This prevents a race condition where sometimes an Initialize message
could arrive before the homescreen was fully booted -- and Recovery
homescreen would cancel it as part of its bootup sequence.
this makes sense, really: close_others() requests UI exclusivity, and
that is something that generally happens at the same places we emit a
ButtonRequest
The original wait_layout was unreliable, because there are no guarantees
re order of arrival of the respective events. Still, TT's event handling
is basically deterministic, so as long as the host sent its messages
close enough to each other, the order worked out.
This is no longer the case with the introduction of loop.spawn: TT's
behavior is still deterministic, but now ButtonAck is processed *before*
the corresponding wait_layout, so the waiting side waits forever.
In the new process, the host must first register to receive layout
events, and then receives all of them (so the number of calls to
wait_layout must match the number of layout changes).
DebugLinkWatchLayout message must be version-gated, because of an
unfortunate collection of bugs in previous versions wrt unknown message
handling; and this interests us because upgrade-tests are using
wait_layout feature.
this prevents a certain class of UI test failure. It also localizes the
use of debuglink signals into the layout classes instead of call sites,
which is a design we were already using for confirm_signals
this involves some changes to the workflow defaults:
* workflow.start_default() takes no arguments
* workflow.set_default() (originally replace_default) configures the
default that will be started by next call to start_default().
The intended usecase is to set_default() first and then start it
separately.
* apps.base.set_homescreen() factors out the logic originally in
main.py, that decides which homescreen should be launched. This uses
set_default() call. start_default() is then used explicitly in main.py
