Desktop: call device unlock what this platform calls it, not Windows Hello everywhere

src/DodoSSH.Client.App/Views/SettingsPreferencesPage.axaml

@@ -136,7 +136,7 @@
       <Border Classes="settingscard">
         <StackPanel Margin="24,20" Spacing="10">
           <TextBlock Classes="settingsrowcaption"
-                     Text="Unlocking with Windows Hello moved to Security — it registers this machine rather than a preference of this screen's, and Security is where the rest of this machine's trust facts live." />
+                     Text="Unlocking with this machine's device key moved to Security — it registers this machine rather than a preference of this screen's, and Security is where the rest of this machine's trust facts live." />
           <TextBlock Classes="settingsrowcaption"
                      Text="Terminal font, cursor and scrollback — the renderer hard-codes those three. Text size above is the one that is not." />
           <TextBlock Classes="settingsrowcaption"

src/DodoSSH.Client.App/Views/SettingsSecurityPage.axaml

@@ -70,15 +70,15 @@
           <Border Classes="settingsrow last">
             <Grid ColumnDefinitions="*,Auto">
               <StackPanel Grid.Column="0" Spacing="6" Margin="0,0,16,0" MaxWidth="640">
-                <TextBlock Classes="settingsrowtitle" Text="Windows Hello on this machine" />
+                <TextBlock Classes="settingsrowtitle" Text="{Binding DeviceUnlock.Name}" />
                 <TextBlock Classes="settingsrowcaption"
-                           Text="Registers this machine so a later launch can open the keychain with a Windows confirmation instead of your passphrase. Your passphrase keeps working."
+                           Text="{Binding DeviceUnlock.Offer}"
                            IsVisible="{Binding CanRegisterDevice}" />
                 <TextBlock Classes="settingsrowcaption"
-                           Text="Registered · the TPM holds a device key that can open the keychain with a Windows confirmation."
+                           Text="{Binding DeviceUnlock.Registered}"
                            IsVisible="{Binding CanForgetDevice}" />
                 <TextBlock Classes="settingsrowcaption"
-                           Text="This machine has nowhere to keep a device key, so the keychain will keep asking for your passphrase. That needs a TPM and a Windows keystore willing to release the key."
+                           Text="{Binding DeviceUnlock.Unavailable}"
                            IsVisible="{Binding HasNoDeviceKeyOption}" />
               </StackPanel>
               <Button Grid.Column="1" Classes="accent" Height="38" Content="REGISTER"

src/DodoSSH.Client.App/Views/UnlockCard.axaml

@@ -44,15 +44,15 @@
               IsEnabled="{Binding !IsBusy}" />
       <!--
         Shown only when this machine has both a registered wrap and a keystore still willing to release the
-        key. Absent rather than disabled, because a greyed-out "Use Windows Hello" on a machine that never
+        key. Absent rather than disabled, because a greyed-out "Use Touch ID" on a machine that never
         had it invites the reading that something is broken — and the passphrase box beside it is not a
         fallback, it is the ordinary way in.
       -->
-      <Button Classes="ghost" Content="USE WINDOWS HELLO"
+      <Button Classes="ghost" Content="{Binding DeviceUnlock.Button}"
               Command="{Binding UnlockWithDeviceCommand}"
               IsEnabled="{Binding !IsBusy}"
               IsVisible="{Binding CanUnlockWithDevice}"
-              ToolTip.Tip="Opens the keychain with this machine's device key. Windows will ask you to confirm." />
+              ToolTip.Tip="{Binding DeviceUnlock.Tip}" />
     </StackPanel>
 
     <TextBlock Classes="hint" Text="{Binding StatusMessage}" TextWrapping="Wrap" />

src/DodoSSH.Client.Shell/ViewModels/DeviceUnlockWording.cs

@@ -0,0 +1,85 @@
+namespace DodoSSH.Client.Shell.ViewModels;
+
+/// <summary>
+/// What unlocking with this machine's device key is called here, and what it asks the person for.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The words used to be Windows's everywhere: "USE WINDOWS HELLO" on a Mac, "Waiting for Windows…" over a
+/// Linux PIN prompt, and a settings row that told a MacBook it needed a TPM. Each desktop has its own device
+/// key store with its own gesture — see <c>WindowsDeviceKeyStore</c>, <c>MacDeviceKeyStore</c> and
+/// <c>LinuxDeviceKeyStore</c> — and a button has to name the one the person is about to be shown, or it reads
+/// as a feature for some other machine.
+/// </para>
+/// <para>
+/// One record rather than a property per sentence on the shell, so that the five places these words appear
+/// cannot disagree about which platform they are on.
+/// </para>
+/// </remarks>
+/// <param name="Name">What the feature is called, as a settings row's title.</param>
+/// <param name="Button">The unlock card's button, in the capitals every button here uses.</param>
+/// <param name="Wait">The status line while the platform's prompt is up.</param>
+/// <param name="Gesture">What opens the keychain instead of the passphrase, to finish a sentence.</param>
+/// <param name="Keeper">What holds the key, to finish "Registered · …".</param>
+/// <param name="Needs">What a machine with no device key store lacks, as a sentence of its own.</param>
+internal sealed record DeviceUnlockWording(
+    string Name,
+    string Button,
+    string Wait,
+    string Gesture,
+    string Keeper,
+    string Needs)
+{
+    internal static DeviceUnlockWording Windows { get; } = new(
+        "Windows Hello on this machine",
+        "USE WINDOWS HELLO",
+        "Waiting for Windows…",
+        "a Windows confirmation",
+        "the TPM holds a device key",
+        "That needs a TPM and a Windows keystore willing to release the key.");
+
+    internal static DeviceUnlockWording Mac { get; } = new(
+        "Touch ID on this Mac",
+        "USE TOUCH ID",
+        "Waiting for Touch ID…",
+        "Touch ID or your login password",
+        "the Secure Enclave holds a device key",
+        "That needs a Mac with a Secure Enclave and a login password set.");
+
+    internal static DeviceUnlockWording Linux { get; } = new(
+        "A device PIN on this machine",
+        "USE DEVICE PIN",
+        "Waiting for your PIN…",
+        "a PIN the TPM checks",
+        "the TPM holds a device key",
+        "That needs a TPM 2.0 this account is allowed to use.");
+
+    internal static DeviceUnlockWording Android { get; } = new(
+        "Fingerprint unlock on this phone",
+        "USE FINGERPRINT",
+        "Waiting for your fingerprint…",
+        "your fingerprint",
+        "the phone's keystore holds a device key",
+        "That needs a screen lock and a keystore willing to release the key.");
+
+    /// <summary>The wording for the platform this process is running on.</summary>
+    internal static DeviceUnlockWording ForThisPlatform { get; } =
+        OperatingSystem.IsAndroid() ? Android
+        : OperatingSystem.IsMacOS() ? Mac
+        : OperatingSystem.IsLinux() ? Linux
+        : Windows;
+
+    /// <summary>The settings caption for a machine that can register.</summary>
+    internal string Offer =>
+        $"Registers this machine so a later launch can open the keychain with {Gesture} instead of your passphrase. Your passphrase keeps working.";
+
+    /// <summary>The settings caption for a machine that has.</summary>
+    internal string Registered => $"Registered · {Keeper} that can open the keychain with {Gesture}.";
+
+    /// <summary>The settings caption for a machine that cannot.</summary>
+    internal string Unavailable =>
+        $"This machine has nowhere to keep a device key, so the keychain will keep asking for your passphrase. {Needs}";
+
+    /// <summary>The unlock button's tooltip.</summary>
+    internal string Tip => $"Opens the keychain with this machine's device key, after {Gesture}.";
+}

src/DodoSSH.Client.Shell/ViewModels/MainWindowViewModel.cs

@@ -2819,8 +2819,10 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
     /// Naming the wrong operating system here is not cosmetic — it is the sentence a user reads while
     /// deciding whether the prompt in front of them is the one this application asked for.
     /// </remarks>
-    private static string GestureWait =>
-        OperatingSystem.IsAndroid() ? "Waiting for your fingerprint…" : "Waiting for Windows…";
+    private static string GestureWait => DeviceUnlockWording.ForThisPlatform.Wait;
+
+    /// <summary>What unlocking with the device key is called on this platform; the views read it whole.</summary>
+    internal DeviceUnlockWording DeviceUnlock { get; } = DeviceUnlockWording.ForThisPlatform;
 
     /// <summary>Opens the vault with this machine's device key instead of the passphrase.</summary>
     /// <remarks>

tests/DodoSSH.Client.App.Tests/DeviceUnlockWordingTests.cs

@@ -0,0 +1,64 @@
+using DodoSSH.Client.Shell.ViewModels;
+
+namespace DodoSSH.Client.App.Tests;
+
+/// <summary>
+/// That unlocking with the device key is described in the words of the platform it runs on.
+/// </summary>
+/// <remarks>
+/// The unlock card offered "USE WINDOWS HELLO" on a Mac and the settings page told a Linux machine it needed a
+/// Windows keystore. Each platform's wording is checked for every other platform's names, because that is the
+/// mistake: a sentence borrowed from the one platform the feature was written on first.
+/// </remarks>
+public sealed class DeviceUnlockWordingTests
+{
+    public static TheoryData<string> Platforms => ["Windows", "Mac", "Linux", "Android"];
+
+    [Theory]
+    [MemberData(nameof(Platforms))]
+    public void EachPlatform_NamesOnlyItsOwnGesture(string platform)
+    {
+        var wording = For(platform);
+
+        var foreign = new Dictionary<string, string[]>(StringComparer.Ordinal)
+        {
+            ["Windows"] = ["Touch ID", "Secure Enclave", "fingerprint", "PIN"],
+            ["Mac"] = ["Windows", "TPM", "fingerprint", "PIN"],
+            ["Linux"] = ["Windows", "Touch ID", "Secure Enclave", "fingerprint"],
+            ["Android"] = ["Windows", "TPM", "Touch ID", "Secure Enclave"],
+        }[platform];
+
+        string[] said =
+            [wording.Name, wording.Button, wording.Wait, wording.Offer, wording.Registered, wording.Unavailable, wording.Tip];
+
+        foreach (var sentence in said)
+        {
+            sentence.ShouldNotBeNullOrWhiteSpace();
+
+            foreach (var name in foreign)
+            {
+                sentence.ShouldNotContain(name, Case.Sensitive, $"{platform}: \"{sentence}\"");
+            }
+        }
+
+        wording.Button.ShouldBe(wording.Button.ToUpperInvariant(), "every button on these screens is in capitals");
+    }
+
+    [Fact]
+    public void TheWordingInUse_IsThisMachines()
+    {
+        var expected = OperatingSystem.IsMacOS() ? DeviceUnlockWording.Mac
+            : OperatingSystem.IsLinux() ? DeviceUnlockWording.Linux
+            : DeviceUnlockWording.Windows;
+
+        DeviceUnlockWording.ForThisPlatform.ShouldBeSameAs(expected);
+    }
+
+    private static DeviceUnlockWording For(string platform) => platform switch
+    {
+        "Windows" => DeviceUnlockWording.Windows,
+        "Mac" => DeviceUnlockWording.Mac,
+        "Linux" => DeviceUnlockWording.Linux,
+        _ => DeviceUnlockWording.Android,
+    };
+}