feat: add IRC 512-byte message truncation

Split outgoing messages at UTF-8 safe boundaries to comply with
RFC 2812 line limit. Accounts for PRIVMSG overhead and CRLF.

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

src/derp/bot.py

@@ -6,21 +6,42 @@ import asyncio
 import base64
 import fnmatch
 import logging
+import random
 import time
 from datetime import datetime, timezone
 from pathlib import Path
 
 from derp import __version__
-from derp.irc import IRCConnection, Message, format_msg, parse
+from derp.irc import _MAX_IRC_LINE, IRCConnection, Message, format_msg, parse
 from derp.plugin import Handler, PluginRegistry
 from derp.state import StateStore
 
 log = logging.getLogger(__name__)
 
-RECONNECT_DELAY = 30
 _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."""
+    encoded = text.encode("utf-8")
+    if len(encoded) <= max_bytes:
+        return [text]
+    chunks: list[str] = []
+    while encoded:
+        if len(encoded) <= max_bytes:
+            chunks.append(encoded.decode("utf-8"))
+            break
+        cut = max_bytes
+        # Walk backward to avoid breaking a multi-byte codepoint
+        while cut > 0 and (encoded[cut] & 0xC0) == 0x80:
+            cut -= 1
+        if cut == 0:
+            cut = max_bytes  # degenerate: force split
+        chunks.append(encoded[:cut].decode("utf-8"))
+        encoded = encoded[cut:]
+    return chunks
+
+
 class _TokenBucket:
     """Token bucket rate limiter for outgoing messages."""
 
@@ -62,6 +83,7 @@ class Bot:
         self._running = False
         self._started: float = time.monotonic()
         self._tasks: set[asyncio.Task] = set()
+        self._reconnect_delay: float = 5.0
         self._admins: list[str] = config.get("bot", {}).get("admins", [])
         self._opers: set[str] = set()  # hostmasks of known IRC operators
         self._caps: set[str] = set()  # negotiated IRCv3 caps
@@ -74,16 +96,24 @@ class Bot:
         )
 
     async def start(self) -> None:
-        """Connect, register, join channels, and enter the main loop."""
+        """Connect, register, join channels, and enter the main loop.
+
+        Uses exponential backoff with jitter on reconnect (5s -> 300s cap).
+        Delay resets after a successful connection.
+        """
         self._running = True
         while self._running:
             try:
                 await self._connect_and_run()
+                self._reconnect_delay = 5.0  # reset on clean run
             except (OSError, ConnectionError) as exc:
                 log.error("connection lost: %s", exc)
             if self._running:
-                log.info("reconnecting in %ds...", RECONNECT_DELAY)
-                await asyncio.sleep(RECONNECT_DELAY)
+                jitter = self._reconnect_delay * 0.25 * (2 * random.random() - 1)
+                delay = self._reconnect_delay + jitter
+                log.info("reconnecting in %.0fs...", delay)
+                await asyncio.sleep(delay)
+                self._reconnect_delay = min(self._reconnect_delay * 2, 300.0)
 
     async def _connect_and_run(self) -> None:
         """Single connection lifecycle."""
@@ -358,10 +388,17 @@ class Bot:
     # -- Public API for plugins --
 
     async def send(self, target: str, text: str) -> None:
-        """Send a PRIVMSG to a target (channel or nick), rate-limited."""
+        """Send a PRIVMSG to a target (channel or nick), rate-limited.
+
+        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
+        max_text = _MAX_IRC_LINE - overhead
         for line in text.split("\n"):
-            await self._bucket.acquire()
-            await self.conn.send(format_msg("PRIVMSG", target, line))
+            for chunk in _split_utf8(line, max_text):
+                await self._bucket.acquire()
+                await self.conn.send(format_msg("PRIVMSG", target, chunk))
 
     async def reply(self, msg: Message, text: str) -> None:
         """Reply to the source of a message (channel or PM)."""

src/derp/irc.py

@@ -9,6 +9,8 @@ from dataclasses import dataclass
 
 log = logging.getLogger(__name__)
 
+_MAX_IRC_LINE = 512  # bytes including \r\n (RFC 2812)
+
 
 def _unescape_tag_value(value: str) -> str:
     """Unescape an IRCv3 message tag value per the spec."""