The earlier trim dropped the only test of the `routed_profile_fire() and
not is_multiplex_active()` branch in the external-worker handoff: the
process flag is OFF (a desktop tick is not a multiplexer) yet a fire routed
to a sibling profile must serialize `multiplex_active=True` and hand the
worker an env without the launch profile's residue, and the context must
not outlive the handoff span. Without it that branch could regress to the
pre-fix behaviour unnoticed.
(cherry picked from commit 5850a50a81)
(cherry picked from commit 440bee6ccf9d48eecf91769787f6daa3fd3ea00c)
3b3b61ff4c