From d17b5cab9d9f4f3cc964d8326cd6696ccb330b5e Mon Sep 17 00:00:00 2001
From: Heal75 <18739377+Heal75@users.noreply.github.com>
Date: Fri, 2 Oct 2026 08:59:04 +0200
Subject: [PATCH] fix(parser): ignore CSI sequences with a private prefix in
 SGR

`CSI > Ps m` (XTMODKEYS, used to enable modifyOtherKeys) and `CSI ? Ps m`
reached the SGR handler with the prefix dropped, so `ESC[>4m` was executed as
SGR 4 and switched underline on for everything printed afterwards.

Return early from the SGR handler when the sequence has a prefix.
---
 lib/src/core/escape/parser.dart       |  3 +++
 test/src/core/escape/parser_test.dart | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/lib/src/core/escape/parser.dart b/lib/src/core/escape/parser.dart
index 0c7e74a9..c9da20ac 100644
--- a/lib/src/core/escape/parser.dart
+++ b/lib/src/core/escape/parser.dart
@@ -408,6 +408,9 @@ class EscapeParser {
   ///
   /// https://terminalguide.namepad.de/seq/csi_sm/
   void _csiHandleSgr() {
+    // `CSI > Ps m` (XTMODKEYS) and `CSI ? Ps m` are not SGR.
+    if (_csi.prefix != null) return;
+
     final params = _csi.params;
 
     if (params.isEmpty) {
diff --git a/test/src/core/escape/parser_test.dart b/test/src/core/escape/parser_test.dart
index 96fa5bb1..b93f1443 100644
--- a/test/src/core/escape/parser_test.dart
+++ b/test/src/core/escape/parser_test.dart
@@ -13,5 +13,24 @@ void main() {
       parser.write('\x1b[8;24;80t');
       verify(parser.handler.resize(80, 24));
     });
+
+    test('does not treat CSI > Ps m as SGR', () {
+      final parser = EscapeParser(MockEscapeHandler());
+      // XTMODKEYS, e.g. sent by programs enabling modifyOtherKeys.
+      parser.write('\x1b[>4m');
+      verifyNever(parser.handler.setCursorUnderline());
+    });
+
+    test('does not treat CSI ? Ps m as SGR', () {
+      final parser = EscapeParser(MockEscapeHandler());
+      parser.write('\x1b[?4m');
+      verifyNever(parser.handler.setCursorUnderline());
+    });
+
+    test('still parses plain SGR', () {
+      final parser = EscapeParser(MockEscapeHandler());
+      parser.write('\x1b[4m');
+      verify(parser.handler.setCursorUnderline()).called(1);
+    });
   });
 }