fix(input): preserve alt-prefixed control keys (#2543)

refs #2514

3 files changed, 38 insertions, 6 deletions

diff --git a/docs/next/CHANGELOG.md b/docs/next/CHANGELOG.md
index 5d123a8c..72d3b0f5 100644
--- a/docs/next/CHANGELOG.md
+++ b/docs/next/CHANGELOG.md
@@ -14,6 +14,7 @@
 - Experimental pane graphics now support bounded named layers, acknowledged full-RGBA primary-layer direct file frames on audited local terminals, owned BGRA fallback, exact pixel mouse input, and placement-only resize replay.
 
 ### Fixed
+- Fish `Ctrl+Alt` keybindings now work in panes after legacy Alt-prefixed control bytes are decoded with both modifiers. (#2514)
 - `herdr config check` now reports unknown built-in theme names instead of silently accepting them. (#2452)
 - macOS `herdr --remote` clients now keep the accepted bridge socket blocking, preventing an immediate disconnect after the protocol handshake. (#2478, thanks @mathijshenquet)
 - Prefix keybindings now preserve Shift in WezTerm Kitty keyboard mode, so commands such as config reload no longer trigger their unshifted action. (#2435)
diff --git a/src/input/parse.rs b/src/input/parse.rs
index 085757c3..b2318339 100644
--- a/src/input/parse.rs
+++ b/src/input/parse.rs
@@ -87,12 +87,9 @@ fn parse_legacy_key_sequence(data: &str) -> Option<TerminalKey> {
         _ if data.starts_with('\x1b') => {
             let rest = data.strip_prefix('\x1b')?;
             if rest.chars().count() == 1 {
-                let ch = rest.chars().next()?;
-                let mut modifiers = KeyModifiers::ALT;
-                if ch.is_ascii_uppercase() {
-                    modifiers |= KeyModifiers::SHIFT;
-                }
-                Some(TerminalKey::new(KeyCode::Char(ch), modifiers))
+                let mut key = parse_legacy_key_sequence(rest)?;
+                key.modifiers |= KeyModifiers::ALT;
+                Some(key)
             } else {
                 None
             }
@@ -550,6 +547,23 @@ mod tests {
     }
 
     #[test]
+    fn parse_legacy_alt_control_letter_composes_modifiers() {
+        let key = parse_terminal_key_sequence("\x1b\x06")
+            .expect("ctrl-alt-f legacy sequence should parse");
+        assert_terminal_key_eq(
+            key.clone(),
+            KeyCode::Char('f'),
+            KeyModifiers::CONTROL | KeyModifiers::ALT,
+            crossterm::event::KeyEventKind::Press,
+            None,
+        );
+        assert_eq!(
+            encode_terminal_key(key, KeyboardProtocol::Legacy),
+            b"\x1b\x06"
+        );
+    }
+
+    #[test]
     fn unknown_legacy_ss3_sequence_remains_unsupported() {
         assert!(parse_terminal_key_sequence("\x1bOz").is_none());
     }
diff --git a/src/pane/terminal.rs b/src/pane/terminal.rs
index 91fcb4fe..a6e5c1da 100644
--- a/src/pane/terminal.rs
+++ b/src/pane/terminal.rs
@@ -4593,6 +4593,23 @@ mod tests {
     }
 
     #[test]
+    fn ghostty_kitty_pane_preserves_legacy_ctrl_alt_letter() {
+        let (tx, _rx) = mpsc::channel(4);
+        let terminal = crate::ghostty::Terminal::new(80, 24, 0).unwrap();
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+        pane.process_pty_bytes(pane_id, 0, b"\x1b[>5u", &tx);
+
+        let mut events = crate::raw_input::parse_raw_input_bytes_sync(b"\x1b\x06");
+        let crate::raw_input::RawInputEvent::Key(key) = events.remove(0) else {
+            panic!("expected key event");
+        };
+        let encoded = pane.encode_terminal_key(key, pane.keyboard_protocol().unwrap());
+
+        assert_eq!(encoded, b"\x1b[102;7u");
+    }
+
+    #[test]
     fn ghostty_pane_characterizes_ctrl_backspace_encoding() {
         let (tx, _rx) = mpsc::channel(4);
         let legacy = GhosttyPaneTerminal::new(