Let a shared vault arrive, a bucket be found, and a vault be deleted

Three things a user reported, one of which was a real bug and one of which was
not the bug it looked like.

**A vault shared with somebody never reached their machine.** The grant was
correct at both ends: the sharing client verified the recipient's key against the
key log and wrapped every generation to it, the server stored it, and /me would
have returned it. Nothing asked. VaultSession.RefreshVaultsAsync — the method
whose own summary says it is "called after a share and on a periodic pass" — had
no caller anywhere in the application, so the vault list was whatever the last
browser sign-in cached. A restart did not help: an offline unlock reads that same
cache. The vault appeared only if the recipient happened to sign in through the
browser again, which is why this looked like sharing being broken rather than
like a list that was never re-read.

So every synchronisation pass now re-reads it, before it syncs. SyncOnceAsync
takes the whole server rather than its sync half for that reason, and the order
matters: a vault admitted by the refresh is one that same pass then pulls, where
the other order would show a newly shared vault as an empty one until the minute
after. The shell is told only when the set actually changed — it rebuilds the tab
strip's vault menu from the session's list, and doing that on every quiet pass
would rebuild a menu once a minute for nothing.

The test needed the fake server to be able to do something no test here had
needed before: hand this account a vault it did not make. ShareVaultWithMe wraps
a real key to the encryption key this account enrolled, so the keyring opens it
exactly as it opens a real colleague's — a helper that filled the field with
bytes would let a vault appear in the list and never prove it could be read.

**Adding an S3 bucket on the desktop works, and could not be found.** The report
was that it is not possible; driving the real XAML headlessly says otherwise —
Keychain, + BUCKET, and the editor saves. What is true is that S3 is where
somebody goes looking, and from there SELECT BUCKET opened a combo box with
nothing in it and no sentence anywhere saying that a bucket is a keychain item.
From where the user was standing that is indistinguishable from an application
with no way to add one.

The empty state now says what a bucket is and offers a button that lands on the
keychain with the editor already open — navigating to the screen and leaving
+ BUCKET to be found among five buttons would be most of the same problem. The
phone gets the sentence and no button: its keychain screen reads and deletes and
edits nothing, so there is no editor to send anybody to, and naming the machine
that has one beats an empty control that reads as a screen still loading.

The keychain screen's layout test grew the two categories it never covered.
Tags and buckets arrived after it was written, and the header strip it measures
is one that has overflowed twice before.

**A vault can now be deleted.** DELETE /api/v1/vaults/{id}, gated on Admin —
the line the rename already drew, for a stronger version of its reason, since
this takes the vault from everybody in it at once. The row is soft-deleted and
every grant to it withdrawn in one write; VaultAccessService filters on the stamp
at both ends, so from that moment the vault is absent from every member's /me and
every call naming it answers 404. Their clients notice on the pass described
above.

The team behind it is archived when it owned nothing else, which is the mirror of
renaming it: a vault made from the vaults screen gets a team named after it that
nobody was ever shown, and leaving that behind would leave a membership list no
screen has a row for. That is a second call rather than one transaction —
archiving is TeamService's, it refuses while a team owns vaults, and it can only
tell that this one no longer does once the deletion is committed. A crash between
the two leaves an empty team: invisible, archivable afterwards, harmless, and a
better failure than a vault that could not be deleted because tidying up after it
did not work.

Two refusals worth stating. The personal vault cannot be deleted at either end:
it is created by enrollment, everything filed nowhere else lives in it, and no
call would make another. And the items are kept — ciphertext behind a vault
nothing will resolve, so deleting them buys no confidentiality while destroying
what an operator undoing a mistake would need.

The client drops the key from the keyring and the row from the cache rather than
waiting for a refresh, so the list is right immediately; the items stay, as they
stay for a vault whose grant was withdrawn, because a copy is on every other
member's machine too and removing these rows would be the client pretending to a
reach it does not have. The confirmation says that out loud before it is
answered. It is the one sentence this screen must not leave implied: deletion is
no more retroactive than revocation is. See ADR 0001.

Desktop only, deliberately. The Android vaults screen offers no rename and no
hand-over either, so adding delete alone there would be the one destructive vault
operation on a screen with no other.

Three places asserted that a vault can never be deleted — TeamService's refusal
message, the TeamNotEmpty problem code, and ADR 0009 — and each now names the
route instead.

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

@@ -313,13 +313,24 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     /// removes the thread from the question rather than making the test guess it right.
     /// </para>
     /// </param>
+    /// <param name="addBucket">
+    /// Takes the user to where a bucket is made, or null in a head that has nowhere to take them.
+    /// <para>
+    /// A delegate rather than this screen making one itself, and it is the same seam the vaults screen uses
+    /// for the shell: a bucket is a keychain item, the editor that writes one belongs to the keychain screen,
+    /// and duplicating it here would be a second form writing the same secret. What this screen owns is the
+    /// knowledge that somebody standing on it with no buckets needs to be sent somewhere.
+    /// </para>
+    /// </param>
     internal TransfersViewModel(
         ISftpSessionFactory sftp,
         TimeProvider clock,
-        Action<Action>? post = null)
+        Action<Action>? post = null,
+        Action? addBucket = null)
     {
         this.sftp = sftp;
         this.post = post ?? (action => Dispatcher.UIThread.Post(action));
+        this.addBucket = addBucket;
 
         // The supplier answers with whatever session is current at the moment a transfer starts, which is
         // what lets a queue survive a disconnect and reconnect without every queued row failing.
@@ -332,6 +343,32 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
         RemoteEntries.CollectionChanged += (_, _) => OnPropertyChanged(nameof(HasRemoteEntries));
         LocalEntries.CollectionChanged += (_, _) => OnPropertyChanged(nameof(HasLocalEntries));
         Transfers.CollectionChanged += (_, _) => OnPropertyChanged(nameof(HasTransfers));
+
+        // The fourth, and it follows a list this screen does not own: the buckets are refilled from the
+        // vault on every synchronisation pass, so the invitation these flags decide between has to change
+        // with them rather than at the moment somebody pressed something. That is the path that matters —
+        // adding the first bucket happens on another screen, and this one has to notice when it comes back.
+        Buckets.CollectionChanged += (_, _) => RaiseBucketState();
+    }
+
+    /// <summary>Where a bucket is made, or null in a head with nowhere to send anybody.</summary>
+    private readonly Action? addBucket;
+
+    /// <summary>Goes to the keychain with the bucket editor open.</summary>
+    /// <remarks>
+    /// The dead end this replaces was a real one: SELECT BUCKET opened a picker with nothing in it, and
+    /// nothing anywhere on the screen said that a bucket is made on the keychain screen. Somebody who had
+    /// come to S3 to add one had arrived at the place it is used and been shown no route to the place it is
+    /// created.
+    /// </remarks>
+    [RelayCommand]
+    private void AddBucket()
+    {
+        // Closed first, so returning here from the keychain does not find a picker still open over a list
+        // that has since gained the bucket it was empty of.
+        IsChoosingRemote = false;
+
+        addBucket?.Invoke();
     }
 
     /// <summary>The hosts that can be connected to, which is the vault's list.</summary>
@@ -352,6 +389,28 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     [ObservableProperty]
     private ObjectStoreRowViewModel? selectedBucket;
 
+    /// <summary>
+    /// Whether there is a bucket to open at all.
+    /// </summary>
+    /// <remarks>
+    /// The question this screen used to answer by showing an empty combo box. A bucket is made on the
+    /// keychain screen and nowhere else, and S3 is where somebody goes looking for it — so a picker with
+    /// nothing in it and no sentence beside it was, from where the user was standing, an application with no
+    /// way to add a bucket. See <see cref="AddBucket"/>.
+    /// </remarks>
+    internal bool HasBuckets => Buckets.Count > 0;
+
+    /// <summary>Whether this screen is on S3 with a bucket to offer.</summary>
+    /// <remarks>
+    /// The two flags are resolved here rather than combined in markup, because a binding cannot say "and" —
+    /// and because the pair is one question with two answers, which is easier to keep straight in one place
+    /// than in four <c>IsVisible</c> expressions that have to stay each other's opposites.
+    /// </remarks>
+    internal bool ShowsBucketChoice => ShowsBucketPicker && HasBuckets;
+
+    /// <summary>Whether this screen is on S3 with nothing to open yet.</summary>
+    internal bool ShowsNoBuckets => ShowsBucketPicker && !HasBuckets;
+
     /// <summary>
     /// Which sort of remote the right-hand pane is about to open.
     /// </summary>
@@ -1641,16 +1700,30 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     partial void OnRemoteChanged(RemoteKind value)
     {
         OnPropertyChanged(nameof(ShowsHostPicker));
-        OnPropertyChanged(nameof(ShowsBucketPicker));
         OnPropertyChanged(nameof(ConnectLabel));
         OnPropertyChanged(nameof(SelectedHostAsksForAPassword));
 
+        RaiseBucketState();
+
         // Arriving at the other destination shows its invitation rather than a picker somebody left open on
         // this one — and the picker it would have left open is the wrong one, since the two kinds have
         // different lists behind them.
         IsChoosingRemote = false;
     }
 
+    /// <summary>Raises the three flags that answer "is there a bucket to open".</summary>
+    /// <remarks>
+    /// Together, because they are one fact read three ways and a caller that raised two of them would leave
+    /// an invitation and an empty state on screen at once.
+    /// </remarks>
+    private void RaiseBucketState()
+    {
+        OnPropertyChanged(nameof(ShowsBucketPicker));
+        OnPropertyChanged(nameof(HasBuckets));
+        OnPropertyChanged(nameof(ShowsBucketChoice));
+        OnPropertyChanged(nameof(ShowsNoBuckets));
+    }
+
     partial void OnIsConnectedChanged(bool value)
     {
         OnPropertyChanged(nameof(CanDownload));