fix(Onboarding): Back button appears on loading screen

- don't clear the stack, we might need it to show errors during login
(while displaying splash screen)
- use the `backAvailableHint` instead on the splash screen itself to
hide the back button
- when a login error happens, unwind (or recreate) the stack to show the
LoginScreen page again, together with the error message
- add a simulation of these 2 scenarios to StoryBook, together with
showing the splash screen after a login

Fixes #17352

storybook/pages/OnboardingLayoutPage.qml

@@ -166,6 +166,12 @@ SplitView {
 
             // password signals
             signal accountLoginError(string error, bool wrongPassword)
+
+            // (test) error handler
+            onAccountLoginError: function (error, wrongPassword) {
+                ctrlLoginResult.result = "<font color='red'>⛔</font>"
+                onboarding.unwindToLoginScreen()
+            }
         }
 
         biometricsAvailable: ctrlBiometrics.checked
@@ -179,7 +185,6 @@ SplitView {
             logs.logEvent("onFinished", ["flow", "data"], arguments)
 
             console.warn("!!! SIMULATION: SHOWING SPLASH")
-            stack.clear()
             stack.push(splashScreen, { runningProgressAnimation: true })
         }
 
@@ -188,7 +193,7 @@ SplitView {
 
             // SIMULATION: emit an error in case of wrong password or PIN
             if (method === Onboarding.LoginMethod.Password && data.password !== mockDriver.password) {
-                onboardingStore.accountLoginError("The impossible has happened", Math.random() < 0.5) // randomly fail between a wrong pass and some other error
+                onboardingStore.accountLoginError("", true)
                 ctrlLoginResult.result = "<font color='red'>⛔</font>"
             } else if (method === Onboarding.LoginMethod.Keycard && data.pin !== mockDriver.pin) {
                 onboardingStore.keycardRemainingPinAttempts-- // SIMULATION: decrease the remaining PIN attempts
@@ -200,6 +205,7 @@ SplitView {
                 ctrlLoginResult.result = "<font color='red'>⛔</font>"
             } else {
                 ctrlLoginResult.result = "<font color='green'>✔</font>"
+                stack.push(splashScreen, { runningProgressAnimation: true })
             }
         }
 
@@ -359,6 +365,7 @@ SplitView {
         id: splashScreen
 
         DidYouKnowSplashScreen {
+            readonly property bool backAvailableHint: false
             property bool runningProgressAnimation
 
             NumberAnimation on progress {
@@ -460,6 +467,18 @@ SplitView {
                     visible: ctrlLoginScreen.checked
                     text: "Login result: %1".arg(result)
                 }
+
+                Button {
+                    text: "Unwind"
+                    visible: ctrlLoginScreen.checked && onboarding.stack.depth > 1 && !(onboarding.currentPage instanceof DidYouKnowSplashScreen)
+                    onClicked: onboarding.unwindToLoginScreen()
+                }
+
+                Button {
+                    text: "Simulate login error"
+                    visible: ctrlLoginScreen.checked && onboarding.currentPage instanceof DidYouKnowSplashScreen
+                    onClicked: onboarding.onboardingStore.accountLoginError("SIMULATION: Something bad happened", false)
+                }
             }
 
             RowLayout {

ui/app/AppLayouts/Onboarding2/OnboardingLayout.qml

@@ -24,7 +24,7 @@ Page {
     property bool networkChecksEnabled: true
     property alias keycardPinInfoPageDelay: onboardingFlow.keycardPinInfoPageDelay
 
-    readonly property alias stack: onboardingFlow
+    readonly property alias stack: onboardingFlow // TODO remove external stack access
     readonly property string currentPageName: stack.topLevelItem ? Utils.objectTypeName(stack.topLevelItem) : ""
 
     signal shareUsageDataRequested(bool enabled)
@@ -49,6 +49,16 @@ Page {
         d.resetState()
     }
 
+    // clear the stack down to the LoginScreen, or recreate it
+    // the purpose is to return from main/splash screen in case of a late stage error
+    // and use the below error handler (onAccountLoginError)
+    function unwindToLoginScreen() {
+        onboardingFlow.pop(null, StackView.PopTransition)
+        if (!onboardingFlow.loginScreen) {
+            restartFlow()
+        }
+    }
+
     function setBiometricResponse(secret: string, error = "",
                                   detailedError = "",
                                   wrongFingerprint = false) {
@@ -216,10 +226,10 @@ Page {
         }
     }
 
+    // error handler for the LoginScreen
     Connections {
         target: root.onboardingStore
 
-        // (password) login
         function onAccountLoginError(error: string, wrongPassword: bool) {
             const loginScreen = onboardingFlow.loginScreen
 

ui/main.qml

@@ -198,7 +198,7 @@ StatusWindow {
         Theme.changeTheme(localAppSettings.theme, systemPalette.isCurrentSystemThemeDark())
         Theme.changeFontSize(localAccountSensitiveSettings.fontSize)
 
-        d.runMockedKeycardControllerWindow() // FIXME this is run twice with onboardingV1
+        d.runMockedKeycardControllerWindow()
     }
 
     //TODO remove direct backend access
@@ -395,6 +395,7 @@ StatusWindow {
     Component {
         id: splashScreenV2
         DidYouKnowSplashScreen {
+            readonly property bool backAvailableHint: false
             readonly property string pageClassName: "Splash"
             property bool runningProgressAnimation
             messagesEnabled: true
@@ -475,7 +476,6 @@ StatusWindow {
                     console.error("!!! ONBOARDING FINISHED WITH ERROR:", error)
                     return
                 }
-                stack.clear()
                 stack.push(splashScreenV2, { runningProgressAnimation: true })
             }
 
@@ -500,7 +500,7 @@ StatusWindow {
                     moveToAppMain()
                 }
                 onAccountLoginError: function (error, wrongPassword) {
-                    onboardingLayout.stack.pop()
+                    onboardingLayout.unwindToLoginScreen() // error handled internally
                 }
             }