Let the desktop client replace itself, and give the repository one version

Packaging for Windows, and the updater that only exists once something is
packaged. Velopack, win-x64, fed from the project's own forge — never from the
deployment a client signs in to, which is ADR 0011 rule 2 carried over
unchanged and is why the feed address is a constant in the code rather than a
setting. See docs/adr/0012-desktop-distribution-and-updates.md.

**Nothing is ever installed while somebody is using it.** A newer build is found
on a six-hourly pass, downloaded in the background, and then waits — for a
restart the user presses, or for the next launch they were going to do anyway.
That is a policy rather than caution: this application argues at length that
locking keeps shells running, because a lock that destroyed work would stop
being used, and a restart does not keep them. Having taught that, it owes the
user the choice at the one moment it stops being true, and the sentence saying
so counts the shells it would close.

**The version is now derived from the v* tag**, by MinVer, for everything. There
was no version before this — no property anywhere, so every assembly reported
the SDK's 1.0.0 and the API served that string as its serverVersion to every
client that asked. The tag was already the version of record for the container
image; this makes it the version of record full stop. MinVer's failure mode is
answering plausibly rather than failing, and here a wrong version is a client
that never updates, so it is guarded twice: fetch-depth 0 on every checkout, and
a step that fails a tag build when the tag and the computed version disagree.

**The pack id is DodoSSH.Desktop and not DodoSSH**, which is the one decision
here that would have destroyed data. Velopack installs to %LOCALAPPDATA%\<packId>
and removes that whole directory on uninstall, and %LOCALAPPDATA%\DodoSSH is
where ClientPaths keeps the encrypted cache, the outbox of changes not yet
pushed, and the device key. The obvious id would have had the uninstaller
silently delete work the server has never seen — the thing the application
refuses to do without a counted confirmation. Velopack's own advice to move user
data to roaming %APPDATA% is declined for the reason ClientPaths already gives.

**Releases are cut by a person, and CI gains no job that could.** The tempting
argument is that a forge write token is not a signing key. It does not survive
contact with what the token does: Velopack clients trust their feed and do not
verify a package signature when they apply one, so whoever can write a release
can ship an update every install runs. That is the capability ADR 0011 rule 1
puts on a machine which is not a runner, reached through a different door. The
mechanical objection — vpk needs Windows and the runners are Linux — is the
smaller of the two and is recorded beside it, because somebody will fix one and
believe they are done.

Unsigned for now, deliberately and with the cost stated where a user reads it:
SmartScreen warns once per person, on Setup.exe, because Mark-of-the-Web is
applied by the browser that downloaded it. In-app updates are fetched by the
application and applied from a local file, and never trip it.

The banner is a fourth row of the window rather than an overlay. Anything drawn
in the terminal's rectangle is sliced by the native child window that composites
above it — the defect this window has shipped once — and a sibling row is the
arrangement TitleBar and StatusBar already prove works.

----

Three defects surfaced on the way, none of them in the feature being built.

**A settings key absent from the file came back as the CLR default, not the
declared one.** The JSON source generator builds a record through a synthesised
parameterised constructor and assigns every property from its argument array, so
a property initializer runs and is then overwritten by a default for anything the
file did not contain. A settings.json of {} read back a font size of 0, clamped
up to the 8px floor rather than the 13px the renderer draws at. It could not bite
while there was one setting, because that setting was written on every save and
so was never absent; adding a second would have turned automatic update checks
off for every existing profile, silently, the opposite of the documented default.
Reflection-based deserialisation of the same JSON answers correctly, which is why
every way of checking it by hand agrees except the one that ships. The defaults
now live on the constructor parameters, which is the only place the generator
reads them from.

**Declaring a RuntimeIdentifier on the desktop head broke the server's image
build.** It is the obvious way to let a self-contained publish restore under
locked mode, and it writes a net10.0/win-x64 target into the lock file of every
project the head references transitively — including DodoSSH.Contracts and
DodoSSH.Crypto, which the API builds too. The Dockerfile restores those with no
RID and fails NU1004. Found by running docker build rather than by reading. The
RID stays out of the committed state; the two commands that need one ask for it
unlocked, and the release script puts the lock files back.

**A Docker ARG named VERSION silently sets MSBuild's Version.** An ARG is an
environment variable for the rest of the stage, MSBuild reads environment
variables as properties, and property names are case-insensitive. With the
workflow passing main-<short sha> on a main build the publish died with
NETSDK1018 pointing at DodoSSH.Contracts, a project nobody had touched. The build
stage's argument is ASSEMBLY_VERSION now, empty except on a tag build.

All three are in docs/platform-flags.md, which is where the next person will look.

----

Verified: the whole solution builds and restores locked; 289 shell, 93 layout and
54 session tests pass, including the regression test for the settings defect and
a measurement of the banner at the window's minimum width. vpk pack runs end to
end and reports "Verified VelopackApp.Run()" against Program.Main. The API image
builds correctly both as a main build and as a tag build, carrying 1.0.0 and
0.1.0 respectively.

Not verified, and it needs a published release to be: installing, updating and
uninstalling on a real machine. That is Phase 15 of docs/manual-checks.md, and
the pack id and the WebView2 profile fix are reasoned and commented but only
proved by walking it. Two things to watch at the first upload — the reverse
proxy's body-size limit for a 64 MB asset, and whether vpk upload gitea is happy
with Gitea 1.27.1.

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

@@ -288,6 +288,15 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
 
     private readonly VaultsViewModel vaults;
 
+    /// <summary>
+    /// Where newer builds come from, and how far one has got.
+    /// </summary>
+    /// <remarks>
+    /// A process-lifetime object like <see cref="transfers"/>, and for a reason that is its own rather than
+    /// borrowed: this one outlives a lock because the release channel is not the vault.
+    /// </remarks>
+    private readonly UpdateViewModel updateScreen;
+
     /// <summary>
     /// The tab standing in for each connection that has been asked for and has not answered yet.
     /// </summary>
@@ -347,6 +356,13 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
     /// What to call this machine. Optional, and the default is right for every head that runs on a desktop
     /// operating system — see the field it is kept in for the one that it is not right for.
     /// </param>
+    /// <param name="updates">
+    /// Where newer builds of this client come from. Optional, and the default is a channel that reports
+    /// itself unavailable — which is a deliberate difference from <paramref name="deviceKeys"/>, which every
+    /// head passes explicitly. With an optional parameter, "the phone has no updater" is enforced by the
+    /// absence of a line rather than by a line somebody has to remember to keep a no-op; and ADR 0011 settles
+    /// the Android head's distribution separately, so it must never acquire one by accident.
+    /// </param>
     internal MainWindowViewModel(
         ClientPaths paths,
         ClientCacheFactory caches,
@@ -359,7 +375,8 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
         Argon2Profile? passphraseProfile = null,
         ResumeHandler? resume = null,
         Func<string, Task>? copyToClipboard = null,
-        string? deviceName = null)
+        string? deviceName = null,
+        IUpdateChannel? updates = null)
     {
         this.paths = paths;
         this.caches = caches;
@@ -404,6 +421,8 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
 
         settings = new ClientSettingsStore(paths);
 
+        updateScreen = CreateUpdateScreen(updates);
+
         // Read straight away rather than at first use, so the value is right before anything can read it —
         // a phone draws its terminal buttons from this, and a size that arrived a moment later would show
         // as the interface correcting itself.
@@ -412,6 +431,37 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
         _ = TellRendererTheFontSizeAsync();
     }
 
+    /// <summary>
+    /// Builds the updater, kept for the life of the process like the workspace and the transfer queue.
+    /// </summary>
+    /// <remarks>
+    /// A method rather than four more lines in the constructor, because the restart delegate needs a
+    /// paragraph of its own and the constructor is already at the length the analyzers allow.
+    /// </remarks>
+    private UpdateViewModel CreateUpdateScreen(IUpdateChannel? updates)
+    {
+        // The channel is captured rather than reached through the view model, which keeps the restart
+        // delegate free of a reference to the object it is being handed to.
+        var channel = updates ?? new UnavailableUpdateChannel();
+
+        return new UpdateViewModel(
+            channel,
+            settings,
+            clock,
+            () => workspace.LiveSessionCount,
+
+            // Everything this application does on the way out, and only then the swap. Applying an update
+            // ends the process, and disposing this view model is what zeroes the identity keys, the vault
+            // keys and the cache key — so the other order would leave them sitting in a memory image the
+            // installer is about to write over, and would abandon a transfer still writing to a part file.
+            restart: async update =>
+            {
+                await DisposeAsync().ConfigureAwait(true);
+
+                channel.ApplyAndRestart(update);
+            });
+    }
+
     /// <remarks>
     /// <para>
     /// The page starts at its own default and has no way to know what was stored, so somebody has to tell
@@ -568,6 +618,14 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
     /// </remarks>
     internal TransfersViewModel Transfers => transfers;
 
+    /// <summary>Where newer builds come from, which the window binds whether or not a vault is open.</summary>
+    /// <remarks>
+    /// Bound from the titlebar's banner and from the preferences screen, and it answers on a locked shell
+    /// too — the banner is drawn outside the unlocked half of the window on purpose, because a machine left
+    /// locked overnight is exactly the one that will have found an update by morning.
+    /// </remarks>
+    internal UpdateViewModel Updates => updateScreen;
+
     /// <summary>
     /// Shells that were left running when the vault was locked.
     /// </summary>
@@ -1625,6 +1683,12 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
     /// </remarks>
     internal async Task StartAsync(CancellationToken cancellationToken)
     {
+        // Before anything that can return early, and outside the try: looking for a newer build does not
+        // depend on there being a profile, a server or a vault, and a machine that never gets past the setup
+        // screen is still one that should not be running a build with a hole in it. Start() is a no-op on a
+        // copy that cannot replace itself.
+        updateScreen.Start();
+
         try
         {
             paths.EnsureCreated();
@@ -2467,6 +2531,11 @@ internal sealed partial class MainWindowViewModel : ObservableObject, IAsyncDisp
         workspace.SessionEnded -= OnWorkspaceSessionEnded;
         workspace.FontSizeStepRequested -= OnFontSizeStepRequested;
 
+        // Early, and it only cancels a timer and waits for a pass in flight. It has to come before the
+        // vault because the restart path disposes this whole object and then applies the update — so a
+        // check still running would be writing into a view model the process is about to replace.
+        await updateScreen.DisposeAsync().ConfigureAwait(false);
+
         knownHosts.Close();
 
         // Detached before it is disposed, so a session torn down after this point finds nothing to post to