RMW state locks can be stolen from live owners or retry indefinitely #406

Problem

The local read-modify-write lock reclaims an existing marker solely because its wait deadline expires. A still-running writer can therefore lose exclusivity, and a non-removable marker can cause an unbounded retry loop.

Reproduction

On unmodified ce30de7ca94115cb73fa991538c6d2595ac2622a, hold a per-project RMW marker past the two-second acquisition deadline. The competing call enters the critical section even when the first owner is still alive. Make the stale marker non-removable and the retry path can continue beyond its deadline. The retained regression tests reproduce both conditions with isolated filesystem fixtures.

Intended correction

Record a PID and unique ownership token, bound stale recovery, and reclaim only an unchanged marker whose owner is demonstrably gone. Unknown, malformed, legacy PID-less and permission-denied owners fail closed. Release removes only the marker still owned by that acquisition.

This concerns the local state RMW lock, not the distributed skill-publishing problem in #340.