Persist, reattach, and reconcile session microVM lifecycles

Parent: #526

Outcome

A session owns one durable microVM environment generation that can be detached and reattached across harness restarts, and can be deleted/reconciled without leaks or accidental empty-environment recreation.

Scope

• Add an internal provisioning/lifecycle manager without widening tool.Environment into a service locator.
• Define and persist the environment state machine from reservation through worktree preparation, artifact verification, VM readiness, session persistence, attachment, detachment, stop, deletion, and tombstone.
• Persist owner UID/optional principal, session ID, EnvironmentRef, generation, path mapping, resolved profile, artifact digests, runtime process identity, endpoint identity, and cleanup state.
• Make creation idempotent and rollback provisional resources if session persistence fails.
• Resolve the exact persisted ref/generation at run entry; never recreate an empty VM or fall back to local.
• Define detach versus suspend/stop versus permanent delete.
• Add durable cleanup/reconciliation for host or daemon crashes, PID reuse, stale sockets, stale worktrees, child environments, and partial deletion.
• Apply per-user/deployment quotas for booting/active VMs, CPU, RAM, disk/inodes, execs, forks, image pulls, and boot rate.

Acceptance

• Restarting mecated or microvmd reattaches the exact valid environment generation or fails with an actionable precondition error.
• Unknown, foreign, stale, destroyed, incompatible, or mismatched refs never create replacement state.
• CloseSession detaches and leaves the session reattachable; explicit deletion eventually removes VM resources and session worktree according to preservation rules.
• Crashes at every lifecycle transition converge without leaked VMs, sockets, worktrees, quotas, or deletion of another environment.
• Two daemon processes racing the same ref cannot both own it.
• Cleanup paths are canonical-base-confined and never derive recursive-delete authority from model/caller text.