implement thread migration for local backups

src/core/backup_reader.py

@@ -701,6 +701,7 @@ class BackupReader:
         self._stickers: List[BackupSticker] = []
         self._members: List[BackupMember] = []
         self._member_map: Dict[int, BackupMember] = {}
+        self._thread_info: Dict[int, Dict[str, Any]] = {}  # channel_id -> metadata (like name, parentID)
 
     # ── startup ──────────────────────────────────────────────────────────
 
@@ -898,6 +899,14 @@ class BackupReader:
 
         try:
             data = json.loads(json_file.read_text(encoding="utf-8"))
+            
+            # Cache thread info if this is a thread
+            if "parentID" in data:
+                self._thread_info[channel_id] = {
+                    "name": data.get("channelName", "Unknown Thread"),
+                    "parent_id": int(data["parentID"])
+                }
+            
             return data.get("messages", [])
         except Exception as e:
             logger.error(f"[Backup] Failed to load messages for channel {channel_id}: {e}")
@@ -910,6 +919,16 @@ class BackupReader:
         # Resolve channel object
         channel = next((c for c in self._channels if c.id == channel_id), None)
         
+        # If not found in channels, check if it's a known thread
+        if not channel and channel_id in self._thread_info:
+            info = self._thread_info[channel_id]
+            # Create a stub BackupChannel for the thread
+            channel = BackupChannel({
+                "id": str(channel_id),
+                "name": info["name"],
+                "type": "thread"
+            }, category_id=info["parent_id"], guild=self.guild)
+        
         return BackupMessage(
             msg_data,
             author=author,

src/fluxer/migrate_message.py

@@ -109,6 +109,8 @@ async def migrate_messages(
         "messages": 0, 
         "threads": 0, 
         "attachments": 0,
+        "first_message_url": "",
+        "last_message_url": "",
         "last_message_content": "",
         "last_message_author": ""
     }
@@ -128,7 +130,8 @@ async def migrate_messages(
             # Skip system messages like "pinned a message", etc.
             # We treat thread_starter_message (type 21) as our thread marker.
             if msg.type == context.discord_reader.MESSAGE_TYPE_THREAD_STARTER:
-                content = f"> <<< THREAD: **{msg.channel.name}** >>>"
+                channel_name = msg.channel.name if msg.channel else "Unknown Thread"
+                content = f"> <<< THREAD: **{channel_name}** >>>"
             elif msg.type not in [context.discord_reader.MESSAGE_TYPE_DEFAULT, context.discord_reader.MESSAGE_TYPE_REPLY]:
                 # If we are skipping the parent, we STILL need to check for a thread!
                 if hasattr(msg, 'thread') and msg.thread:

src/stoat/migrate_message.py

@@ -136,7 +136,8 @@ async def migrate_messages(
             # We treat thread_starter_message (type 21) as our thread marker.
             content = "" # Initialize content
             if msg.type == context.discord_reader.MESSAGE_TYPE_THREAD_STARTER:
-                content = f"> <<< THREAD: **{msg.channel.name}** >>>"
+                channel_name = msg.channel.name if msg.channel else "Unknown Thread"
+                content = f"> <<< THREAD: **{channel_name}** >>>"
                 # If it's a thread starter and we already processed the thread at the top,
                 # we might be double-posting. But we want it as a marker.
             elif msg.type not in [context.discord_reader.MESSAGE_TYPE_DEFAULT, context.discord_reader.MESSAGE_TYPE_REPLY]: