[mhellevang]

Follow-up to the review comment on #227, which got merged before the fix landed.

OnBusReset called HandleBusReset with the registry's lock_ held. The session's executor lets the calling thread run work that other threads queue meanwhile (a client's Logout(), also Login() or AbandonSuspended()). When that work fires a callback, the callback takes lock_ again on the same thread.

Fix as suggested: copy the sessions out under the lock, keep executor->OnBusReset() and the retiring-entry cleanup under it, and call HandleBusReset after releasing it.

Test: SessionRegistryTests.BusResetRunsSessionWorkOutsideRegistryLock. A login is in flight; when the reset cancels its timeout, another thread queues work on the session (new one-shot onNextCancel hook in FakeSessionScheduler). Before the fix it aborts on the recursive IOLockLock.

Host suite green.