[Step II] - replace onCommit with preferred_fidelity #2351

// SnapshotFidelity orders the state layers a snapshot can hold, lowest to
// highest. Each level includes the ones below it.
enum SnapshotFidelity {
  SNAPSHOT_FIDELITY_UNSPECIFIED = 0;
  // Durable volumes only. The actor resumes by cold-booting its containers
  // from the OCI image with the volumes restored.
  SNAPSHOT_FIDELITY_VOLUMES = 1;
  // Volumes plus the root filesystem changes made since boot. Not yet
  // supported by any sandbox runtime; templates may not request it.
  SNAPSHOT_FIDELITY_ROOTFS = 2;
  // Volumes, root filesystem changes, and process memory. The actor resumes
  // where it left off.
  SNAPSHOT_FIDELITY_MEMORY = 3;
  // Keep this in sync with the maximums on fields of this type.
}

// SnapshotConfig selects what actor snapshots capture and where they are
// stored.
message SnapshotConfig {
  // storage_location ... (unchanged text, renumbered to = 1)
  string storage_location = 1;

  // preferred_fidelity is the fidelity every snapshot of an actor captures,
  // both the node-local one taken on pause and the one uploaded on suspend.
  // ROOTFS is not supported yet and is rejected. Defaults to MEMORY when
  // unset.
  //
  // +k8s:required
  // +k8s:minimum=1
  // +k8s:maximum=3 # keep this in sync with the SnapshotFidelity enum
  // +k8s:customValidation # ROOTFS is not supported yet
  SnapshotFidelity preferred_fidelity = 2;
}