## ADDED Requirements

### Requirement: Snapshot creation

The system SHALL provide `sandbox.snapshot()` to create a point-in-time filesystem snapshot.

Parameters:
- `expiration?: number` — TTL in milliseconds (0 for no expiration)

#### Scenario: Snapshot stops the session and returns Snapshot instance

- **WHEN** `sandbox.snapshot()` is called on a running sandbox
- **THEN** the current session SHALL be stopped and a `Snapshot` SHALL be returned

### Requirement: Snapshot retrieval and listing

The system SHALL provide `Snapshot.get()`, `Snapshot.list()`, and `Snapshot.tree()` for managing snapshots.

#### Scenario: Retrieve snapshot by ID

- **WHEN** `Snapshot.get({ snapshotId: "snap_abc" })` is called
- **THEN** it SHALL return the snapshot with matching ID

#### Scenario: List snapshots with pagination

- **WHEN** `Snapshot.list({ name: "my-sandbox" })` is called
- **THEN** it SHALL return a paginated list of snapshots for that sandbox

#### Scenario: Ancestry tree is accessible

- **WHEN** `Snapshot.tree({ snapshotId: "snap_abc" })` is called
- **THEN** it SHALL return the ancestry tree of the snapshot

### Requirement: Snapshot deletion

The system SHALL provide `snapshot.delete()` to remove a snapshot.

#### Scenario: Deleted snapshot is no longer listable

- **WHEN** `snapshot.delete()` is called and then `Snapshot.list()` is called
- **THEN** the deleted snapshot SHALL no longer appear in the list

### Requirement: Snapshot-based sandbox creation

The system SHALL support creating sandboxes from snapshots via `Sandbox.create({ source: { type: "snapshot", snapshotId } })`.

#### Scenario: Sandbox created from snapshot has matching filesystem

- **WHEN** a sandbox is created with a snapshot source and a file is written, then another sandbox is created from the resulting snapshot
- **THEN** the second sandbox SHALL contain the file from the first

### Requirement: Snapshot retention

The system SHALL support `keepLastSnapshots` retention policy on sandboxes.

#### Scenario: Retention evicts oldest snapshots

- **WHEN** a sandbox has `keepLastSnapshots: { count: 3 }` and a 4th snapshot is created
- **THEN** the oldest snapshot SHALL be evicted