feat: add advisory device claims and daemonless ownership status (Stage 1)

[thymikee]

Parent: #1320

Depends on completed Stage 0: #1323

Summary

Implement Stage 1 of cross-worktree device ownership: a shared owner-identity and liveness model, advisory host-global local-device claims, and a daemonless agent-device device status inspection surface.

Stage 1 is deliberately observational. It must prove the claim model and lifecycle without rejecting an open or reclaiming resources. Enforcement, --stale, platform reconciliation, forced release, and remote lease projection remain later stages.

Required behavior

Shared owner primitives

• Extract the reusable PID + process-start-time identity and stale-owner classification currently proven by Apple runner leases; keep runner-lease behavior unchanged.
• Classify at least live, owner-process-dead/PID-reused, owner-state-dir-gone, corrupt/inconsistent, and unknown/transient-filesystem-failure.
• Treat only ENOENT/ENOTDIR as proof of absence. Permission and transient filesystem failures fail closed.
• Keep process-lock serialization and atomic tmp+rename persistence shared rather than cloning a second staleness implementation.

Advisory local claims

• Store versioned, user-private claims under ~/.agent-device/device-claims/.
• Derive claim keys from canonical provider/platform/device identity for registered local targets; do not hardcode only iOS and Android.
• Record session identity, workspace, state directory, owner PID/start time, timestamps, and an opaque ownership token suitable for compare-before-clear.
• Write/update claims only at lifecycle transitions. Do not add host-global claim I/O to session-bound command hot paths.
• Acquire advisory state before local platform preparation and clear it after safe session teardown, including failed-open rollback.
• Because enforcement is disabled, a verified live foreign claim must not block the operation and must never be overwritten. Preserve the existing owner and emit structured advisory conflict diagnostics.
• Clear a claim only when its token and owner identity still match. Late cleanup from an old owner must not erase a newer claim.
• Remote targets do not create host-local claim files.

Daemonless status

• Add agent-device device status and selector-scoped status using the singular device command group from feat: add cross-worktree device ownership and safe recovery #1320.
• Read claim files directly without starting or contacting a daemon.
• Inspection is side-effect-free: never reclaim, delete, rename, or quarantine a stale/corrupt claim.
• Return compact structured ownership data including device key, platform/device identity, owner session/workspace/state dir, classification, and the future recovery command shape where determinable.
• Corrupt or unreadable finalized claims remain visible as inconsistent/unknown rather than being treated as free.
• Update command metadata/schema, CLI help, user docs, and focused SkillGym guidance where the public surface requires it.

Explicit non-goals

• No ownership enforcement or DEVICE_IN_USE rejection yet.
• No automatic reclaim, device release, --stale, or --force.
• No Apple runner takeover or Android resource reconciliation.
• No remote provider-lease projection.
• No descriptor-wide DeviceClaimPolicy rollout; that belongs to Stage 2.

Acceptance criteria

• A local session produces an advisory claim that another worktree can inspect with device status while no daemon is started in the inspecting worktree.
• Local open/close and failed-open rollback write and clear claims at the correct lifecycle boundaries.
• A second live owner is observed but neither blocked nor allowed to overwrite the first owner during Stage 1.
• Token mismatch and PID-reuse tests prove stale cleanup cannot clear a successor claim.
• Process-dead, state-dir-gone, corrupt, permission-error, and transient-I/O classifications are covered and fail closed.
• iOS and Android lifecycle tests exercise the same platform-neutral claim store; canonical identity is registry-derived and remains extensible to other local Apple-family targets.
• Remote sessions create no local claim.
• device status has a test proving it does not start a daemon and performs no mutation.
• Existing Apple runner lease behavior remains covered after shared primitive extraction.
• Relevant affected checks pass, and manual two-worktree evidence demonstrates create → inspect → close → free behavior.

Implementation notes

• Read CONTEXT.md, the relevant ADRs, feat: add cross-worktree device ownership and safe recovery #1320, and the merged Stage 0 implementation before choosing seams.
• Prefer a deep platform-neutral ownership module and keep CLI rendering separate from claim persistence/classification.
• If implementation reveals that advisory single-owner records cannot safely represent observed contention without data loss, preserve the authoritative existing record and report the limitation; do not silently expand Stage 1 into enforcement.

[thymikee]

Stage 1 is implemented in #1329.

Evidence: an isolated cross-process/worktree-style run created a local Android advisory claim, device status --json reported it as live with owner/session metadata, and matching-owner cleanup removed it so status returned no claims. The implementation also has regression coverage for failed-open rollback, remote/no-local-claim, token mismatch/PID reuse, and fail-closed I/O classification.

Validation is detailed in the PR; the serialized provider suite passed 140/140. The full serialized coverage run had one pre-existing Apple concurrent-build flake that passed on isolated retry.