* fix: detect PID recycling in session write lock staleness check
The session lock uses isPidAlive() to determine if a lock holder is
still running. In containers, PID recycling can cause a different
process to inherit the same PID, making the lock appear valid when
the original holder is dead.
Record the process start time (field 22 of /proc/pid/stat) in the
lock file and compare it during staleness checks. If the PID is alive
but its start time differs from the recorded value, the lock is
treated as stale and reclaimed immediately.
Backward compatible: lock files without starttime are handled with
the existing PID-alive + age-based logic. Non-Linux platforms skip
the starttime check entirely (getProcessStartTime returns null).
* shared: harden pid starttime parsing
* sessions: validate lock pid/starttime payloads
* changelog: note recycled PID lock recovery fix
* changelog: credit hiroki and vincent on lock recovery fix
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Co-authored-by: HirokiKobayashi-R <hiroki@rhems-japan.co.jp>
