protocol: read CASEMAPPING from CAPAB and verify it matches echos ascii identity folding, warning on mismatch instead of silently desyncing

api/src/lib.rs

@@ -69,6 +69,9 @@ pub enum NetEvent {
     // The ircd's live channel-mode set from its `CAPAB CHANMODES` burst — mode
     // letters, param arity, and prefix (status) modes incl custom ones like `Y`.
     ChanModeRegistry { modes: Vec<ChanModeCap> },
+    // The ircd's `CASEMAPPING` from its `CAPAB CAPABILITIES` burst. echo folds
+    // identifiers as ascii, so it verifies this matches and warns otherwise.
+    Casemapping { name: String },
     // A server split away (SQUIT). `server` is its SID; every user behind it — and
     // behind any server in its subtree — is gone, since a split is signalled once
     // rather than as a QUIT per user.

modules/protocol/inspircd/src/lib.rs

@@ -330,6 +330,13 @@ impl Protocol for InspIrcd {
                         vec![NetEvent::ChanModeRegistry { modes }]
                     }
                 }
+                // CAPAB CAPABILITIES :K=V … — a KV list; we care about CASEMAPPING.
+                Some(s) if s.eq_ignore_ascii_case("CAPABILITIES") => {
+                    match rest.split_whitespace().find_map(|t| t.trim_start_matches(':').strip_prefix("CASEMAPPING=")) {
+                        Some(name) => vec![NetEvent::Casemapping { name: name.to_string() }],
+                        None => vec![],
+                    }
+                }
                 _ => vec![],
             },
             _ => vec![NetEvent::Unknown { line: line.to_string() }],
@@ -656,6 +663,15 @@ mod tests {
         assert!(p.parse("CAPAB CHANMODES :ban=b").is_empty(), "other CAPAB subcommands ignored");
     }
 
+    // CAPAB CAPABILITIES surfaces CASEMAPPING (echo verifies it's ascii).
+    #[test]
+    fn parses_capab_casemapping() {
+        let mut p = proto();
+        assert!(matches!(p.parse("CAPAB CAPABILITIES :NICKMAX=31 CASEMAPPING=ascii CHANMAX=65").as_slice(),
+            [NetEvent::Casemapping { name }] if name == "ascii"));
+        assert!(p.parse("CAPAB CAPABILITIES :NICKMAX=31 CHANMAX=65").is_empty(), "no CASEMAPPING token -> nothing");
+    }
+
     // CAPAB CHANMODES surfaces mode arity + prefix modes, including a custom prefix
     // like ojoin's Y (symbol !, rank 9000000) that the hardcoded set doesn't know.
     #[test]

src/engine/mod.rs

@@ -1116,6 +1116,16 @@ impl Engine {
                 self.db.set_live_chanmodes(modes);
                 Vec::new()
             }
+            NetEvent::Casemapping { name } => {
+                // echo folds identifiers as ascii. Verify the ircd agrees, rather than
+                // assuming it silently — a mismatch would desync account/channel identity.
+                if name.eq_ignore_ascii_case("ascii") {
+                    tracing::info!(casemapping = %name, "ircd casemapping matches echo (ascii)");
+                } else {
+                    tracing::warn!(casemapping = %name, "ircd CASEMAPPING is not ascii — echo compares identifiers as ascii, so nicks/channels differing only by rfc1459-equivalent characters may be mismatched; keep the ircd on CASEMAPPING=ascii");
+                }
+                Vec::new()
+            }
             NetEvent::UserConnect { uid, nick, host, ip } => {
                 let arriving_nick = nick.clone();
                 self.network.user_connect(uid.clone(), nick, host, ip.clone());