Populate usage.Events and return an empty StreamMetadata.Tags (#411, #412)

src/Polecat/DocumentStore.EventStore.cs

@@ -315,8 +315,18 @@ Task IEventStore.CompactStreamAsync(string streamKey, CancellationToken token)
 
         // Event-type registry — populates the explorer's "known event types"
         // panel without forcing operators to crack open assembly metadata.
+        //
+        // #411: BOTH collections have to be filled. EventStoreUsage carries the event registry
+        // twice — Events (List<EventDescriptor>) and RegisteredEventTypes
+        // (List<EventTypeDescriptor>) — and Marten populates both. Filling only
+        // RegisteredEventTypes left usage.Events empty, which reads to a consumer as "this store
+        // has no event types configured" rather than "this store describes them elsewhere".
         foreach (var registered in Options.EventGraph.AllKnownEventTypes())
         {
+            usage.Events.Add(new EventDescriptor(
+                registered.EventTypeName,
+                TypeDescriptor.For(registered.EventType)));
+
             usage.RegisteredEventTypes.Add(new EventTypeDescriptor(
                 EventType: TypeDescriptor.For(registered.EventType),
                 Alias: registered.EventTypeName,

src/Polecat/Events/Internal/PcStreamsRowReader.cs

@@ -105,12 +105,20 @@
 
     /// <summary>
     ///     Read the row the reader is positioned on into a
     ///     <see cref="StreamMetadata"/>. <paramref name="firstEventAt"/> comes
     ///     from a JOIN against <c>pc_events</c> (not part of <c>pc_streams</c>
     ///     itself); when it's <see langword="null"/> the row's own <c>created</c>
     ///     column is used as the fallback, mirroring the pre-consolidation
     ///     behavior in <c>DocumentStore.GetStreamMetadataAsync</c>.
     /// </summary>
+    /// <summary>
+    ///     Shared empty tag set for <see cref="StreamMetadata.Tags"/>. Polecat does not persist
+    ///     DCB stream tags yet, so every row reports the same immutable empty dictionary rather
+    ///     than allocating one per stream.
+    /// </summary>
+    private static readonly IReadOnlyDictionary<string, string> EmptyTags =
+        new Dictionary<string, string>();
+
     internal static StreamMetadata ReadStreamMetadata(
         DbDataReader reader,
         string defaultTenantId,
@@ -134,7 +142,12 @@
             LastSnapshotVersion: null,
             IsArchived: isArchived,
             TenantId: tenantId,
-            Tags: null!);
+            // #412: an empty dictionary, never null. StreamMetadata.Tags is declared as a
+            // non-nullable IReadOnlyDictionary, so "this stream has no tags" is spelled with an
+            // empty collection -- a null forces every consumer that trusts the declaration into a
+            // NullReferenceException instead of an empty loop. The `null!` that used to be here
+            // silenced the compiler's warning rather than answering it.
+            Tags: EmptyTags);
     }
 
     private static string StreamIdToString(object value) => value switch