fix(tdlib): handle 1.8.64 renames in searchChatMessages + message reply_to

Audit of every TDLib call site against the live 1.8.64 schema in
node_modules/@prebuilt-tdlib/types/tdlib-types.d.ts surfaced three
additional silent breakages beyond the getForumTopics fix in 106700b.

1. searchChatMessages parameter restructure
   The top-level `message_thread_id` and `saved_messages_topic_id`
   request fields were collapsed into a single tagged-union
   `topic_id: MessageTopic$Input`. Three call sites affected:

   - topics.ts getTopicMessages — was passing message_thread_id, now
     sends topic_id with the messageTopicForum variant carrying
     forum_topic_id. Without this the topic scan returns the whole
     channel (or nothing) instead of just the topic.
   - download.ts getChannelMessages — used to pass message_thread_id: 0;
     just omit the topic_id field entirely for a flat scan.
   - rebuild.ts — same treatment.

2. message.reply_to_message_id replaced with reply_to tagged union
   On incoming messages, the flat `reply_to_message_id` field was
   replaced with `reply_to: MessageReplyTo` (messageReplyToMessage or
   messageReplyToStory). Our reply-chain grouping needs the message-ID
   case.

   Added extractReplyToMessageId() that reads both old and new shapes
   so a transition build or future downgrade still works.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

worker/src/rebuild.ts

@@ -308,14 +308,15 @@ async function scanDestinationChannel(
     }>(client, {
       _: "searchChatMessages",
       chat_id: Number(chatId),
+      // No topic context for a flat destination scan. TDLib 1.8.64+ replaced
+      // `message_thread_id` / `saved_messages_topic_id` with a single
+      // optional `topic_id`; for a flat scan we just omit it.
       query: "",
       from_message_id: currentFromId,
       offset: 0,
       limit: 100,
       filter: { _: "searchMessagesFilterDocument" },
       sender_id: null,
-      message_thread_id: 0,
-      saved_messages_topic_id: 0,
     });
 
     if (!result.messages || result.messages.length === 0) break;

worker/src/tdlib/download.ts

@@ -39,7 +39,15 @@ interface TdMessage {
   id: number;
   date: number;
   media_album_id?: string;
+  // TDLib 1.8.50 exposed `reply_to_message_id` directly on the message.
+  // 1.8.64+ replaced it with a tagged-union `reply_to: MessageReplyTo`.
+  // Read both for resilience across versions.
   reply_to_message_id?: number;
+  reply_to?: {
+    _: string;
+    chat_id?: number;
+    message_id?: number;
+  };
   content: {
     _: string;
     document?: {
@@ -66,6 +74,24 @@ interface TdMessage {
   };
 }
 
+/**
+ * Pick the right "the message I'm replying to" ID across TDLib versions.
+ *  - 1.8.50 and earlier expose it directly as `reply_to_message_id`.
+ *  - 1.8.64+ expose `reply_to: MessageReplyTo` (tagged union); a reply to
+ *    a regular message has `_: "messageReplyToMessage"` with `message_id`.
+ *  - Story replies (`_: "messageReplyToStory"`) intentionally return null
+ *    here — they aren't useful for our reply-chain grouping.
+ */
+function extractReplyToMessageId(msg: TdMessage): bigint | undefined {
+  if (msg.reply_to_message_id) {
+    return BigInt(msg.reply_to_message_id);
+  }
+  if (msg.reply_to && msg.reply_to._ === "messageReplyToMessage" && msg.reply_to.message_id) {
+    return BigInt(msg.reply_to.message_id);
+  }
+  return undefined;
+}
+
 interface TdFile {
   id: number;
   size: number;
@@ -202,12 +228,14 @@ export async function getChannelMessages(
       const result = await invokeWithTimeout<{ messages: TdMessage[]; total_count?: number }>(client, {
         _: "searchChatMessages",
         chat_id: Number(chatId),
+        // No topic_id for a flat (non-forum) channel scan. TDLib 1.8.64+
+        // dropped the top-level `message_thread_id: 0` we used to pass; the
+        // type-narrow now is "omit the field entirely if not in a topic".
         query: "",
         from_message_id: fromMessageId,
         offset: 0,
         limit: Math.min(limit, 100),
         filter,
-        message_thread_id: 0,
       });
 
       if (!result.messages || result.messages.length === 0) break;
@@ -233,7 +261,7 @@ export async function getChannelMessages(
             fileSize: BigInt(doc.document.size),
             date: new Date(msg.date * 1000),
             mediaAlbumId: msg.media_album_id && msg.media_album_id !== "0" ? msg.media_album_id : undefined,
-            replyToMessageId: msg.reply_to_message_id ? BigInt(msg.reply_to_message_id) : undefined,
+            replyToMessageId: extractReplyToMessageId(msg),
             caption: msg.content?.caption?.text || undefined,
             remoteUniqueId: doc.document.remote?.unique_id || undefined,
           });

worker/src/tdlib/topics.ts

@@ -239,14 +239,20 @@ export async function getTopicMessages(
     }>(client, {
       _: "searchChatMessages",
       chat_id: Number(chatId),
+      // TDLib 1.8.64+ replaced the top-level `message_thread_id` and
+      // `saved_messages_topic_id` parameters with a single tagged-union
+      // `topic_id: MessageTopic$Input`. For a forum topic, use the
+      // messageTopicForum variant carrying the forum_topic_id.
+      topic_id: {
+        _: "messageTopicForum",
+        forum_topic_id: Number(topicId),
+      },
       query: "",
-      message_thread_id: Number(topicId),
       from_message_id: currentFromId,
       offset: 0,
       limit: Math.min(limit, 100),
       filter: null,
       sender_id: null,
-      saved_messages_topic_id: 0,
     });
 
     if (!result.messages || result.messages.length === 0) break;