Make a vault the thing you create, and let a window set one aside

Everything a shared vault needs was already here and arranged the wrong way
round. A vault has to belong to a team, so creating one meant going to the teams
screen, founding an organisation, and only then adding a vault to it — which the
NEW VAULT button named after the team, so a team with three of them held three
vaults called the same thing and nothing told them apart. Somebody who wants to
share four servers with two colleagues is not asking to found anything.

So the form asks for a name and nothing else. The team is derived from it, slug
included, and created with this account as its owner; the vault goes inside; and
the members, roles, invitations and key holders that hang off a team are all on
screen the moment it exists. The tab strip's New vault entry lands there with the
new vault selected, which is where the next thing anybody wants to do already is.

That is two calls, and the first can succeed alone. When it does the team is
kept: the id is minted once into pendingVaultTeamId, so pressing CREATE again
resends the identical create — which the server treats as the same team — and
retries the vault, and the message says all of that rather than "creating the
vault failed". Archiving the orphan instead would be a client deleting something
on the user's behalf because a later step failed, which is the kind of tidying
that eventually archives a team somebody has just been added to. A slug taken by
somebody else is retried once with a disambiguated one and never in a loop; a
name with no a-z or 0-9 anywhere in it falls back to the team's own id rather
than to a refusal pointing at a field nobody was shown.

The other half is the caret beside Vaults. Being in four teams means four teams'
machines in front of you all day, and the answer is a switch per vault rather
than four sign-ins. Switching one off takes its hosts, groups, keys and pins off
the screens that list them and does nothing else: it still syncs, its key stays
in the keyring, it stays choosable as somewhere to file a new item, and a shown
host that authenticates with a key filed in it still connects. That last one is
what shaped the design. TryBuildAuthentication resolves a binding out of the
keychain's typed list and a cross-vault binding is legal, so filtering the reload
loops — the obvious implementation — would have turned a preference about reading
into an outage. Only the projections a person reads consult IsVaultShown; every
Reload*Async stays whole, including the dialled-endpoint set that decides which
pins are described as unused, because that is a hint which invites deleting
trust.

Snippets, logs and buckets needed no code and the comment says so out loud: all
three read ActiveVaultId alone, and the personal vault is drawn in the menu
ticked and cannot be switched off — it is the active vault, the group and tag
editors' target, and the save picker's fallback, so hiding it would empty half
the application rather than filter it.

The preference is a column on the cache's vault row, which is what makes it
survive both a relaunch and the /me refresh that runs every minute: Apply does
not touch it, deliberately, because the server has never been told which vaults
this machine is showing. It is in the encrypted cache rather than settings.json
because it is a list of vault ids and that file's own doc comment says what may
go in it. VaultSession cannot see the type at all — ReadableVaults is what the
sync loop walks, and a filter reaching it would be a vault that quietly stopped
syncing, found out weeks later from a host that was never there.

The strip's note refusing a MenuFlyout stands and is unchanged. This flyout
sidesteps the question rather than answering it: the handler selects the Vaults
tab first, which collapses the renderer, so nothing native is under the popup by
the time it opens — the move QuickConnect already makes. A headless test asserts
that ordering, which is as far as headless can go with no native window, and
manual check 1.6 is the other half.

The phone is out of scope on purpose: it has no tab strip and its teams screen's
vault section is read-only. The plumbing is in Client.Shell, so it can adopt this
later; until then nothing there is ever hidden, which is today's behaviour.

1514 tests pass. Fifteen are new in VaultVisibilityTests, and the ones worth
naming are the guards: a hidden vault still syncs, still holds keys that
authenticate hosts on screen, still appears in the save picker, and still counts
towards which pins nothing dials.

Not fixed, and noted here because it is next door: VaultGrantService's team-vault
create refuses a taken vault id rather than returning the existing vault, while
VaultSharing's own remark claims a create whose response was lost is safe to
resend. A lost 200 therefore leaves a vault whose key the client's catch already
zeroed, openable by nobody.

tests/DodoSSH.Client.App.Tests/FakeVaultServer.Teams.cs

@@ -52,6 +52,24 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
     /// </remarks>
     internal bool CorruptKeyLog { get; set; }
 
+    /// <summary>Slugs this fake refuses, as the real server refuses one already in use.</summary>
+    /// <remarks>
+    /// A vault's slug is derived from its name rather than typed, so a collision is something the client
+    /// has to get out of on its own — and a fake that accepted every slug could not tell whether it does.
+    /// </remarks>
+    internal HashSet<string> TakenSlugs { get; } = new(StringComparer.Ordinal);
+
+    /// <summary>How many vault creates to refuse before answering normally.</summary>
+    /// <remarks>
+    /// Creating a vault of its own is two calls, and the failure worth testing is the one between them:
+    /// the team is made and the vault is not. One refusal is enough to leave the client in that state and
+    /// let the test press CREATE again.
+    /// </remarks>
+    internal int VaultCreateFailures { get; set; }
+
+    /// <summary>How many team creates have been asked for, for a test to assert on.</summary>
+    internal int TeamCreates { get; private set; }
+
     /// <summary>Registers another account, as though they had signed in and enrolled here.</summary>
     /// <returns>Their user id.</returns>
     internal Guid AddAccount(string email, string displayName)
@@ -87,6 +105,24 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
         CreateTeamRequest request,
         CancellationToken cancellationToken)
     {
+        TeamCreates++;
+
+        // Idempotent on the client-chosen id, as the real one is. That is the whole of how a create whose
+        // second half failed is retried without leaving a second team behind, so a fake that made one
+        // anyway would let the bug through.
+        if (teams.Find(row => row.TeamId == request.TeamId) is { } existing)
+        {
+            return Task.FromResult(existing);
+        }
+
+        if (TakenSlugs.Contains(request.Slug))
+        {
+            throw new DodoSshApiException(
+                System.Net.HttpStatusCode.Conflict,
+                ProblemCodes.TeamSlugTaken,
+                $"The slug '{request.Slug}' is already in use.");
+        }
+
         var team = new TeamSummary(
             request.TeamId,
             request.Name,
@@ -388,6 +424,16 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
         CreateTeamVaultRequest request,
         CancellationToken cancellationToken)
     {
+        if (VaultCreateFailures > 0)
+        {
+            VaultCreateFailures--;
+
+            throw new DodoSshApiException(
+                System.Net.HttpStatusCode.ServiceUnavailable,
+                code: null,
+                "The server is not answering.");
+        }
+
         var vault = new VaultSummary(
             request.VaultId,
             request.Name,