docs(plan): pin ZFS integration smoke green against real zpool

`BLOCKSTOR_ZFS_POOL=blockstor-test go test -v ./pkg/storage/zfs/...`
on the dev stand walks the full Provider through the real `zfs` /
`zpool` binaries and passes — closes the loop on whether the ZFS
provider's wire shape is correct (it is).

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

Author: kvaps

PLAN.md

@@ -251,7 +251,7 @@ Full scope list lives in `docs/csi-api-surface.md` (to be created in Phase 1).
 - [x] Generated Go bindings (`make proto` → `pkg/satellite/proto/*.pb.go`)
 - [x] Controller-side gRPC server (`pkg/satellitecontroller`) that satellites dial; Hello registers/idempotently-updates the Node CRD and returns ClusterID. 3 contract tests green.
 - [x] `pkg/satellite.Agent` actually dials the controller and round-trips Hello (2 end-to-end tests). Wired into `cmd/main.go` via `--satellite-grpc-bind-address` (default `:7000`) and `--cluster-id`.
-- [x] StoragePool: LVM-thin (`pkg/storage/lvm`) and ZFS / ZFS_THIN (`pkg/storage/zfs`) providers behind `pkg/storage.Provider` interface; FakeExec drives them in unit tests, RealExec wraps os/exec in production
+- [x] StoragePool: LVM-thin (`pkg/storage/lvm`) and ZFS / ZFS_THIN (`pkg/storage/zfs`) providers behind `pkg/storage.Provider` interface; FakeExec drives them in unit tests, RealExec wraps os/exec in production. **ZFS integration smoke** (opt-in via `BLOCKSTOR_ZFS_POOL`): `pkg/storage/zfs/zfs_integration_test.go` walks CreateVolume / VolumeStatus / CreateSnapshot / DeleteSnapshot / DeleteVolume + PoolStatus against a real `zpool` on the dev stand and is green (verified against `blockstor-test` pool, 240 MiB loop-backed, 2026-05-08).
 - [x] ConfFileBuilder in Go (`pkg/drbd/conffile.go`) — port from upstream Java; deterministic output, 7 contract tests green
 - [x] `drbdadm up/down/adjust/create-md/primary/secondary` exec wrappers behind interface (`pkg/drbd/drbdadm.go`); 7 contract tests via FakeExec
 - [x] `drbdsetup events2` listener (`pkg/drbd/events2.go`): line parser + Watcher streaming `Event{Action,Kind,Fields}` to a channel; 7 contract tests