Function mergeUserMessages

src/utils/messages.ts:2411–2449

(a: UserMessage, b: UserMessage)

}

export function mergeUserMessages(a: UserMessage, b: UserMessage): UserMessage {
  const lastContent = normalizeUserTextContent(a.message.content)
  const currentContent = normalizeUserTextContent(b.message.content)
  if (feature('HISTORY_SNIP')) {
    // A merged message is only meta if ALL merged messages are meta. If any
    // operand is real user content, the result must not be flagged isMeta
    // (so [id:] tags get injected and it's treated as user-visible content).
    // Gated behind the full runtime check because changing isMeta semantics
    // affects downstream callers (e.g., VCR fixture hashing in SDK harness
    // tests), so this must only fire when snip is actually enabled — not
    // for all ants.
    const { isSnipRuntimeEnabled } =
      // eslint-disable-next-line @typescript-eslint/no-require-imports
      require('../services/compact/snipCompact.js') as typeof import('../services/compact/snipCompact.js')
    if (isSnipRuntimeEnabled()) {
      return {
        ...a,
        isMeta: a.isMeta && b.isMeta ? (true as const) : undefined,
        uuid: a.isMeta ? b.uuid : a.uuid,
        message: {
          ...a.message,
          content: hoistToolResults(
            joinTextAtSeam(lastContent, currentContent),
          ),
        },
      }
    }
  }
  return {
    ...a,
    // Preserve the non-meta message's uuid so [id:] tags (derived from uuid)
    // stay stable across API calls (meta messages like system context get fresh uuids each call)
    uuid: a.isMeta ? b.uuid : a.uuid,
    message: {
      ...a.message,
      content: hoistToolResults(joinTextAtSeam(lastContent, currentContent)),
    },
  }
}

function mergeAdjacentUserMessages(
  msgs: (UserMessage | AssistantMessage)[],