🧹 feat: Bound Managed Environment Storage

[danny-avila]

Summary

Dependency reuse without a lifecycle still accumulates old versions, and low disk can interrupt installation before the worker persists its recovery state. Add opt-in snapshot retention/count/byte budgets and a free-space admission floor for managed preparation, including workers without snapshot support.

Behavior

• Low space starts no setup command. Ready checkouts can still perform their normal readiness check.
• Cleanup touches only reproducible, privately owned snapshots with valid worker manifests. Active/current keys, unknown data and all source worktrees remain intact.
• An explicit operator command previews by default; --apply performs maintenance without restarting the worker.
• A full cache does not turn successful preparation into a failed/quarantined checkout. Skip publication with a diagnostic when nothing safe can be evicted.

per-key preparation lock ── install / restore / readiness
              │
              └─ short maintenance lock
                    ├─ bounded inventory + worker manifests
                    ├─ try-lock inactive LRU entries / abandoned staging
                    └─ budget check + atomic publication

Kernel try-locks are non-blocking and do not mask cleanup errors as contention. Budget checking and publication share the maintenance lock, while installations for independent keys remain concurrent. Abandoned staging needs both a manifest and a free owner-key lock.

Stacked on #288. All settings are opt-in; existing environment definitions retain their behavior. Budgets count logical snapshot payload, not reflink physical allocation or working checkout copies. Free-space checks are soft admission, not disk reservations or arbitrary shell-write quotas. This deliberately does not delete .verification, source worktrees, dirty/unpushed changes, unknown installs or shared mutable npm/uv caches; those need their own ownership/usage lifecycle. Hard containment requires deployment filesystem quotas and separate control-state storage.

Verification

• Worker TypeScript build passed.
• 52 focused tests passed, including real native-SRT/APFS preparation and restore, shared resources, hardlink rejection, changed-input eviction, kernel-lock crash recovery, preserved active keys and source, dry-run/apply CLI, low-space no-dispatch and abandoned-staging recovery.
• git diff --check passed.

No live worker, deployment, filesystem quota or production cleanup was changed.