The stale-bridge cleanup accepted a "node" + session-path cmdline substring
as kill evidence for legacy pidfiles (pid line only). A log tail, editor, or
grep that merely mentions the session path matches that same substring, so
the cleanup could SIGTERM a stranger process.
Require the kernel start-time fingerprint and fail closed when the pidfile
lacks one; the bridge-port scan (which verifies a node-executable listener)
reaps the orphan instead. The refusal reason in the warning now distinguishes
a fingerprint-less legacy pidfile from a recycled PID.
Flip the legacy-pidfile regression test to assert the fail-closed outcome.
Fixes#116883
7a23b00101