#2308 feat: add fenced managed lease admission

Summary

Adds neutral admission for one managed lease incarnation. It verifies returned TTL, reconciles ambiguous renewal against the exact durable request attempt, coalesces renewal work, and preserves each caller's deadline and cancellation. Fencing permanently rejects further execution, including after late renewal completion.

Command horizons use the canonical core timeout policy and reserve the existing 5-second teardown plus 11-second recording cleanup budgets. Ordinary teardown still requires a real session.

A separate contract correction replaces provisional readiness with task-taking managedDevice.admit, allowing downstream dispatch inside confirmation. run remains transport/cleanup-only. It also removes the unused ResolvedNativeAsset and NativeAssetResolver types. #2312 owns the reviewed consumer adaptation; this PR has no runtime activation. ADR 0021 documents that boundary and distinguishes fencing from teardown quiescence. Skills are unchanged.

Validation

Head 1df42d51f50e7dfb3162f113f74a76829c9b8272 is based on published #2307 97f4e7057f3c4d6dead9df39a6a7645063c877e4, rooted in requested main snapshot 80997b6bf1dda30ca57d74dc42036f6b447e16ad. All three commits are unchanged by range-diff; no conflicts.

• Independent adversarial review of the final restack: READY.
• Fresh exact-head pnpm check:affected --run passed: 3,258 tests / 431 files. The focused suite passed 462 tests, including all 418 exact-parent eager-closure cases, under the host-wide gate lock.
• Preserved planted-red horizon proof: removing recording reservation yields 5,000 ms instead of 16,000 ms; restoration passes.

Coverage and Integration pass. The iOS retry fails at a depth-1 snapshot after AX target resolution falls back to XCTest. This is not live managed-device acceptance.