Function detectPruning

agents/e2e/context-pruning-threshold.e2e.test.ts:230–273

* Detects whether context pruning occurred by checking for: * 1. tag (context-pruner's output) * 2. Previous message(s) omitted due to length (trimMessagesToFitTokenLimit fallback) * 3. Significant message count reduction (>50% fewer messages than original)

(
  finalMessages: Message[],
  originalMessageCount: number,
)

 * 3. Significant message count reduction (>50% fewer messages than original)
 */
function detectPruning(
  finalMessages: Message[],
  originalMessageCount: number,
): {
  wasPruned: boolean
  hasSummary: boolean
  hasTrimFallback: boolean
  messageReduction: number
} {
  const hasSummary = finalMessages.some((msg) => {
    if (msg.role !== 'user' || !Array.isArray(msg.content)) return false
    return msg.content.some(
      (part) =>
        typeof part === 'object' &&
        'type' in part &&
        part.type === 'text' &&
        typeof (part as any).text === 'string' &&
        (part as any).text.includes('<conversation_summary>'),
    )
  })

  const hasTrimFallback = finalMessages.some((msg) => {
    if (!Array.isArray(msg.content)) return false
    return msg.content.some(
      (part) =>
        typeof part === 'object' &&
        'type' in part &&
        part.type === 'text' &&
        typeof (part as any).text === 'string' &&
        (part as any).text.includes('Previous message(s) omitted'),
    )
  })

  // Message reduction: if fewer than 50% of original messages remain
  const messageReduction =
    originalMessageCount > 0
      ? 1 - finalMessages.length / originalMessageCount
      : 0

  const wasPruned =
    hasSummary || hasTrimFallback || messageReduction > 0.5

  return { wasPruned, hasSummary, hasTrimFallback, messageReduction }
}

/**
 * Verifies tool-call/tool-result pair integrity.