Function copyPlanForFork

src/utils/plans.ts:239–264

(
  log: LogOption,
  targetSessionId: SessionId,
)

 * and forked sessions from clobbering each other's plan files.
 */
export async function copyPlanForFork(
  log: LogOption,
  targetSessionId: SessionId,
): Promise<boolean> {
  const originalSlug = getSlugFromLog(log)
  if (!originalSlug) {
    return false
  }

  const plansDir = getPlansDirectory()
  const originalPlanPath = join(plansDir, `${originalSlug}.md`)

  // Generate a new slug for the forked session (do NOT reuse the original)
  const newSlug = getPlanSlug(targetSessionId)
  const newPlanPath = join(plansDir, `${newSlug}.md`)
  try {
    await copyFile(originalPlanPath, newPlanPath)
    return true
  } catch (error) {
    if (isENOENT(error)) {
      return false
    }
    logError(error)
    return false
  }
}

/**
 * Recover plan content from the message history. Plan content can appear in