Merge branch 'main' into the desktop updater, and give way on two numbers

Main landed a realtime push feature while this branch was building the updater,
and the two collided in three places. Every one of them resolves the same way:
main got there first, so this branch moves.

**Two ADRs were both numbered 0012.** Main's is realtime push; this one is now
[ADR 0013](docs/adr/0013-desktop-distribution-and-updates.md). Git did not call
this a conflict — the filenames differ — so it would have merged quietly and left
the directory with two 0012s and every cross-reference ambiguous. Renumbered here
along with the nine places that point at it.

**Two manual-check phases were both numbered 15**, and that one git did catch.
Main's "Changes that arrive without a timer" keeps 15; installing and updating
the desktop client becomes Phase 16, with its checks and every reference to them
renumbered. The file's own rule is that a number is for life, which is exactly
why the one that had not been pushed is the one that gives way.

**The merge rewrote several files with CRLF**, and `.editorconfig` asks for LF on
everything except `*.ps1`. That is not cosmetic here: IDE0055 is an error and
`EnforceCodeStyleInBuild` is on, so it failed the build on three lines of
App.axaml.cs whose only change in this branch was an ADR number in a comment.
Forty-six files normalised back to LF; the release script keeps CRLF, which is
what `.gitattributes` and `.editorconfig` both already say for a PowerShell file.

Nothing else conflicted. The updater does not touch the sync loop or the event
stream, and the one file both sides edited heavily — MainWindowViewModel — merged
without a hunk in common.

Verified after merging: the solution restores locked and builds clean, and 304
shell, 100 layout, 54 session, 28 client-api and 25 contracts tests pass. The
first two counts are higher than before the merge because main's own tests came
with it and pass alongside these.

src/DodoSSH.Client.Session/ServerConnection.cs

@@ -150,6 +150,17 @@ public interface IVaultServer : IDisposable
     /// <summary>Vault key grants: who can open a vault, and who let them.</summary>
     IVaultGrantApi Grants { get; }
 
+    /// <summary>
+    /// Notices that something changed, so a synchronisation need not wait for the timer.
+    /// </summary>
+    /// <remarks>
+    /// Always present, never null: a server that does not offer the feature — or a test standing in
+    /// for one — supplies <see cref="IdleVaultEventStream"/>, which simply never delivers. That keeps
+    /// every caller on one shape, because the correct behaviour without a socket is the behaviour
+    /// with a silent one: synchronise on the timer. See ADR 0012.
+    /// </remarks>
+    IVaultEventStream Events { get; }
+
     /// <summary>Obtains the identity provider's signature over a key statement.</summary>
     IKeyBindingAuthorizer KeyBinding { get; }
 
@@ -197,7 +208,8 @@ public sealed class ServerConnection : IVaultServer
         MetaResponse meta,
         OidcClient oidc,
         RefreshingAccessTokenProvider tokens,
-        DodoSshApiClient api)
+        DodoSshApiClient api,
+        TimeProvider clock)
     {
         ServerUrl = serverUrl;
         this.http = http;
@@ -206,6 +218,14 @@ public sealed class ServerConnection : IVaultServer
         Oidc = oidc;
         this.tokens = tokens;
         Api = api;
+
+        // Decided from what this server said it supports rather than attempted and allowed to fail,
+        // which is the same capability negotiation SyncOptions below does — see ADR 0002. A client
+        // that dialled anyway would reconnect against a 404 for the whole session, and would look
+        // from the outside exactly like one whose network was eating WebSockets.
+        Events = meta.Features.Contains(VaultEvents.Feature, StringComparer.Ordinal)
+            ? new VaultEventStream(serverUrl, tokens, clock)
+            : IdleVaultEventStream.Instance;
     }
 
     /// <summary>The server this is connected to.</summary>
@@ -238,6 +258,9 @@ public sealed class ServerConnection : IVaultServer
     /// <inheritdoc />
     public IVaultGrantApi Grants => Api;
 
+    /// <inheritdoc />
+    public IVaultEventStream Events { get; }
+
     /// <inheritdoc />
     public IKeyBindingAuthorizer KeyBinding => Oidc;
 
@@ -311,7 +334,8 @@ public sealed class ServerConnection : IVaultServer
                 meta,
                 oidc,
                 refreshing,
-                new DodoSshApiClient(transport, refreshing));
+                new DodoSshApiClient(transport, refreshing),
+                clock);
         }
         catch
         {
@@ -382,7 +406,8 @@ public sealed class ServerConnection : IVaultServer
                 meta,
                 oidc,
                 refreshing,
-                new DodoSshApiClient(transport, refreshing));
+                new DodoSshApiClient(transport, refreshing),
+                clock);
         }
         catch
         {
@@ -400,6 +425,12 @@ public sealed class ServerConnection : IVaultServer
         }
 
         disposed = true;
+
+        // First, and without waiting: the socket's own loops read the token provider and the transport
+        // below, so tearing either down while it is still dialling would surface as a fault on a
+        // background thread at the moment a user signed out.
+        Events.Dispose();
+
         tokens.Dispose();
         http.Dispose();
     }