[msdmazvoid]

Summary

Adds first-class storage classes so one kouja agent can serve multiple LVM backends on the same physical host, for example NVMe, SSD, and HDD pools.

storage:
  classes:
    nvme: kouja-nvme
    ssd: kouja-ssd
    hdd: kouja-hdd

• Adds storage.classes config mapping class names to LVM volume groups.
• Includes class-referenced VGs in first-start registration via EffectiveVGs.
• Adds storage_class to the agent CreateVolume request, Volume, and Capacity protobuf messages.
• Returns the class on capacity and volume responses; raw VG names remain valid and act as their own class when no mapping exists.
• Extends CSI StorageClass parameters with class (and storageClass alias). vg remains supported.
• CSI host selection and GetCapacity now filter by storage class, so a PVC lands only on a host advertising that class.
• Records the selected class in KoujaVolumePlacement.
• Adds a class to volume context and documents the multi-backend setup.
• Adds Ginkgo/Gomega tests for config mapping, agent resolution/capacity, CSI selection, capacity filtering, and placement.

Compatibility

Existing callers that pass only vg continue to work. If a class is not configured on the agent, it falls back to the raw VG name.

Test plan

• go test -tags=unit ./...
• go test -tags=integration ./test/integration/...
• go test -tags=e2e ./test/e2e/...
• go test -tags=csi_sanity ./test/csi/...
• make coverage-check (80.8%)
• go vet ./...
• golangci-lint run
• GitHub Actions CI

[msdmazvoid]

QEMU end-to-end validation completed for this change:

• Two Debian 13 QEMU/KVM VMs, host with loop-backed VGs kouja-nvme and kouja-hdd.
• Host enabled classes only via storage.classes: nvme: kouja-nvme, hdd: kouja-hdd.
• GET /v1/capacity returned both VGs with storageClass: nvme/hdd.
• Direct API create with storageClass: hdd created the LV in kouja-hdd, returned storageClass: hdd, logged in over iSCSI with CHAP, and passed an 8 MiB write/read MD5 check.
• Active-session delete returned SESSION_ACTIVE; after logout, delete succeeded and left no LV/target/backstore.
• storageClass: nvme created in kouja-nvme; an explicit conflicting vg was rejected with InvalidArgument.
• A real CSI controller selected the hdd class, created and published a volume, returned storage_class: hdd in the volume context, and completed the same 8 MiB write/read before unpublish/delete.

Recorded in docs/e2e.md.

[msdmazvoid]

Added the client-facing storage-class discovery request:

• gRPC: VolumeService.ListStorageClasses
• HTTP: GET /v1/storage-classes
• Returns class name, backing VG/UUID/state, total/free/allocatable bytes, extent size, maximum volume size, and observation time.
• No admin role required; any authenticated caller/controller/node certificate can query it.
• Verified over mTLS in QEMU with a caller certificate and two active classes.