fix: detect oper status when users join channels

Previously the bot only sent WHO on connect (001), so users joining
after the initial scan were never checked for oper status. Now sends
WHO <nick> on every JOIN event to detect opers mid-session.

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

src/derp/bot.py

@@ -265,6 +265,12 @@ class Bot:
             if "*" in flags:
                 self._opers.add(f"{nick}!{user}@{host}")
 
+        # JOIN — WHO the joining user to detect oper status
+        if msg.command == "JOIN" and msg.nick and msg.nick != self.nick:
+            channel = msg.params[0] if msg.params else ""
+            if channel:
+                await self.conn.send(format_msg("WHO", msg.nick))
+
         # QUIT — remove departed nicks from oper set
         if msg.command == "QUIT" and msg.prefix:
             self._opers.discard(msg.prefix)

tests/test_integration.py

@@ -292,6 +292,27 @@ class TestAdmin:
         assert not any("Permission denied" in r for r in replies)
         assert any("Opers:" in r for r in replies)
 
+    def test_oper_detection_on_join(self):
+        """User joining a channel triggers WHO; oper detected mid-session."""
+        h = _Harness(channels=["#test"])
+        h.inject_registration()
+        # User joins the channel after the bot is already connected
+        h.conn.inject(":oper!oper@operhost JOIN #test")
+        # Server responds to the WHO triggered by the JOIN
+        h.conn.inject(
+            ":server 352 test #test oper operhost irc.server oper H* "
+            ":0 Oper Name"
+        )
+        h.privmsg("oper", "#test", "!admins", user="oper", host="operhost")
+        asyncio.run(h.run())
+
+        # Verify WHO was sent for the joining nick
+        who_sent = [s for s in h.conn.sent if "WHO" in s and "oper" in s]
+        assert len(who_sent) >= 1
+        replies = h.sent_privmsgs("#test")
+        assert not any("Permission denied" in r for r in replies)
+        assert any("oper!oper@operhost" in r for r in replies)
+
 
 # -- Channel filter ---------------------------------------------------------