Registers the MQTT subscription channel with the manager (idempotent) and,
if no global order has been set yet, makes MQTT the default channel.
This runs synchronously on purpose: registerChannel adds the channel to
the manager's map before its first await, so by the time this function sets
the global order the channel is already present. Doing it synchronously avoids
the order-clobber race that consumer apps had to defend against (where an
async registration reset the channel order after the app had configured it).
Registers the MQTT subscription channel with the manager (idempotent) and, if no global order has been set yet, makes MQTT the default channel.
This runs synchronously on purpose:
registerChanneladds the channel to the manager's map before its firstawait, so by the time this function sets the global order the channel is already present. Doing it synchronously avoids the order-clobber race that consumer apps had to defend against (where an async registration reset the channel order after the app had configured it).