HandlerExec in task mode now sets is_running_=false when rule_pointers_
and once_exec_queue_ are both empty. Manager cleanup uses two-phase
lock (shared_lock scan + unique_lock destroy/erase) synchronized with
exec_task via handles_mutex. exec_task checks is_running_ before submit
and destroys dead handlers to prevent task loss. Also fix logReset
self-assignment no-op.
