Create and manage Fly volumes via Machines API: create, attach to machines, extend size, and manage snapshots

Documented steps

1. Create volume: POST to https://api.machines.dev/v1/apps/{app}/volumes with JSON body: {name: '<vol_name>', size_gb: <size>, region: '<region>', snapshot_retention: <days>}
2. List volumes: GET https://api.machines.dev/v1/apps/{app}/volumes returns array with attached_machine_id, size_gb, region, and status
3. Get volume details: GET https://api.machines.dev/v1/apps/{app}/volumes/{volume_id} includes attachment info and snapshot retention settings
4. Extend volume size: PUT https://api.machines.dev/v1/apps/{app}/volumes/{volume_id}/extend with JSON {size_gb: <new_size>} (can only increase, never shrink)
5. Attach to machine: update machine config via POST /v1/apps/{app}/machines/{id} and include in config.mounts: [{volume_id: '<vol_id>', path: '<destination>'}]
6. List snapshots: GET https://api.machines.dev/v1/apps/{app}/volumes/{volume_id}/snapshots shows available restore points
7. Create snapshot: POST https://api.machines.dev/v1/apps/{app}/volumes/{volume_id}/snapshots (beta feature) creates on-demand backup
8. Delete volume: DELETE https://api.machines.dev/v1/apps/{app}/volumes/{volume_id} (only succeeds if no attached machines)
9. Snapshot retention: configure 1-60 days (default 5); automatic daily backups enabled by default; volumes encrypted by default
10. Use flyctl shortcut: fly volumes create/list/extend/destroy for CLI-based operations
11. Docs: https://fly.io/docs/machines/api/volumes-resource/