Function detectTurnInterruption

src/utils/conversationRecovery.ts:272–333

* Determines whether the conversation was interrupted mid-turn based on the * last message after filtering. An assistant as last message (after filtering * unresolved tool_uses) is treated as a completed turn because stop_reason is * always null on persisted messages in the streaming path. * *

(
  messages: NormalizedMessage[],
)

 * interruption. Attachments are kept as part of the turn.
 */
function detectTurnInterruption(
  messages: NormalizedMessage[],
): InternalInterruptionState {
  if (messages.length === 0) {
    return { kind: 'none' }
  }

  // Find the last turn-relevant message, skipping system/progress and
  // synthetic API error assistants. Error assistants are already filtered
  // before API send (normalizeMessagesForAPI) — skipping them here lets
  // auto-resume fire after retry exhaustion instead of reading the error as
  // a completed turn.
  const lastMessageIdx = messages.findLastIndex(
    m =>
      m.type !== 'system' &&
      m.type !== 'progress' &&
      !(m.type === 'assistant' && m.isApiErrorMessage),
  )
  const lastMessage =
    lastMessageIdx !== -1 ? messages[lastMessageIdx] : undefined

  if (!lastMessage) {
    return { kind: 'none' }
  }

  if (lastMessage.type === 'assistant') {
    // In the streaming path, stop_reason is always null on persisted messages
    // because messages are recorded at content_block_stop time, before
    // message_delta delivers the stop_reason. After filterUnresolvedToolUses
    // has removed assistant messages with unmatched tool_uses, an assistant as
    // the last message means the turn most likely completed normally.
    return { kind: 'none' }
  }

  if (lastMessage.type === 'user') {
    if (lastMessage.isMeta || lastMessage.isCompactSummary) {
      return { kind: 'none' }
    }
    if (isToolUseResultMessage(lastMessage)) {
      // Brief mode (#20467) drops the trailing assistant text block, so a
      // completed brief-mode turn legitimately ends on SendUserMessage's
      // tool_result. Without this check, resume misclassifies every
      // brief-mode session as interrupted mid-turn and injects a phantom
      // "Continue from where you left off." before the user's real next
      // prompt. Look back one step for the originating tool_use.
      if (isTerminalToolResult(lastMessage, messages, lastMessageIdx)) {
        return { kind: 'none' }
      }
      return { kind: 'interrupted_turn' }
    }
    // Plain text user prompt — CC hadn't started responding
    return { kind: 'interrupted_prompt', message: lastMessage }
  }

  if (lastMessage.type === 'attachment') {
    // Attachments are part of the user turn — the user provided context but
    // the assistant never responded.
    return { kind: 'interrupted_turn' }