fix(lock): fail closed when owner metadata is unreadable or invalid

[cursor]

Summary

This change fixes stale-lock recovery so we never treat unreadable or unparsable owner.json as an absent owner. Previously any read or JSON error was swallowed and the lock directory could be removed while mutual exclusion was still required, which risks concurrent lifecycle mutations or inconsistent state.

Linked Artifacts

• OpenSpec: openspec/specs/agent-update/spec.md (lock stale recovery and preserving live locks)

Validation

• bun run memory:check
• bun run lint
• bun run format:check
• bun run typecheck
• bun run test (if behavior changed)
• Not run, explained below

Release Intent

• Release: patch - resource lock stale recovery must not delete locks when owner metadata cannot be interpreted

Docs Updated

• Not needed
• docs/...
• openspec/...
• Follow-up issue or OpenSpec change created instead

Scope Check

• I did not add a new ad hoc root-level Markdown file.
• I updated the relevant issue, ADR, spec, runbook, or captured the missing doc work as follow-up.
• I did not silently expand project scope without recording it explicitly.

Closure Check

• Working tree was clean after commit.
• Branch was pushed and this PR is the active delivery artifact.
• OpenSpec change is not needed, still active by design until merge, already archived, or queued for agent-driven archive closure.
• Release is not applicable, delegated to release automation, or verified.

Notes

Regression coverage includes Unix chmod removing read access on owner.json, and invalid JSON contents; both must surface ResourceLockError without deleting the lock directory.