Function copyFileHistoryForResume

src/utils/fileHistory.ts:924–1048

(log: LogOption)

 * Copy file history snapshots for a given log option.
 */
export async function copyFileHistoryForResume(log: LogOption): Promise<void> {
  if (!fileHistoryEnabled()) {
    return
  }

  const fileHistorySnapshots = log.fileHistorySnapshots
  if (!fileHistorySnapshots || log.messages.length === 0) {
    return
  }
  const lastMessage = log.messages[log.messages.length - 1]
  const previousSessionId = lastMessage?.sessionId
  if (!previousSessionId) {
    logError(
      new Error(
        `FileHistory: Failed to copy backups on restore (no previous session id)`,
      ),
    )
    return
  }

  const sessionId = getSessionId()
  if (previousSessionId === sessionId) {
    logForDebugging(
      `FileHistory: No need to copy file history for resuming with same session id: ${sessionId}`,
    )
    return
  }

  try {
    // All backups share the same directory: {configDir}/file-history/{sessionId}/
    // Create it once upfront instead of once per backup file
    const newBackupDir = join(
      getClaudeConfigHomeDir(),
      'file-history',
      sessionId,
    )
    await mkdir(newBackupDir, { recursive: true })

    // Migrate all backup files from the previous session to current session.
    // Process all snapshots in parallel; within each snapshot, links also run in parallel.
    let failedSnapshots = 0
    await Promise.allSettled(
      fileHistorySnapshots.map(async snapshot => {
        const backupEntries = Object.values(snapshot.trackedFileBackups).filter(
          (backup): backup is typeof backup & { backupFileName: string } =>
            backup.backupFileName !== null,
        )

        const results = await Promise.allSettled(
          backupEntries.map(async ({ backupFileName }) => {
            const oldBackupPath = resolveBackupPath(
              backupFileName,
              previousSessionId,
            )
            const newBackupPath = join(newBackupDir, backupFileName)

            try {
              await link(oldBackupPath, newBackupPath)