Don't start an implicit EF Core transaction on ScheduleAsync for a Wolverine-mapped DbContext (closes #3121)

src/Persistence/EfCoreTests/end_to_end_efcore_persistence.cs

@@ -193,6 +193,37 @@ public void outbox_for_db_context_mapped()
             .DbContext.ShouldBeSameAs(context);
     }
 
+    [Fact]
+    public async Task persisting_against_mapped_dbcontext_does_not_start_an_explicit_transaction()
+    {
+        await Host.ResetResourceState();
+
+        var envelope = new Envelope
+        {
+            Data = [1, 2, 3, 4],
+            OwnerId = 5,
+            Destination = TransportConstants.RepliesUri,
+            MessageType = "foo",
+            ContentType = EnvelopeConstants.JsonContentType,
+            Status = EnvelopeStatus.Scheduled,
+            ScheduledTime = DateTimeOffset.UtcNow.AddMinutes(1)
+        };
+
+        using var nested = Host.Services.CreateScope();
+        var messaging = nested.ServiceProvider.GetRequiredService<IDbContextOutbox<SampleMappedDbContext>>()
+            .ShouldBeOfType<DbContextOutbox<SampleMappedDbContext>>();
+
+        // Regression for #3121 -- scheduling/incoming persistence against a Wolverine-mapped
+        // DbContext must NOT begin an explicit EF Core transaction. SaveChanges provides its
+        // own implicit transaction, and the outgoing path already behaves this way.
+        await messaging.Transaction!.PersistIncomingAsync(envelope);
+        messaging.DbContext.Database.CurrentTransaction.ShouldBeNull();
+
+        // Symmetry check: the outgoing path likewise leaves the transaction alone
+        await messaging.Transaction!.PersistOutgoingAsync(envelope);
+        messaging.DbContext.Database.CurrentTransaction.ShouldBeNull();
+    }
+
     [Fact]
     public async Task persist_an_outgoing_envelope_raw()
     {

src/Persistence/Wolverine.EntityFrameworkCore/Internals/EfCoreEnvelopeTransaction.cs

@@ -98,17 +98,27 @@ public async Task PersistOutgoingAsync(Envelope[] envelopes)
 
     public async Task PersistIncomingAsync(Envelope envelope)
     {
-        if (DbContext.Database.CurrentTransaction == null)
-        {
-            await DbContext.Database.BeginTransactionAsync();
-        }
-
         if (DbContext.IsWolverineEnabled())
         {
+            // For a Wolverine-mapped DbContext the envelope is just tracked and flushed by
+            // SaveChangesAsync, so don't force an explicit transaction here. We defer to whatever
+            // the ambient transaction mode established: in Eager middleware mode a transaction was
+            // already begun (EnrollDbContextInTransaction / StartDatabaseTransactionForDbContext) and
+            // the tracked entity enrolls into it at SaveChanges; in Lightweight/lazy mode there is no
+            // transaction and SaveChanges provides its own implicit one. This mirrors
+            // PersistOutgoingAsync and keeps ScheduleAsync from starting a transaction the caller
+            // never asked for (see #3121).
             DbContext.Add(new IncomingMessage(envelope));
         }
         else
         {
+            // The raw branch issues an ADO command that has to share the caller's transaction, so
+            // here we do need an explicit one when none is already in flight.
+            if (DbContext.Database.CurrentTransaction == null)
+            {
+                await DbContext.Database.BeginTransactionAsync();
+            }
+
             var conn = DbContext.Database.GetDbConnection();
             var tx = DbContext.Database.CurrentTransaction!.GetDbTransaction();
             var builder = _database.ToCommandBuilder();