fix: account for server prefix in IRC line splitting

The 512-byte IRC limit includes the :nick!user@host prefix the server
prepends when relaying. Reserve 64 bytes for it and prefer splitting at
space boundaries instead of mid-word. Also strip the command prefix and
"Commands:" label from help output to keep the listing compact.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/core.py

@@ -52,7 +52,7 @@ async def cmd_help(bot, message):
         k for k, v in bot.registry.commands.items()
         if bot._plugin_allowed(v.plugin, channel)
     )
-    await bot.reply(message, f"Commands: {', '.join(bot.prefix + n for n in names)}")
+    await bot.reply(message, ", ".join(names))
 
 
 @command("version", help="Show bot version")

src/derp/bot.py

@@ -22,7 +22,10 @@ _AMBIGUOUS = object()  # sentinel for ambiguous prefix matches
 
 
 def _split_utf8(text: str, max_bytes: int) -> list[str]:
-    """Split text into chunks that fit within max_bytes when UTF-8 encoded."""
+    """Split text into chunks that fit within max_bytes when UTF-8 encoded.
+
+    Prefers splitting at space boundaries to avoid mid-word breaks.
+    """
     encoded = text.encode("utf-8")
     if len(encoded) <= max_bytes:
         return [text]
@@ -37,6 +40,11 @@ def _split_utf8(text: str, max_bytes: int) -> list[str]:
             cut -= 1
         if cut == 0:
             cut = max_bytes  # degenerate: force split
+        else:
+            # Try to find a space to split at (within last 25% of chunk)
+            space = encoded.rfind(b" ", cut // 4, cut)
+            if space > 0:
+                cut = space + 1  # keep the space in the first chunk
         chunks.append(encoded[:cut].decode("utf-8"))
         encoded = encoded[cut:]
     return chunks
@@ -436,7 +444,10 @@ class Bot:
         Long lines are split at UTF-8 safe boundaries to stay within
         the IRC 512-byte line limit (RFC 2812).
         """
-        overhead = len(f"PRIVMSG {target} :".encode("utf-8")) + 2  # +CRLF
+        # Server prepends ":nick!user@host " when relaying; account for it.
+        # Use 64 bytes as conservative estimate for the source prefix.
+        prefix_overhead = 64
+        overhead = prefix_overhead + len(f"PRIVMSG {target} :".encode("utf-8")) + 2
         max_text = _MAX_IRC_LINE - overhead
         for line in text.split("\n"):
             for chunk in _split_utf8(line, max_text):