fix: handle message length overflow in streaming mode (#1783)

Stream consumer now splits messages that exceed the platform's
MAX_MESSAGE_LENGTH. When accumulated text grows past the safe limit,
the current message is finalized and a new message is started for the
overflow — same as how normal sends chunk long responses.

Split point prefers line boundaries (rfind newline) for clean breaks.
Works for all platforms (Telegram 4096, Discord 2000, etc.) by reading
the adapter's MAX_MESSAGE_LENGTH at runtime.

Also added a safety net in the Telegram adapter: if edit_message_text
still hits MESSAGE_TOO_LONG (e.g. markdown formatting expansion), it
truncates and returns success so the stream consumer doesn't die.

Co-authored-by: Test <test@test.com>

gateway/stream_consumer.py

@@ -87,6 +87,10 @@ class GatewayStreamConsumer:
 
     async def run(self) -> None:
         """Async task that drains the queue and edits the platform message."""
+        # Platform message length limit — leave room for cursor + formatting
+        _raw_limit = getattr(self.adapter, "MAX_MESSAGE_LENGTH", 4096)
+        _safe_limit = max(500, _raw_limit - len(self.cfg.cursor) - 100)
+
         try:
             while True:
                 # Drain all available items from the queue
@@ -112,6 +116,21 @@ class GatewayStreamConsumer:
                 )
 
                 if should_edit and self._accumulated:
+                    # Split overflow: if accumulated text exceeds the platform
+                    # limit, finalize the current message and start a new one.
+                    while (
+                        len(self._accumulated) > _safe_limit
+                        and self._message_id is not None
+                    ):
+                        split_at = self._accumulated.rfind("\n", 0, _safe_limit)
+                        if split_at < _safe_limit // 2:
+                            split_at = _safe_limit
+                        chunk = self._accumulated[:split_at]
+                        await self._send_or_edit(chunk)
+                        self._accumulated = self._accumulated[split_at:].lstrip("\n")
+                        self._message_id = None
+                        self._last_sent_text = ""
+
                     display_text = self._accumulated
                     if not got_done:
                         display_text += self.cfg.cursor