fix(messagestore): match TEXT-stored UUID form in FTS bulk insert and LoadByGuids

messages.Id is declared BLOB but stored as TEXT because Microsoft.Data.Sqlite
binds Guid parameters as UUID strings (UpsertMessage uses AddWithValue with
a Guid). RebuildFtsIndex cast reader.GetValue(0) to byte[] and threw
InvalidCastException at the first row. LoadByGuids bound byte[] params
against the TEXT-stored Id and would have returned no rows once the index
had built.

- RebuildFtsIndex reads via GetGuid and stores ToString() in
  messages_fts.message_guid.
- LoadByGuids parses incoming UUID strings and binds them as Guid so
  Microsoft.Data.Sqlite re-serialises to TEXT, matching the messages.Id
  storage form.
- DbViewer caller variable renamed hexIds -> guidHits for clarity.

HellionChat/MessageStore.cs

@@ -690,7 +690,12 @@ internal class MessageStore : IDisposable
             {
                 ct.ThrowIfCancellationRequested();
 
-                var guidBytes = (byte[])reader.GetValue(0);
+                // messages.Id is BLOB-typed in the schema but stored as TEXT
+                // because Microsoft.Data.Sqlite binds Guid parameters as UUID
+                // strings by default (UpsertMessage uses AddWithValue("$Id",
+                // message.Id)). reader.GetValue(0) therefore returns string,
+                // not byte[]; GetGuid parses the TEXT form regardless.
+                var idGuid = reader.GetGuid(0);
                 var senderChunks = MessagePackSerializer.Deserialize<List<Chunk>>(
                     reader.GetFieldValue<byte[]>(1),
                     MsgPackOptions
@@ -700,7 +705,7 @@ internal class MessageStore : IDisposable
                     MsgPackOptions
                 );
 
-                pG.Value = Convert.ToHexString(guidBytes);
+                pG.Value = idGuid.ToString();
                 pS.Value = ChunkUtil.ToRawString(senderChunks);
                 pC.Value = ChunkUtil.ToRawString(contentChunks);
                 insert.ExecuteNonQuery();
@@ -760,24 +765,27 @@ internal class MessageStore : IDisposable
         }
     }
 
-    // Joins hex-encoded GUIDs from FullTextSearch back to Message rows. The
-    // primary key is BLOB, so we decode the hex back to bytes for the IN(...)
-    // lookup. SQLite has a hard parameter limit of 999 in default builds, so
-    // we chunk the input -- a 1000-hit FTS query never explodes the SELECT.
-    // Result ordering is not guaranteed; callers re-sort (e.g. DbViewer sorts
-    // by Date descending in Sub-Task 4.4).
-    public IReadOnlyList<Message> LoadByGuids(IReadOnlyList<string> hexIds)
+    // Joins UUID strings from FullTextSearch back to Message rows. messages.Id
+    // is BLOB-declared in the schema but actually stored as TEXT (UUID form)
+    // because Microsoft.Data.Sqlite serialises Guid parameters as strings by
+    // default. Binding the lookup parameters as Guid keeps the same TEXT
+    // storage form on both sides so the IN(...) compare matches. SQLite has a
+    // hard parameter limit of 999 in default builds, so we chunk the input --
+    // a 1000-hit FTS query never explodes the SELECT. Result ordering is not
+    // guaranteed; callers re-sort (e.g. DbViewer sorts by Date descending in
+    // Sub-Task 4.4).
+    public IReadOnlyList<Message> LoadByGuids(IReadOnlyList<string> guidStrings)
     {
-        if (hexIds.Count == 0)
+        if (guidStrings.Count == 0)
             return Array.Empty<Message>();
 
         lock (_readLock)
         {
-            var result = new List<Message>(hexIds.Count);
+            var result = new List<Message>(guidStrings.Count);
             const int chunkSize = 500;
-            for (var offset = 0; offset < hexIds.Count; offset += chunkSize)
+            for (var offset = 0; offset < guidStrings.Count; offset += chunkSize)
             {
-                var batch = hexIds.Skip(offset).Take(chunkSize).ToList();
+                var batch = guidStrings.Skip(offset).Take(chunkSize).ToList();
                 using var cmd = Connection.CreateCommand();
                 var placeholders = string.Join(",", batch.Select((_, i) => $"$id{i}"));
                 cmd.CommandText = $"""
@@ -787,7 +795,7 @@ internal class MessageStore : IDisposable
                     WHERE Id IN ({placeholders}) AND Deleted = false;
                     """;
                 for (var i = 0; i < batch.Count; i++)
-                    cmd.Parameters.AddWithValue($"$id{i}", Convert.FromHexString(batch[i]));
+                    cmd.Parameters.AddWithValue($"$id{i}", Guid.Parse(batch[i]));
 
                 using var reader = cmd.ExecuteReader();
                 while (reader.Read())

HellionChat/Ui/DbViewer.cs

@@ -485,8 +485,8 @@ public class DbViewer : Window
         // still serves the page.
         if (UseFullTextSearch && Plugin.MessageManager.Store.IsFtsIndexBuilt)
         {
-            var hexIds = Plugin.MessageManager.Store.FullTextSearch(SimpleSearchTerm);
-            var resolved = Plugin.MessageManager.Store.LoadByGuids(hexIds);
+            var guidHits = Plugin.MessageManager.Store.FullTextSearch(SimpleSearchTerm);
+            var resolved = Plugin.MessageManager.Store.LoadByGuids(guidHits);
             return new ConcurrentStack<Message>(resolved.OrderByDescending(m => m.Date));
         }