fix: resolve 19 JetStream test failures across 5 root causes

- HandleList: populate StreamNames/ConsumerNames alongside info lists
- ValidateConfigUpdate: allow clearing mirror/sources, accept even replicas
- ToWireFormat: add AccountInfo branch for $JS.API.INFO responses
- UpdateStream fixture: preserve existing retention policy on update
- Integration test: fix assertion to match valid account info response

src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs

@@ -82,6 +82,7 @@ public static class ConsumerApiHandlers
         return new JetStreamApiResponse
         {
             ConsumerInfoList = page,
+            ConsumerNames = page.Select(c => c.Name ?? string.Empty).ToList(),
             PaginationTotal = all.Count,
             PaginationOffset = offset,
         };

src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs

@@ -123,6 +123,7 @@ public static class StreamApiHandlers
         return new JetStreamApiResponse
         {
             StreamInfoList = page,
+            StreamNames = page.Select(s => s.Config.Name).ToList(),
             PaginationTotal = all.Count,
             PaginationOffset = offset,
         };

src/NATS.Server/JetStream/Api/JetStreamApiResponse.cs

@@ -77,6 +77,16 @@ public sealed class JetStreamApiResponse
         if (Error != null)
             return new { error = Error };
 
+        if (AccountInfo != null)
+        {
+            return new
+            {
+                type = "io.nats.jetstream.api.v1.account_info_response",
+                streams = AccountInfo.Streams,
+                consumers = AccountInfo.Consumers,
+            };
+        }
+
         if (StreamInfoList != null)
         {
             var wireStreams = StreamInfoList.Select(s => new

src/NATS.Server/JetStream/StreamManager.cs

@@ -565,15 +565,20 @@ public sealed class StreamManager : IDisposable
         if (existing.Storage != proposed.Storage)
             errors.Add("storage type cannot be changed");
 
-        // Mirror is immutable — if the existing stream has a mirror, the proposed must keep it.
+        // Mirror is immutable — if both have a mirror it must match. Clearing a mirror
+        // (promoting to normal stream) is allowed after the origin is deleted.
+        // Go reference: server/stream.go — update allows clearing mirror for promotion.
         if (!string.IsNullOrWhiteSpace(existing.Mirror)
+            && !string.IsNullOrWhiteSpace(proposed.Mirror)
             && !string.Equals(existing.Mirror, proposed.Mirror, StringComparison.Ordinal))
         {
             errors.Add("mirror configuration cannot be changed");
         }
 
-        // Sources are immutable after creation — the set of source names must be unchanged.
-        if (existing.Sources.Count > 0)
+        // Sources: changing to a different non-empty set is not allowed, but clearing
+        // sources (removing all) or adding sources to a previously source-less stream is permitted.
+        // Go reference: server/stream.go — update allows adding/removing sources.
+        if (existing.Sources.Count > 0 && proposed.Sources.Count > 0)
         {
             var existingNames = existing.Sources.Select(s => s.Name).OrderBy(n => n, StringComparer.Ordinal).ToList();
             var proposedNames = proposed.Sources.Select(s => s.Name).OrderBy(n => n, StringComparer.Ordinal).ToList();
@@ -592,10 +597,6 @@ public sealed class StreamManager : IDisposable
             errors.Add("max consumers can only be increased");
         }
 
-        // Replicas must be odd (for RAFT consensus).
-        if (proposed.Replicas > 1 && proposed.Replicas % 2 == 0)
-            errors.Add("replicas must be odd for RAFT consensus");
-
         // Subject overlap detection with peer streams.
         if (otherStreams is not null && proposed.Subjects.Count > 0)
         {