Sync: take the server having no such item as a delete done, not a rejection nobody can clear

src/DodoSSH.Client.Sync/SyncEngine.cs

@@ -539,6 +539,17 @@ public sealed class SyncEngine
         return resealed;
     }
 
+    /// <summary>Whether a refused operation is a delete of an item the server never had.</summary>
+    /// <remarks>
+    /// A delete queued over a create that never reached the server carries no expected version, and the
+    /// server's only reason to refuse one of those is that it has no such item — which is the state the delete
+    /// asked for, so it is done. It used to be parked as a rejection: a "conflict" about an item nobody else
+    /// had ever seen, which the user could neither resolve nor dismiss. A create that did land is no exception
+    /// to this — the server has the item then, and applies the delete.
+    /// </remarks>
+    private static bool DeletesSomethingNeverCreated(PendingOperation operation) =>
+        operation is { Operation: SyncOperation.Delete, ExpectedVersion: null };
+
     /// <returns>Whether this answer warrants another push round.</returns>
     private async Task<bool> HandleAsync(
         Guid vaultId,
@@ -581,6 +592,10 @@ public sealed class SyncEngine
                     cancellationToken).ConfigureAwait(false);
                 return false;
 
+            case SyncOperationStatus.Invalid when DeletesSomethingNeverCreated(operation):
+                await outbox.CompleteAsync(operation, cancellationToken).ConfigureAwait(false);
+                return false;
+
             case SyncOperationStatus.Invalid:
                 await RejectAsync(
                     vaultId,

tests/DodoSSH.Client.Sync.Tests/UnpushedDeleteTests.cs

@@ -147,7 +147,8 @@ public sealed class UnpushedDeleteTests
         // The ambiguous case, and the reason the attempt count is part of the test rather than just the
         // expected version. A create that was dispatched may have been applied by a server whose answer never
         // arrived. Dropping it locally would strand a row nobody can see and nobody can delete; a tombstone
-        // that turns out to be unnecessary is refused once and can be dealt with.
+        // that turns out to be unnecessary is refused once, and the refusal is taken as the delete being done —
+        // see the two tests after this one.
         using var harness = await CreateAsync();
         var laptop = harness.First;
 
@@ -166,6 +167,64 @@ public sealed class UnpushedDeleteTests
         tombstone.Operation.ShouldBe(SyncOperation.Delete);
     }
 
+    /// <remarks>
+    /// The rest of that story, when the create never did land. The tombstone carries no expected version, and
+    /// the server refuses it because it has no such item — which is what the delete wanted. It used to be
+    /// parked as a rejection the user could neither resolve nor dismiss, with a pending count stuck above zero.
+    /// </remarks>
+    [Fact]
+    public async Task ATombstoneForACreateThatNeverLanded_IsDoneWhenTheServerSaysItHasNoSuchItem()
+    {
+        using var harness = await CreateAsync();
+        var laptop = harness.First;
+
+        var entityId = await laptop.CreateAsync(Host("in-flight"));
+        var queued = (await laptop.Outbox.ListAllAsync(VaultId, Token)).ShouldHaveSingleItem();
+        await laptop.Outbox.MarkDispatchedAsync(queued.Sequence, Token);
+
+        await laptop.DeleteAsync(entityId);
+
+        var report = await laptop.SyncAsync();
+
+        report.Parked.ShouldBe(0, "the server not having the item is the delete succeeding");
+        (await laptop.Outbox.ListAllAsync(VaultId, Token)).ShouldBeEmpty();
+        harness.Server.RowCount.ShouldBe(0);
+    }
+
+    /// <remarks>
+    /// And when it did land, the shortcut above must not be what answers. The pull brings the item back first,
+    /// at a version the tombstone never knew about, and the engine's ordinary rule for that applies: the delete
+    /// gives way, the item stays, and the user is told — nothing parked, nothing lost, nothing stuck in the
+    /// outbox. Deleting it again is then an ordinary delete of an item the server holds.
+    /// </remarks>
+    [Fact]
+    public async Task ATombstoneForACreateThatDidLand_GivesWayToIt_RatherThanBeingTakenAsDone()
+    {
+        using var harness = await CreateAsync();
+        var laptop = harness.First;
+
+        var entityId = await laptop.CreateAsync(Host("in-flight"));
+
+        // The create reaches the server with its answer lost: the server holds the item while the laptop's own
+        // row still says "sent, unanswered".
+        var queued = (await laptop.Outbox.ListAllAsync(VaultId, Token)).ShouldHaveSingleItem();
+        await laptop.Outbox.MarkDispatchedAsync(queued.Sequence, Token);
+        harness.Server.ExternalUpsert(entityId, queued.Payload.ShouldNotBeNull(), queued.Fields);
+
+        await laptop.DeleteAsync(entityId);
+        var report = await laptop.SyncAsync();
+
+        report.DeletesAbandoned.ShouldBe(1, "the user is told the item came back");
+        report.Parked.ShouldBe(0);
+        (await laptop.Outbox.ListAllAsync(VaultId, Token)).ShouldBeEmpty();
+        harness.Server.RowCount.ShouldBe(1);
+
+        await laptop.DeleteAsync(entityId);
+        await laptop.SyncAsync();
+
+        harness.Server.RowCount.ShouldBe(0, "deleting it again reaches the server");
+    }
+
     /// <remarks>
     /// The path most likely to meet this in practice, which is why it gets its own test rather than trusting
     /// the generic repository: trust is pinned by connecting and withdrawn from the host editor, so trusting a