Add the member the directory cannot see, rather than inviting them

ADD MEMBER quietly issued an invitation instead of adding anybody, for everyone
who had signed in here and not yet enrolled. The screen told them that address
had no account, the members list did not change, and the person only actually
joined on the next hourly sweep.

The client decided whether an address had an account by asking the public-key
directory, and the directory answers a narrower question than that. It drops
every account with no current key — deliberately, because an entry exists to be
wrapped to and one carrying no key is a check a caller forgets exactly once. An
account exists from its owner's first authenticated request and publishes
nothing until they choose a passphrase on their own machine, so every account is
missing from the directory for that whole window and some indefinitely. A miss
there is not an absent account, and reading it as one was the bug.

The server would have taken the add. TeamService.AddMemberAsync only requires
the account row, and TeamMemberSummary.IsEnrolled exists precisely so a member
with no key can be listed — added on Monday, enrolled on Tuesday. The client
never asked.

So the directory is still asked first and the miss is retried as an add by
address, and only a server saying there is no such account reaches the
invitation. AddTeamMemberRequest gained an Email used when UserId is empty. The
lookup-first ordering is kept because it is load-bearing for sharing and not for
this: the key verified before a vault key is wrapped is the one the lookup
returned, and nothing is wrapped by adding somebody. That is why resolving the
address server-side is safe here and would not be there.

NoSuchAccount is its own code rather than folded into InvalidTeam, because it is
the one add failure the caller can act on unprompted — there is nobody to add,
so invite them — and a code shared with a rejected role would leave them
guessing which had happened. It does answer whether an address has an account
here, which CreateTeamInvitationRequest deliberately does not. That is the
property traded for the fix; the exposure is bounded by the admin check the add
already needed, and it is the same fact the member list shows a moment later.
Adding by a user id that does not exist now answers 404 no-such-account rather
than 400 invalid-team, and nothing depended on the old pairing.

The two silent returns are gone. Offline and no-team-selected set nothing and
returned, so those failures were visible only as a flicker of the busy flag —
which reads as a button that does nothing at all. The success line reads the
enrollment flag too, because pointing an unenrolled member at SHARE KEY is
pointing at a button that will refuse; their row already says it holds no key.

Why nothing caught it. FakeVaultServer had one list, so it could not tell an
account that does not exist from one that exists and has not enrolled — the
distinction this whole path turns on — and every account it knew was enrolled by
construction. It grows an accounts list beside the directory and reports
IsEnrolled from whether the directory has them, rather than hardcoding true. The
regression test asserts Invitations is empty, which is what fails against the
old behaviour. Four tests: that pair in the shell suite, and in the API suite an
unenrolled account added by address after its own directory lookup comes back
empty, and an unknown address refused under the new code. 1495 tests pass.

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

@@ -31,6 +31,17 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
     private readonly List<DirectoryEntry> directory = [];
     private readonly Dictionary<Guid, List<TeamInvitationSummary>> invitations = [];
 
+    /// <summary>
+    /// Every account on this fake server, enrolled or not.
+    /// </summary>
+    /// <remarks>
+    /// Kept apart from <see cref="directory"/> because the real server keeps them apart, and the gap
+    /// between the two is where a real bug lived: the directory omits anybody who has not published a
+    /// key, so a fake that had only one list could not tell an account that does not exist from one
+    /// that exists and has not enrolled — which is exactly the distinction the add path turns on.
+    /// </remarks>
+    private readonly List<(Guid UserId, string Email, string DisplayName)> accounts = [];
+
     /// <inheritdoc />
     public ITeamApi Teams => this;
 
@@ -75,6 +86,27 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
             KeyGeneration: 1,
             KeyLogSequence: sequence));
 
+        accounts.Add((userId, email, displayName));
+
+        return userId;
+    }
+
+    /// <summary>
+    /// Registers an account that has signed in here but has not enrolled a key.
+    /// </summary>
+    /// <remarks>
+    /// Normal rather than exotic: an account exists from its owner's first authenticated request and
+    /// stays keyless until they choose a passphrase on their own machine. It is absent from the
+    /// directory throughout, because a directory entry exists to be wrapped to and this one has nothing
+    /// to wrap. It can still be made a member — membership grants nothing readable.
+    /// </remarks>
+    /// <returns>Their user id.</returns>
+    internal Guid AddUnenrolledAccount(string email, string displayName)
+    {
+        var userId = Guid.CreateVersion7();
+
+        accounts.Add((userId, email, displayName));
+
         return userId;
     }
 
@@ -241,27 +273,40 @@ internal sealed partial class FakeVaultServer : ITeamApi, IDirectoryApi, IVaultG
         return members.TryGetValue(teamId, out var list) ? [.. list] : [];
     }
 
-    /// <inheritdoc />
+    /// <summary>Adds a member, resolved by id when the caller has one and by address otherwise.</summary>
+    /// <remarks>
+    /// Resolved against <see cref="accounts"/> rather than <see cref="directory"/>, which is the whole
+    /// point of the two being separate here: an account with no published key is missing from the
+    /// directory and is still perfectly addable. <c>IsEnrolled</c> is reported from whether the
+    /// directory has them rather than hardcoded, so a member row can say it holds no key.
+    /// </remarks>
     public Task<TeamMemberSummary> AddTeamMemberAsync(
         Guid teamId,
         AddTeamMemberRequest request,
         CancellationToken cancellationToken)
     {
-        var entry = directory.Find(candidate => candidate.UserId == request.UserId)
-            ?? throw new DodoSshApiException(
-                System.Net.HttpStatusCode.BadRequest,
-                ProblemCodes.InvalidTeam,
+        var account = request.UserId != Guid.Empty
+            ? accounts.Find(candidate => candidate.UserId == request.UserId)
+            : accounts.Find(candidate => string.Equals(
+                candidate.Email, request.Email, StringComparison.OrdinalIgnoreCase));
+
+        if (account.UserId == Guid.Empty)
+        {
+            throw new DodoSshApiException(
+                System.Net.HttpStatusCode.NotFound,
+                ProblemCodes.NoSuchAccount,
                 "No such account on this server.");
+        }
 
         // LastActiveAt is left null: this account has been added, not seen. The owner's row carries a
         // real one, so both branches of the interface's "last active / never" split are exercised.
         var member = new TeamMemberSummary(
-            entry.UserId,
-            entry.Email,
-            entry.DisplayName,
+            account.UserId,
+            account.Email,
+            account.DisplayName,
             request.Role,
             TeamMemberStatus.Active,
-            IsEnrolled: true,
+            IsEnrolled: directory.Exists(entry => entry.UserId == account.UserId),
             DateTimeOffset.UnixEpoch,
             LastActiveAt: null);