespaceOnlyAssistantMessages.
 */
function ensureNonEmptyAssistantContent(
  messages: (UserMessage | AssistantMessage)[],
): (UserMessage | AssistantMessage)[] {
  if (messages.length === 0) {
    return messages
  }

  let hasChanges = false
  const result = messages.map((message, index) => {
    // Skip non-assistant messages
    if (message.type !== 'assistant') {
      return message
    }

    // Skip the final message (allowed to be empty for prefill)
    if (index === messages.length - 1) {
      return message
    }

    // Check if content is empty
    const content = message.message.content
    if (Array.isArray(content) && content.length === 0) {
      hasChanges = true
      logEvent('tengu_fixed_empty_assistant_content', {
        messageUUID:
          message.uuid as AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
        messageIndex: index,
      })

      return {
        ...message,
        message: {
          ...message.message,
          content: [
            { type: 'text' as const, text: NO_CONTENT_MESSAGE, citations: [] },
          ],
        },
      }
    }

    return message
  })

  return hasChanges ? result : messages
}

/**
 * Filter orphaned thinking-only assistant messages.