fido_u2f: properly close u2f layout when other layout starts

As it's currently impossible to close() the layout generator from the outside, loop.signal() was added, and any started layout signals to terminate.

src/apps/fido_u2f/__init__.py

@@ -353,7 +353,7 @@ class ConfirmState:
             return False
         return True
 
-    def setup(self, action: int, checksum: bytes, app_id: bytes) -> None:
+    def setup(self, action: int, checksum: bytes, app_id: bytes) -> bool:
         if workflow.workflows:
             return False
 
@@ -379,6 +379,10 @@ class ConfirmState:
 
     @ui.layout
     async def confirm_layout(self) -> None:
+        workflow.fido_u2f_stop_signal.reset()
+        await loop.spawn(self.confirm_layout_inner(), workflow.fido_u2f_stop_signal)
+
+    async def confirm_layout_inner(self) -> None:
         from trezor.ui.confirm import ConfirmDialog, CONFIRMED
         from trezor.ui.text import Text
 

src/apps/wallet/sign_tx/__init__.py

@@ -16,7 +16,6 @@ from apps.wallet.sign_tx import (
 )
 
 
-@ui.layout
 async def sign_tx(ctx, msg, keychain):
     signer = signing.sign_tx(msg, keychain)
 

src/trezor/loop.py

@@ -185,6 +185,9 @@ class signal(Syscall):
     """
 
     def __init__(self):
+        self.reset()
+
+    def reset(self):
         self.value = _NO_VALUE
         self.task = None
 

src/trezor/workflow.py

@@ -5,6 +5,9 @@ layouts = []
 default = None
 default_layout = None
 
+# HACK: workaround way to stop the u2f layout from the outside
+fido_u2f_stop_signal = loop.signal()
+
 
 def onstart(w):
     workflows.append(w)
@@ -44,6 +47,7 @@ def restartdefault():
 def onlayoutstart(l):
     closedefault()
     layouts.append(l)
+    fido_u2f_stop_signal.send(None)
 
 
 def onlayoutclose(l):