remove any reply preamble from parsed Message

Otherwise some message handlers might be thrown off by seeing a trigger
that's actually just the quoted part of a previous message.
The full message body is still always available via the event property.

hotdog/models.py

@@ -1,12 +1,13 @@
 import asyncio
 from dataclasses import dataclass, field
+from itertools import dropwhile
 from random import random
 from time import time as now
 from typing import *
 
 import nio
 
-from .html import HtmlDocument, parse_html
+from .html import HtmlDocument, detach, find, parse_html
 
 JobCallback = Callable[["Job"], None]
 
@@ -106,6 +107,18 @@ class Message:
             else None
         )
 
+        # Remove any "reply" preamble.
+        is_reply = plain.startswith("> <@")
+        if is_reply:
+            lines = dropwhile(
+                lambda l: l.startswith("> "), plain.splitlines(keepends=False)
+            )
+            nextline = next(lines)
+            if nextline == "":
+                plain = "\n".join(lines)
+        if html and (reply := next(find(html, "mx-reply"), None)):
+            detach(reply)
+
         self.text = plain
         self.html = html
         self.tokens = Tokens.from_str(plain)