Let a team change hands, and be joined by somebody with no account yet

M3 built teams and stopped short of the two operations that decide who
controls one. Both were written down as refusals rather than omissions:
ADR 0009 listed ownership transfer under "deliberately not built", and
design-import-gaps said an invitation needed "a token with a lifetime and an
outbound mail path". One of those reasons had expired and the other never
applied — an invitation does not need a token if it is not a thing anybody
presents.

Handing a team over is one write. The member you name becomes owner and you
become an admin, in a single transaction, because ownership is sole: promoting
first leaves the team owned twice, demoting first leaves it owned by nobody,
and there is nobody left with the authority to finish a transfer that stopped
in the middle. That is also why it is not two calls to the role endpoint, which
refuses Owner outright. The outgoing owner is demoted rather than removed —
removing them would revoke their vault key grants and flag every team vault for
rekey, which is a far larger act than the one asked for, and somebody handing
over a team is usually staying in it. It unblocks the thing that was impossible
before: an owner can now leave, by handing the team on first.

An invitation is a standing instruction rather than a message. This server has
no outbound mail path, so nothing is sent and there is nothing for the invitee
to present. The row says the next account signing in with that address joins
this team at this role, and telling them to sign in is the caller's job over a
channel this server does not carry. A link nobody can deliver would be worse
than none. It lives in its own table rather than becoming a membership with
MembershipStatus.Invited, and that member stays unwritten for the reason it
always was: team_membership.user_id is not nullable and carries a foreign key,
so somebody who has never signed in has nothing for that row to point at.
Widening it would make the unique index on (team, user) meaningless, because
PostgreSQL counts every NULL as distinct.

Verification is the security boundary, and nothing in this server read it
before. A claim requires the access token to assert email_verified. An
invitation decides what the server will serve, so one claimable by anybody able
to obtain a token carrying somebody else's address is a way into a team — which
is precisely the attack OidcOptions.AllowEmailLinking exists to refuse, and it
would have been reintroduced by the back door. There is deliberately no setting
that relaxes it: a flag that exists is one somebody turns on for the afternoon
their provider is misconfigured. Absence is refused rather than trusted, and
logged, because a provider that never sends the claim otherwise leaves every
invitation pending with nothing anywhere saying why.

Claiming happens at just-in-time provisioning and again on an hourly sweep. The
sweep is what makes it recoverable rather than one-shot — an invitation issued
between an account being created and that person next signing in would
otherwise be stranded for ever — and it shares its rate with the last-seen
write because both are housekeeping nobody is waiting on.

Archiving is refused while a team owns a vault, and that refusal is the end of
the road rather than a step on it. A team vault is readable because of
membership, so archiving one that still owned vaults would take them away from
everybody holding a key, including the caller, quietly and all at once. Nothing
in this product deletes a vault, so no order of operations gets past it today —
which is stated with a count of what is in the way, for the reason the SFTP
layer refuses a recursive delete: a refusal is visible and a quiet removal is
not. It is owner-only, as handing over is; renaming is not, because a rename is
visible to everybody and reversible by anybody who can do it. The slug is not
renameable at all: it is unique only among live teams, so a rename could take
one an archived team is still holding, and that team could then never be
restored.

LAST ACTIVE is real and coarse on purpose. UserAccount.LastSeenAtUtc is
refreshed on ordinary authenticated requests, at most once per account per
hour, through ExecuteUpdateAsync — user_account carries the xmin concurrency
token, so a read-then-write on the hot path would start losing races between
one user's own overlapping requests. An hour is the granularity the question is
actually asked at, and the interface draws it to the day rather than the minute
so it does not read as a precision that is not there. The remarks in Contracts
and in the view model that argued at length for the column's absence are
rewritten rather than extended; both had become false.

Two endpoints already existed and nothing called them. ChangeTeamMemberRole and
ListVaultGrants have been reachable since M3. The role picker refuses Owner
itself rather than letting the server do it, since the interface already knew
the rule; the key-holder list sits under the vault rather than beside the
member, because a grant is per vault and a count on a member row would imply
per-item sharing, which is M5. It lists withdrawn and stale grants and says
which they are — a list that dropped them would show a departed colleague as
merely absent rather than as somebody whose key was taken away — and staleness
is decided by comparing generations, since a grant can be Active and still open
nothing.

ADD MEMBER stopped being a dead end. An address the directory did not know used
to end at a sentence telling the user their colleague had to sign in first. It
invites them instead, from the same button, because which of the two applies is
a fact about the server's account table rather than about what the user is
doing; which one happened is reported afterwards, because that decides what
they do next. An address that merely has an account is invited rather than
refused: refusing would have made the endpoint an oracle for which addresses
have accounts here, answerable by anybody willing to create a team first.

The phone has a TEAMS screen, behind MORE, and it is the reverse of every other
row in design-import-gaps: a shipped screen the design had no slot for. It is
there because an invitation is claimed by signing in, so somebody told they are
now in a team is at least as likely to be holding a phone — and a membership
visible only on a head they never installed is one they cannot see. It draws
SHARE KEY and nothing that takes something away: wrapping a key is the one act
on that screen a server cannot perform at all, and the desktop guards its
revocations with a tooltip, which is a control a touch screen cannot show.

Two defects were found by an adversarial pass and both were green against the
whole suite at the time. The owner-only check on archiving and handing over had
been weakened to the admin check while their messages and comments still said
owner — and since nothing behind the archive endpoint re-checks it, an admin
the owner had promoted could have archived the team out from under them. And
the rename endpoint built its response with a hardcoded Owner role, so an admin
who renamed a team was handed a summary claiming they owned it, and a client
trusting that instead of re-listing would have offered them the two owner-only
buttons the server then refuses.

The new table gets its constraints tested rather than merely migrated: live
uniqueness per (team, address), the citext proof that an address typed by a
person matches one cased by a provider, and reissue after both revocation and
acceptance. The teams screen gets its first entries in the layout suite, at the
minimum window with every list populated and with each of the two states that
cover half of it — it had none, and it just grew four sections and a second
line in the member row.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/DodoSSH.Api/Authorization/CurrentUserContext.cs

@@ -17,6 +17,38 @@ public interface ICurrentUserContext
     Task<UserAccount> GetOrProvisionAsync(CancellationToken cancellationToken);
 }
 
+/// <summary>
+/// Turns pending team invitations addressed to a verified email into memberships.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Declared here, beside its only caller, and implemented in <c>Features/Teams</c>. The direction is
+/// deliberate: sign-in is what an invitation waits for, so the sign-in path names the shape it needs
+/// and the teams feature supplies it — rather than <see cref="ICurrentUserContext"/>, which every
+/// endpoint in the server depends on, growing a reference into one feature's folder.
+/// </para>
+/// </remarks>
+public interface ITeamInvitationClaim
+{
+    /// <summary>
+    /// Claims every live invitation addressed to <paramref name="email"/> for this account.
+    /// </summary>
+    /// <param name="user">The account signing in.</param>
+    /// <param name="email">The address the token asserted, or null if it asserted none.</param>
+    /// <param name="emailVerified">
+    /// Whether the provider marked that address verified. False refuses the claim outright and is the
+    /// whole of what stops an invitation being taken by anybody able to assert somebody else's
+    /// address.
+    /// </param>
+    /// <param name="cancellationToken">Cancellation.</param>
+    /// <returns>How many invitations became memberships.</returns>
+    Task<int> ClaimAsync(
+        UserAccount user,
+        string? email,
+        bool emailVerified,
+        CancellationToken cancellationToken);
+}
+
 /// <summary>
 /// Request-scoped caller identity with just-in-time provisioning.
 /// </summary>
@@ -29,9 +61,23 @@ internal sealed class CurrentUserContext(
     IHttpContextAccessor accessor,
     DodoDbContext database,
     IOptions<Setup.OidcOptions> oidcOptions,
+    ITeamInvitationClaim invitations,
     TimeProvider clock)
     : ICurrentUserContext
 {
+    /// <summary>
+    /// How stale <see cref="UserAccount.LastSeenAtUtc"/> may get before a request refreshes it.
+    /// </summary>
+    /// <remarks>
+    /// An hour, and coarse on purpose in both directions. Writing it on every request would put an
+    /// UPDATE on the hot path of every authenticated call and — because <c>user_account</c> carries
+    /// the xmin concurrency token — would start losing races between a user's own overlapping
+    /// requests. Writing it never is what made the old "last active" column impossible to offer
+    /// honestly. An hour answers the question a colleague actually asks, which is "this week or not",
+    /// and it is also the window on which a pending invitation is swept for.
+    /// </remarks>
+    private static readonly TimeSpan LastSeenWindow = TimeSpan.FromHours(1);
+
     private UserAccount? cached;
 
     /// <inheritdoc />
@@ -55,14 +101,90 @@ internal sealed class CurrentUserContext(
         var options = oidcOptions.Value;
         var email = principal.FindFirstValue(options.EmailClaim);
         var displayName = principal.FindFirstValue(options.NameClaim);
+        var emailVerified = IsVerified(principal, options.EmailVerifiedClaim);
 
-        cached = await FindAsync(issuer, subject, cancellationToken).ConfigureAwait(false)
-            ?? await ProvisionAsync(issuer, subject, email, displayName, cancellationToken)
+        var existing = await FindAsync(issuer, subject, cancellationToken).ConfigureAwait(false);
+
+        if (existing is null)
+        {
+            cached = await ProvisionAsync(issuer, subject, email, displayName, cancellationToken)
                 .ConfigureAwait(false);
 
+            // A first sign-in is exactly what an invitation is waiting for, so it is claimed at once
+            // rather than on the next hourly sweep — which would leave somebody staring at a team
+            // list that does not yet contain the team they were told they had been added to.
+            await invitations
+                .ClaimAsync(cached, email, emailVerified, cancellationToken)
+                .ConfigureAwait(false);
+
+            return cached;
+        }
+
+        cached = existing;
+
+        await RefreshLastSeenAsync(existing, email, emailVerified, cancellationToken)
+            .ConfigureAwait(false);
+
         return cached;
     }
 
+    /// <summary>
+    /// Records that this account is active, and sweeps for invitations it can now claim.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The two are one operation because they want the same rate. Both are housekeeping nobody is
+    /// waiting on, and doing them together costs one extra round trip per account per hour rather
+    /// than two.
+    /// </para>
+    /// <para>
+    /// The sweep is what makes claiming recoverable rather than one-shot. A claim that failed at
+    /// provisioning — or an invitation issued in the window between an account being created and this
+    /// person next signing in — is picked up here instead of being stranded for ever.
+    /// </para>
+    /// <para>
+    /// <c>ExecuteUpdateAsync</c> rather than the change tracker, and the predicate rather than a
+    /// read-then-write: <c>user_account</c> carries the xmin concurrency token, so two overlapping
+    /// requests from one user would each read the row, each set the timestamp, and the second would
+    /// fail on a version that had moved under it. This writes at most one row and cannot conflict.
+    /// The tracked entity is deliberately left alone — a value up to an hour stale in memory changes
+    /// nothing, and marking it modified would enlist the user row in whatever the request saves next.
+    /// </para>
+    /// </remarks>
+    private async Task RefreshLastSeenAsync(
+        UserAccount user,
+        string? email,
+        bool emailVerified,
+        CancellationToken cancellationToken)
+    {
+        var now = clock.GetUtcNow();
+
+        if (user.LastSeenAtUtc is { } seen && now - seen < LastSeenWindow)
+        {
+            return;
+        }
+
+        await database.Users
+            .Where(u => u.Id == user.Id
+                && (u.LastSeenAtUtc == null || u.LastSeenAtUtc < now - LastSeenWindow))
+            .ExecuteUpdateAsync(
+                setters => setters.SetProperty(u => u.LastSeenAtUtc, now),
+                cancellationToken)
+            .ConfigureAwait(false);
+
+        await invitations
+            .ClaimAsync(user, email, emailVerified, cancellationToken)
+            .ConfigureAwait(false);
+    }
+
+    /// <remarks>
+    /// A JWT boolean arrives as the string "true", so this parses rather than compares against a
+    /// constant. Anything else — absent, "false", or a value this does not understand — is false,
+    /// because the failure that matters is treating an unverified address as verified.
+    /// </remarks>
+    private static bool IsVerified(ClaimsPrincipal principal, string claimType) =>
+        bool.TryParse(principal.FindFirstValue(claimType), out var verified) && verified;
+
     private Task<UserAccount?> FindAsync(string issuer, string subject, CancellationToken cancellationToken) =>
         database.Users.SingleOrDefaultAsync(
             u => u.Issuer == issuer && u.Subject == subject && u.DeletedAtUtc == null,