fix recent messages by handling valueless and escaped irc tags

The recent-messages API now serializes empty IRCv3 tags as bare keys
(e.g. `emotes`) instead of `emotes=`, which threw a RangeError in the
tag parser and silently dropped every recent message. Parse tags per the
IRCv3 spec: treat bare and empty values as equivalent, split on the first
`=` so values may contain `=`, and unescape values in a single pass
(\: \s \ \r \n). Also guard user extraction against prefixes without
`!`, and isolate per-message parse failures in _handleIRCData so one bad
message can no longer abort an entire batch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/fixtures/irc_messages.dart

@@ -9,6 +9,19 @@ const basicPrivmsg =
     'tmi-sent-ts=1234567890123;turbo=0;user-id=67890;user-type= '
     ':testuser!testuser@testuser.tmi.twitch.tv PRIVMSG #channel :Hello World';
 
+/// Exercises the full IRCv3 tag escape set plus a value that itself contains
+/// '='. Uses a raw string so the backslashes are literal wire bytes.
+const messageWithEscapedTagChars =
+    r'@a-space=one\stwo;a-semi=left\:right;a-slash=a\\b;a-equals=k=v;'
+    r'a-double=x\\sy;display-name=EscapeAll;mod=0 '
+    r':escapeall!escapeall@escapeall.tmi.twitch.tv PRIVMSG #channel :hi';
+
+/// A message whose prefix is not the usual `nick!user@host` form (no '!').
+/// The parser should fall back to the login tag instead of throwing.
+const messageNoBangPrefix =
+    '@login=fallbackuser;mod=0;id=nobang-1 '
+    ':some.server.example PRIVMSG #channel :server style';
+
 /// A chat message with emotes in the tags
 /// Note: emote positions are 0-indexed byte positions in the message
 /// "Kappa LUL" - Kappa is at 0-4, LUL is at 6-8
@@ -138,6 +151,16 @@ const historicalMessage =
     'tmi-sent-ts=1234567890123;turbo=0;user-id=12121;user-type= '
     ':histuser!histuser@histuser.tmi.twitch.tv PRIVMSG #channel :Historical message';
 
+/// A historical message as serialized by the recent-messages API, which emits
+/// empty tags as bare keys (e.g. `emotes`, `flags`) instead of the `key=` form
+/// that live Twitch IRC uses.
+const historicalMessageBareTags =
+    '@badges=raging-wolf-helm/1;emotes;first-msg=0;tmi-sent-ts=1234567890123;'
+    'flags;mod=0;returning-chatter=0;rm-received-ts=1234567890456;color=#1E90FF;'
+    'id=hist-bare-123;room-id=12345;historical=1;user-type;turbo=0;subscriber=0;'
+    'badge-info;display-name=BareUser;user-id=18181 '
+    ':bareuser!bareuser@bareuser.tmi.twitch.tv PRIVMSG #channel :Bare tag message';
+
 /// A message from a shared chat session (source room different from current)
 const sharedChatMessage =
     '@badge-info=;badges=;color=#00BFFF;display-name=SharedUser;emotes=;'

test/models/irc_test.dart

@@ -27,6 +27,27 @@ void main() {
         expect(msg.message, 'test message');
       });
 
+      test('unescapes the full IRCv3 tag escape set', () {
+        final msg = IRCMessage.fromString(messageWithEscapedTagChars);
+
+        expect(msg.tags['a-space'], 'one two');
+        expect(msg.tags['a-semi'], 'left;right');
+        expect(msg.tags['a-slash'], r'a\b');
+        // Only the first '=' splits key/value; later '=' stays in the value.
+        expect(msg.tags['a-equals'], 'k=v');
+        // `\\` consumes both backslashes; the following 's' is a literal letter,
+        // not a `\s` space escape (single-pass unescaping).
+        expect(msg.tags['a-double'], r'x\sy');
+      });
+
+      test('falls back to login tag when prefix has no "!"', () {
+        // An unexpected prefix shape must not throw and drop the message.
+        final msg = IRCMessage.fromString(messageNoBangPrefix);
+
+        expect(msg.user, 'fallbackuser');
+        expect(msg.message, 'server style');
+      });
+
       test('handles message with no color tag', () {
         final msg = IRCMessage.fromString(messageNoColor);
 
@@ -223,6 +244,20 @@ void main() {
         expect(msg.tags['historical'], '1');
       });
 
+      test('parses historical message with bare (valueless) tags', () {
+        // The recent-messages API serializes empty tags as bare keys (e.g.
+        // `emotes`, `flags`) instead of `key=`. This previously threw a
+        // RangeError, silently dropping all recent messages.
+        final msg = IRCMessage.fromString(historicalMessageBareTags);
+
+        expect(msg.tags['historical'], '1');
+        expect(msg.tags['display-name'], 'BareUser');
+        expect(msg.message, 'Bare tag message');
+        // Bare tags should be absent from the map, not crash parsing.
+        expect(msg.tags.containsKey('emotes'), isFalse);
+        expect(msg.tags.containsKey('flags'), isFalse);
+      });
+
       test('parses shared chat message with source room', () {
         final msg = IRCMessage.fromString(sharedChatMessage);