Merge branch 'main' into the vaults screen, and let it rotate keys too

Main built vault key rotation while this branch was reshaping the screen that
would drive it, so the two met in the same three files. Every other conflict was
textual and resolved by taking both; these are the ones where a decision had to
be made.

**The view model.** Main taught TeamsViewModel three things and this branch had
renamed and rewritten it into VaultsViewModel. All three are ported rather than
dropped, because each is a behaviour rather than wording: adding somebody now
wraps the vault to them on the spot instead of leaving SHARE KEY to be pressed,
removing somebody rotates the vault and hands the new key to whoever is left, and
a share reports how many generations were wrapped. The session calls they reach —
ShareTeamVaultsAsync and RekeyTeamVaultsAsync — are scoped to a membership list
rather than to one vault, and they are called that way here rather than narrowed:
adding somebody is a change to the list, so every vault the list carries is one
they can now fetch. This screen makes lists that carry one vault, so the sentences
name one; where a list carries several, naming them all is the honest report, and
the members section already says the list is shared.

AddMemberAsync ran two lines over the length limit once the sharing was in it, so
the calls behind it moved to AddOrInviteAsync and the three-way refusal to
WhyNobodyCanBeAdded — the command reads as its guards now, which is what it was
before the sharing arrived.

**The tests.** Main's four new cases are ported to the vault-first API, including
the one that matters most: the tampered key log is corrupted *before* the add,
because the add is now a route to a wrap and a test that corrupted it afterwards
would be asserting about the manual route only. SelectingAVault_ListsWhoHoldsAKey
now expects two holders rather than one — main's fake records the creator's own
self-grant, and a key-holder list that omitted it would show the one person who
can certainly open a new vault as somebody who cannot.

**The README.** The limits list is six rather than four or five: main's rotation
entries and this branch's "a vault cannot be deleted" describe different things
and both are true. "The rekey is flagged, never performed" is gone, since it is
now performed, and M3 reads *Done* rather than *Done, except rekey*.

One thing worth writing down that neither side had. An invitation claimed at
sign-in still leaves the key owed, where an add does not: at the moment an
invitation is issued there is no account and no published key to wrap to, and the
claim happens on the invitee's machine, which holds nothing. Manual check 12.1
says so, because a reader who knows adding shares would otherwise read that step
as stale.

1561 tests pass.

src/DodoSSH.Api/Features/Identity/IdentityService.cs

@@ -81,15 +81,25 @@ internal sealed class IdentityService(DodoDbContext database, IVaultAccessServic
         {
             var vault = access.Vault!;
 
-            // The grant must match both the current key generation and the exact identity key it
-            // was wrapped to. A grant left over from a superseded key is not merely stale — the
-            // client's current private key cannot open it, so offering it would produce a tag
-            // failure the user reads as data corruption.
-            var grant = grants.Find(g =>
-                g.VaultId == vault.Id
-                && g.KeyGeneration == vault.KeyGeneration
-                && key is not null
-                && g.RecipientKeyFingerprint.AsSpan().SequenceEqual(key.FingerprintSha256));
+            // The grant must match the exact identity key it was wrapped to. One left over from a
+            // superseded identity key is not merely stale — the client's current private key cannot
+            // open it, so offering it would produce a tag failure the user reads as data corruption.
+            var mine = grants
+                .Where(g => g.VaultId == vault.Id
+                    && key is not null
+                    && g.RecipientKeyFingerprint.AsSpan().SequenceEqual(key.FingerprintSha256))
+                .ToList();
+
+            var grant = mine.Find(g => g.KeyGeneration == vault.KeyGeneration);
+
+            // Everything older, oldest first. A rotation does not re-encrypt what is already stored —
+            // each item keeps the generation it was sealed under — so a client holding only the
+            // current key would read the vault's whole history as corrupt. See RekeyVaultRequest.
+            var prior = mine
+                .Where(g => g.KeyGeneration < vault.KeyGeneration)
+                .OrderBy(g => g.KeyGeneration)
+                .Select(g => new VaultKeyWrap((uint)g.KeyGeneration, g.WrappedKey))
+                .ToArray();
 
             summaries.Add(new VaultSummary(
                 VaultId: vault.Id,
@@ -103,7 +113,8 @@ internal sealed class IdentityService(DodoDbContext database, IVaultAccessServic
                 // re-wrap it; the client has to say so rather than showing an empty vault.
                 WrappedVaultKey: grant?.WrappedKey,
 
-                RekeyRequired: vault.RekeyRequired));
+                RekeyRequired: vault.RekeyRequired,
+                PriorKeyWraps: prior));
         }
 
         return summaries;

src/DodoSSH.Api/Features/Teams/TeamLog.cs

@@ -76,6 +76,21 @@ internal static partial class TeamLog
     internal static partial void GrantRevoked(
         ILogger logger, Guid vaultId, Guid recipientId, Guid actorId);
 
+    /// <remarks>
+    /// Warning, because a rotation is the one operation that changes what every other member's key is
+    /// worth: until each of them is wrapped the new generation, they hold the vault's history and
+    /// cannot read anything written since. An operator seeing members report an unreadable vault needs
+    /// this line and its timestamp to explain it.
+    /// </remarks>
+    [LoggerMessage(
+        EventId = 2115,
+        Level = LogLevel.Warning,
+        Message = "Rotated the key of vault {VaultId} to generation {KeyGeneration}, by {ActorId}. "
+            + "Earlier grants are kept so stored items stay readable; every other member needs the new "
+            + "generation wrapped to them before they can read anything written from now on.")]
+    internal static partial void VaultRekeyed(
+        ILogger logger, Guid vaultId, int keyGeneration, Guid actorId);
+
     [LoggerMessage(
         EventId = 2108,
         Level = LogLevel.Information,

src/DodoSSH.Api/Features/Teams/VaultGrantEndpoints.cs

@@ -186,6 +186,70 @@ internal sealed class IssueVaultGrantEndpoint(
     }
 }
 
+/// <summary>Moves this vault to a fresh key.</summary>
+/// <remarks>
+/// Gated on Share rather than on a rotation permission of its own. Rotating decides who can read what
+/// is written next, which is the same question sharing and withdrawing answer, and a fourth permission
+/// would be a distinction nobody administering a team would be able to explain.
+/// </remarks>
+internal sealed class RekeyVaultEndpoint(
+    ICurrentUserContext currentUser,
+    IVaultAccessService vaultAccess,
+    VaultGrantService grants)
+    : Endpoint<RekeyVaultRequest, Results<Ok<VaultSummary>, NotFound, ProblemHttpResult>>
+{
+    /// <inheritdoc />
+    public override void Configure()
+    {
+        Post("/api/v1/vaults/{vaultId:guid}/rekey");
+
+        Policies(Auth.EnrolledPolicy);
+
+        Description(b => b
+            .WithName("RekeyVault")
+            .WithSummary("Advances this vault's key generation, wrapped to the caller.")
+            .WithTags("Vaults"));
+    }
+
+    /// <inheritdoc />
+    public override async Task<Results<Ok<VaultSummary>, NotFound, ProblemHttpResult>> ExecuteAsync(
+        RekeyVaultRequest req,
+        CancellationToken ct)
+    {
+        var user = await currentUser.GetOrProvisionAsync(ct).ConfigureAwait(false);
+        var access = await vaultAccess
+            .ResolveAsync(user.Id, Route<Guid>("vaultId"), ct)
+            .ConfigureAwait(false);
+
+        if (!access.Granted || !access.Permissions.HasFlag(PermissionFlags.Read))
+        {
+            return TypedResults.NotFound();
+        }
+
+        if (!access.Permissions.HasFlag(PermissionFlags.Share))
+        {
+            return Problems.Coded(
+                StatusCodes.Status403Forbidden,
+                ProblemCodes.Forbidden,
+                "You do not have permission to share this vault, so you cannot rotate its key.");
+        }
+
+        try
+        {
+            var summary = await grants
+                .RekeyAsync(user, access.Vault!, (int)access.Permissions, req, ct)
+                .ConfigureAwait(false);
+
+            return TypedResults.Ok(summary);
+        }
+        catch (VaultGrantInvalidException exception)
+        {
+            return Problems.Coded(
+                StatusCodes.Status400BadRequest, ProblemCodes.InvalidVaultGrant, exception.Message);
+        }
+    }
+}
+
 /// <summary>Withdraws a member's key to this vault.</summary>
 /// <remarks>
 /// 404 for a member who holds no live grant, rather than a bland 204, for the reason device

src/DodoSSH.Api/Features/Teams/VaultGrantService.cs

@@ -217,6 +217,13 @@ internal sealed class VaultGrantService(
     }
 
     /// <summary>Lists who can open a vault.</summary>
+    /// <remarks>
+    /// One row per holder, not one per grant. A rotated vault holds several grants per member — one per
+    /// generation, which is what lets them read its history — and a listing that showed each of them
+    /// would answer "who can open this" with the same person three times. The row carries the best key
+    /// they hold: the live grant at the highest generation, or, for somebody whose access has been
+    /// withdrawn, the most recent grant they had, so the withdrawal is still visible.
+    /// </remarks>
     internal async Task<VaultGrantsResponse> ListGrantsAsync(
         Vault vault,
         CancellationToken cancellationToken)
@@ -228,13 +235,25 @@ internal sealed class VaultGrantService(
             .ToListAsync(cancellationToken)
             .ConfigureAwait(false);
 
+        var holders = grants
+            .GroupBy(g => g.RecipientUserId!.Value)
+            .Select(group => group
+                .OrderByDescending(g => g.RevokedAtUtc is null)
+                .ThenByDescending(g => g.KeyGeneration)
+                .First())
+
+            // The order the first grant of each holder was made in, so the list reads as the vault was
+            // shared rather than reshuffling itself every time somebody is re-wrapped.
+            .OrderBy(g => grants.Find(first => first.RecipientUserId == g.RecipientUserId)!.CreatedAtUtc)
+            .ToList();
+
         return new VaultGrantsResponse(
             VaultId: vault.Id,
             KeyGeneration: (uint)vault.KeyGeneration,
             RekeyRequired: vault.RekeyRequired,
             Grants:
             [
-                .. grants.Select(g => new VaultGrantSummary(
+                .. holders.Select(g => new VaultGrantSummary(
                     g.RecipientUserId!.Value,
                     g.RecipientUser?.Email,
                     g.RecipientUser?.DisplayName,
@@ -248,10 +267,18 @@ internal sealed class VaultGrantService(
 
     /// <summary>Wraps a vault key to another member.</summary>
     /// <remarks>
-    /// Re-issuing to a recipient who already holds a live grant replaces it in place rather than
-    /// inserting a second row, because the unique index permits exactly one live grant per recipient
-    /// per generation — and because the operation somebody is actually performing when they do this
-    /// is "wrap it again", after a rotation or a botched first attempt.
+    /// <para>
+    /// Re-issuing to a recipient who already holds a live grant <em>for that generation</em> replaces it
+    /// in place rather than inserting a second row, because the unique index permits exactly one live
+    /// grant per recipient per generation — and because the operation somebody is actually performing
+    /// when they do this is "wrap it again", after a botched first attempt.
+    /// </para>
+    /// <para>
+    /// A recipient may hold one grant per generation at once, and after a rotation they need to: an item
+    /// is sealed under whatever generation was current when it was written, so somebody given only the
+    /// newest key would find everything older unreadable. Which generations get wrapped is the sharing
+    /// client's decision — it is the only party that can tell which ones it holds.
+    /// </para>
     /// </remarks>
     internal async Task IssueGrantAsync(
         UserAccount actor,
@@ -264,10 +291,12 @@ internal sealed class VaultGrantService(
         var granterKey = await RequireCurrentKeyAsync(actor.Id, cancellationToken)
             .ConfigureAwait(false);
 
+        var generation = (int)request.KeyGeneration;
+
         var existing = await database.VaultKeyGrants
             .SingleOrDefaultAsync(
                 g => g.VaultId == vault.Id
-                    && g.KeyGeneration == vault.KeyGeneration
+                    && g.KeyGeneration == generation
                     && g.RecipientUserId == request.RecipientUserId
                     && g.RevokedAtUtc == null,
                 cancellationToken)
@@ -277,7 +306,7 @@ internal sealed class VaultGrantService(
         {
             Id = Guid.CreateVersion7(),
             VaultId = vault.Id,
-            KeyGeneration = vault.KeyGeneration,
+            KeyGeneration = generation,
             Kind = GrantKind.Member,
             RecipientUserId = request.RecipientUserId,
             CreatedAtUtc = clock.GetUtcNow(),
@@ -304,7 +333,7 @@ internal sealed class VaultGrantService(
         await database.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
 
         TeamLog.GrantIssued(
-            logger, vault.Id, vault.KeyGeneration, request.RecipientUserId, actor.Id);
+            logger, vault.Id, generation, request.RecipientUserId, actor.Id);
     }
 
     /// <summary>
@@ -335,7 +364,11 @@ internal sealed class VaultGrantService(
         RequireDigest(request.RecipientKeyFingerprint, "recipient key fingerprint");
         RequireDigest(request.KeyLogHead, "key log head");
 
-        if (request.KeyGeneration != (uint)vault.KeyGeneration)
+        // Any generation the vault has actually reached, not only the current one — sharing a rotated
+        // vault means handing over its history as well as its present. A generation ahead of the
+        // current one is refused: nothing is sealed under it, so the grant would open nothing, and
+        // accepting it would let a client move the vault forward without the transaction that does so.
+        if (request.KeyGeneration is 0 || request.KeyGeneration > (uint)vault.KeyGeneration)
         {
             throw new VaultGrantInvalidException(
                 $"This vault is at key generation {vault.KeyGeneration}. A grant for generation "
@@ -374,6 +407,170 @@ internal sealed class VaultGrantService(
         }
     }
 
+    /// <summary>
+    /// Moves a vault to a fresh key generation, wrapped to the caller.
+    /// </summary>
+    /// <returns>The vault as the caller now sees it, at the generation this call created.</returns>
+    /// <remarks>
+    /// <para>
+    /// <b>What the server contributes is the moment, not the key.</b> It cannot generate a vault key, tell
+    /// that the one it is handed differs from the old one, or check that the caller held the old one at
+    /// all. What it can do — and what nothing else can — is advance the generation exactly once, so two
+    /// admins rotating the same vault at the same time do not both walk away believing they succeeded.
+    /// The stale one's generation is no longer one past the current, and it is refused.
+    /// </para>
+    /// <para>
+    /// <b>Earlier grants are left standing.</b> They are what the remaining members read the vault's
+    /// history with: an item carries the generation it was sealed under, and nothing here re-encrypts
+    /// items — only a client holding both keys could. The departed member is cut off by the revocation
+    /// that removal already performed, which takes every generation they held.
+    /// </para>
+    /// <para>
+    /// The rekey flag is cleared here rather than when the last member is re-wrapped, because it records
+    /// that a membership change left the vault owing a rotation, and the rotation is this. Who still
+    /// needs the new key is a different question, and the grant list answers it by generation.
+    /// </para>
+    /// </remarks>
+    internal async Task<VaultSummary> RekeyAsync(
+        UserAccount actor,
+        Vault vault,
+        int permissions,
+        RekeyVaultRequest request,
+        CancellationToken cancellationToken)
+    {
+        var key = await RequireRotatableAsync(actor, vault, request, cancellationToken)
+            .ConfigureAwait(false);
+
+        var now = clock.GetUtcNow();
+        var generation = (int)request.KeyGeneration;
+
+        AddSelfGrant(actor, vault, key, generation, request, now);
+
+        vault.KeyGeneration = generation;
+        vault.RekeyRequired = false;
+        vault.RekeyReason = RekeyReason.None;
+        vault.UpdatedAtUtc = now;
+
+        try
+        {
+            // One SaveChanges, so the row and the grant land together. The vault's xmin concurrency
+            // token is what makes the generation check above binding rather than advisory: a second
+            // rotation that read the same generation fails here instead of overwriting this one.
+            await database.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            // Reported as the same refusal the pre-check gives, because it is the same situation seen a
+            // moment later — and a 500 about a concurrency token would tell the user nothing they could
+            // act on. Retrying is safe: the caller generates a fresh key and reads the generation again.
+            throw new VaultGrantInvalidException(
+                "Somebody else rotated this vault while this rotation was being recorded. Read it again "
+                + "and rotate from the generation they left behind.");
+        }
+
+        TeamLog.VaultRekeyed(logger, vault.Id, generation, actor.Id);
+
+        var prior = await database.VaultKeyGrants
+            .Where(g => g.VaultId == vault.Id
+                && g.RecipientUserId == actor.Id
+                && g.KeyGeneration < generation
+                && g.State == GrantState.Active
+                && g.RevokedAtUtc == null)
+            .OrderBy(g => g.KeyGeneration)
+            .Select(g => new VaultKeyWrap((uint)g.KeyGeneration, g.WrappedKey))
+            .ToListAsync(cancellationToken)
+            .ConfigureAwait(false);
+
+        return new VaultSummary(
+            VaultId: vault.Id,
+            Name: vault.Name,
+            IsPersonal: false,
+            TeamId: vault.TeamId,
+            KeyGeneration: request.KeyGeneration,
+            Permissions: permissions,
+            WrappedVaultKey: request.WrappedVaultKey,
+            RekeyRequired: false,
+            PriorKeyWraps: prior);
+    }
+
+    /// <summary>Records the rotating client's grant for the generation it has just created.</summary>
+    private void AddSelfGrant(
+        UserAccount actor,
+        Vault vault,
+        UserKey key,
+        int generation,
+        RekeyVaultRequest request,
+        DateTimeOffset now) =>
+        database.VaultKeyGrants.Add(new VaultKeyGrant
+        {
+            Id = Guid.CreateVersion7(),
+            VaultId = vault.Id,
+            KeyGeneration = generation,
+            Kind = GrantKind.Member,
+            RecipientUserId = actor.Id,
+            RecipientKeyFingerprint = key.FingerprintSha256,
+            WrappedKey = request.WrappedVaultKey,
+            GranterUserId = actor.Id,
+            GranterKeyFingerprint = key.FingerprintSha256,
+
+            // No key log head, as every self-grant carries none: there is no third party whose key
+            // could have been substituted when you wrap something to yourself.
+            KeyLogHead = null,
+            Signature = request.GrantSignature,
+            State = GrantState.Active,
+            CreatedAtUtc = now,
+        });
+
+    /// <summary>
+    /// Everything that can be checked about a rotation before it is recorded.
+    /// </summary>
+    /// <returns>The caller's current identity key, which the new grant is filed against.</returns>
+    private async Task<UserKey> RequireRotatableAsync(
+        UserAccount actor,
+        Vault vault,
+        RekeyVaultRequest request,
+        CancellationToken cancellationToken)
+    {
+        if (vault.OwnerKind != VaultOwnerKind.Team || vault.TeamId is null)
+        {
+            throw new VaultGrantInvalidException(
+                "Only a team vault can be rotated. A personal vault has one reader, so a rotation "
+                + "would re-wrap a key to the same person and change nothing about who can read it.");
+        }
+
+        RequireWrappedKey(request.WrappedVaultKey);
+        RequireSignature(request.GrantSignature);
+
+        if (request.KeyGeneration != (uint)vault.KeyGeneration + 1)
+        {
+            throw new VaultGrantInvalidException(
+                $"This vault is at key generation {vault.KeyGeneration}, so the next one is "
+                + $"{vault.KeyGeneration + 1} and not {request.KeyGeneration}. Read the vault again — "
+                + "somebody else has rotated it since you last looked.");
+        }
+
+        var key = await RequireCurrentKeyAsync(actor.Id, cancellationToken).ConfigureAwait(false);
+
+        // Held now, not merely permitted. The new key has to be wrapped from the old one, and an
+        // account that cannot open the current generation cannot have done that — so a request from
+        // one is either a mistake or an attempt to strand every other member behind a key nobody has.
+        var holdsCurrent = await database.VaultKeyGrants
+            .AnyAsync(
+                g => g.VaultId == vault.Id
+                    && g.KeyGeneration == vault.KeyGeneration
+                    && g.RecipientUserId == actor.Id
+                    && g.State == GrantState.Active
+                    && g.RevokedAtUtc == null,
+                cancellationToken)
+            .ConfigureAwait(false);
+
+        return holdsCurrent
+            ? key
+            : throw new VaultGrantInvalidException(
+                "You hold no key to this vault at its current generation, so you cannot rotate it. Ask "
+                + "a member who does.");
+    }
+
     /// <summary>
     /// Withdraws a member's key grant.
     /// </summary>

src/DodoSSH.Api/Setup/EndpointRegistration.cs

@@ -60,10 +60,11 @@ internal static class EndpointRegistration
             typeof(ListVaultGrantsEndpoint),
             typeof(IssueVaultGrantEndpoint),
             typeof(RevokeVaultGrantEndpoint),
+            typeof(RekeyVaultEndpoint),
 
             // Registered as each feature lands:
             //   Identity   — key rotation, passphrase change
-            //   Vaults     — rekey, per-item ACLs
+            //   Vaults     — per-item ACLs
             //   Relay      — tickets and the WebSocket
             //   Audit, Admin
         });

src/DodoSSH.Client.Android/App.axaml.cs

@@ -74,27 +74,37 @@ public sealed partial class DodoSshApp : Avalonia.Application
 
         workspace.Start();
 
+        // Before anything can queue a transfer, which is the only moment at which emptying this is
+        // provably safe. What it clears is the copy a stopped upload leaves behind on purpose — kept so
+        // RESUME has something to read — and whatever a process death interrupted. See DocumentStaging.
+        DocumentStaging.Sweep();
+
+        var viewModel = ComposeShell(paths, caches, workspace, knownHosts, connections);
+
         // Difference 2: the foreground service, which is what makes TerminalWorkspace's promise — that a
         // shell outlives a vault lock — true on a platform that stops backgrounded processes.
         //
-        // Still zero transfers, and the reason moved rather than went away. v2 built the files screen, so
-        // this head can now browse a remote — but it cannot start a transfer, because both directions need
-        // the system document picker that scoped storage forces and that is not built (see FilesScreen).
-        // So the count is zero because the queue provably cannot have anything in it, not because nothing
-        // was wired. This is still the seam it arrives through: when the picker lands, this reads the
-        // queue and Refresh() gets called as transfers start and finish.
+        // The transfer count is real now that the document picker gives this head a way to start one, and
+        // it is the half that matters most here: a shell survives backgrounding because somebody is looking
+        // at it, and an upload has to survive precisely when nobody is — the screen is off and the phone is
+        // in a pocket. Queued counts as active, so putting five files in the queue and locking the phone
+        // moves five files.
+        //
         // A local rather than a field, matching the desktop head: an Avalonia Application has no disposal
         // hook, so a field holding a disposable would have nowhere honest to release it. It stays alive
         // because it is subscribed to the workspace, which lives as long as the process.
-        //
-        // Refresh() is called once here. Calling it again when a shell opens is what the terminal screen
-        // will wire, and there is nothing to wire it to yet — the workspace announces sessions ending on
-        // its own, which is the half that would otherwise leave a notification up over nothing.
-        var keepAlive = new SessionKeepAlive(workspace, activeTransfers: () => 0);
+        var keepAlive = new SessionKeepAlive(
+            workspace,
+            activeTransfers: () => viewModel.Transfers.ActiveTransfers);
+
+        // The other end of the same wire: the workspace announces its own sessions ending, and the queue
+        // announces transfers appearing and finishing. Without this the notification would come up when an
+        // upload started and stay up after it finished, which is the failure this class exists to prevent.
+        viewModel.Transfers.ActivityChanged += (_, _) => keepAlive.Refresh();
 
         keepAlive.Refresh();
 
-        return new PhoneShell { DataContext = ComposeShell(paths, caches, workspace, knownHosts, connections) };
+        return new PhoneShell { DataContext = viewModel };
     }
 
     /// <remarks>

src/DodoSSH.Client.Android/Platform/DocumentStaging.cs

@@ -0,0 +1,220 @@
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+
+namespace DodoSSH.Client.Android.Platform;
+
+/// <summary>
+/// Turns documents chosen in the system picker into ordinary local files the transfer queue can upload.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <b>The way in, and the only one this head has.</b> Android has no browsable local filesystem for a
+/// second pane to show — the decision docs/android-port.md took before any of this was built — so a file
+/// leaves this phone by being pointed at in the system picker, which hands back a <c>content://</c> URI
+/// belonging to whichever app owns the document.
+/// </para>
+/// <para>
+/// <b>Copied rather than streamed, and that is a requirement rather than a shortcut.</b> A document URI has
+/// no path behind it, its stream is not promised to be seekable, and the grant that opens it can be revoked
+/// or the document edited while an upload is in flight. <c>FileTransferQueue</c> needs all three of the
+/// things that costs: a path, a length it can trust, and a seek so a resumed upload starts from the byte
+/// the last attempt reached. So the document is copied into this application's own cache first and the copy
+/// is what gets queued — a real file, behaving like every other thing in that queue.
+/// </para>
+/// <para>
+/// <b>One directory per file, named by a UUIDv7.</b> Two documents chosen in one go can have the same
+/// display name, and two picks a minute apart certainly can; a shared staging directory would make the
+/// second copy overwrite the first, which is a data-loss bug that only shows up when somebody uploads two
+/// files called <c>config</c>. The directory is the uniqueness, so the file inside it can keep the name the
+/// picker gave it — which is the name the remote end gets, because <c>QueueUploads</c> takes it from the
+/// path.
+/// </para>
+/// </remarks>
+internal static class DocumentStaging
+{
+    /// <summary>Everything staged in either direction, under one directory so a sweep is one call.</summary>
+    private static string Root =>
+        Path.Combine(PhoneEnvironment.CacheDirectory, "staging");
+
+    /// <summary>A path in the staging area for a file of this name, with the directory made.</summary>
+    /// <remarks>
+    /// <b>One directory per file, named by a UUIDv7</b> — see the type's own remarks for why the uniqueness
+    /// is the directory rather than the name. Used by both directions: a document copied in for upload, and
+    /// a download on its way out to the document the save picker made.
+    /// </remarks>
+    internal static string NewStagingPath(string? name)
+    {
+        var folder = Path.Combine(Root, Guid.CreateVersion7().ToString("n"));
+        Directory.CreateDirectory(folder);
+
+        return Path.Combine(folder, SafeName(name));
+    }
+
+    /// <summary>
+    /// Asks for documents and copies each one into the cache, returning the paths of the copies.
+    /// </summary>
+    /// <remarks>
+    /// Multiple by design: the queue moves one file at a time, but choosing them is a trip out to another
+    /// application and back, and making somebody take that trip once per file is the kind of thing a phone
+    /// is judged on. An empty list means the picker was dismissed, which is not an error and is reported as
+    /// nothing having happened rather than as a failure.
+    /// </remarks>
+    internal static async Task<IReadOnlyList<string>> PickAsync(
+        TopLevel top,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(top);
+
+        var chosen = await top.StorageProvider
+            .OpenFilePickerAsync(new FilePickerOpenOptions
+            {
+                Title = "Files to upload",
+                AllowMultiple = true,
+            })
+            .ConfigureAwait(true);
+
+        if (chosen.Count == 0)
+        {
+            return [];
+        }
+
+        var staged = new List<string>(chosen.Count);
+
+        foreach (var document in chosen)
+        {
+            staged.Add(await CopyInAsync(document, cancellationToken).ConfigureAwait(true));
+        }
+
+        return staged;
+    }
+
+    /// <summary>
+    /// Asks where a download should end up, and returns the document the picker made.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// <c>ACTION_CREATE_DOCUMENT</c>, which is the only way a file leaves this application: everything else
+    /// on this phone is either the app's own private storage or somewhere it has no permission to write.
+    /// The suggested name is the remote file's, because that is the name the person was looking at when
+    /// they pressed the button, and they can change it in the picker like any other save.
+    /// </para>
+    /// <para>
+    /// <b>The document exists as soon as this returns</b> — the picker creates it, empty, and a download
+    /// that then fails leaves that empty file behind. Nothing here can prevent it: the alternative is
+    /// raising the picker after the transfer, minutes later, over whatever the person moved on to, and on
+    /// Android often while the application is backgrounded and cannot show one at all.
+    /// </para>
+    /// </remarks>
+    internal static async Task<IStorageFile?> PickDestinationAsync(TopLevel top, string name)
+    {
+        ArgumentNullException.ThrowIfNull(top);
+
+        return await top.StorageProvider
+            .SaveFilePickerAsync(new FilePickerSaveOptions
+            {
+                Title = "Save file",
+                SuggestedFileName = name,
+                ShowOverwritePrompt = true,
+            })
+            .ConfigureAwait(true);
+    }
+
+    /// <summary>Copies a finished download out to the document the picker made.</summary>
+    /// <remarks>
+    /// The write is truncating rather than appending, which matters on a retry: the picker's document is
+    /// created when it is dismissed and a second attempt writes over the empty — or partly written — file
+    /// rather than after it.
+    /// </remarks>
+    internal static async Task DeliverAsync(IStorageFile destination, string localPath)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+
+        var source = new FileStream(
+            localPath, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 81920, useAsync: true);
+
+        await using (source.ConfigureAwait(false))
+        {
+            var target = await destination.OpenWriteAsync().ConfigureAwait(false);
+
+            await using (target.ConfigureAwait(false))
+            {
+                if (target.CanSeek)
+                {
+                    target.SetLength(0);
+                }
+
+                await source.CopyToAsync(target).ConfigureAwait(false);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Deletes everything left in the staging directory.
+    /// </summary>
+    /// <remarks>
+    /// Called once at composition, before anything can have queued a transfer, which is what makes deleting
+    /// the lot safe: at that moment nothing in there belongs to a transfer that could still want it. What it
+    /// is for is the residue a stopped upload leaves deliberately — the copy is kept so RESUME has something
+    /// to read — a download whose delivery failed, and whatever a process death left behind mid-copy.
+    /// </remarks>
+    internal static void Sweep()
+    {
+        try
+        {
+            if (Directory.Exists(Root))
+            {
+                Directory.Delete(Root, recursive: true);
+            }
+        }
+        catch (Exception exception) when (exception is IOException or UnauthorizedAccessException)
+        {
+            // A cache that could not be emptied is not a reason to refuse to start. Android reclaims this
+            // directory itself when the device runs short of storage.
+        }
+    }
+
+    private static async Task<string> CopyInAsync(IStorageFile document, CancellationToken cancellationToken)
+    {
+        var path = NewStagingPath(document.Name);
+
+        // Off the interface thread from here down — this is a byte copy of something that can be a hundred
+        // megabytes, and nothing in it touches a control. The caller's own await is what comes back to the
+        // interface thread to queue the result. Hence the two-step disposal: configuring the await on a
+        // using declaration would leave the variable a ConfiguredAsyncDisposable rather than a stream.
+        var source = await document.OpenReadAsync().ConfigureAwait(false);
+
+        await using (source.ConfigureAwait(false))
+        {
+            var target = new FileStream(
+                path, FileMode.CreateNew, FileAccess.Write, FileShare.None, bufferSize: 81920, useAsync: true);
+
+            await using (target.ConfigureAwait(false))
+            {
+                await source.CopyToAsync(target, cancellationToken).ConfigureAwait(false);
+            }
+        }
+
+        return path;
+    }
+
+    /// <summary>
+    /// The display name reduced to something that can be a file name here and a name on the remote.
+    /// </summary>
+    /// <remarks>
+    /// A picker's display name comes from whichever application owns the document and is not obliged to be
+    /// a valid file name — it can carry a separator, which without this would write outside the directory
+    /// staging just made, and would then be joined onto the remote path by <c>QueueUploads</c>. Both are
+    /// worth refusing at the one point where the name enters this application.
+    /// </remarks>
+    private static string SafeName(string? name)
+    {
+        var trimmed = Path.GetFileName(name ?? string.Empty).Trim();
+
+        if (trimmed.Length == 0 || trimmed is "." or "..")
+        {
+            return "file";
+        }
+
+        return string.Join('_', trimmed.Split(Path.GetInvalidFileNameChars()));
+    }
+}

src/DodoSSH.Client.Android/Platform/PhoneEnvironment.cs

@@ -77,6 +77,18 @@ internal static class PhoneEnvironment
         }
     }
 
+    /// <summary>Where this phone keeps copies that only have to survive the thing that made them.</summary>
+    /// <remarks>
+    /// <c>cacheDir</c> — per-app like <see cref="Paths"/>, and unlike it, reclaimable: Android deletes from
+    /// here when the device runs short of storage. That is the right trade for the upload staging in
+    /// <see cref="DocumentStaging"/>, whose files are worthless the moment their transfer finishes, and it
+    /// is why the profile is not kept here. The cost is stated rather than hidden: a file reclaimed under
+    /// storage pressure while its upload is still running fails that upload.
+    /// </remarks>
+    public static string CacheDirectory =>
+        Require().CacheDir?.AbsolutePath
+        ?? throw new InvalidOperationException("Android returned no cacheDir for this application.");
+
     /// <summary>
     /// The activity currently on screen, or null while the app is backgrounded.
     /// </summary>

src/DodoSSH.Client.Android/Views/FilesScreen.axaml

@@ -19,17 +19,28 @@
     browsable local filesystem to put in the other half. TransfersViewModel's local pane — LocalPath,
     LocalRoots, LocalEntries — is desktop-only and is left alone here rather than shown empty.
 
-    ◆ **And that is why neither DOWNLOAD nor UPLOAD is on this screen.** Both commands exist and both work;
-    what they work *against* is the local pane. `QueueDownloads` writes to `Path.Combine(LocalPath, name)`,
-    and `LocalPath` starts at `LocalDirectory.Home` — `SpecialFolder.UserProfile`, which on Android is the
-    application's own private directory. A download would report success and put the file somewhere the
-    person who asked for it cannot open it, which is worse than not offering it: a refusal is visible and a
-    file in `/data/user/0/…` is not. The way in and out is the system document picker, which is the shape
-    docs/android-port.md decided on and is the next piece of work.
+    ◆ **ADD FILES is the way in, and it is the system document picker rather than an UPLOAD button.** There
+    is nothing local to select from, so the gesture cannot be "choose on the left, press the arrow": it is
+    "point at a document wherever it lives, and it goes to the directory showing". What Android hands back
+    is a `content://` URI, so `DocumentStaging` copies it into this application's cache and queues the copy —
+    the queue needs a path, a length and a seek, and a document URI promises none of the three. See that
+    class for why the copy is a requirement rather than a shortcut, and `QueueStagedUploads` for when it is
+    deleted again.
 
-    So what ships is browsing a remote, and the two remote-side operations that need nothing local —
-    opening a directory and deleting. The queue is drawn because a transfer can still be running when this
-    screen is opened; it is simply not something this head can start yet.
+    ◆ **SAVE FILE is the way out, and it is the save picker rather than a DOWNLOAD button.** `QueueDownloads`
+    writes to `Path.Combine(LocalPath, name)`, and `LocalPath` on Android is the application's own private
+    directory — a download that way would report success and leave the file where the person who asked for
+    it cannot open it. So this head does not use it: `QueueDeliveredDownload` runs the transfer into the
+    cache and hands the finished bytes to the document `ACTION_CREATE_DOCUMENT` made.
+
+    The destination is chosen *before* the transfer, which is a decision with a visible cost — the picker
+    creates the document when it is dismissed, so a download that then fails leaves an empty file where it
+    was pointed. The alternative is a picker raised minutes later, over whatever the person moved on to and
+    frequently while this application is backgrounded, where Android will not show one at all.
+
+    So what ships is browsing a remote and moving files both ways, plus the two remote-side operations that
+    need nothing local — opening a directory and deleting. The queue is drawn under the actions, because
+    this head can now fill it.
 
     ◆ **The host key prompts are here too.** File transfer is a second, separate authenticated connection
     and it makes its own trust decision — the host records a second login. So this screen carries its own
@@ -255,6 +266,70 @@
           </StackPanel>
         </Border>
 
+        <!--
+          ◆ The queue, above the actions and only when it has something in it. Bounded and scrolling rather
+          than growing: five files queued must not push the buttons off the bottom of the screen, which on a
+          phone is how a screen becomes unusable rather than merely tall.
+        -->
+        <ScrollViewer MaxHeight="164" IsVisible="{Binding HasTransfers}"
+                      VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Disabled">
+          <ItemsControl ItemsSource="{Binding Transfers}">
+            <ItemsControl.ItemTemplate>
+              <DataTemplate x:DataType="vm:TransferRowViewModel">
+                <Grid ColumnDefinitions="14,*,Auto" Margin="0,3">
+                  <TextBlock Grid.Column="0" Classes="mono" FontSize="12" Text="{Binding Arrow}"
+                             VerticalAlignment="Center" Foreground="{StaticResource AccentText}" />
+
+                  <StackPanel Grid.Column="1" Margin="8,0" Spacing="3">
+                    <TextBlock Classes="mono" FontSize="12" Text="{Binding Name}"
+                               TextTrimming="CharacterEllipsis" />
+                    <ProgressBar Height="3" Minimum="0" Maximum="100" Value="{Binding Percent}"
+                                 Foreground="{StaticResource Accent}"
+                                 Background="{StaticResource Raised}" />
+                    <TextBlock Classes="detail" Text="{Binding Progress}"
+                               TextTrimming="CharacterEllipsis" />
+                  </StackPanel>
+
+                  <!--
+                    One button per row, never two: whichever of the three applies to the state it is in.
+                    A phone row has space for a name, a bar and one 44-pixel target, and the three are
+                    mutually exclusive by construction — IsRunning and CanRetry cannot both hold.
+                  -->
+                  <StackPanel Grid.Column="2" VerticalAlignment="Center">
+                    <Button Classes="secondary" MinHeight="36" Padding="10,0" Content="STOP"
+                            IsVisible="{Binding IsRunning}"
+                            Command="{Binding $parent[views:FilesScreen].((vm:TransfersViewModel)DataContext).CancelTransferCommand}"
+                            CommandParameter="{Binding}" />
+                    <Button Classes="secondary" MinHeight="36" Padding="10,0" Content="{Binding RetryLabel}"
+                            IsVisible="{Binding CanRetry}"
+                            Command="{Binding $parent[views:FilesScreen].((vm:TransfersViewModel)DataContext).RetryTransferCommand}"
+                            CommandParameter="{Binding}" />
+                  </StackPanel>
+                </Grid>
+              </DataTemplate>
+            </ItemsControl.ItemTemplate>
+          </ItemsControl>
+        </ScrollViewer>
+
+        <Button Classes="secondary" Height="40" Content="CLEAR FINISHED" HorizontalAlignment="Stretch"
+                IsVisible="{Binding HasTransfers}" Command="{Binding ClearCompletedCommand}" />
+
+        <!--
+          ◆ The two directions, on their own row above the pair below — because DELETE is the button on this
+          screen that nothing can undo, and it must not sit at a thumb's width from the ones somebody presses
+          often. ADD FILES is the primary of the two: it is the one that needs no selection, and the one this
+          screen exists for on a phone.
+
+          SAVE FILE takes the selected row rather than several, and that asymmetry is the platform's: the
+          save picker names one destination. CanDownload is the desktop's own flag for the same question —
+          a file is selected and something is connected — and is reused rather than restated here.
+        -->
+        <Grid ColumnDefinitions="*,8,*" IsVisible="{Binding !IsConfirmingRemoteDeletion}">
+          <Button Grid.Column="0" Classes="primary" Height="44" Content="ADD FILES" Click="OnAddFiles" />
+          <Button Grid.Column="2" Classes="secondary" Height="44" Content="SAVE FILE" Click="OnSaveFile"
+                  IsEnabled="{Binding CanDownload}" />
+        </Grid>
+
         <Grid ColumnDefinitions="*,8,*" IsVisible="{Binding !IsConfirmingRemoteDeletion}">
           <Button Grid.Column="0" Classes="secondary" Height="44" Content="DELETE"
                   Command="{Binding DeleteRemoteCommand}" IsEnabled="{Binding CanDeleteRemote}" />
@@ -263,18 +338,11 @@
         </Grid>
 
         <TextBlock Classes="body" IsVisible="{Binding !IsConfirmingRemoteDeletion}"
-                   Text="Copying files to and from this phone needs the system document picker, which is not built yet — see the note at the top of this screen. Browsing, opening and deleting work." />
+                   Text="ADD FILES picks documents to send. SAVE FILE asks where the selected file should be kept — the file is created there when you choose it, so a transfer that fails leaves it empty." />
 
         <TextBlock Classes="detail" Foreground="{StaticResource TextDim}" TextWrapping="Wrap"
                    Text="{Binding Status}" />
 
-        <!--
-          There is no queue on this screen, and that follows from the note at the top rather than being a
-          separate decision: nothing here can enqueue a transfer, so a queue would be a region that is
-          empty for every possible state of the application. It comes back with the document picker, along
-          with the two buttons that would fill it.
-        -->
-
       </StackPanel>
     </Border>
 

src/DodoSSH.Client.Android/Views/FilesScreen.axaml.cs

@@ -3,6 +3,7 @@ using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Markup.Xaml;
 
+using DodoSSH.Client.Android.Platform;
 using DodoSSH.Client.Shell.ViewModels;
 
 namespace DodoSSH.Client.Android.Views;
@@ -29,8 +30,9 @@ internal sealed partial class FilesScreen : UserControl
     /// fires after the list has moved its selection, which is what lets this read it.
     /// </para>
     /// <para>
-    /// A file is left selected rather than opened. There is nothing this head could do with it — see the
-    /// note about the document picker at the top of the screen — and the actions below act on the selection.
+    /// A file is left selected rather than downloaded, and that is deliberate now rather than forced: the
+    /// actions below act on the selection, and a tap that started a transfer would make selecting a row to
+    /// read its size the same gesture as fetching it.
     /// </para>
     /// </remarks>
     private void OnRemoteEntryTapped(object? sender, TappedEventArgs e)
@@ -40,4 +42,93 @@ internal sealed partial class FilesScreen : UserControl
             transfers.OpenRemoteCommand.Execute(null);
         }
     }
+
+    /// <summary>
+    /// Picks documents in the system picker and queues them for upload.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// In the head rather than in the shared view model, for the reason every other platform difference is:
+    /// the picker is Android's, the staging directory is this application's cache, and the desktop reaches
+    /// its local files by browsing a pane that does not exist here. What crosses back into shared code is
+    /// what the queue understands — paths — through <see cref="TransfersViewModel.QueueStagedUploads"/>.
+    /// </para>
+    /// <para>
+    /// <b>Failures land in the screen's own status line</b>, which is where every other refusal on this
+    /// screen already is. The picker itself is a trip out to another application, and it can come back with
+    /// a document that has since been deleted or a grant that was revoked; the exception's message is more
+    /// use than "the upload failed", and a phone has nowhere else to put it.
+    /// </para>
+    /// </remarks>
+    private async void OnAddFiles(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not TransfersViewModel transfers || TopLevel.GetTopLevel(this) is not { } top)
+        {
+            return;
+        }
+
+        try
+        {
+            var staged = await DocumentStaging.PickAsync(top, CancellationToken.None).ConfigureAwait(true);
+
+            if (staged.Count == 0)
+            {
+                return;
+            }
+
+            transfers.QueueStagedUploads(staged);
+        }
+        catch (Exception exception) when (exception is not OutOfMemoryException)
+        {
+            transfers.Status = $"Those files could not be read: {exception.Message}";
+        }
+    }
+
+    /// <summary>
+    /// Asks where the chosen remote file should be saved, then queues it.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The other direction, and the asymmetry with <see cref="OnAddFiles"/> is the platform's rather than
+    /// this screen's: coming in, several documents can be pointed at in one trip; going out, the save picker
+    /// names one destination, so this acts on the selected row. Asking for five destinations in a row to
+    /// download five files would be a worse screen than pressing the button five times.
+    /// </para>
+    /// <para>
+    /// Nothing is queued when the picker is dismissed. The document it makes when it is *not* dismissed
+    /// exists from that moment, which is why the queueing follows immediately — see
+    /// <c>DocumentStaging.PickDestinationAsync</c>.
+    /// </para>
+    /// </remarks>
+    private async void OnSaveFile(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not TransfersViewModel transfers || TopLevel.GetTopLevel(this) is not { } top)
+        {
+            return;
+        }
+
+        if (transfers.SelectedRemoteEntry is not { IsFile: true } row)
+        {
+            transfers.Status = "Choose a file on the host to save.";
+            return;
+        }
+
+        try
+        {
+            if (await DocumentStaging.PickDestinationAsync(top, row.Name).ConfigureAwait(true)
+                is not { } destination)
+            {
+                return;
+            }
+
+            transfers.QueueDeliveredDownload(
+                row,
+                DocumentStaging.NewStagingPath(row.Name),
+                path => DocumentStaging.DeliverAsync(destination, path));
+        }
+        catch (Exception exception) when (exception is not OutOfMemoryException)
+        {
+            transfers.Status = $"That file could not be saved: {exception.Message}";
+        }
+    }
 }

src/DodoSSH.Client.Api/DodoSshApiClient.cs

@@ -211,6 +211,21 @@ public interface IVaultGrantApi
         IssueVaultGrantRequest request,
         CancellationToken cancellationToken);
 
+    /// <summary>
+    /// Advances this vault to a fresh key generation, wrapped to the caller.
+    /// </summary>
+    /// <returns>The vault at its new generation, with the caller's grants for the earlier ones.</returns>
+    /// <remarks>
+    /// The key is generated by the caller and sealed to itself; the server contributes the moment it
+    /// takes effect, which is the one part a client cannot decide on its own. Wrapping the new
+    /// generation to everybody else is a separate act, and it is the caller's — see
+    /// <see cref="IssueVaultGrantAsync"/>.
+    /// </remarks>
+    Task<VaultSummary> RekeyVaultAsync(
+        Guid vaultId,
+        RekeyVaultRequest request,
+        CancellationToken cancellationToken);
+
     /// <summary>
     /// Withdraws a member's key to this vault.
     /// </summary>
@@ -606,6 +621,18 @@ public sealed class DodoSshApiClient(HttpClient http, IAccessTokenProvider token
             JsonContent.Create(request, DodoSshJsonContext.Default.IssueVaultGrantRequest),
             cancellationToken);
 
+    /// <inheritdoc />
+    public Task<VaultSummary> RekeyVaultAsync(
+        Guid vaultId,
+        RekeyVaultRequest request,
+        CancellationToken cancellationToken) =>
+        SendAsync(
+            HttpMethod.Post,
+            string.Create(CultureInfo.InvariantCulture, $"/api/v1/vaults/{vaultId}/rekey"),
+            JsonContent.Create(request, DodoSshJsonContext.Default.RekeyVaultRequest),
+            DodoSshJsonContext.Default.VaultSummary,
+            cancellationToken);
+
     /// <inheritdoc />
     public Task<bool> RevokeVaultGrantAsync(
         Guid vaultId,

src/DodoSSH.Client.Session/AccountProvisioner.cs

@@ -196,5 +196,6 @@ public sealed class AccountProvisioner(
             summary.KeyGeneration,
             summary.Permissions,
             summary.WrappedVaultKey,
-            summary.RekeyRequired);
+            summary.RekeyRequired,
+            summary.PriorKeyWraps);
 }

src/DodoSSH.Client.Session/VaultSession.cs

@@ -295,6 +295,31 @@ public sealed partial class VaultSession : IAsyncDisposable
         return engine.SyncAsync(vaultId, cancellationToken);
     }
 
+    /// <summary>
+    /// Moves one vault's stored items onto its current key.
+    /// </summary>
+    /// <param name="api">The transport. Supplied per call, as <see cref="SyncAsync"/> takes its own.</param>
+    /// <param name="vaultId">The vault to re-seal.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <remarks>
+    /// What a rotation leaves to be finished. Rotating re-keys the vault and not its contents, so until
+    /// this has run the items already stored are still sealed under keys a departed member may hold. It
+    /// is resumable, so a pass that fails part way is re-run rather than recovered — see
+    /// <see cref="VaultResealer"/>.
+    /// </remarks>
+    public Task<ResealReport> ResealVaultAsync(
+        ISyncApi api,
+        Guid vaultId,
+        CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        ArgumentNullException.ThrowIfNull(api);
+
+        var resealer = new VaultResealer(api, Items, Outbox, keyring, clock, options);
+
+        return resealer.ResealAsync(vaultId, cancellationToken);
+    }
+
     /// <summary>
     /// Runs one synchronisation pass over every vault this session can read.
     /// </summary>

src/DodoSSH.Client.Session/VaultSharing.cs

@@ -14,10 +14,67 @@ namespace DodoSSH.Client.Session;
 /// is the interesting outcome and the reason for it is the whole of what a user needs to see.
 /// </param>
 /// <param name="Message">One line for a person. Never contains key material.</param>
+/// <param name="Generations">
+/// How many generations of the vault key were wrapped. One for a vault that has never been rotated;
+/// more for one that has, because its older items are still sealed under the keys they were written
+/// with and a recipient given only the newest would find them unreadable.
+/// </param>
 public sealed record ShareOutcome(
     bool Shared,
     RecipientVerification Verification,
-    string Message);
+    string Message,
+    int Generations = 0);
+
+/// <summary>What sharing or rotating one vault did, named so a message can say which vault.</summary>
+/// <param name="VaultId">The vault.</param>
+/// <param name="Name">Its display name.</param>
+/// <param name="Outcome">What happened, when the attempt was made.</param>
+/// <param name="Failure">
+/// Why it was not, when it failed. Carried rather than thrown for the reason a per-vault sync report
+/// carries its own: one unreachable vault must not stop the others, and a vault that silently did not
+/// get the key is the outcome this whole design exists to make visible.
+/// </param>
+public sealed record VaultShareReport(
+    Guid VaultId,
+    string Name,
+    ShareOutcome? Outcome,
+    Exception? Failure)
+{
+    /// <summary>Whether a grant was recorded for this vault.</summary>
+    public bool Succeeded => Outcome is { Shared: true };
+}
+
+/// <summary>What rotating one vault did.</summary>
+/// <param name="VaultId">The vault.</param>
+/// <param name="Name">Its display name.</param>
+/// <param name="KeyGeneration">The generation it now holds, or zero if it was not rotated.</param>
+/// <param name="Shared">The members the new key was wrapped to.</param>
+/// <param name="NotShared">
+/// The members it was not, with the reason. A rotation that re-wrapped to nobody has locked the
+/// remaining members out of everything written from now on, which they must be told rather than left
+/// to discover.
+/// </param>
+/// <param name="Failure">Why the rotation itself did not happen, when it did not.</param>
+/// <param name="Reseal">
+/// What moving the vault's stored items onto the new key achieved, or null when the rotation did not
+/// get that far. A rotation without this has re-keyed the vault and not its contents, which is a
+/// different guarantee — see <see cref="VaultResealer"/>.
+/// </param>
+public sealed record VaultRekeyReport(
+    Guid VaultId,
+    string Name,
+    uint KeyGeneration,
+    IReadOnlyList<Guid> Shared,
+    IReadOnlyList<(Guid UserId, string Reason)> NotShared,
+    Exception? Failure,
+    ResealReport? Reseal = null)
+{
+    /// <summary>Whether the vault moved to a new key.</summary>
+    public bool Rotated => Failure is null && KeyGeneration > 0;
+
+    /// <summary>Whether everything in the vault is now sealed under that new key.</summary>
+    public bool Sealed => Reseal is { Complete: true };
+}
 
 /// <summary>
 /// Sharing, from the side that holds the keys.
@@ -160,6 +217,13 @@ public sealed partial class VaultSession
     /// <see cref="VerifiedRecipient.Fingerprint"/> with them over a channel this server does not carry;
     /// that is the only step that closes the gap, and the outcome message says so.
     /// </para>
+    /// <para>
+    /// <b>Every generation this session holds is wrapped, not only the newest.</b> A rotation does not
+    /// re-encrypt what is already stored, so a vault that has been rotated twice holds items under three
+    /// keys — and a recipient handed only the current one would open the vault to find most of it
+    /// unreadable. This is also the only party that can do it: the server holds ciphertext it cannot
+    /// read, and the recipient holds nothing yet.
+    /// </para>
     /// </remarks>
     public async Task<ShareOutcome> ShareVaultAsync(
         IVaultGrantApi grants,
@@ -172,7 +236,7 @@ public sealed partial class VaultSession
         ArgumentNullException.ThrowIfNull(grants);
         ArgumentNullException.ThrowIfNull(directory);
 
-        if (!keyring.TryGet(vaultId, out var vaultKey, out var keyGeneration))
+        if (!keyring.TryGet(vaultId, out _, out _))
         {
             throw new VaultUnreadableException(vaultId);
         }
@@ -189,17 +253,292 @@ public sealed partial class VaultSession
         }
 
         var recipient = verification.Recipient!;
+        var generations = keyring.GenerationsHeld(vaultId);
 
-        await IssueAsync(grants, vaultId, vaultKey, keyGeneration, recipient, cancellationToken)
-            .ConfigureAwait(false);
+        // Oldest first, so an interruption leaves the recipient holding history without the present
+        // rather than the reverse. Both are incomplete; only one of them looks like a working vault
+        // that is quietly missing its recent items.
+        foreach (var generation in generations)
+        {
+            if (!keyring.TryGetAt(vaultId, generation, out var vaultKey))
+            {
+                continue;
+            }
+
+            await IssueAsync(grants, vaultId, vaultKey, generation, recipient, cancellationToken)
+                .ConfigureAwait(false);
+        }
 
         return new ShareOutcome(
             true,
             verification,
             "Shared. Check the fingerprint with them out of band — everything the client can verify on "
-            + "its own only proves this server has been consistent with itself.");
+            + "its own only proves this server has been consistent with itself.",
+            generations.Count);
     }
 
+    /// <summary>
+    /// Moves a vault to a fresh key and hands it to the members who are left.
+    /// </summary>
+    /// <param name="grants">The grant calls.</param>
+    /// <param name="directory">The directory and the key log that makes it checkable.</param>
+    /// <param name="sync">
+    /// The synchronisation calls, for the last step: moving what is already stored onto the new key.
+    /// </param>
+    /// <param name="vaultId">The vault to rotate.</param>
+    /// <param name="recipients">
+    /// Who should hold the new key. The caller's own id may be in here and is ignored: this session
+    /// wrapped the new key to itself as part of the rotation.
+    /// </param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <remarks>
+    /// <para>
+    /// <b>Three acts, and only the first is atomic.</b> The generation advances in one server
+    /// transaction, so there is no moment at which two clients disagree about which key is current.
+    /// Wrapping it to each remaining member is a separate call per member, each verified against the key
+    /// log the same way an ordinary share is — and any of them can fail. A member who was missed holds
+    /// the vault's history and cannot read anything written since, which the report says so the
+    /// interface can too.
+    /// </para>
+    /// <para>
+    /// <b>The third act is re-sealing what is already there</b>, and it is what makes the rotation worth
+    /// the name: until it has run, the vault's stored items are still sealed under keys the departed
+    /// member may have kept. It runs last for a reason — it needs the new key, and it is the only step
+    /// that can be interrupted without leaving anything broken, because a vault at mixed generations
+    /// stays readable to everybody holding the grants. A pass that stops half way is re-run.
+    /// </para>
+    /// <para>
+    /// <b>What none of it can do</b> is take back what the departed member already pulled onto their own
+    /// machine. Retroactive revocation is not achievable; rotate the credentials themselves. See
+    /// ADR 0001.
+    /// </para>
+    /// </remarks>
+    public async Task<VaultRekeyReport> RekeyVaultAsync(
+        IVaultGrantApi grants,
+        IDirectoryApi directory,
+        ISyncApi sync,
+        Guid vaultId,
+        IReadOnlyList<Guid> recipients,
+        CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        ArgumentNullException.ThrowIfNull(grants);
+        ArgumentNullException.ThrowIfNull(directory);
+        ArgumentNullException.ThrowIfNull(sync);
+        ArgumentNullException.ThrowIfNull(recipients);
+
+        if (!keyring.TryGet(vaultId, out _, out var keyGeneration))
+        {
+            throw new VaultUnreadableException(vaultId);
+        }
+
+        var name = Vaults.FirstOrDefault(vault => vault.VaultId == vaultId)?.Name ?? "this vault";
+        var summary = await RotateAsync(grants, vaultId, keyGeneration, cancellationToken)
+            .ConfigureAwait(false);
+
+        var shared = new List<Guid>();
+        var missed = new List<(Guid UserId, string Reason)>();
+
+        foreach (var recipient in recipients.Distinct().Where(id => id != Profile.UserId))
+        {
+            try
+            {
+                var outcome = await ShareVaultAsync(
+                        grants, directory, vaultId, recipient, cancellationToken)
+                    .ConfigureAwait(false);
+
+                if (outcome.Shared)
+                {
+                    shared.Add(recipient);
+                }
+                else
+                {
+                    missed.Add((recipient, outcome.Message));
+                }
+            }
+            catch (Exception exception) when (exception is not OperationCanceledException)
+            {
+                // One member's key being unusable — never enrolled, rotated their identity key mid-call
+                // — is not a reason to leave the rest of the team without the new one.
+                missed.Add((recipient, exception.Message));
+            }
+        }
+
+        // Synced before re-sealing, and it is not tidiness. The pass rewrites each item against the
+        // version the server holds, so a mirror that is behind produces a batch of conflicts instead of
+        // a re-sealed vault — and the sync also carries out anything queued here, which the push path
+        // re-seals on the way rather than leaving to be found later.
+        await SyncAsync(sync, vaultId, cancellationToken).ConfigureAwait(false);
+
+        var resealed = await ResealVaultAsync(sync, vaultId, cancellationToken).ConfigureAwait(false);
+
+        return new VaultRekeyReport(
+            vaultId, name, summary.KeyGeneration, shared, missed, Failure: null, resealed);
+    }
+
+    /// <summary>Generates the next vault key, records it, and takes it into the keyring.</summary>
+    /// <remarks>
+    /// The key is adopted only after the server has accepted the rotation. The other order would leave
+    /// this session sealing items under a generation the vault never reached, and every one of them
+    /// would be unreadable to everybody including its author at the next unlock.
+    /// </remarks>
+    private async Task<VaultSummary> RotateAsync(
+        IVaultGrantApi grants,
+        Guid vaultId,
+        uint keyGeneration,
+        CancellationToken cancellationToken)
+    {
+        var generation = keyGeneration + 1;
+        var vaultKey = VaultKeys.Create();
+        var now = clock.GetUtcNow();
+
+        try
+        {
+            var wrapped = VaultKeys.WrapTo(
+                vaultKey, bundle.EncryptionPublicKey, vaultId, generation);
+
+            var fingerprint = DshCrypto.ComputeFingerprint(
+                bundle.EncryptionPublicKey, bundle.SigningPublicKey);
+
+            var canonical = GrantStatementCodec.Encode(
+                vaultId,
+                generation,
+                GrantPurpose.Member,
+                granteeUserId: Profile.UserId,
+                granteeKeyFingerprint: fingerprint,
+                wrappedKey: wrapped,
+                granterUserId: Profile.UserId,
+                granterKeyFingerprint: fingerprint,
+
+                // Absent, as in every self-grant: there is no third party whose key could have been
+                // substituted when you wrap something to yourself.
+                keyLogHead: default,
+                grantedAt: now);
+
+            var summary = await grants.RekeyVaultAsync(
+                    vaultId,
+                    new RekeyVaultRequest(
+                        KeyGeneration: generation,
+                        WrappedVaultKey: wrapped,
+                        GrantSignature: GrantStatementCodec.Sign(bundle.SigningKey, canonical),
+                        GrantedAt: now),
+                    cancellationToken)
+                .ConfigureAwait(false);
+
+            var stored = ToStored(summary);
+
+            await Vault.UpsertAsync(stored, cancellationToken).ConfigureAwait(false);
+
+            keyring.Adopt(vaultId, vaultKey, summary.KeyGeneration);
+
+            Vaults = await Vault.ListAsync(cancellationToken).ConfigureAwait(false);
+
+            return summary;
+        }
+        catch
+        {
+            // Never reached the keyring, so this is the only thing that can release it.
+            CryptographicOperations.ZeroMemory(vaultKey);
+            throw;
+        }
+    }
+
+    /// <summary>
+    /// Hands every team vault this session can open to one member.
+    /// </summary>
+    /// <returns>One report per vault, in the order they were attempted.</returns>
+    /// <remarks>
+    /// What "adding somebody to a team" means in full. Membership is a server-side authorization change
+    /// and takes effect at once; a key is a cryptographic act only a machine holding one can perform, so
+    /// this is the half that has to happen here. A vault this session cannot open is skipped rather than
+    /// failed — somebody else holds its key, and this client has nothing to wrap.
+    /// </remarks>
+    public async Task<IReadOnlyList<VaultShareReport>> ShareTeamVaultsAsync(
+        IVaultGrantApi grants,
+        IDirectoryApi directory,
+        Guid teamId,
+        Guid recipientUserId,
+        CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        ArgumentNullException.ThrowIfNull(grants);
+        ArgumentNullException.ThrowIfNull(directory);
+
+        var reports = new List<VaultShareReport>();
+
+        foreach (var vault in TeamVaults(teamId))
+        {
+            try
+            {
+                var outcome = await ShareVaultAsync(
+                        grants, directory, vault.VaultId, recipientUserId, cancellationToken)
+                    .ConfigureAwait(false);
+
+                reports.Add(new VaultShareReport(vault.VaultId, vault.Name, outcome, null));
+            }
+            catch (Exception exception) when (exception is not OperationCanceledException)
+            {
+                reports.Add(new VaultShareReport(vault.VaultId, vault.Name, null, exception));
+            }
+        }
+
+        return reports;
+    }
+
+    /// <summary>
+    /// Rotates every team vault this session can open, handing each new key to the members who remain.
+    /// </summary>
+    /// <returns>One report per vault, in the order they were attempted.</returns>
+    /// <remarks>
+    /// What "removing somebody from a team" means in full, and the reason it is per vault rather than
+    /// per team: a key belongs to a vault, and a client can only rotate the ones it can currently open.
+    /// A vault it cannot is left alone and stays flagged for rekey, which is the honest state — somebody
+    /// who holds its key has to finish the job.
+    /// </remarks>
+    public async Task<IReadOnlyList<VaultRekeyReport>> RekeyTeamVaultsAsync(
+        IVaultGrantApi grants,
+        IDirectoryApi directory,
+        ISyncApi sync,
+        Guid teamId,
+        IReadOnlyList<Guid> recipients,
+        CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        ArgumentNullException.ThrowIfNull(grants);
+        ArgumentNullException.ThrowIfNull(directory);
+        ArgumentNullException.ThrowIfNull(sync);
+        ArgumentNullException.ThrowIfNull(recipients);
+
+        var reports = new List<VaultRekeyReport>();
+
+        foreach (var vault in TeamVaults(teamId))
+        {
+            try
+            {
+                reports.Add(
+                    await RekeyVaultAsync(
+                            grants, directory, sync, vault.VaultId, recipients, cancellationToken)
+                        .ConfigureAwait(false));
+            }
+            catch (Exception exception) when (exception is not OperationCanceledException)
+            {
+                reports.Add(new VaultRekeyReport(
+                    vault.VaultId, vault.Name, KeyGeneration: 0, [], [], exception));
+            }
+        }
+
+        return reports;
+    }
+
+    /// <summary>The team's vaults this session actually holds a current key for.</summary>
+    /// <remarks>
+    /// Materialised before the loops above use it, because both of them write to <see cref="Vaults"/>
+    /// through the vault store — and a rotation part-way through a lazily evaluated sequence would be
+    /// enumerating a list that has been replaced underneath it.
+    /// </remarks>
+    private List<StoredVault> TeamVaults(Guid teamId) =>
+        [.. Vaults.Where(vault => vault.TeamId == teamId && keyring.CanRead(vault.VaultId))];
+
     /// <summary>
     /// Re-reads which vaults the server says are reachable, and opens any that have become readable.
     /// </summary>
@@ -226,14 +565,18 @@ public sealed partial class VaultSession
 
         foreach (var vault in Vaults)
         {
-            if (keyring.CanRead(vault.VaultId))
-            {
-                continue;
-            }
+            // Attempted even for a vault that already opens, because the answer can have grown: a
+            // rotated vault arrives with a new current generation, and a vault shared by somebody who
+            // holds more of its history arrives with wraps this session did not have. Admitting is
+            // idempotent, so the only thing an unconditional call costs is the unwrap it skips.
+            var readable = keyring.CanRead(vault.VaultId);
 
             if (keyring.TryAdmit(bundle, vault))
             {
-                admitted++;
+                if (!readable)
+                {
+                    admitted++;
+                }
             }
             else
             {
@@ -336,5 +679,6 @@ public sealed partial class VaultSession
             summary.KeyGeneration,
             summary.Permissions,
             summary.WrappedVaultKey,
-            summary.RekeyRequired);
+            summary.RekeyRequired,
+            summary.PriorKeyWraps);
 }

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

@@ -260,6 +260,27 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     private readonly FileTransferQueue queue;
     private readonly Action<Action> post;
 
+    /// <summary>
+    /// Local files that exist only so this queue could move them — see <see cref="QueueStagedUploads"/> and
+    /// <see cref="QueueDeliveredDownload"/>.
+    /// </summary>
+    /// <remarks>
+    /// Compared case-insensitively because the paths come back through the queue's snapshots rather than
+    /// straight from the caller, and a comparison that a casing round trip could break would leak a file
+    /// per transfer on any head that ever normalises one.
+    /// </remarks>
+    private readonly HashSet<string> staged = new(StringComparer.OrdinalIgnoreCase);
+
+    /// <summary>
+    /// What to do with a completed download whose real destination this layer cannot write to.
+    /// </summary>
+    /// <remarks>
+    /// Keyed by transfer rather than by path so a retry keeps its delivery: the queue reuses the id, and a
+    /// download that failed once and succeeded on the second attempt must still end up where the person
+    /// pointed. See <see cref="QueueDeliveredDownload"/>.
+    /// </remarks>
+    private readonly Dictionary<Guid, Func<string, Task>> deliveries = [];
+
     private VaultViewModel? vault;
     private VaultKnownHostStore? knownHosts;
     private IRemoteFileStore? session;
@@ -522,6 +543,23 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
 
     internal ObservableCollection<TransferRowViewModel> Transfers { get; } = [];
 
+    /// <summary>Raised on the UI thread whenever a transfer appears or changes state.</summary>
+    /// <remarks>
+    /// For a head that has to tell the operating system what this process is doing — Android's foreground
+    /// service, which must be up for as long as bytes are moving and down afterwards. An event rather than
+    /// letting that head watch <see cref="Transfers"/> itself: the collection announces rows arriving and
+    /// leaving, and the transition that matters most is neither of those but a row going from RUNNING to
+    /// DONE without moving.
+    /// </remarks>
+    internal event EventHandler? ActivityChanged;
+
+    /// <summary>How many transfers are moving or waiting to move.</summary>
+    /// <remarks>
+    /// Queued counts as active. A queue with three files in it and one of them running is a process that
+    /// must not be stopped, and the two that have not started yet are exactly the ones a stop would lose.
+    /// </remarks>
+    internal int ActiveTransfers => Transfers.Count(row => row.IsRunning);
+
     internal bool HasTransfers => Transfers.Count > 0;
 
     /// <summary>Whether a download of the chosen remote file would have somewhere to go.</summary>
@@ -982,6 +1020,143 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
         Status = Describe(queued, "upload into", RemotePath, directories, missing);
     }
 
+    /// <summary>
+    /// Queues copies that were made for this upload and belong to nothing else, so they are deleted once
+    /// the transfer no longer needs them.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// <b>This exists for the phone, and the copy is not an implementation detail that could be avoided.</b>
+    /// Android hands a chosen document over as a <c>content://</c> URI with no path behind it and no promise
+    /// that the stream can be seeked — and this queue seeks, because an upload resumes from the byte the
+    /// last attempt reached. So the head copies the document into the application's own cache first and
+    /// hands over the copy, which is a real file that behaves like every other thing in this queue.
+    /// </para>
+    /// <para>
+    /// <b>Released on success and on discard, never on failure.</b> A failed or stopped upload is offered a
+    /// RESUME or a RETRY, and both read the local file again — deleting it at the moment it stopped would
+    /// turn one visible failure into a second, stranger one. What is left after a failure is swept at the
+    /// next launch by the head that made it, which is the only place that knows where it put it.
+    /// </para>
+    /// </remarks>
+    internal void QueueStagedUploads(IReadOnlyList<string> paths)
+    {
+        ArgumentNullException.ThrowIfNull(paths);
+
+        foreach (var path in paths)
+        {
+            staged.Add(path);
+        }
+
+        QueueUploads(paths);
+    }
+
+    /// <summary>
+    /// Queues one download into a local file this application made, and hands the finished bytes to
+    /// something that knows where they were really meant to go.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// <b>The mirror of <see cref="QueueStagedUploads"/>, and it exists for the same reason.</b> A phone has
+    /// no directory a download could simply be written into: what the person chose is a document handed back
+    /// by the system's save picker, which this layer cannot open and the queue could not resume against. So
+    /// the transfer runs into the cache like any other, and <paramref name="deliver"/> — supplied by the head
+    /// that raised the picker — copies the result out once there is a result to copy.
+    /// </para>
+    /// <para>
+    /// <b>The destination is chosen before the transfer starts, not after.</b> A picker raised on completion
+    /// would arrive minutes later over whatever the person had moved on to, and on a phone it would often
+    /// arrive while the application is in the background, where Android will not show it at all. The cost is
+    /// stated where a person will meet it: the save picker creates the document when it is dismissed, so a
+    /// download that then fails leaves an empty file where it was pointed.
+    /// </para>
+    /// <para>
+    /// <b>Delivery failure does not delete the bytes.</b> They were fetched over somebody's network and the
+    /// staged copy is all that is left of them; it stays for the next launch's sweep rather than being
+    /// thrown away at the one moment it is worth the most.
+    /// </para>
+    /// </remarks>
+    /// <param name="row">The remote file to fetch.</param>
+    /// <param name="localPath">Where to stage it — a path the head owns and will sweep.</param>
+    /// <param name="deliver">Copies the staged file to wherever it was really meant to go.</param>
+    internal void QueueDeliveredDownload(
+        RemoteEntryRowViewModel row,
+        string localPath,
+        Func<string, Task> deliver)
+    {
+        ArgumentNullException.ThrowIfNull(row);
+        ArgumentNullException.ThrowIfNull(deliver);
+
+        if (!IsConnected)
+        {
+            Status = "Connect to a host first.";
+            return;
+        }
+
+        if (!row.IsFile)
+        {
+            Status = "Only files can be transferred.";
+            return;
+        }
+
+        staged.Add(localPath);
+        deliveries[queue.Enqueue(TransferDirection.Download, localPath, row.FullPath, row.Entry.Length)] =
+            deliver;
+
+        Status = $"Queued {row.Name} for download.";
+    }
+
+    /// <remarks>
+    /// Fire-and-forget from the queue's own event, which cannot await: the transfer is over as far as the
+    /// queue is concerned, and what is left is a copy this class owns and a callback the head gave it. The
+    /// status line is the only report either way, which is the same place every other outcome on this screen
+    /// is reported.
+    /// </remarks>
+    private async Task DeliverAsync(string localPath, Func<string, Task> deliver)
+    {
+        var name = Path.GetFileName(localPath);
+
+        try
+        {
+            await deliver(localPath).ConfigureAwait(true);
+
+            Status = $"Saved {name}.";
+            ReleaseStaged(localPath);
+        }
+        catch (Exception exception) when (exception is not OutOfMemoryException)
+        {
+            Status = $"{name} was downloaded but could not be saved where you chose: {exception.Message}";
+        }
+    }
+
+    /// <remarks>
+    /// The directory goes only if it is empty, and that is the whole of the safety here: staging puts one
+    /// file in a directory of its own, so an empty parent is this transfer's and a parent with anything else
+    /// in it is not something this method is entitled to reason about. Failures are ignored rather than
+    /// reported — a cached copy that outlives its transfer is swept at the next launch, and there is nothing
+    /// a person could do with the news.
+    /// </remarks>
+    private void ReleaseStaged(string localPath)
+    {
+        if (!staged.Remove(localPath))
+        {
+            return;
+        }
+
+        try
+        {
+            File.Delete(localPath);
+
+            if (Path.GetDirectoryName(localPath) is { Length: > 0 } folder)
+            {
+                Directory.Delete(folder);
+            }
+        }
+        catch (Exception exception) when (exception is IOException or UnauthorizedAccessException)
+        {
+        }
+    }
+
     /// <summary>Queues every one of these remote entries for download into the local directory showing.</summary>
     /// <inheritdoc cref="QueueUploads" path="/remarks" />
     internal void QueueDownloads(IReadOnlyList<RemoteEntryRowViewModel> rows)
@@ -1061,6 +1236,11 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
         if (await queue.DiscardAsync(row.Id, cancellationToken).ConfigureAwait(true))
         {
             Transfers.Remove(row);
+
+            // Discarding is the deliberate end of a stopped transfer — the row is gone and with it the
+            // RESUME the staged copy was being kept for, and any delivery that was waiting on it.
+            deliveries.Remove(row.Id);
+            ReleaseStaged(row.Transfer.LocalPath);
         }
     }
 
@@ -1388,13 +1568,33 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     private void OnTransferChanged(object? sender, TransferChangedEventArgs e) =>
         post(() =>
         {
+            // Completed only, and the reason is in QueueStagedUploads: a stopped upload still has a RESUME
+            // button that will read this file again.
+            if (e.Transfer.State is TransferState.Completed)
+            {
+                // A staged download is not finished when the queue says so — it is finished when the bytes
+                // reach the document the person picked, and only the head can put them there. So the copy
+                // is released by the delivery rather than here, or it would be deleted on the way.
+                if (deliveries.Remove(e.Transfer.Id, out var deliver))
+                {
+                    _ = DeliverAsync(e.Transfer.LocalPath, deliver);
+                }
+                else
+                {
+                    ReleaseStaged(e.Transfer.LocalPath);
+                }
+            }
+
             if (Transfers.FirstOrDefault(row => row.Id == e.Transfer.Id) is { } existing)
             {
                 existing.Transfer = e.Transfer;
-                return;
+            }
+            else
+            {
+                Transfers.Add(new TransferRowViewModel(e.Transfer));
             }
 
-            Transfers.Add(new TransferRowViewModel(e.Transfer));
+            ActivityChanged?.Invoke(this, EventArgs.Empty);
         });
 
     /// <remarks>

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

@@ -7303,7 +7303,12 @@ internal sealed partial class VaultViewModel(
 
         if (report.RekeyRequired)
         {
-            notes.Add("this keychain was rekeyed and your access needs re-issuing");
+            // What is readable and what is not, because the two differ and the difference is the whole
+            // of what somebody in this state needs to know: the keys they hold still open everything
+            // written before the rotation, and nothing written since.
+            notes.Add(
+                "this keychain was rekeyed — you can still read what was here, and need the new key "
+                + "before you can see anything written since");
         }
 
         return replayed + "Synchronised, but: " + string.Join("; ", notes) + ".";

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

@@ -904,12 +904,7 @@ internal sealed partial class VaultsViewModel(
         {
             // Never silent. This command's failures used to be visible only as a flicker of the busy
             // flag, which reads as a button that does nothing at all.
-            Status = connection() is null
-                ? "Offline. Adding somebody changes who the server will serve, so it needs a connection."
-                : SelectedIsPersonal
-                    ? "Your personal vault is yours alone and cannot be shared. Make a vault for the "
-                        + "things you want to share, and put them in it."
-                    : "Select a vault on the left first — somebody is added to one vault, not to all.";
+            Status = WhyNobodyCanBeAdded();
             return;
         }
 
@@ -921,62 +916,183 @@ internal sealed partial class VaultsViewModel(
             return;
         }
 
-        await RunAsync(async () =>
+        await RunAsync(() => AddOrInviteAsync(server, teamId, email, cancellationToken))
+            .ConfigureAwait(true);
+    }
+
+    /// <summary>Which of the three reasons the ADD button had nothing to act on.</summary>
+    private string WhyNobodyCanBeAdded() => connection() is null
+        ? "Offline. Adding somebody changes who the server will serve, so it needs a connection."
+        : SelectedIsPersonal
+            ? "Your personal vault is yours alone and cannot be shared. Make a vault for the things you "
+                + "want to share, and put them in it."
+            : "Select a vault on the left first — somebody is added to one vault, not to all.";
+
+    /// <summary>The calls behind <see cref="AddMemberAsync"/>, once its arguments are known good.</summary>
+    private async Task AddOrInviteAsync(
+        IVaultServer server,
+        Guid teamId,
+        string email,
+        CancellationToken cancellationToken)
+    {
+        var found = await server.Directory.LookupByEmailAsync(email, cancellationToken)
+            .ConfigureAwait(true);
+
+        var request = found.Count > 0
+            ? new AddTeamMemberRequest(found[0].UserId, NewMemberRole)
+            : new AddTeamMemberRequest(Guid.Empty, NewMemberRole, email);
+
+        TeamMemberSummary member;
+
+        try
         {
-            var found = await server.Directory.LookupByEmailAsync(email, cancellationToken)
+            member = await server.Teams
+                .AddTeamMemberAsync(teamId, request, cancellationToken)
                 .ConfigureAwait(true);
+        }
+        catch (DodoSshApiException exception)
+            when (string.Equals(exception.Code, ProblemCodes.NoSuchAccount, StringComparison.Ordinal))
+        {
+            // The address really is unknown here, which only the server can say. This is the one
+            // route to an invitation, and it is now a fact rather than an inference from silence.
+            await InviteAsync(server, teamId, email, cancellationToken).ConfigureAwait(true);
+            return;
+        }
 
-            var request = found.Count > 0
-                ? new AddTeamMemberRequest(found[0].UserId, NewMemberRole)
-                : new AddTeamMemberRequest(Guid.Empty, NewMemberRole, email);
+        InviteEmail = string.Empty;
 
-            TeamMemberSummary member;
+        // Before the reload, so the vault list this screen redraws already shows what they can open. The
+        // sharing is what makes the membership worth anything, and doing it here rather than leaving a
+        // SHARE KEY button to be pressed is the difference between adding a colleague and adding a
+        // colleague who then waits for somebody to notice.
+        var shared = await ShareWithAsync(server, teamId, member, cancellationToken).ConfigureAwait(true);
 
-            try
-            {
-                member = await server.Teams
-                    .AddTeamMemberAsync(teamId, request, cancellationToken)
-                    .ConfigureAwait(true);
-            }
-            catch (DodoSshApiException exception)
-                when (string.Equals(
-                    exception.Code, ProblemCodes.NoSuchAccount, StringComparison.Ordinal))
-            {
-                // The address really is unknown here, which only the server can say. This is the one
-                // route to an invitation, and it is now a fact rather than an inference from silence.
-                await InviteAsync(server, teamId, email, cancellationToken).ConfigureAwait(true);
-                return;
-            }
+        await ReloadAsync(cancellationToken).ConfigureAwait(true);
 
-            InviteEmail = string.Empty;
+        Status = Describe(member, shared);
+    }
 
-            await ReloadAsync(cancellationToken).ConfigureAwait(true);
+    /// <summary>
+    /// Wraps every vault behind this membership list that this machine can open to somebody just added.
+    /// </summary>
+    /// <returns>What to tell the user about the keys, or null when there was nothing to say.</returns>
+    /// <remarks>
+    /// <para>
+    /// The membership list rather than the one vault, and that is not a slip: adding somebody is a
+    /// change to the list, so it is every vault the list carries that they can now fetch. This screen
+    /// makes lists that carry one vault, so the sentence names one — and where it does not, naming them
+    /// all is the honest report of what just happened.
+    /// </para>
+    /// <para>
+    /// Skipped outright for an account with no identity key: there is nothing to wrap to, and a
+    /// refusal per vault would bury that one fact under a list. Their row says so, and adding them was
+    /// still worth doing.
+    /// </para>
+    /// <para>
+    /// A failure here is reported and never thrown. The membership has already been recorded on the
+    /// server and is not undone by a key that could not be wrapped — so the honest outcome is "they are
+    /// in it, and this vault still needs sharing", which is a state somebody can act on.
+    /// </para>
+    /// </remarks>
+    private async Task<string?> ShareWithAsync(
+        IVaultServer server,
+        Guid teamId,
+        TeamMemberSummary member,
+        CancellationToken cancellationToken)
+    {
+        if (!member.IsEnrolled)
+        {
+            return null;
+        }
 
-            Status = Describe(member);
-        }).ConfigureAwait(true);
+        if (session() is not { } open)
+        {
+            // Distinguished from holding no keys, because the two lead somewhere different: this one is
+            // fixed by unlocking, and the other by asking somebody who holds the vault.
+            return "Nothing was shared with them — a vault key is wrapped on an unlocked machine, and "
+                + "this keychain is locked.";
+        }
+
+        var reports = await open
+            .ShareTeamVaultsAsync(
+                server.Grants, server.Directory, teamId, member.UserId, cancellationToken)
+            .ConfigureAwait(true);
+
+        if (reports.Count == 0)
+        {
+            return null;
+        }
+
+        var shared = reports.Where(report => report.Succeeded).ToList();
+        var refused = reports.Where(report => !report.Succeeded).ToList();
+
+        var sentence = shared.Count > 0
+            ? $"Shared {VaultCount(shared.Count)} with them: {Join(shared.Select(r => r.Name))}."
+            : null;
+
+        if (refused.Count == 0)
+        {
+            return sentence;
+        }
+
+        // Named one by one rather than counted. Each of these is a vault somebody now expects them to
+        // be able to open, and which one it is decides who has to fix it.
+        var reasons = refused.Select(report =>
+            $"'{report.Name}' ({report.Failure?.Message ?? report.Outcome?.Message})");
+
+        return (sentence is null ? string.Empty : sentence + " ")
+            + $"Could not share {Join(reasons)}.";
+    }
+
+    /// <summary>"1 vault" or "3 vaults", for a sentence that has to read either way.</summary>
+    private static string VaultCount(int count) =>
+        string.Create(CultureInfo.CurrentCulture, $"{count} vault{(count == 1 ? string.Empty : "s")}");
+
+    /// <summary>Joins names into a phrase a person would say, rather than a comma-separated list.</summary>
+    private static string Join(IEnumerable<string> parts)
+    {
+        var list = parts.ToList();
+
+        return list.Count switch
+        {
+            0 => string.Empty,
+            1 => list[0],
+            2 => $"{list[0]} and {list[1]}",
+            _ => string.Join(", ", list.Take(list.Count - 1)) + " and " + list[^1],
+        };
     }
 
     /// <summary>
     /// What just happened to the account that was added, and what is still owed them.
     /// </summary>
     /// <remarks>
-    /// Both branches say out loud that nothing readable was granted, because the single most common
-    /// misunderstanding this design invites is that adding somebody gave them the vault. The unenrolled
-    /// branch says more, and has to: their row will sit in the list saying it holds no key, and without
-    /// this somebody would read that as the addition having half-failed rather than as a colleague who
-    /// has not finished setting their machine up. It is also the one case where SHARE KEY cannot be the
-    /// next step, so pointing at it would be pointing at a button that will refuse.
+    /// <para>
+    /// The enrolled branch reports what the keys did, because that is the half of "adding somebody"
+    /// that this machine performs and the half that can partly fail. A vault that could not be wrapped
+    /// is named there rather than left to be noticed when they say they cannot open it.
+    /// </para>
+    /// <para>
+    /// The unenrolled branch says more, and has to: their row will sit in the list saying it holds no
+    /// key, and without this somebody would read that as the addition having half-failed rather than as
+    /// a colleague who has not finished setting their machine up. Nothing was shared with them and
+    /// nothing could have been — there is no key to wrap to — so the membership is all there is yet.
+    /// </para>
     /// </remarks>
-    private static string Describe(TeamMemberSummary member)
+    private static string Describe(TeamMemberSummary member, string? shared)
     {
         var who = member.Email ?? member.DisplayName ?? "the account";
 
-        return member.IsEnrolled
-            ? $"Added {who}. They cannot read anything yet — press SHARE KEY to wrap this vault's key "
-                + "to them."
-            : $"Added {who}. They have no key yet, so their row says so and this vault cannot be shared "
-                + "with them until they finish signing in on their own machine. The membership is real "
-                + "in the meantime.";
+        if (!member.IsEnrolled)
+        {
+            return $"Added {who}. They have no key yet, so their row says so and this vault cannot be "
+                + "shared with them until they finish signing in on their own machine. The membership "
+                + "is real in the meantime.";
+        }
+
+        return shared is null
+            ? $"Added {who}. This machine holds no key to give them — press SHARE KEY from one that "
+                + "does."
+            : $"Added {who}. {shared}";
     }
 
     /// <summary>
@@ -1158,7 +1274,14 @@ internal sealed partial class VaultsViewModel(
         }).ConfigureAwait(true);
     }
 
-    /// <summary>Removes somebody, revoking every key grant they hold from this vault.</summary>
+    /// <summary>
+    /// Removes somebody, revoking their grants and rotating the vaults they could read.
+    /// </summary>
+    /// <remarks>
+    /// The removal and the rotation are separate acts and only the first is the server's. Nothing here
+    /// undoes the removal if the rotation fails, and nothing waits for it: the membership change is what
+    /// stops them fetching anything more, and it has already happened by then.
+    /// </remarks>
     [RelayCommand]
     private async Task RemoveMemberAsync(CancellationToken cancellationToken)
     {
@@ -1169,21 +1292,127 @@ internal sealed partial class VaultsViewModel(
             return;
         }
 
+        // Read before the removal, because afterwards this list no longer contains them — and it is the
+        // list of who the new key goes to.
+        var remaining = Members
+            .Where(row => row.UserId != member.UserId)
+            .Select(row => row.UserId)
+            .ToList();
+
         await RunAsync(async () =>
         {
             await server.Teams
                 .RemoveTeamMemberAsync(teamId, member.UserId, cancellationToken)
                 .ConfigureAwait(true);
 
+            var rotated = await RotateAfterRemovalAsync(server, teamId, remaining, cancellationToken)
+                .ConfigureAwait(true);
+
             await ReloadAsync(cancellationToken).ConfigureAwait(true);
 
             // The honest sentence, not the reassuring one. See ADR 0001: revocation is not retroactive,
-            // and a message implying otherwise is the one thing this screen must not say.
-            Status = $"Removed {member.Name}. They can no longer fetch this vault, and anything they had "
-                + "already downloaded is still on their machine — rotate the credentials that matter.";
+            // and a message implying otherwise is the one thing this screen must not say. The rotation
+            // is described in the same breath for the same reason — it decides what happens next, not
+            // what already happened.
+            Status = $"Removed {member.Name}. {rotated} Anything they had already downloaded is still "
+                + "on their machine — rotate the credentials that matter.";
         }).ConfigureAwait(true);
     }
 
+    /// <summary>
+    /// Rotates every vault behind this membership list that this machine can open, handing each new key
+    /// to the members who remain.
+    /// </summary>
+    /// <returns>What to tell the user about the keys. Never null — something always happened.</returns>
+    /// <remarks>
+    /// The list rather than the one vault, for the reason <see cref="ShareWithAsync"/> gives: removing
+    /// somebody is a change to the list, so every vault it carries is one they have just lost. A vault
+    /// this machine cannot open is not rotated and is not counted as a failure: its key belongs to
+    /// somebody else, the server has flagged it as owing a rekey, and its row says so until one of them
+    /// does it.
+    /// </remarks>
+    private async Task<string> RotateAfterRemovalAsync(
+        IVaultServer server,
+        Guid teamId,
+        IReadOnlyList<Guid> remaining,
+        CancellationToken cancellationToken)
+    {
+        if (session() is not { } open)
+        {
+            return "Their key grants are withdrawn, so they can fetch nothing more. Unlock your "
+                + "keychain to rotate the vault keys themselves.";
+        }
+
+        var reports = await open
+            .RekeyTeamVaultsAsync(
+                server.Grants, server.Directory, server.Sync, teamId, remaining, cancellationToken)
+            .ConfigureAwait(true);
+
+        if (reports.Count == 0)
+        {
+            return "Their key grants are withdrawn, so they can fetch nothing more. This machine holds "
+                + "no key to any of it, so there was nothing here to rotate.";
+        }
+
+        var rotated = reports.Where(report => report.Rotated).ToList();
+        var failed = reports.Where(report => !report.Rotated).ToList();
+
+        var sentences = new List<string>();
+
+        if (rotated.Count > 0)
+        {
+            sentences.AddRange(Describe(rotated));
+        }
+
+        if (failed.Count > 0)
+        {
+            sentences.Add(
+                $"Could not rotate {Join(failed.Select(r => $"'{r.Name}' ({r.Failure?.Message})"))}.");
+        }
+
+        return string.Join(" ", sentences);
+    }
+
+    /// <summary>What the vaults that did rotate are now worth, in the order somebody needs it.</summary>
+    private IEnumerable<string> Describe(List<VaultRekeyReport> rotated)
+    {
+        yield return
+            $"Rotated {VaultCount(rotated.Count)} — {Join(rotated.Select(r => r.Name))} — so nothing "
+            + "written from now on is readable to them.";
+
+        // Two different promises, so two different sentences. A vault whose items were all moved onto
+        // the new key is closed to them completely; one where some were left is closed to what happens
+        // next, and the difference is not the interface's to blur.
+        var sealedUp = rotated.Count(report => report.Sealed);
+
+        yield return sealedUp == rotated.Count
+            ? "Everything already stored was re-sealed under the new key too, so their old key opens "
+                + "nothing."
+            : $"{sealedUp} of {rotated.Count} had everything already stored re-sealed under the new "
+                + "key; the rest still hold items under the old one and will be picked up next time. "
+                + "Rotate the credentials that mattered either way.";
+
+        // The members who did not get the new key. They are still in the vault and can still write, but
+        // until somebody wraps it to them they will find it stops updating. Distinct by id rather than
+        // by name, because two accounts can share a display name and collapsing them would tell
+        // somebody one person is owed a key when two are.
+        var missed = rotated
+            .SelectMany(report => report.NotShared.Select(entry => entry.UserId))
+            .Distinct()
+            .Select(Name)
+            .ToList();
+
+        if (missed.Count > 0)
+        {
+            yield return $"The new key did not reach {Join(missed)} — press SHARE KEY for them, or "
+                + "they will stop seeing changes.";
+        }
+    }
+
+    /// <summary>What to call a member in a sentence, from the list this screen already has.</summary>
+    private string Name(Guid userId) =>
+        Members.FirstOrDefault(row => row.UserId == userId)?.Name ?? userId.ToString();
+
     /// <summary>
     /// Wraps the selected vault's key to the selected member.
     /// </summary>
@@ -1216,8 +1445,16 @@ internal sealed partial class VaultsViewModel(
                 .ShareVaultAsync(server.Grants, server.Directory, vault.VaultId, member.UserId, cancellationToken)
                 .ConfigureAwait(true);
 
+            // The generation count is said out loud when there is more than one, because it is the
+            // answer to a question somebody will have about a rotated vault: whether the person they
+            // just shared it with can see what was in it before the rotation.
+            var history = outcome.Generations > 1
+                ? $" All {outcome.Generations} generations of the key were wrapped, so they can read "
+                    + "what was in the vault before it was last rotated."
+                : string.Empty;
+
             Status = outcome.Shared
-                ? $"Shared '{vault.Name}' with {member.Name}. {outcome.Message}"
+                ? $"Shared '{vault.Name}' with {member.Name}. {outcome.Message}{history}"
                 : $"Did not share '{vault.Name}': {outcome.Message}";
 
             await LoadGrantsAsync(cancellationToken).ConfigureAwait(true);

src/DodoSSH.Client.Storage/CacheRows.cs

@@ -159,6 +159,31 @@ internal sealed class CachedVaultRow
     public DateTimeOffset UpdatedAtUtc { get; set; }
 }
 
+/// <summary>
+/// A vault key this user holds for a generation the vault has moved past.
+/// </summary>
+/// <remarks>
+/// <para>
+/// A table rather than a column, because there is one of these per rotation and the vault row has one
+/// of everything else. The current generation's wrap stays on <see cref="CachedVaultRow"/>: it is what
+/// unlocking needs, and burying it in a child table would make the common case the awkward one.
+/// </para>
+/// <para>
+/// Cached for the reason the current wrap is. An item keeps the generation it was sealed under, so a
+/// machine that came back from a rotation with only the newest key would read everything written
+/// before it as corrupt — offline, with no way to ask for the rest.
+/// </para>
+/// </remarks>
+internal sealed class CachedVaultKeyWrapRow
+{
+    public Guid VaultId { get; set; }
+
+    public uint KeyGeneration { get; set; }
+
+    /// <summary>The vault key at this generation, sealed to this user's X25519 key.</summary>
+    public byte[] WrappedKey { get; set; } = [];
+}
+
 /// <summary>
 /// The last state of an item that the server confirmed.
 /// </summary>

src/DodoSSH.Client.Storage/ClientCacheContext.cs

@@ -123,7 +123,8 @@ public sealed class ClientCacheContext(DbContextOptions<ClientCacheContext> opti
             entity.Property(row => row.SealedRefreshToken).IsRequired();
         });
 
-    private static void ConfigureVaults(ModelBuilder modelBuilder) =>
+    private static void ConfigureVaults(ModelBuilder modelBuilder)
+    {
         modelBuilder.Entity<CachedVaultRow>(entity =>
         {
             entity.ToTable("vault");
@@ -132,6 +133,18 @@ public sealed class ClientCacheContext(DbContextOptions<ClientCacheContext> opti
             entity.Property(row => row.Name).IsRequired();
         });
 
+        // No foreign key to the vault row, deliberately. The two are written by the same store in the
+        // same call, and a cascade would make "which of these two tables is authoritative" a question
+        // the schema answers rather than the code — while buying nothing, since a wrap for a vault this
+        // machine can no longer see is removed by the same pass that removes the vault.
+        modelBuilder.Entity<CachedVaultKeyWrapRow>(entity =>
+        {
+            entity.ToTable("vault_key_wrap");
+            entity.HasKey(row => new { row.VaultId, row.KeyGeneration });
+            entity.Property(row => row.WrappedKey).IsRequired();
+        });
+    }
+
     private static void ConfigureItems(ModelBuilder modelBuilder) =>
         modelBuilder.Entity<CachedItemRow>(entity =>
         {

src/DodoSSH.Client.Storage/Migrations/20260803202241_AddVaultKeyWrapHistory.Designer.cs

@@ -0,0 +1,465 @@
+// <auto-generated />
+using System;
+using DodoSSH.Client.Storage;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+
+#nullable disable
+
+namespace DodoSSH.Client.Storage.Migrations
+{
+    [DbContext(typeof(ClientCacheContext))]
+    [Migration("20260803202241_AddVaultKeyWrapHistory")]
+    partial class AddVaultKeyWrapHistory
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder.HasAnnotation("ProductVersion", "10.0.10");
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.CachedItemRow", b =>
+                {
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<int>("EntityType")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("entity_type");
+
+                    b.Property<Guid>("EntityId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("entity_id");
+
+                    b.Property<byte>("AadVersion")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("aad_version");
+
+                    b.Property<long>("ChangeSequence")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("change_sequence");
+
+                    b.Property<Guid?>("DataKeyId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("data_key_id");
+
+                    b.Property<bool>("IsDeleted")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("is_deleted");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<byte[]>("Payload")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("payload");
+
+                    b.Property<byte[]>("ProtectedFields")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("protected_fields");
+
+                    b.Property<long>("UpdatedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("updated_at_utc");
+
+                    b.Property<int>("Version")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("version");
+
+                    b.Property<byte[]>("WrappedDataKey")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_data_key");
+
+                    b.HasKey("VaultId", "EntityType", "EntityId")
+                        .HasName("pk_item");
+
+                    b.HasIndex("VaultId", "ChangeSequence")
+                        .HasDatabaseName("ix_item_vault_id_change_sequence");
+
+                    b.HasIndex("VaultId", "EntityType")
+                        .HasDatabaseName("ix_item_vault_id_entity_type");
+
+                    b.ToTable("item", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.CachedVaultKeyWrapRow", b =>
+                {
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<byte[]>("WrappedKey")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_key");
+
+                    b.HasKey("VaultId", "KeyGeneration")
+                        .HasName("pk_vault_key_wrap");
+
+                    b.ToTable("vault_key_wrap", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.CachedVaultRow", b =>
+                {
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<bool>("Hidden")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("hidden");
+
+                    b.Property<bool>("IsPersonal")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("is_personal");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<string>("Name")
+                        .IsRequired()
+                        .HasColumnType("TEXT")
+                        .HasColumnName("name");
+
+                    b.Property<int>("Permissions")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("permissions");
+
+                    b.Property<bool>("RekeyRequired")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("rekey_required");
+
+                    b.Property<Guid?>("TeamId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("team_id");
+
+                    b.Property<long>("UpdatedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("updated_at_utc");
+
+                    b.Property<byte[]>("WrappedVaultKey")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_vault_key");
+
+                    b.HasKey("VaultId")
+                        .HasName("pk_vault");
+
+                    b.ToTable("vault", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.ConflictRow", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("id");
+
+                    b.Property<bool>("Acknowledged")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("acknowledged");
+
+                    b.Property<byte[]>("Detail")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("detail");
+
+                    b.Property<long>("DetectedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("detected_at_utc");
+
+                    b.Property<Guid>("EntityId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("entity_id");
+
+                    b.Property<int>("EntityType")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("entity_type");
+
+                    b.Property<int>("Kind")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("kind");
+
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.HasKey("Id")
+                        .HasName("pk_conflict");
+
+                    b.HasIndex("VaultId", "Acknowledged")
+                        .HasDatabaseName("ix_conflict_vault_id_acknowledged");
+
+                    b.HasIndex("VaultId", "EntityType", "EntityId")
+                        .HasDatabaseName("ix_conflict_vault_id_entity_type_entity_id");
+
+                    b.ToTable("conflict", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.OutboxRow", b =>
+                {
+                    b.Property<long>("Sequence")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("sequence");
+
+                    b.Property<byte>("AadVersion")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("aad_version");
+
+                    b.Property<byte?>("AncestorAadVersion")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("ancestor_aad_version");
+
+                    b.Property<Guid?>("AncestorDataKeyId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("ancestor_data_key_id");
+
+                    b.Property<uint?>("AncestorKeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("ancestor_key_generation");
+
+                    b.Property<byte[]>("AncestorPayload")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("ancestor_payload");
+
+                    b.Property<byte[]>("AncestorProtectedFields")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("ancestor_protected_fields");
+
+                    b.Property<int?>("AncestorVersion")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("ancestor_version");
+
+                    b.Property<byte[]>("AncestorWrappedDataKey")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("ancestor_wrapped_data_key");
+
+                    b.Property<int>("Attempts")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("attempts");
+
+                    b.Property<Guid?>("DataKeyId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("data_key_id");
+
+                    b.Property<Guid>("EntityId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("entity_id");
+
+                    b.Property<int>("EntityType")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("entity_type");
+
+                    b.Property<int?>("ExpectedVersion")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("expected_version");
+
+                    b.Property<bool>("IsParked")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("is_parked");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<string>("LastError")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("last_error");
+
+                    b.Property<int>("Operation")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("operation");
+
+                    b.Property<Guid>("OperationId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("operation_id");
+
+                    b.Property<byte[]>("Payload")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("payload");
+
+                    b.Property<byte[]>("ProtectedFields")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("protected_fields");
+
+                    b.Property<long>("QueuedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("queued_at_utc");
+
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<byte[]>("WrappedDataKey")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_data_key");
+
+                    b.HasKey("Sequence")
+                        .HasName("pk_outbox");
+
+                    b.HasIndex("OperationId")
+                        .IsUnique()
+                        .HasDatabaseName("ix_outbox_operation_id");
+
+                    b.HasIndex("VaultId", "EntityType", "EntityId")
+                        .IsUnique()
+                        .HasDatabaseName("ix_outbox_vault_id_entity_type_entity_id");
+
+                    b.HasIndex("VaultId", "IsParked", "Sequence")
+                        .HasDatabaseName("ix_outbox_vault_id_is_parked_sequence");
+
+                    b.ToTable("outbox", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.RememberedSignInRow", b =>
+                {
+                    b.Property<int>("Id")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("id");
+
+                    b.Property<byte[]>("SealedRefreshToken")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("sealed_refresh_token");
+
+                    b.Property<long>("UpdatedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("updated_at_utc");
+
+                    b.HasKey("Id")
+                        .HasName("pk_remembered_sign_in");
+
+                    b.ToTable("remembered_sign_in", null, t =>
+                        {
+                            t.HasCheckConstraint("ck_remembered_sign_in_singleton", "id = 1");
+                        });
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.SyncStateRow", b =>
+                {
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<string>("Cursor")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("cursor");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<long?>("LastPulledAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("last_pulled_at_utc");
+
+                    b.Property<long?>("LastPushedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("last_pushed_at_utc");
+
+                    b.Property<long>("ServerTimeSkewMs")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("server_time_skew_ms");
+
+                    b.HasKey("VaultId")
+                        .HasName("pk_sync_state");
+
+                    b.ToTable("sync_state", (string)null);
+                });
+
+            modelBuilder.Entity("DodoSSH.Client.Storage.UnlockMaterialRow", b =>
+                {
+                    b.Property<int>("Id")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("id");
+
+                    b.Property<Guid?>("DeviceId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("device_id");
+
+                    b.Property<byte[]>("DeviceWrappedPrivateKey")
+                        .HasColumnType("BLOB")
+                        .HasColumnName("device_wrapped_private_key");
+
+                    b.Property<string>("DisplayName")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("display_name");
+
+                    b.Property<string>("Email")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("email");
+
+                    b.Property<string>("Issuer")
+                        .IsRequired()
+                        .HasColumnType("TEXT")
+                        .HasColumnName("issuer");
+
+                    b.Property<string>("KdfAlgorithm")
+                        .IsRequired()
+                        .HasColumnType("TEXT")
+                        .HasColumnName("kdf_algorithm");
+
+                    b.Property<int>("KdfMemoryKibibytes")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("kdf_memory_kibibytes");
+
+                    b.Property<int>("KdfParallelism")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("kdf_parallelism");
+
+                    b.Property<int>("KdfPasses")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("kdf_passes");
+
+                    b.Property<byte[]>("KdfSalt")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("kdf_salt");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<string>("ServerUrl")
+                        .IsRequired()
+                        .HasColumnType("TEXT")
+                        .HasColumnName("server_url");
+
+                    b.Property<string>("Subject")
+                        .IsRequired()
+                        .HasColumnType("TEXT")
+                        .HasColumnName("subject");
+
+                    b.Property<long>("UpdatedAtUtc")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("updated_at_utc");
+
+                    b.Property<Guid>("UserId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("user_id");
+
+                    b.Property<byte[]>("WrappedPrivateKey")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_private_key");
+
+                    b.HasKey("Id")
+                        .HasName("pk_unlock_material");
+
+                    b.ToTable("unlock_material", null, t =>
+                        {
+                            t.HasCheckConstraint("ck_unlock_material_singleton", "id = 1");
+                        });
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

src/DodoSSH.Client.Storage/Migrations/20260803202241_AddVaultKeyWrapHistory.cs

@@ -0,0 +1,35 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace DodoSSH.Client.Storage.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddVaultKeyWrapHistory : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "vault_key_wrap",
+                columns: table => new
+                {
+                    vault_id = table.Column<Guid>(type: "TEXT", nullable: false),
+                    key_generation = table.Column<uint>(type: "INTEGER", nullable: false),
+                    wrapped_key = table.Column<byte[]>(type: "BLOB", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("pk_vault_key_wrap", x => new { x.vault_id, x.key_generation });
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "vault_key_wrap");
+        }
+    }
+}

src/DodoSSH.Client.Storage/Migrations/ClientCacheContextModelSnapshot.cs

@@ -83,6 +83,27 @@ namespace DodoSSH.Client.Storage.Migrations
                     b.ToTable("item", (string)null);
                 });
 
+            modelBuilder.Entity("DodoSSH.Client.Storage.CachedVaultKeyWrapRow", b =>
+                {
+                    b.Property<Guid>("VaultId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("vault_id");
+
+                    b.Property<uint>("KeyGeneration")
+                        .HasColumnType("INTEGER")
+                        .HasColumnName("key_generation");
+
+                    b.Property<byte[]>("WrappedKey")
+                        .IsRequired()
+                        .HasColumnType("BLOB")
+                        .HasColumnName("wrapped_key");
+
+                    b.HasKey("VaultId", "KeyGeneration")
+                        .HasName("pk_vault_key_wrap");
+
+                    b.ToTable("vault_key_wrap", (string)null);
+                });
+
             modelBuilder.Entity("DodoSSH.Client.Storage.CachedVaultRow", b =>
                 {
                     b.Property<Guid>("VaultId")

src/DodoSSH.Client.Storage/StoredTypes.cs

@@ -71,6 +71,11 @@ public sealed record StoredUnlockMaterial(
 /// <param name="Permissions">Effective permissions, as a flags value.</param>
 /// <param name="WrappedVaultKey">The vault key sealed to this user. Null while awaiting re-wrap.</param>
 /// <param name="RekeyRequired">Whether a membership change has left this vault needing a rekey.</param>
+/// <param name="PriorKeyWraps">
+/// The same key at every generation before <paramref name="KeyGeneration"/> that this user still holds
+/// a grant for. Empty for a vault that has never been rotated, and what makes one that has readable
+/// back to its first item.
+/// </param>
 public sealed record StoredVault(
     Guid VaultId,
     string Name,
@@ -79,7 +84,8 @@ public sealed record StoredVault(
     uint KeyGeneration,
     int Permissions,
     byte[]? WrappedVaultKey,
-    bool RekeyRequired)
+    bool RekeyRequired,
+    IReadOnlyList<VaultKeyWrap>? PriorKeyWraps = null)
 {
     /// <summary>
     /// The <c>Write</c> bit of <see cref="Permissions"/>.

src/DodoSSH.Client.Storage/VaultStore.cs

@@ -1,3 +1,4 @@
+using DodoSSH.Contracts;
 using Microsoft.EntityFrameworkCore;
 
 namespace DodoSSH.Client.Storage;
@@ -25,7 +26,9 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
             .ToListAsync(cancellationToken)
             .ConfigureAwait(false);
 
-        return [.. rows.Select(ToStored)];
+        var wraps = await ReadWrapsAsync(context, cancellationToken).ConfigureAwait(false);
+
+        return [.. rows.Select(row => ToStored(row, wraps.GetValueOrDefault(row.VaultId, [])))];
     }
 
     /// <summary>Reads one vault.</summary>
@@ -39,7 +42,19 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
             .SingleOrDefaultAsync(r => r.VaultId == vaultId, cancellationToken)
             .ConfigureAwait(false);
 
-        return row is null ? null : ToStored(row);
+        if (row is null)
+        {
+            return null;
+        }
+
+        var wraps = await context.Set<CachedVaultKeyWrapRow>()
+            .AsNoTracking()
+            .Where(w => w.VaultId == vaultId)
+            .OrderBy(w => w.KeyGeneration)
+            .ToListAsync(cancellationToken)
+            .ConfigureAwait(false);
+
+        return ToStored(row, [.. wraps.Select(ToWrap)]);
     }
 
     /// <summary>
@@ -81,10 +96,20 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
             }
 
             Apply(row, vault, now);
+
+            await ApplyWrapsAsync(context, vault, cancellationToken).ConfigureAwait(false);
         }
 
         context.RemoveRange(existing.Values);
 
+        // The wraps of a vault that is gone from the list go with it. They are keys to something this
+        // machine can no longer fetch, and keeping them would be keeping key material for a vault the
+        // user has been told they no longer have.
+        foreach (var dropped in existing.Keys)
+        {
+            await RemoveWrapsAsync(context, dropped, cancellationToken).ConfigureAwait(false);
+        }
+
         await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
     }
 
@@ -116,6 +141,8 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
 
         Apply(row, vault, clock.GetUtcNow());
 
+        await ApplyWrapsAsync(context, vault, cancellationToken).ConfigureAwait(false);
+
         await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
     }
 
@@ -182,7 +209,66 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
         row.UpdatedAtUtc = now;
     }
 
-    private static StoredVault ToStored(CachedVaultRow row) =>
+    /// <summary>
+    /// Replaces one vault's earlier-generation wraps with what the server reported.
+    /// </summary>
+    /// <remarks>
+    /// Deleted and re-inserted rather than merged. There are a handful of these per vault at most, the
+    /// server's list is authoritative, and a merge would have to decide what a wrap present here and
+    /// absent there means — which is "that grant was revoked", and the answer to that is to drop it.
+    /// </remarks>
+    private static async Task ApplyWrapsAsync(
+        ClientCacheContext context,
+        StoredVault vault,
+        CancellationToken cancellationToken)
+    {
+        await RemoveWrapsAsync(context, vault.VaultId, cancellationToken).ConfigureAwait(false);
+
+        foreach (var wrap in vault.PriorKeyWraps ?? [])
+        {
+            context.Add(new CachedVaultKeyWrapRow
+            {
+                VaultId = vault.VaultId,
+                KeyGeneration = wrap.KeyGeneration,
+                WrappedKey = wrap.WrappedKey,
+            });
+        }
+    }
+
+    private static async Task RemoveWrapsAsync(
+        ClientCacheContext context,
+        Guid vaultId,
+        CancellationToken cancellationToken)
+    {
+        var stale = await context.Set<CachedVaultKeyWrapRow>()
+            .Where(w => w.VaultId == vaultId)
+            .ToListAsync(cancellationToken)
+            .ConfigureAwait(false);
+
+        context.RemoveRange(stale);
+    }
+
+    private static async Task<Dictionary<Guid, IReadOnlyList<VaultKeyWrap>>> ReadWrapsAsync(
+        ClientCacheContext context,
+        CancellationToken cancellationToken)
+    {
+        var rows = await context.Set<CachedVaultKeyWrapRow>()
+            .AsNoTracking()
+            .OrderBy(row => row.KeyGeneration)
+            .ToListAsync(cancellationToken)
+            .ConfigureAwait(false);
+
+        return rows
+            .GroupBy(row => row.VaultId)
+            .ToDictionary(
+                group => group.Key,
+                group => (IReadOnlyList<VaultKeyWrap>)[.. group.Select(ToWrap)]);
+    }
+
+    private static VaultKeyWrap ToWrap(CachedVaultKeyWrapRow row) =>
+        new(row.KeyGeneration, row.WrappedKey);
+
+    private static StoredVault ToStored(CachedVaultRow row, IReadOnlyList<VaultKeyWrap> priorWraps) =>
         new(
             row.VaultId,
             row.Name,
@@ -191,5 +277,6 @@ public sealed class VaultStore(IDbContextFactory<ClientCacheContext> contexts, T
             row.KeyGeneration,
             row.Permissions,
             row.WrappedVaultKey,
-            row.RekeyRequired);
+            row.RekeyRequired,
+            priorWraps);
 }

src/DodoSSH.Client.Sync/ItemReconciler.cs

@@ -144,14 +144,19 @@ internal sealed class ItemReconciler<TSecret>(
     {
         ArgumentNullException.ThrowIfNull(pending);
 
-        if (!keyring.TryGet(vaultId, out var vaultKey, out var generation) || pending.Payload is null)
+        if (!keyring.TryGet(vaultId, out var vaultKey, out var generation)
+            || pending.Payload is null
+            || !keyring.TryGetAt(vaultId, pending.Payload.KeyGeneration, out var queuedKey))
         {
             return "This item has no usable vault key.";
         }
 
+        // Opened under the generation it was queued at and re-sealed under the current one. Those
+        // differ whenever a rotation lands between an offline edit and its push, and re-sealing is
+        // the point: what goes back to the server has to be readable by everybody holding the new key.
         var local = kind.TryOpen(
             pending.Payload,
-            vaultKey.Span,
+            queuedKey.Span,
             pending.EntityId,
             SyncVersions.NextVersion(pending.ExpectedVersion));
 
@@ -253,8 +258,16 @@ internal sealed class ItemReconciler<TSecret>(
 
         var (local, remoteSecret, vaultKey, generation) = opened.Value;
 
-        var ancestor = kind.TryOpen(
-            pending.Ancestor.Payload, vaultKey.Span, remote.EntityId, pending.Ancestor.Version);
+        // The ancestor is the version the server last confirmed, so it carries its own generation —
+        // typically the oldest of the three when a rotation has happened since.
+        var ancestor =
+            keyring.TryGetAt(vaultId, pending.Ancestor.Payload.KeyGeneration, out var ancestorKey)
+                ? kind.TryOpen(
+                    pending.Ancestor.Payload,
+                    ancestorKey.Span,
+                    remote.EntityId,
+                    pending.Ancestor.Version)
+                : null;
 
         if (ancestor is null)
         {
@@ -313,10 +326,11 @@ internal sealed class ItemReconciler<TSecret>(
         }
 
         var local = pending.Payload is null
+            || !keyring.TryGetAt(vaultId, pending.Payload.KeyGeneration, out var queuedKey)
             ? null
             : kind.TryOpen(
                 pending.Payload,
-                vaultKey.Span,
+                queuedKey.Span,
                 remote.EntityId,
                 SyncVersions.NextVersion(pending.ExpectedVersion));
 
@@ -419,21 +433,26 @@ internal sealed class ItemReconciler<TSecret>(
     {
         if (!keyring.TryGet(vaultId, out var vaultKey, out var generation)
             || pending.Payload is null
-            || remote.Payload is null)
+            || remote.Payload is null
+            || !keyring.TryGetAt(vaultId, pending.Payload.KeyGeneration, out var queuedKey)
+            || !keyring.TryGetAt(vaultId, remote.Payload.KeyGeneration, out var remoteKey))
         {
             await ParkAsync(vaultId, remote.EntityId, pending, report, cancellationToken)
                 .ConfigureAwait(false);
             return null;
         }
 
+        // Each side under its own generation. The two genuinely differ after a rotation: what the
+        // server holds was sealed before it, and the queued edit after — or the other way round, for a
+        // client that rotated while this one was offline.
         var local = kind.TryOpen(
             pending.Payload,
-            vaultKey.Span,
+            queuedKey.Span,
             remote.EntityId,
             SyncVersions.NextVersion(pending.ExpectedVersion));
 
         var remoteSecret = kind.TryOpen(
-            remote.Payload, vaultKey.Span, remote.EntityId, remote.Version);
+            remote.Payload, remoteKey.Span, remote.EntityId, remote.Version);
 
         if (local is null || remoteSecret is null)
         {

src/DodoSSH.Client.Sync/SyncEngine.cs

@@ -350,13 +350,16 @@ public sealed class SyncEngine
 
         foreach (var operation in pending)
         {
+            var payload = await CurrentAsync(vaultId, operation, cancellationToken)
+                .ConfigureAwait(false);
+
             operations.Add(new SyncPushOperation(
                 operation.OperationId,
                 operation.EntityType,
                 operation.EntityId,
                 operation.Operation,
                 operation.ExpectedVersion,
-                operation.Payload,
+                payload,
                 operation.Fields));
 
             byOperationId[operation.OperationId] = operation;
@@ -393,6 +396,68 @@ public sealed class SyncEngine
             pending.Count, conflicted, pending.Count == options.MaxOperationsPerPush);
     }
 
+    /// <summary>
+    /// The payload to send, re-sealed under the current key if it was queued before a rotation.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// <b>Nothing may reach the server under a superseded generation, and this is where that is
+    /// enforced.</b> A change queued offline is sealed under whatever key was current when it was made,
+    /// and a rotation can land in between — so sending it as it stands would store a brand-new item
+    /// under the key the person who was just removed still holds. The vault's own re-sealing pass cannot
+    /// help: it runs over what the server holds, and this has not been sent yet.
+    /// </para>
+    /// <para>
+    /// The revised payload is written back to the outbox before it goes, so a push whose answer is lost
+    /// is retried as the same bytes. Re-sealing on each attempt instead would produce a different
+    /// envelope every time, which is harmless on the wire and would leave the queued row disagreeing
+    /// with what the server may already have accepted.
+    /// </para>
+    /// </remarks>
+    private async Task<EncryptedPayload?> CurrentAsync(
+        Guid vaultId,
+        PendingOperation operation,
+        CancellationToken cancellationToken)
+    {
+        if (operation.Payload is not { } payload
+            || !keyring.TryGet(vaultId, out _, out var generation)
+            || payload.KeyGeneration >= generation)
+        {
+            return operation.Payload;
+        }
+
+        var version = SyncVersions.NextVersion(operation.ExpectedVersion);
+
+        var resealed = PayloadReseal.TryReseal(
+            keyring,
+            vaultId,
+            operation.EntityType,
+            operation.EntityId,
+            payload,
+            openAtVersion: version,
+            sealAtVersion: version);
+
+        if (resealed is null)
+        {
+            // The generation this change was queued under is one this session no longer holds. It goes
+            // as it stands: the server takes it either way, and a queued edit that cannot be re-sealed
+            // is still the user's work.
+            return payload;
+        }
+
+        await outbox.ReviseAsync(
+                operation.Sequence,
+                operation.Operation,
+                operation.ExpectedVersion,
+                resealed,
+                operation.Fields,
+                operation.Ancestor,
+                cancellationToken)
+            .ConfigureAwait(false);
+
+        return resealed;
+    }
+
     /// <returns>Whether this answer warrants another push round.</returns>
     private async Task<bool> HandleAsync(
         Guid vaultId,

src/DodoSSH.Client.Sync/VaultItemRepository.cs

@@ -82,7 +82,10 @@ internal sealed class VaultItemRepository<TSecret>(
         Guid vaultId,
         CancellationToken cancellationToken)
     {
-        if (!keyring.TryGet(vaultId, out var vaultKey, out _))
+        // TryGet rather than CanRead, which answers false for a disposed keyring where this has to
+        // throw: a locked session being read from is a caller holding something it should have let go
+        // of, and the exception is what says so.
+        if (!keyring.TryGet(vaultId, out _, out _))
         {
             throw new VaultUnreadableException(vaultId);
         }
@@ -104,31 +107,17 @@ internal sealed class VaultItemRepository<TSecret>(
         {
             if (pendingByEntity.Remove(item.EntityId, out var local))
             {
-                AddPending(listed, ref unreadable, vaultKey, local);
+                AddPending(listed, ref unreadable, vaultId, local);
                 continue;
             }
 
-            if (item.IsDeleted || item.Payload is null)
-            {
-                continue;
-            }
-
-            var opened = kind.TryOpen(item.Payload, vaultKey.Span, item.EntityId, item.Version);
-
-            if (opened is null)
-            {
-                unreadable++;
-                continue;
-            }
-
-            listed.Add(new VaultItem<TSecret>(
-                item.EntityId, opened.Secret, item.Version, false, false, opened.IsReadOnly));
+            AddMirrored(listed, ref unreadable, vaultId, item);
         }
 
         // Whatever is left has no mirror row yet: items created here and not yet accepted.
         foreach (var local in pendingByEntity.Values)
         {
-            AddPending(listed, ref unreadable, vaultKey, local);
+            AddPending(listed, ref unreadable, vaultId, local);
         }
 
         return new ItemListing<TSecret>(listed, unreadable);
@@ -211,7 +200,7 @@ internal sealed class VaultItemRepository<TSecret>(
         // the payload was sealed at, which is why the pending and mirror cases differ: a pending payload
         // holds the version the server will assign, and a mirror row holds the one it has.
         var before = IsAudited
-            ? Open(vaultKey, entityId, pending, ancestor)
+            ? Open(vaultId, entityId, pending, ancestor)
             : null;
 
         await outbox.QueueAsync(
@@ -327,15 +316,10 @@ internal sealed class VaultItemRepository<TSecret>(
         PendingOperation? pending,
         CancellationToken cancellationToken)
     {
-        if (!keyring.TryGet(vaultId, out var vaultKey, out _))
-        {
-            return null;
-        }
-
         var ancestor = await MirrorAncestorAsync(vaultId, entityId, cancellationToken)
             .ConfigureAwait(false);
 
-        return Open(vaultKey, entityId, pending, ancestor)?.Label;
+        return Open(vaultId, entityId, pending, ancestor)?.Label;
     }
 
     /// <summary>
@@ -348,23 +332,29 @@ internal sealed class VaultItemRepository<TSecret>(
     /// at the version the server <em>will</em> assign, and a mirror row holds the one it has.
     /// </remarks>
     private TSecret? Open(
-        ReadOnlyMemory<byte> vaultKey,
+        Guid vaultId,
         Guid entityId,
         PendingOperation? pending,
         StoredAncestor? ancestor)
     {
         if (pending is { Operation: SyncOperation.Upsert, Payload: { } queued })
         {
-            return kind.TryOpen(
-                queued,
-                vaultKey.Span,
-                entityId,
-                SyncVersions.NextVersion(pending.ExpectedVersion))?.Secret;
+            return keyring.TryGetAt(vaultId, queued.KeyGeneration, out var queuedKey)
+                ? kind.TryOpen(
+                    queued,
+                    queuedKey.Span,
+                    entityId,
+                    SyncVersions.NextVersion(pending.ExpectedVersion))?.Secret
+                : null;
         }
 
-        return ancestor is null
-            ? null
-            : kind.TryOpen(ancestor.Payload, vaultKey.Span, entityId, ancestor.Version)?.Secret;
+        if (ancestor is null
+            || !keyring.TryGetAt(vaultId, ancestor.Payload.KeyGeneration, out var vaultKey))
+        {
+            return null;
+        }
+
+        return kind.TryOpen(ancestor.Payload, vaultKey.Span, entityId, ancestor.Version)?.Secret;
     }
 
     /// <summary>
@@ -401,10 +391,43 @@ internal sealed class VaultItemRepository<TSecret>(
         }
     }
 
+    /// <summary>Adds one row of the server's mirror to a listing, or counts it as unreadable.</summary>
+    private void AddMirrored(
+        List<VaultItem<TSecret>> listed,
+        ref int unreadable,
+        Guid vaultId,
+        StoredItem item)
+    {
+        if (item.IsDeleted || item.Payload is null)
+        {
+            return;
+        }
+
+        // The generation the item names, not the vault's current one. A rotated vault holds items
+        // written under two or three keys at once, and a list that assumed the newest would report
+        // everything older as unreadable.
+        if (!keyring.TryGetAt(vaultId, item.Payload.KeyGeneration, out var vaultKey))
+        {
+            unreadable++;
+            return;
+        }
+
+        var opened = kind.TryOpen(item.Payload, vaultKey.Span, item.EntityId, item.Version);
+
+        if (opened is null)
+        {
+            unreadable++;
+            return;
+        }
+
+        listed.Add(new VaultItem<TSecret>(
+            item.EntityId, opened.Secret, item.Version, false, false, opened.IsReadOnly));
+    }
+
     private void AddPending(
         List<VaultItem<TSecret>> listed,
         ref int unreadable,
-        ReadOnlyMemory<byte> vaultKey,
+        Guid vaultId,
         PendingOperation local)
     {
         if (local.Operation == SyncOperation.Delete)
@@ -419,6 +442,14 @@ internal sealed class VaultItemRepository<TSecret>(
             return;
         }
 
+        // A queued change is sealed under whatever generation was current when it was queued, which is
+        // not necessarily the current one: a rotation can land between an offline edit and its push.
+        if (!keyring.TryGetAt(vaultId, local.Payload.KeyGeneration, out var vaultKey))
+        {
+            unreadable++;
+            return;
+        }
+
         var version = SyncVersions.NextVersion(local.ExpectedVersion);
         var opened = kind.TryOpen(local.Payload, vaultKey.Span, local.EntityId, version);
 

src/DodoSSH.Client.Sync/VaultKeyring.cs

@@ -15,6 +15,13 @@ namespace DodoSSH.Client.Sync;
 /// "the keys exist only while unlocked" a property of the code and not of everyone's discipline.
 /// </para>
 /// <para>
+/// <b>A vault has a key per generation, and this holds every one it was granted.</b> A rotation does not
+/// re-encrypt what is already stored — each item keeps the generation it was sealed under — so reading a
+/// rotated vault means opening items under two or three different keys, chosen per item rather than per
+/// vault. Writing uses the newest, which is what <see cref="TryGet"/> answers; reading an item asks for
+/// the generation that item names, which is <see cref="TryGetAt"/>.
+/// </para>
+/// <para>
 /// A grant that will not open is not an error: it means the vault has been rekeyed and this client's
 /// grant has not been re-wrapped yet, or the grant was fabricated. Both leave the vault temporarily
 /// unreadable and both are reported rather than thrown, so one bad grant does not take the other vaults
@@ -23,7 +30,7 @@ namespace DodoSSH.Client.Sync;
 /// </remarks>
 public sealed class VaultKeyring : IDisposable
 {
-    private readonly Dictionary<Guid, byte[]> keys = [];
+    private readonly Dictionary<Guid, Dictionary<uint, byte[]>> keys = [];
     private readonly Dictionary<Guid, uint> generations = [];
     private bool disposed;
 
@@ -51,6 +58,12 @@ public sealed class VaultKeyring : IDisposable
         {
             foreach (var vault in vaults)
             {
+                // The history first, and never conditional on the current generation opening. A member
+                // who has been rotated past but not yet re-wrapped can still read everything written
+                // before the rotation, and dropping those keys because the newest grant is missing
+                // would turn "you cannot see the last hour's changes" into "the vault is empty".
+                keyring.OpenPriorWraps(bundle, vault);
+
                 if (vault.WrappedVaultKey is null)
                 {
                     // The server said so itself: a grant awaiting re-wrap after a rekey.
@@ -70,8 +83,7 @@ public sealed class VaultKeyring : IDisposable
                     continue;
                 }
 
-                keyring.keys[vault.VaultId] = key;
-                keyring.generations[vault.VaultId] = vault.KeyGeneration;
+                keyring.Adopt(vault.VaultId, key, vault.KeyGeneration);
             }
 
             keyring.Unopened = unopened;
@@ -94,26 +106,49 @@ public sealed class VaultKeyring : IDisposable
     /// </param>
     /// <param name="keyGeneration">The generation this key is for.</param>
     /// <remarks>
-    /// Creating a team vault is the only case: the client generates the key, wraps it to itself and
-    /// sends the wrap, so the plaintext is already here and unwrapping the server's copy back would be
-    /// a round trip to learn something this process just chose. Adopting it also means the new vault is
-    /// usable immediately rather than at the next unlock, which is what somebody who just pressed
-    /// "create" expects.
+    /// <para>
+    /// Two cases, and they are the same operation: creating a team vault, and rotating one. Both
+    /// generate the key here, wrap it to this user and send the wrap, so the plaintext is already in
+    /// this process and unwrapping the server's copy back would be a round trip to learn something it
+    /// just chose. Adopting it also means the vault is usable immediately rather than at the next
+    /// unlock, which is what somebody who has just pressed a button expects.
+    /// </para>
+    /// <para>
+    /// This generation becomes the one writes are sealed under. A key for a generation the vault has
+    /// moved <em>past</em> goes in through <see cref="AdoptPrior"/> instead, which is not the same
+    /// operation: it makes old items readable and must not walk the write target backwards.
+    /// </para>
     /// </remarks>
     public void Adopt(Guid vaultId, byte[] vaultKey, uint keyGeneration)
     {
         ObjectDisposedException.ThrowIf(disposed, this);
         ArgumentNullException.ThrowIfNull(vaultKey);
 
-        if (keys.TryGetValue(vaultId, out var previous))
-        {
-            CryptographicOperations.ZeroMemory(previous);
-        }
+        Store(vaultId, vaultKey, keyGeneration);
 
-        keys[vaultId] = vaultKey;
-        generations[vaultId] = keyGeneration;
+        Promote(vaultId, keyGeneration);
+    }
 
-        Unopened = [.. Unopened.Where(id => id != vaultId)];
+    /// <summary>
+    /// Takes a vault key for a generation the vault has already moved past.
+    /// </summary>
+    /// <param name="vaultId">The vault.</param>
+    /// <param name="vaultKey">
+    /// The plaintext key. <b>The keyring takes ownership</b>, exactly as <see cref="Adopt"/> does.
+    /// </param>
+    /// <param name="keyGeneration">The superseded generation this key opens.</param>
+    /// <remarks>
+    /// Holding one of these is what lets a rotated vault be read at all: items are not re-encrypted by a
+    /// rotation, so everything written before it is still sealed under the key it was written with.
+    /// Nothing is ever <em>written</em> under one, which is why this does not touch the current
+    /// generation and does not make an otherwise unreadable vault readable.
+    /// </remarks>
+    public void AdoptPrior(Guid vaultId, byte[] vaultKey, uint keyGeneration)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        ArgumentNullException.ThrowIfNull(vaultKey);
+
+        Store(vaultId, vaultKey, keyGeneration);
     }
 
     /// <summary>
@@ -132,13 +167,23 @@ public sealed class VaultKeyring : IDisposable
         ArgumentNullException.ThrowIfNull(bundle);
         ArgumentNullException.ThrowIfNull(vault);
 
+        // Attempted whatever happens to the current generation, and before it. A share of a vault that
+        // has been rotated since it was created arrives as a current wrap plus its history, and the
+        // history is not a consolation prize — without it the recipient sees a vault full of items that
+        // will not decrypt.
+        OpenPriorWraps(bundle, vault);
+
         if (vault.WrappedVaultKey is null)
         {
             return false;
         }
 
-        if (keys.ContainsKey(vault.VaultId) && generations[vault.VaultId] == vault.KeyGeneration)
+        if (Held(vault.VaultId, vault.KeyGeneration) is not null)
         {
+            // Already open at this generation. Promoted rather than returned early, because a vault
+            // that was rotated and re-granted arrives here with a generation this keyring has been
+            // treating as historic, and it is now the one writes belong under.
+            Promote(vault.VaultId, vault.KeyGeneration);
             return true;
         }
 
@@ -157,14 +202,26 @@ public sealed class VaultKeyring : IDisposable
 
     /// <summary>Records that a vault cannot be read, so the interface can say so.</summary>
     /// <remarks>
+    /// <para>
     /// The counterpart of <see cref="TryAdmit"/> for the case where the grant did not open. Kept
     /// explicit rather than inferred from the absence of a key, because "no key" is also what a vault
     /// this session has never heard of looks like.
+    /// </para>
+    /// <para>
+    /// <b>It also gives up the write target, and that is the load-bearing half.</b> The usual way to
+    /// reach here is another client having rotated the vault: this session still holds the previous
+    /// generation's key and it is no longer the current one. Going on treating it as current would seal
+    /// new items under a superseded key — readable here, unreadable to everybody else, and with nothing
+    /// to show the author that anything was wrong. The keys themselves are kept, because the items
+    /// already written under them are still readable through <see cref="TryGetAt"/>.
+    /// </para>
     /// </remarks>
     public void MarkUnreadable(Guid vaultId)
     {
         ObjectDisposedException.ThrowIf(disposed, this);
 
+        generations.Remove(vaultId);
+
         if (!Unopened.Contains(vaultId))
         {
             Unopened = [.. Unopened, vaultId];
@@ -172,20 +229,27 @@ public sealed class VaultKeyring : IDisposable
     }
 
     /// <summary>
-    /// Borrows a vault's key.
+    /// Borrows a vault's current key: the one new items are sealed under.
     /// </summary>
     /// <remarks>
     /// The returned memory is the keyring's own buffer, not a copy, and is zeroed when the keyring is
     /// disposed. Callers must not retain it past the operation they borrowed it for.
+    /// <para>
+    /// False for a vault this session holds only the history of — one rotated past a grant that has not
+    /// been re-wrapped yet. That is deliberate: writing under a superseded key would produce an item
+    /// nobody else could read, and the honest answer is that the vault is not writable until the new
+    /// key arrives.
+    /// </para>
     /// </remarks>
     public bool TryGet(Guid vaultId, out ReadOnlyMemory<byte> vaultKey, out uint keyGeneration)
     {
         ObjectDisposedException.ThrowIf(disposed, this);
 
-        if (keys.TryGetValue(vaultId, out var key))
+        if (generations.TryGetValue(vaultId, out var current)
+            && Held(vaultId, current) is { } key)
         {
             vaultKey = key;
-            keyGeneration = generations[vaultId];
+            keyGeneration = current;
             return true;
         }
 
@@ -194,8 +258,52 @@ public sealed class VaultKeyring : IDisposable
         return false;
     }
 
-    /// <summary>Whether this vault can be read at all.</summary>
-    public bool CanRead(Guid vaultId) => !disposed && keys.ContainsKey(vaultId);
+    /// <summary>
+    /// Borrows the key one particular generation of a vault was sealed under.
+    /// </summary>
+    /// <param name="vaultId">The vault.</param>
+    /// <param name="keyGeneration">The generation the item names.</param>
+    /// <param name="vaultKey">The key, borrowed on the same terms as <see cref="TryGet"/>.</param>
+    /// <returns>Whether this session holds that generation.</returns>
+    /// <remarks>
+    /// What every read goes through, because an item names the generation it was sealed under and a
+    /// rotated vault holds items from more than one. False means that item is unreadable here and says
+    /// nothing about the rest of the vault — which is why a caller counts it rather than failing.
+    /// </remarks>
+    public bool TryGetAt(Guid vaultId, uint keyGeneration, out ReadOnlyMemory<byte> vaultKey)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+
+        if (Held(vaultId, keyGeneration) is { } key)
+        {
+            vaultKey = key;
+            return true;
+        }
+
+        vaultKey = default;
+        return false;
+    }
+
+    /// <summary>
+    /// Every generation of one vault's key that this session holds, oldest first.
+    /// </summary>
+    /// <remarks>
+    /// Read when sharing: a recipient given only the newest key would find the vault's history
+    /// undecryptable, so the sharing client wraps each of these in turn. It is the only party that can
+    /// — the server holds ciphertext, and the recipient holds nothing yet.
+    /// </remarks>
+    public IReadOnlyList<uint> GenerationsHeld(Guid vaultId)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+
+        return keys.TryGetValue(vaultId, out var held) ? [.. held.Keys.Order()] : [];
+    }
+
+    /// <summary>Whether this vault can be read and written at its current generation.</summary>
+    public bool CanRead(Guid vaultId) =>
+        !disposed
+        && generations.TryGetValue(vaultId, out var current)
+        && Held(vaultId, current) is not null;
 
     /// <inheritdoc />
     public void Dispose()
@@ -207,14 +315,70 @@ public sealed class VaultKeyring : IDisposable
 
         disposed = true;
 
-        foreach (var key in keys.Values)
+        foreach (var held in keys.Values)
         {
-            CryptographicOperations.ZeroMemory(key);
+            foreach (var key in held.Values)
+            {
+                CryptographicOperations.ZeroMemory(key);
+            }
         }
 
         keys.Clear();
         generations.Clear();
     }
+
+    /// <summary>Opens whatever superseded generations this vault came with.</summary>
+    /// <remarks>
+    /// A wrap that will not open is skipped rather than reported. It means one historic grant is
+    /// unusable — the items under that generation stay unreadable and are counted as such where they
+    /// are listed — and it is not a reason to refuse the generations that did open.
+    /// </remarks>
+    private void OpenPriorWraps(UserSecretBundle bundle, StoredVault vault)
+    {
+        foreach (var wrap in vault.PriorKeyWraps ?? [])
+        {
+            if (Held(vault.VaultId, wrap.KeyGeneration) is not null)
+            {
+                continue;
+            }
+
+            var key = VaultKeys.TryUnwrap(
+                bundle.EncryptionKey, wrap.WrappedKey, vault.VaultId, wrap.KeyGeneration);
+
+            if (key is not null)
+            {
+                AdoptPrior(vault.VaultId, key, wrap.KeyGeneration);
+            }
+        }
+    }
+
+    private byte[]? Held(Guid vaultId, uint keyGeneration) =>
+        keys.TryGetValue(vaultId, out var held) && held.TryGetValue(keyGeneration, out var key)
+            ? key
+            : null;
+
+    private void Store(Guid vaultId, byte[] vaultKey, uint keyGeneration)
+    {
+        if (!keys.TryGetValue(vaultId, out var held))
+        {
+            held = [];
+            keys[vaultId] = held;
+        }
+
+        if (held.TryGetValue(keyGeneration, out var previous))
+        {
+            CryptographicOperations.ZeroMemory(previous);
+        }
+
+        held[keyGeneration] = vaultKey;
+    }
+
+    private void Promote(Guid vaultId, uint keyGeneration)
+    {
+        generations[vaultId] = keyGeneration;
+
+        Unopened = [.. Unopened.Where(id => id != vaultId)];
+    }
 }
 
 /// <summary>Thrown when an operation needs a vault key the keyring does not hold.</summary>

src/DodoSSH.Client.Sync/VaultResealer.cs

@@ -0,0 +1,414 @@
+using System.Security.Cryptography;
+using DodoSSH.Client.Api;
+using DodoSSH.Client.Storage;
+using DodoSSH.Contracts;
+using DodoSSH.Crypto;
+
+namespace DodoSSH.Client.Sync;
+
+/// <summary>What one re-sealing pass did.</summary>
+/// <param name="VaultId">The vault.</param>
+/// <param name="KeyGeneration">The generation everything was moved to.</param>
+/// <param name="Resealed">Items now sealed under the current key.</param>
+/// <param name="Deferred">
+/// Items left alone because a local edit is queued for them. Not a failure: a queued change is re-sealed
+/// as it is pushed, so these arrive at the current generation by another route.
+/// </param>
+/// <param name="Unreadable">
+/// Items whose own generation this session holds no key for. They stay where they are — the alternative
+/// is discarding an item nobody can read yet, which is the one outcome that cannot be undone.
+/// </param>
+/// <param name="Contested">
+/// Items somebody else wrote while this pass was running. The server refused the version, and the next
+/// pass picks them up against the version it left behind.
+/// </param>
+public sealed record ResealReport(
+    Guid VaultId,
+    uint KeyGeneration,
+    int Resealed,
+    int Deferred,
+    int Unreadable,
+    int Contested)
+{
+    /// <summary>Whether every item in the vault is now sealed under its current key.</summary>
+    /// <remarks>
+    /// Deferred items count as finished. They are queued changes, and a queued change cannot reach the
+    /// server under a superseded key — <see cref="SyncEngine"/> re-seals it on the way out.
+    /// </remarks>
+    public bool Complete => Unreadable == 0 && Contested == 0;
+
+    /// <summary>Whether anything moved.</summary>
+    public bool MovedAnything => Resealed > 0;
+}
+
+/// <summary>
+/// Moves a rotated vault's stored items onto its current key.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <b>What a rotation on its own does not do.</b> Advancing a vault's generation re-keys the vault and
+/// not its contents: every item stays sealed under the generation it was written with, readable by
+/// anybody holding that generation's grant. That is what keeps a rotation cheap and safe — see
+/// ADR 0010 — and it leaves one gap, which is this pass. Somebody who left with a copy of the old key
+/// could still open old ciphertext they later got hold of. Once this has run, they cannot: every item
+/// is sealed under a key issued after they went.
+/// </para>
+/// <para>
+/// <b>The plaintext is never decoded.</b> An item is opened, and the same bytes are sealed again under
+/// a fresh data key — no codec, no merge, no schema version. So an item written by a newer client
+/// survives this untouched, where re-encoding it through this build's codec would silently drop the
+/// fields this build has no concept of. It also means nothing here needs to know what an item *is*,
+/// which is why one pass covers every type including the ones added later.
+/// </para>
+/// <para>
+/// <b>Resumable by construction, because a vault at mixed generations is readable.</b> Each item is one
+/// ordinary upsert against the version the server holds, so a pass that dies half way leaves a working
+/// vault, and running it again picks up what is left. Nothing here is a transaction and nothing needs
+/// to be.
+/// </para>
+/// </remarks>
+public sealed class VaultResealer
+{
+    private readonly ISyncApi api;
+    private readonly ItemStore items;
+    private readonly OutboxStore outbox;
+    private readonly VaultKeyring keyring;
+    private readonly TimeProvider clock;
+    private readonly SyncOptions options;
+
+    /// <summary>Creates the pass.</summary>
+    public VaultResealer(
+        ISyncApi api,
+        ItemStore items,
+        OutboxStore outbox,
+        VaultKeyring keyring,
+        TimeProvider clock,
+        SyncOptions? options = null)
+    {
+        ArgumentNullException.ThrowIfNull(api);
+        ArgumentNullException.ThrowIfNull(items);
+        ArgumentNullException.ThrowIfNull(outbox);
+        ArgumentNullException.ThrowIfNull(keyring);
+        ArgumentNullException.ThrowIfNull(clock);
+
+        this.api = api;
+        this.items = items;
+        this.outbox = outbox;
+        this.keyring = keyring;
+        this.clock = clock;
+        this.options = options ?? SyncOptions.Default;
+    }
+
+    /// <summary>Re-seals everything in one vault that is not already on its current key.</summary>
+    /// <param name="vaultId">The vault.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <remarks>
+    /// Answers with a report of zero for a vault this session cannot write to, rather than throwing.
+    /// Being rotated past and not yet re-wrapped is the ordinary state for a member between somebody
+    /// else's rotation and their own re-grant, and it is not this pass's business to complain about it.
+    /// </remarks>
+    public async Task<ResealReport> ResealAsync(Guid vaultId, CancellationToken cancellationToken)
+    {
+        if (!keyring.TryGet(vaultId, out _, out var generation))
+        {
+            return new ResealReport(vaultId, KeyGeneration: 0, 0, 0, 0, 0);
+        }
+
+        var queued = await QueuedAsync(vaultId, cancellationToken).ConfigureAwait(false);
+
+        var tally = new Tally();
+        var batch = new List<Pending>(options.MaxOperationsPerPush);
+
+        foreach (var entityType in ItemKinds.SyncedTypes)
+        {
+            var stored = await items
+                .ListAsync(vaultId, entityType, includeDeleted: false, cancellationToken)
+                .ConfigureAwait(false);
+
+            foreach (var item in stored.Where(item => Behind(item, generation)))
+            {
+                if (queued.Contains((entityType, item.EntityId)))
+                {
+                    tally.Deferred++;
+                    continue;
+                }
+
+                if (Move(vaultId, item) is not { } moved)
+                {
+                    tally.Unreadable++;
+                    continue;
+                }
+
+                batch.Add(moved);
+
+                if (batch.Count == options.MaxOperationsPerPush)
+                {
+                    await SendAsync(vaultId, batch, tally, cancellationToken).ConfigureAwait(false);
+                }
+            }
+        }
+
+        await SendAsync(vaultId, batch, tally, cancellationToken).ConfigureAwait(false);
+
+        return new ResealReport(
+            vaultId, generation, tally.Resealed, tally.Deferred, tally.Unreadable, tally.Contested);
+    }
+
+    /// <summary>Whether an item is still sealed under a key the vault has moved past.</summary>
+    private static bool Behind(StoredItem item, uint generation) =>
+        item.Payload is { } payload && payload.KeyGeneration < generation;
+
+    /// <summary>Re-seals one item, or answers null when this session cannot open it.</summary>
+    private Pending? Move(Guid vaultId, StoredItem item)
+    {
+        var version = SyncVersions.NextVersion(item.Version);
+
+        var payload = PayloadReseal.TryReseal(
+            keyring, vaultId, item.EntityType, item.EntityId, item.Payload!, item.Version, version);
+
+        return payload is null ? null : new Pending(item, payload, version);
+    }
+
+    /// <summary>Sends a batch if there is one, and empties it.</summary>
+    private async Task SendAsync(
+        Guid vaultId,
+        List<Pending> batch,
+        Tally tally,
+        CancellationToken cancellationToken)
+    {
+        if (batch.Count == 0)
+        {
+            return;
+        }
+
+        var outcome = await PushAsync(vaultId, batch, cancellationToken).ConfigureAwait(false);
+
+        tally.Resealed += outcome.Applied;
+        tally.Contested += outcome.Contested;
+
+        batch.Clear();
+    }
+
+    /// <summary>The running counts, so the loop above stays one screen long.</summary>
+    private sealed class Tally
+    {
+        internal int Resealed { get; set; }
+
+        internal int Deferred { get; set; }
+
+        internal int Unreadable { get; set; }
+
+        internal int Contested { get; set; }
+    }
+
+    /// <summary>One item, re-sealed and waiting to be sent.</summary>
+    private sealed record Pending(StoredItem Item, EncryptedPayload Payload, int Version)
+    {
+        internal Guid OperationId { get; } = Guid.CreateVersion7();
+    }
+
+    /// <summary>What one batch achieved.</summary>
+    [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Auto)]
+    private readonly record struct PushOutcome(int Applied, int Contested);
+
+    /// <summary>
+    /// Sends one batch and mirrors what the server accepted.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The mirror is written here rather than left to the next pull, so that a pass followed immediately
+    /// by another does not re-seal everything a second time. It is the same row with the same plaintext
+    /// under a new key, so there is nothing for a reader to notice.
+    /// </para>
+    /// <para>
+    /// A conflict is counted and skipped. There is nothing to merge — this pass changes no content — and
+    /// re-reading the item at the version the other client left is exactly what the next pass does.
+    /// </para>
+    /// </remarks>
+    private async Task<PushOutcome> PushAsync(
+        Guid vaultId,
+        List<Pending> batch,
+        CancellationToken cancellationToken)
+    {
+        var operations = batch
+            .Select(pending => new SyncPushOperation(
+                pending.OperationId,
+                pending.Item.EntityType,
+                pending.Item.EntityId,
+                SyncOperation.Upsert,
+                pending.Item.Version,
+                pending.Payload,
+                pending.Item.Fields))
+            .ToList();
+
+        var response = await api
+            .SyncPushAsync(vaultId, new SyncPushRequest(operations), cancellationToken)
+            .ConfigureAwait(false);
+
+        var applied = 0;
+        var contested = 0;
+
+        foreach (var result in response.Results)
+        {
+            if (batch.Find(pending => pending.OperationId == result.OperationId) is not { } sent)
+            {
+                continue;
+            }
+
+            if (result.Status is not (SyncOperationStatus.Applied or SyncOperationStatus.Duplicate))
+            {
+                contested++;
+                continue;
+            }
+
+            applied++;
+
+            await items.SaveAsync(
+                    sent.Item with
+                    {
+                        Version = result.Version ?? sent.Version,
+                        ChangeSequence = result.ChangeSequence ?? sent.Item.ChangeSequence,
+                        Payload = sent.Payload,
+                        UpdatedAt = clock.GetUtcNow(),
+                    },
+                    cancellationToken)
+                .ConfigureAwait(false);
+        }
+
+        return new PushOutcome(applied, contested);
+    }
+
+    /// <summary>The items a local edit is already queued for.</summary>
+    private async Task<HashSet<(SyncEntityType Type, Guid EntityId)>> QueuedAsync(
+        Guid vaultId,
+        CancellationToken cancellationToken)
+    {
+        var pending = await outbox.ListAllAsync(vaultId, cancellationToken).ConfigureAwait(false);
+
+        return [.. pending.Select(operation => (operation.EntityType, operation.EntityId))];
+    }
+}
+
+/// <summary>
+/// Moving one payload from the key it was sealed under to the one in force now.
+/// </summary>
+/// <remarks>
+/// Used from two places, and both of them matter: the pass above, which walks a rotated vault, and the
+/// push path, which cannot be allowed to send a change queued before a rotation under the key it was
+/// queued with. Between them they are the guarantee that nothing reaches the server under a superseded
+/// generation.
+/// </remarks>
+internal static class PayloadReseal
+{
+    /// <summary>
+    /// Re-seals a payload under the vault's current key.
+    /// </summary>
+    /// <param name="keyring">The open keyring.</param>
+    /// <param name="vaultId">The vault.</param>
+    /// <param name="entityType">What kind of item this is; the AAD binds its resource type.</param>
+    /// <param name="entityId">The item.</param>
+    /// <param name="payload">The payload as it stands, sealed under an earlier generation.</param>
+    /// <param name="openAtVersion">The item version <paramref name="payload"/> is bound to.</param>
+    /// <param name="sealAtVersion">The version the result will be bound to.</param>
+    /// <returns>
+    /// The re-sealed payload, or <see langword="null"/> when this session cannot open the original —
+    /// which means one item stays where it is, and says nothing about the rest of the vault.
+    /// </returns>
+    /// <remarks>
+    /// A fresh data key, not the original one re-wrapped. The two cost the same here, because the AAD
+    /// binds the generation into the payload as well as into the key wrap and the envelope has to be
+    /// re-made either way — and a new key per version is the rule the whole item format is built on.
+    /// </remarks>
+    internal static EncryptedPayload? TryReseal(
+        VaultKeyring keyring,
+        Guid vaultId,
+        SyncEntityType entityType,
+        Guid entityId,
+        EncryptedPayload payload,
+        int openAtVersion,
+        int sealAtVersion)
+    {
+        if (!keyring.TryGetAt(vaultId, payload.KeyGeneration, out var previous)
+            || !keyring.TryGet(vaultId, out var current, out var generation))
+        {
+            return null;
+        }
+
+        var resource = AadResourceTypes.For(entityType);
+
+        var dataKey = ItemKeys.TryUnwrapDataKey(
+            previous.Span,
+            payload.WrappedDataKey,
+            resource,
+            entityId,
+            payload.KeyGeneration,
+            (uint)openAtVersion);
+
+        if (dataKey is null)
+        {
+            return null;
+        }
+
+        try
+        {
+            var plaintext = ItemKeys.TryOpenPayload(
+                dataKey,
+                payload.Envelope,
+                resource,
+                entityId,
+                payload.DataKeyId,
+                payload.KeyGeneration,
+                (uint)openAtVersion);
+
+            if (plaintext is null)
+            {
+                return null;
+            }
+
+            try
+            {
+                return Seal(
+                    plaintext, current.Span, resource, entityId, generation, (uint)sealAtVersion);
+            }
+            finally
+            {
+                // The one place in this file that holds an item's plaintext, and it holds every kind of
+                // item there is — a private key, a password, a snippet with a token pasted into it.
+                CryptographicOperations.ZeroMemory(plaintext);
+            }
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(dataKey);
+        }
+    }
+
+    private static EncryptedPayload Seal(
+        ReadOnlySpan<byte> plaintext,
+        ReadOnlySpan<byte> vaultKey,
+        CryptoSpec.AadResourceType resource,
+        Guid entityId,
+        uint keyGeneration,
+        uint itemVersion)
+    {
+        var dataKey = ItemKeys.CreateDataKey();
+
+        try
+        {
+            var dataKeyId = Guid.CreateVersion7();
+
+            var envelope = ItemKeys.SealPayload(
+                dataKey, plaintext, resource, entityId, dataKeyId, keyGeneration, itemVersion);
+
+            var wrapped = ItemKeys.WrapDataKey(
+                dataKey, vaultKey, resource, entityId, keyGeneration, itemVersion);
+
+            return new EncryptedPayload(
+                envelope, wrapped, dataKeyId, keyGeneration, CryptoSpec.CurrentAadVersion);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(dataKey);
+        }
+    }
+}

src/DodoSSH.Contracts/DodoSshJsonContext.cs

@@ -55,6 +55,7 @@ namespace DodoSSH.Contracts;
 [JsonSerializable(typeof(CreateTeamVaultRequest))]
 [JsonSerializable(typeof(UpdateVaultRequest))]
 [JsonSerializable(typeof(IssueVaultGrantRequest))]
+[JsonSerializable(typeof(RekeyVaultRequest))]
 [JsonSerializable(typeof(VaultGrantsResponse))]
 [JsonSerializable(typeof(KeyLogPage))]
 [JsonSerializable(typeof(SyncPullRequest))]

src/DodoSSH.Contracts/Enrollment.cs

@@ -209,6 +209,16 @@ public sealed record MeResponse(
 /// must complete it.
 /// </param>
 /// <param name="RekeyRequired">Whether a membership change has left this vault needing a rekey.</param>
+/// <param name="PriorKeyWraps">
+/// Generations before <paramref name="KeyGeneration"/> that this caller still holds a grant for.
+/// <para>
+/// Empty for a vault that has never been rotated, which is nearly all of them. It is not empty after
+/// one, and it has to be served: an item is sealed under the generation in force when it was written,
+/// so a client that held only the current key would find every item older than the rotation
+/// undecryptable. See <c>VaultGrantService.RekeyAsync</c> for why old grants are kept rather than
+/// revoked.
+/// </para>
+/// </param>
 public sealed record VaultSummary(
     Guid VaultId,
     string Name,
@@ -217,4 +227,14 @@ public sealed record VaultSummary(
     uint KeyGeneration,
     int Permissions,
     byte[]? WrappedVaultKey,
-    bool RekeyRequired);
+    bool RekeyRequired,
+    IReadOnlyList<VaultKeyWrap>? PriorKeyWraps = null);
+
+/// <summary>A vault key sealed to one recipient, at one generation.</summary>
+/// <remarks>
+/// Only ever the caller's own. <c>VaultGrantSummary</c> deliberately carries no wrap: serving every
+/// member's sealed key to every member would widen what a stolen access token yields for nothing.
+/// </remarks>
+/// <param name="KeyGeneration">The generation this wrap opens.</param>
+/// <param name="WrappedKey">The vault key sealed to the caller's X25519 key. Opaque.</param>
+public sealed record VaultKeyWrap(uint KeyGeneration, byte[] WrappedKey);

src/DodoSSH.Contracts/PublicAPI.Unshipped.txt

@@ -359,6 +359,19 @@ DodoSSH.Contracts.RegisterDeviceResponse.EnrolledAt.get -> System.DateTimeOffset
 DodoSSH.Contracts.RegisterDeviceResponse.EnrolledAt.init -> void
 DodoSSH.Contracts.RegisterDeviceResponse.Equals(DodoSSH.Contracts.RegisterDeviceResponse? other) -> bool
 DodoSSH.Contracts.RegisterDeviceResponse.RegisterDeviceResponse(System.Guid DeviceId, System.DateTimeOffset EnrolledAt) -> void
+DodoSSH.Contracts.RekeyVaultRequest
+DodoSSH.Contracts.RekeyVaultRequest.<Clone>$() -> DodoSSH.Contracts.RekeyVaultRequest!
+DodoSSH.Contracts.RekeyVaultRequest.Deconstruct(out uint KeyGeneration, out byte[]! WrappedVaultKey, out byte[]! GrantSignature, out System.DateTimeOffset GrantedAt) -> void
+DodoSSH.Contracts.RekeyVaultRequest.Equals(DodoSSH.Contracts.RekeyVaultRequest? other) -> bool
+DodoSSH.Contracts.RekeyVaultRequest.GrantedAt.get -> System.DateTimeOffset
+DodoSSH.Contracts.RekeyVaultRequest.GrantedAt.init -> void
+DodoSSH.Contracts.RekeyVaultRequest.GrantSignature.get -> byte[]!
+DodoSSH.Contracts.RekeyVaultRequest.GrantSignature.init -> void
+DodoSSH.Contracts.RekeyVaultRequest.KeyGeneration.get -> uint
+DodoSSH.Contracts.RekeyVaultRequest.KeyGeneration.init -> void
+DodoSSH.Contracts.RekeyVaultRequest.RekeyVaultRequest(uint KeyGeneration, byte[]! WrappedVaultKey, byte[]! GrantSignature, System.DateTimeOffset GrantedAt) -> void
+DodoSSH.Contracts.RekeyVaultRequest.WrappedVaultKey.get -> byte[]!
+DodoSSH.Contracts.RekeyVaultRequest.WrappedVaultKey.init -> void
 DodoSSH.Contracts.RelayConfiguration
 DodoSSH.Contracts.RelayConfiguration.<Clone>$() -> DodoSSH.Contracts.RelayConfiguration!
 DodoSSH.Contracts.RelayConfiguration.Deconstruct(out bool Enabled, out System.Uri? WebSocketUrl) -> void
@@ -712,9 +725,18 @@ DodoSSH.Contracts.VaultGrantSummary.RevokedAt.init -> void
 DodoSSH.Contracts.VaultGrantSummary.State.get -> DodoSSH.Contracts.VaultGrantState
 DodoSSH.Contracts.VaultGrantSummary.State.init -> void
 DodoSSH.Contracts.VaultGrantSummary.VaultGrantSummary(System.Guid RecipientUserId, string? Email, string? DisplayName, uint KeyGeneration, DodoSSH.Contracts.VaultGrantState State, System.Guid GranterUserId, System.DateTimeOffset CreatedAt, System.DateTimeOffset? RevokedAt) -> void
+DodoSSH.Contracts.VaultKeyWrap
+DodoSSH.Contracts.VaultKeyWrap.<Clone>$() -> DodoSSH.Contracts.VaultKeyWrap!
+DodoSSH.Contracts.VaultKeyWrap.Deconstruct(out uint KeyGeneration, out byte[]! WrappedKey) -> void
+DodoSSH.Contracts.VaultKeyWrap.Equals(DodoSSH.Contracts.VaultKeyWrap? other) -> bool
+DodoSSH.Contracts.VaultKeyWrap.KeyGeneration.get -> uint
+DodoSSH.Contracts.VaultKeyWrap.KeyGeneration.init -> void
+DodoSSH.Contracts.VaultKeyWrap.VaultKeyWrap(uint KeyGeneration, byte[]! WrappedKey) -> void
+DodoSSH.Contracts.VaultKeyWrap.WrappedKey.get -> byte[]!
+DodoSSH.Contracts.VaultKeyWrap.WrappedKey.init -> void
 DodoSSH.Contracts.VaultSummary
 DodoSSH.Contracts.VaultSummary.<Clone>$() -> DodoSSH.Contracts.VaultSummary!
-DodoSSH.Contracts.VaultSummary.Deconstruct(out System.Guid VaultId, out string! Name, out bool IsPersonal, out System.Guid? TeamId, out uint KeyGeneration, out int Permissions, out byte[]? WrappedVaultKey, out bool RekeyRequired) -> void
+DodoSSH.Contracts.VaultSummary.Deconstruct(out System.Guid VaultId, out string! Name, out bool IsPersonal, out System.Guid? TeamId, out uint KeyGeneration, out int Permissions, out byte[]? WrappedVaultKey, out bool RekeyRequired, out System.Collections.Generic.IReadOnlyList<DodoSSH.Contracts.VaultKeyWrap!>? PriorKeyWraps) -> void
 DodoSSH.Contracts.VaultSummary.Equals(DodoSSH.Contracts.VaultSummary? other) -> bool
 DodoSSH.Contracts.VaultSummary.IsPersonal.get -> bool
 DodoSSH.Contracts.VaultSummary.IsPersonal.init -> void
@@ -724,13 +746,15 @@ DodoSSH.Contracts.VaultSummary.Name.get -> string!
 DodoSSH.Contracts.VaultSummary.Name.init -> void
 DodoSSH.Contracts.VaultSummary.Permissions.get -> int
 DodoSSH.Contracts.VaultSummary.Permissions.init -> void
+DodoSSH.Contracts.VaultSummary.PriorKeyWraps.get -> System.Collections.Generic.IReadOnlyList<DodoSSH.Contracts.VaultKeyWrap!>?
+DodoSSH.Contracts.VaultSummary.PriorKeyWraps.init -> void
 DodoSSH.Contracts.VaultSummary.RekeyRequired.get -> bool
 DodoSSH.Contracts.VaultSummary.RekeyRequired.init -> void
 DodoSSH.Contracts.VaultSummary.TeamId.get -> System.Guid?
 DodoSSH.Contracts.VaultSummary.TeamId.init -> void
 DodoSSH.Contracts.VaultSummary.VaultId.get -> System.Guid
 DodoSSH.Contracts.VaultSummary.VaultId.init -> void
-DodoSSH.Contracts.VaultSummary.VaultSummary(System.Guid VaultId, string! Name, bool IsPersonal, System.Guid? TeamId, uint KeyGeneration, int Permissions, byte[]? WrappedVaultKey, bool RekeyRequired) -> void
+DodoSSH.Contracts.VaultSummary.VaultSummary(System.Guid VaultId, string! Name, bool IsPersonal, System.Guid? TeamId, uint KeyGeneration, int Permissions, byte[]? WrappedVaultKey, bool RekeyRequired, System.Collections.Generic.IReadOnlyList<DodoSSH.Contracts.VaultKeyWrap!>? PriorKeyWraps = null) -> void
 DodoSSH.Contracts.VaultSummary.WrappedVaultKey.get -> byte[]?
 DodoSSH.Contracts.VaultSummary.WrappedVaultKey.init -> void
 override DodoSSH.Contracts.AddTeamMemberRequest.Equals(object? obj) -> bool
@@ -796,6 +820,9 @@ override DodoSSH.Contracts.RegisterDeviceRequest.ToString() -> string!
 override DodoSSH.Contracts.RegisterDeviceResponse.Equals(object? obj) -> bool
 override DodoSSH.Contracts.RegisterDeviceResponse.GetHashCode() -> int
 override DodoSSH.Contracts.RegisterDeviceResponse.ToString() -> string!
+override DodoSSH.Contracts.RekeyVaultRequest.Equals(object? obj) -> bool
+override DodoSSH.Contracts.RekeyVaultRequest.GetHashCode() -> int
+override DodoSSH.Contracts.RekeyVaultRequest.ToString() -> string!
 override DodoSSH.Contracts.RelayConfiguration.Equals(object? obj) -> bool
 override DodoSSH.Contracts.RelayConfiguration.GetHashCode() -> int
 override DodoSSH.Contracts.RelayConfiguration.ToString() -> string!
@@ -856,6 +883,9 @@ override DodoSSH.Contracts.VaultGrantsResponse.ToString() -> string!
 override DodoSSH.Contracts.VaultGrantSummary.Equals(object? obj) -> bool
 override DodoSSH.Contracts.VaultGrantSummary.GetHashCode() -> int
 override DodoSSH.Contracts.VaultGrantSummary.ToString() -> string!
+override DodoSSH.Contracts.VaultKeyWrap.Equals(object? obj) -> bool
+override DodoSSH.Contracts.VaultKeyWrap.GetHashCode() -> int
+override DodoSSH.Contracts.VaultKeyWrap.ToString() -> string!
 override DodoSSH.Contracts.VaultSummary.Equals(object? obj) -> bool
 override DodoSSH.Contracts.VaultSummary.GetHashCode() -> int
 override DodoSSH.Contracts.VaultSummary.ToString() -> string!
@@ -904,6 +934,8 @@ static DodoSSH.Contracts.RegisterDeviceRequest.operator !=(DodoSSH.Contracts.Reg
 static DodoSSH.Contracts.RegisterDeviceRequest.operator ==(DodoSSH.Contracts.RegisterDeviceRequest? left, DodoSSH.Contracts.RegisterDeviceRequest? right) -> bool
 static DodoSSH.Contracts.RegisterDeviceResponse.operator !=(DodoSSH.Contracts.RegisterDeviceResponse? left, DodoSSH.Contracts.RegisterDeviceResponse? right) -> bool
 static DodoSSH.Contracts.RegisterDeviceResponse.operator ==(DodoSSH.Contracts.RegisterDeviceResponse? left, DodoSSH.Contracts.RegisterDeviceResponse? right) -> bool
+static DodoSSH.Contracts.RekeyVaultRequest.operator !=(DodoSSH.Contracts.RekeyVaultRequest? left, DodoSSH.Contracts.RekeyVaultRequest? right) -> bool
+static DodoSSH.Contracts.RekeyVaultRequest.operator ==(DodoSSH.Contracts.RekeyVaultRequest? left, DodoSSH.Contracts.RekeyVaultRequest? right) -> bool
 static DodoSSH.Contracts.RelayConfiguration.operator !=(DodoSSH.Contracts.RelayConfiguration? left, DodoSSH.Contracts.RelayConfiguration? right) -> bool
 static DodoSSH.Contracts.RelayConfiguration.operator ==(DodoSSH.Contracts.RelayConfiguration? left, DodoSSH.Contracts.RelayConfiguration? right) -> bool
 static DodoSSH.Contracts.RelaySessionSummary.operator !=(DodoSSH.Contracts.RelaySessionSummary? left, DodoSSH.Contracts.RelaySessionSummary? right) -> bool
@@ -944,5 +976,7 @@ static DodoSSH.Contracts.VaultGrantsResponse.operator !=(DodoSSH.Contracts.Vault
 static DodoSSH.Contracts.VaultGrantsResponse.operator ==(DodoSSH.Contracts.VaultGrantsResponse? left, DodoSSH.Contracts.VaultGrantsResponse? right) -> bool
 static DodoSSH.Contracts.VaultGrantSummary.operator !=(DodoSSH.Contracts.VaultGrantSummary? left, DodoSSH.Contracts.VaultGrantSummary? right) -> bool
 static DodoSSH.Contracts.VaultGrantSummary.operator ==(DodoSSH.Contracts.VaultGrantSummary? left, DodoSSH.Contracts.VaultGrantSummary? right) -> bool
+static DodoSSH.Contracts.VaultKeyWrap.operator !=(DodoSSH.Contracts.VaultKeyWrap? left, DodoSSH.Contracts.VaultKeyWrap? right) -> bool
+static DodoSSH.Contracts.VaultKeyWrap.operator ==(DodoSSH.Contracts.VaultKeyWrap? left, DodoSSH.Contracts.VaultKeyWrap? right) -> bool
 static DodoSSH.Contracts.VaultSummary.operator !=(DodoSSH.Contracts.VaultSummary? left, DodoSSH.Contracts.VaultSummary? right) -> bool
 static DodoSSH.Contracts.VaultSummary.operator ==(DodoSSH.Contracts.VaultSummary? left, DodoSSH.Contracts.VaultSummary? right) -> bool

src/DodoSSH.Contracts/Teams.cs

@@ -425,6 +425,37 @@ public sealed record IssueVaultGrantRequest(
     byte[] GrantSignature,
     DateTimeOffset GrantedAt);
 
+/// <summary>
+/// Moves a vault to a fresh key, wrapped to the caller.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The new key is generated by a client that already holds the current one, and arrives sealed to that
+/// same client — the server can neither produce it nor tell that it differs from the old one. What the
+/// server does is decide the moment it takes effect: the generation advances in one transaction, so
+/// there is no instant at which two clients disagree about which generation is current.
+/// </para>
+/// <para>
+/// <b>Grants for earlier generations are kept, not revoked.</b> Every item still carries the generation
+/// it was sealed under, so withdrawing them would make the vault's whole history unreadable to the
+/// people who are still in it. The departed member's grants are revoked — that is what
+/// <c>RevokeGrantAsync</c> and removal from the team already do — and this is what stops them reading
+/// anything written from here on. It does not reach back; see ADR 0001.
+/// </para>
+/// </remarks>
+/// <param name="KeyGeneration">
+/// The generation being created. Must be exactly one past the vault's current one, so two clients
+/// rotating at once cannot both believe they succeeded.
+/// </param>
+/// <param name="WrappedVaultKey">The new vault key, sealed to the caller's own encryption key.</param>
+/// <param name="GrantSignature">Ed25519 signature over the canonical grant tuple.</param>
+/// <param name="GrantedAt">Signing timestamp, part of the signed tuple.</param>
+public sealed record RekeyVaultRequest(
+    uint KeyGeneration,
+    byte[] WrappedVaultKey,
+    byte[] GrantSignature,
+    DateTimeOffset GrantedAt);
+
 /// <summary>One vault key grant, as the sharing interface sees it.</summary>
 /// <remarks>
 /// The wrapped key itself is deliberately not here. A member reads their own through
@@ -457,7 +488,12 @@ public sealed record VaultGrantSummary(
 /// compares against rather than inferring from <see cref="VaultGrantSummary.State"/> alone.
 /// </param>
 /// <param name="RekeyRequired">Whether a membership change has left this vault needing a rekey.</param>
-/// <param name="Grants">Every grant, including revoked ones.</param>
+/// <param name="Grants">
+/// One row per holder, including those whose access has been withdrawn. Not one per grant: a rotated
+/// vault leaves a member holding one grant per generation, and the row carries the best of them — so
+/// <see cref="VaultGrantSummary.KeyGeneration"/> below <paramref name="KeyGeneration"/> means they have
+/// not been wrapped the current key yet, rather than that one of their grants is old.
+/// </param>
 public sealed record VaultGrantsResponse(
     Guid VaultId,
     uint KeyGeneration,