M7 epic: USB hardware inventory and exclusive allocation

[Andreas-Froyland]

Tracking issue. Dependency and status checklists only — implementation stays in narrow linked issues.

Outcome

Physical USB devices are inventoried stably and can be exclusively reserved and attached to exactly one Lab guest, with compensation on failure.

Supersedes

Replaces the "physical USB device inventory wired to actual Proxmox USB passthrough (exclusive ownership, attach/detach around test runs)" scope item of #3 and the physical-hardware element of #2's primary use case. Marked in docs/PLAN.md as a later M7 sub-epic.

Depends on

• M7 leases and cleanup
• M6 guest lifecycle and task operations
• Physical hardware and a Proxmox host available for validation

Scope checklist

• Stable physical USB inventory identity that survives replug and host reboot
• IOMMU and host validation with an explicit unsupported state
• Transactional exclusive reservation: two competing leases serialize correctly
• Attach/detach around a run, with compensation when either side fails
• Hardware-in-the-loop workflow documented end to end

Constrained by

• docs/PLAN.md — M7 and Scheduler correctness risk; ADR-0008
• Reservations are transactional in the database before the external Proxmox call

Non-goals

• Arbitrary PCI passthrough breadth
• Device firmware or driver management