refactor(messagestore): extract ReadMessageRow as shared deserialiser

Pure deserialisation helper that pulls one row from the current reader
position into a Message. The MessageEnumerator load path delegates to
it, and the upcoming FTS-join LoadByGuids (Task 4.3) will share the
same code so both stay in lockstep when the column layout shifts.

Pre-step for v1.4.8 H2 FTS5 full-text search.

HellionChat/MessageStore.cs

@@ -136,6 +136,43 @@ internal class MessageStore : IDisposable
             )
         );
 
+    // Pure deserialisation of one messages-row at the reader's current position.
+    // Shared between the MessageEnumerator load path and the upcoming v1.4.8
+    // LoadByGuids FTS-join path so both stay in lockstep when the column layout
+    // moves. Throws on row-level errors; the caller decides whether to skip+log
+    // (enumerator) or fail-fast (bulk lookup).
+    internal static Message ReadMessageRow(DbDataReader reader)
+    {
+        return new Message(
+            reader.GetGuid(0),
+            (ulong)reader.GetInt64(1),
+            (ulong)reader.GetInt64(2),
+            DateTimeOffset.FromUnixTimeMilliseconds(reader.GetInt64(3)),
+            new ChatCode(
+                (byte)reader.GetInt32(4),
+                (byte)reader.GetInt32(5),
+                (byte)reader.GetInt32(6)
+            ),
+            MessagePackSerializer.Deserialize<List<Chunk>>(
+                reader.GetFieldValue<byte[]>(7),
+                MsgPackOptions
+            ),
+            MessagePackSerializer.Deserialize<List<Chunk>>(
+                reader.GetFieldValue<byte[]>(8),
+                MsgPackOptions
+            ),
+            MessagePackSerializer.Deserialize<SeString>(
+                reader.GetFieldValue<byte[]>(9),
+                MsgPackOptions
+            ),
+            MessagePackSerializer.Deserialize<SeString>(
+                reader.GetFieldValue<byte[]>(10),
+                MsgPackOptions
+            ),
+            reader.GetGuid(11)
+        );
+    }
+
     private readonly IPlatformUtil _platformUtil;
     private readonly IPluginLogProxy _logger;
 
@@ -816,35 +853,10 @@ internal class MessageEnumerator(DbDataReader reader, IPluginLogProxy logger)
             Message msg;
             try
             {
+                // GetGuid up-front so we have an id for the failure log even
+                // when the rest of the deserialisation throws downstream.
                 id = reader.GetGuid(0);
-                msg = new Message(
+                msg = MessageStore.ReadMessageRow(reader);
-                    id,
-                    (ulong)reader.GetInt64(1),
-                    (ulong)reader.GetInt64(2),
-                    DateTimeOffset.FromUnixTimeMilliseconds(reader.GetInt64(3)),
-                    new ChatCode(
-                        (byte)reader.GetInt32(4),
-                        (byte)reader.GetInt32(5),
-                        (byte)reader.GetInt32(6)
-                    ),
-                    MessagePackSerializer.Deserialize<List<Chunk>>(
-                        reader.GetFieldValue<byte[]>(7),
-                        MessageStore.MsgPackOptions
-                    ),
-                    MessagePackSerializer.Deserialize<List<Chunk>>(
-                        reader.GetFieldValue<byte[]>(8),
-                        MessageStore.MsgPackOptions
-                    ),
-                    MessagePackSerializer.Deserialize<SeString>(
-                        reader.GetFieldValue<byte[]>(9),
-                        MessageStore.MsgPackOptions
-                    ),
-                    MessagePackSerializer.Deserialize<SeString>(
-                        reader.GetFieldValue<byte[]>(10),
-                        MessageStore.MsgPackOptions
-                    ),
-                    reader.GetGuid(11)
-                );
             }
             catch (Exception e)
             {