hal/ui: add switch_to_logo()

diff --git a/src/rust/bitbox-hal/src/system.rs b/src/rust/bitbox-hal/src/system.rs
index 91c12dc..ed1983b 100644
--- a/src/rust/bitbox-hal/src/system.rs
+++ b/src/rust/bitbox-hal/src/system.rs
@@ -3,6 +3,10 @@
 #[allow(async_fn_in_trait)]
 pub trait System {
     /// Runs device-specific startup UI/initialization before regular operation.
+    ///
+    /// Startup may briefly show the logo, but it must finish on the lockscreen.
+    /// Here, "lockscreen" means the waiting screen that shows "See the BitBoxApp"
+    /// and the (possibly empty) device name.
     async fn startup();
 
     fn reboot(&mut self) -> !;
diff --git a/src/rust/bitbox-hal/src/ui.rs b/src/rust/bitbox-hal/src/ui.rs
index 746845d..f922a01 100644
--- a/src/rust/bitbox-hal/src/ui.rs
+++ b/src/rust/bitbox-hal/src/ui.rs
@@ -85,6 +85,10 @@ pub trait Ui {
 
     async fn status(&mut self, title: &str, status_success: bool);
 
+    /// Switches the waiting screen from the lockscreen (as described in
+    /// [`crate::system::System::startup`]) to the BitBox logo.
+    fn switch_to_logo(&mut self);
+
     fn progress_create(&mut self, title: &str) -> Self::Progress;
 
     /// If `can_cancel` is `Yes`, the workflow can be cancelled.
diff --git a/src/rust/bitbox02-rust/src/hal/testing/ui.rs b/src/rust/bitbox02-rust/src/hal/testing/ui.rs
index efb7ee5..0a11bc9 100644
--- a/src/rust/bitbox02-rust/src/hal/testing/ui.rs
+++ b/src/rust/bitbox02-rust/src/hal/testing/ui.rs
@@ -138,6 +138,8 @@ impl Ui for TestingUi<'_> {
         }
     }
 
+    fn switch_to_logo(&mut self) {}
+
     async fn enter_string(
         &mut self,
         params: &EnterStringParams<'_>,
diff --git a/src/rust/bitbox02-rust/src/hww.rs b/src/rust/bitbox02-rust/src/hww.rs
index 2111f30..f0c55ee 100644
--- a/src/rust/bitbox02-rust/src/hww.rs
+++ b/src/rust/bitbox02-rust/src/hww.rs
@@ -3,7 +3,7 @@
 pub mod api;
 pub mod noise;
 
-use crate::hal::Memory;
+use crate::hal::{Memory, Ui};
 use alloc::vec::Vec;
 
 const OP_UNLOCK: u8 = b'u';
@@ -106,7 +106,7 @@ pub async fn process_packet(hal: &mut impl crate::hal::Hal, usb_in: Vec<u8>) ->
     // connected. When the device is initialized, we delay this until the unlock call, otherwise
     // there would be a flicker where the logo would be shown before the host invokes unlock.
     if !hal.memory().is_initialized() || usb_in.as_slice() == [OP_UNLOCK] {
-        bitbox02::ui::screen_process_waiting_switch_to_logo();
+        hal.ui().switch_to_logo();
     }
 
     match usb_in.split_first() {
diff --git a/src/rust/bitbox02/src/hal/ui.rs b/src/rust/bitbox02/src/hal/ui.rs
index 31faa44..a5ddcbb 100644
--- a/src/rust/bitbox02/src/hal/ui.rs
+++ b/src/rust/bitbox02/src/hal/ui.rs
@@ -114,6 +114,11 @@ impl Ui for BitBox02Ui {
         crate::ui::status(title, status_success).await
     }
 
+    #[inline(always)]
+    fn switch_to_logo(&mut self) {
+        crate::ui::screen_process_waiting_switch_to_logo();
+    }
+
     #[inline(always)]
     async fn enter_string(
         &mut self,