Function undo

packages/arctic/src/session/benchmark.ts:282–327

(input: { sessionID: string; allowDirty?: boolean })

   * Manual edits made BEFORE apply are preserved (they're in the checkpoint).
   */
  export async function undo(input: { sessionID: string; allowDirty?: boolean }) {
    return withWorktreeLock(async () => {
      const parent = await resolveParent(input.sessionID)
      if (!parent || !isParent(parent)) return parent ?? Session.get(input.sessionID)

      const dirty = await isDirty()
      if (!input.allowDirty && dirty) {
        throw new WorkingTreeDirtyError({ message: "Working tree has uncommitted changes." })
      }

      if (!parent.benchmark.appliedSessionID) {
        // Nothing applied, nothing to undo
        return parent
      }

      if (!parent.benchmark.checkpointSnapshot) {
        throw new SnapshotUnavailableError({
          message: "No checkpoint snapshot available to undo.",
        })
      }

      const appliedSnapshot = await Snapshot.track()
      if (!appliedSnapshot) {
        throw new SnapshotUnavailableError({
          message: "Benchmark mode requires snapshots (git) to be enabled.",
        })
      }

      const appliedChild = await Session.get(parent.benchmark.appliedSessionID)
      if (isChild(appliedChild) && appliedChild.benchmark.parentID === parent.id) {
        await updateChildSnapshot(appliedChild.id, appliedSnapshot)
        const appliedChildWorktree = await ensureChildWorktree(parent, appliedChild)
        await Snapshot.restoreTo(appliedSnapshot, appliedChildWorktree, { cleanUntracked: true })
      }

      // Simply restore the checkpoint
      await Snapshot.restoreTo(parent.benchmark.checkpointSnapshot, Instance.worktree, { cleanUntracked: true })

      return Session.update(parent.id, (draft) => {
        if (draft.benchmark?.type === "parent") {
          draft.benchmark.appliedSessionID = undefined
          draft.benchmark.checkpointSnapshot = undefined
        }
      })
    })
  }

  export function hasDuplicates(models: BenchmarkSchema.Model[]) {
    const seen = new Set<string>()