feat(core/delizia): allow back in multishare setup

### core/embed/rust/src/ui/layout_delizia/ui_firmware.rs
@@ -804,7 +804,7 @@ impl FirmwareUI for UIDelizia {
         _button: TString<'static>,
         active: usize,
         items: [TString<'static>; MAX_CHECKLIST_ITEMS],
-        _back_button: bool,
+        back_button: bool,
     ) -> Result<impl LayoutMaybeTrace, Error> {
         let mut paragraphs = ParagraphVecLong::new();
         for (i, item) in items.into_iter().enumerate() {
@@ -833,13 +833,21 @@ impl FirmwareUI for UIDelizia {
         .with_icon_done_color(theme::GREEN)
         .with_done_offset(theme::CHECKLIST_DONE_OFFSET);
 
-        let layout = RootComponent::new(SwipeUpScreen::new(
-            Frame::with_header(
-                Header::left_aligned(title),
-                SwipeContent::new(checklist_content),
-            )
-            .with_swipeup_footer(None),
-        ));
+        // When going back is possible, the header has a menu button emitting
+        // `FlowMsg::Info`; the menu itself is external, shown from Python.
+        let header = if back_button {
+            Header::left_aligned(title).with_menu_button()
+        } else {
+            Header::left_aligned(title)
+        };
+        let frame = Frame::with_header(header, SwipeContent::new(checklist_content))
+            .with_swipeup_footer(None);
+        let frame = if back_button {
+            frame.with_external_menu()
+        } else {
+            frame
+        };
+        let layout = RootComponent::new(SwipeUpScreen::new(frame));
         Ok(layout)
     }
 

### core/src/trezor/ui/layouts/delizia/reset.py
@@ -89,26 +89,50 @@ async def select_word(
     return words[result]
 
 
+async def _go_back() -> ui.UiResult:
+    return trezorui_api.BACK
+
+
 async def slip39_show_checklist(
     step: int,
     advanced: bool,
     count: int | None = None,
     threshold: int | None = None,
     back_button: bool = False,
 ) -> ui.UiResult:
+    from trezor.ui.layouts.menu import Menu, MenuLeaf, show_menu
+
     items = _slip_39_checklist_items(step, advanced, count, threshold)
     with trezorui_api.show_checklist(
         title=TR.reset__title_shamir_backup,
         button=TR.buttons__continue,
         active=step,
         items=items,
+        back_button=back_button,
     ) as layout:
-        result = await interact(
-            layout, "slip39_checklist", ButtonRequestType.ResetDevice
-        )
-    if result != CONFIRMED:
-        raise ActionCancelled
-    return result
+        br_name_once: str | None = "slip39_checklist"
+        while True:
+            result = await interact(
+                layout,
+                br_name_once,
+                ButtonRequestType.ResetDevice,
+                raise_on_cancel=None,
+            )
+            br_name_once = None  # ButtonRequest should be sent only once
+
+            if result is CONFIRMED:
+                return result
+
+            if result is trezorui_api.INFO:
+                # shows the menu with the "go back" option
+                menu_result = await show_menu(
+                    Menu([MenuLeaf(TR.buttons__go_back, _go_back)])
+                )
+                if menu_result is not None:
+                    return menu_result.value  # BACK
+            else:
+                # not reachable from the UI, only via debuglink
+                raise ActionCancelled
 
 
 def _slip_39_checklist_items(
@@ -153,8 +177,8 @@ async def _prompt_number(
     min_count: int,
     max_count: int,
     br_name: str,
-) -> int:
-    from trezor.ui.layouts.menu import Menu, leaf_from_layout, show_menu
+) -> int | ui.UiResult:
+    from trezor.ui.layouts.menu import Menu, MenuLeaf, leaf_from_layout, show_menu
 
     with trezorui_api.request_number(
         title=title,
@@ -174,7 +198,8 @@ async def _prompt_number(
             br_name_once = None  # ButtonRequest should be sent only once
 
             if result is trezorui_api.CANCELLED:
-                raise ActionCancelled  # user cancelled request number prompt
+                # not reachable from the UI, only via debuglink
+                raise ActionCancelled
 
             if __debug__ and not isinstance(result, tuple):
                 # sent by debuglink. debuglink does not change the number of
@@ -187,15 +212,20 @@ async def _prompt_number(
                 return value
 
             if status is trezorui_api.INFO:
-                # shows the menu with the "more info" screen
-                leaf = leaf_from_layout(
-                    TR.buttons__more_info,
-                    lambda: trezorui_api.show_info_with_cancel(
-                        title="",
-                        items=[("", info(value), False)],
+                # shows the menu with "more info" and "go back" options
+                leaves = [
+                    leaf_from_layout(
+                        TR.buttons__more_info,
+                        lambda: trezorui_api.show_info_with_cancel(
+                            title="",
+                            items=[("", info(value), False)],
+                        ),
                     ),
-                )
-                await show_menu(Menu([leaf]))
+                    MenuLeaf(TR.buttons__go_back, _go_back),
+                ]
+                menu_result = await show_menu(Menu(leaves))
+                if menu_result is not None:
+                    return menu_result.value  # BACK
             else:
                 raise RuntimeError
 

### tests/device_tests/test_msg_backup_device.py
@@ -190,7 +190,7 @@ def test_backup_slip39_advanced(
     assert expected_ms == actual_ms
 
 
-@pytest.mark.models("eckhart")  # going back is supported only on Eckhart
+@pytest.mark.models("delizia,eckhart")  # going back is supported on these layouts
 @pytest.mark.setup_client(needs_backup=True, mnemonic=MNEMONIC_SLIP39_BASIC_20_3of6)
 def test_backup_slip39_basic_back_navigation(
     session: Session, backup_method: messages.BackupMethod
@@ -216,15 +216,13 @@ def test_backup_slip39_basic_back_navigation(
     assert expected_ms == actual_ms
 
 
-@pytest.mark.models("eckhart")  # going back is supported only on Eckhart
+@pytest.mark.models("delizia,eckhart")  # going back is supported on these layouts
 @pytest.mark.setup_client(needs_backup=True, mnemonic=MNEMONIC_SLIP39_ADVANCED_20)
 def test_backup_slip39_advanced_back_navigation(
     session: Session, backup_method: messages.BackupMethod
 ):
     with session.test_ctx as client:
-        IF = InputFlowSlip39AdvancedBackupBackNavigation(
-            session, method=backup_method
-        )
+        IF = InputFlowSlip39AdvancedBackupBackNavigation(session, method=backup_method)
         client.set_input_flow(IF.get())
         device.backup(session, backup_method=backup_method)
 

### tests/input_flows.py
@@ -2730,6 +2730,91 @@ def __init__(
         self.mnemonics: list[str] = []
         self.method = method
 
+    def input_flow_delizia(self) -> BRGeneratorType:
+        assert self.method in (
+            messages.BackupMethod.Display,
+            messages.BackupMethod.N1W1,
+        )
+        if self.method is messages.BackupMethod.Display:
+            assert (yield).name == "backup_intro"
+            self.debug.press_yes()
+
+        # checklist: set number of shares (no going back from the first step)
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # number of shares prompt: change the default 5 to 3
+        assert (yield).name == "slip39_shares"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 5
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: set threshold -- go back via the "Go back" menu item
+        assert (yield).name == "slip39_checklist"
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(0)
+
+        # number of shares prompt: the previously entered value is preselected
+        assert (yield).name == "slip39_shares"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 3
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: set threshold
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # threshold prompt: increase the default 2 to 3, then go back via the
+        # "Go back" menu item
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 2
+        self.debug.click(self.debug.screen_buttons.number_input_plus())
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(1)
+
+        # checklist: set threshold
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # threshold prompt: the default 2 is shown again, increase it to 3
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 2
+        self.debug.click(self.debug.screen_buttons.number_input_plus())
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: write down the shares -- go back via the "Go back" menu
+        # item
+        assert (yield).name == "slip39_checklist"
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(0)
+
+        # threshold prompt: the previously entered value is preselected
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 3
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: write down the shares
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        if self.method is messages.BackupMethod.Display:
+            assert (yield).name == "backup_warning"
+            self.debug.press_yes()
+
+        # Mnemonic phrases
+        self.mnemonics = yield from load_N_shares(self.debug, 3, self.method)
+
     def input_flow_eckhart(self) -> BRGeneratorType:
         assert self.method in (
             messages.BackupMethod.Display,
@@ -2808,6 +2893,117 @@ def __init__(
         self.mnemonics: list[list[str]] = []
         self.method = method
 
+    def input_flow_delizia(self) -> BRGeneratorType:
+        assert self.method in (
+            messages.BackupMethod.Display,
+            messages.BackupMethod.N1W1,
+        )
+        if self.method is messages.BackupMethod.Display:
+            assert (yield).name == "backup_intro"
+            self.debug.press_yes()
+
+        # checklist: set number of groups (no going back from the first step)
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # number of groups prompt: change the default 5 to 2
+        assert (yield).name == "slip39_groups"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 5
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: set group threshold
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # group threshold prompt: keep the default 2
+        assert (yield).name == "slip39_group_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 2
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: set sizes and thresholds of the groups -- go back via the
+        # "Go back" menu item
+        assert (yield).name == "slip39_checklist"
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(0)
+
+        # group threshold prompt: the previously entered value is preselected
+        assert (yield).name == "slip39_group_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 2
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # checklist: set sizes and thresholds of the groups
+        assert (yield).name == "slip39_checklist"
+        self.debug.swipe_up()
+
+        # group 1 shares prompt: change the default 5 to 3
+        assert (yield).name == "slip39_shares"
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.number_input_minus())
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # group 1 threshold prompt: keep the default 2
+        assert (yield).name == "slip39_threshold"
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # group 2 shares prompt: keep the default 5 -- go back via the
+        # "Go back" menu item
+        assert (yield).name == "slip39_shares"
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(1)
+
+        # group 1 threshold prompt: the previously entered value is preselected
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 2
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # group 2 shares prompt: keep the default 5
+        assert (yield).name == "slip39_shares"
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # group 2 threshold prompt: change the default 3 to 4, then go back
+        # via the "Go back" menu item
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 3
+        self.debug.click(self.debug.screen_buttons.number_input_plus())
+        self.debug.click(self.debug.screen_buttons.menu())
+        layout = self.debug.read_layout()
+        assert "ScrolledVerticalMenu" in layout.all_components()
+        self.debug.button_actions.navigate_to_menu_item(1)
+
+        # group 2 shares prompt: the previously entered value is preselected
+        assert (yield).name == "slip39_shares"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 5
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        # group 2 threshold prompt: the default 3 is shown again -- keep it
+        assert (yield).name == "slip39_threshold"
+        layout = self.debug.read_layout()
+        assert layout.find_unique_value_by_key("value", None, only_type=int) == 3
+        self.debug.click(self.debug.screen_buttons.ok())
+
+        if self.method is messages.BackupMethod.Display:
+            assert (yield).name == "backup_warning"
+            self.debug.press_yes()
+
+        # Mnemonic phrases - show & confirm shares for all groups
+        # 2 groups: 2-of-3 and 3-of-5
+        self.mnemonics = yield from load_N_groups(
+            self.debug, [(2, 3), (3, 5)], self.method
+        )
+
     def input_flow_eckhart(self) -> BRGeneratorType:
         assert self.method in (
             messages.BackupMethod.Display,