feat: enable XTerm modifyOtherKeys protocol

This gives better key reporting for XTerm and strict clones that
implement the modifyOtherKeys (CSI-27-~) protocol.

Author: gdamore

input.go

@@ -805,6 +805,23 @@ func (ip *inputProcessor) handleCsi(mode rune, params []byte, intermediate []byt
 	case '_':
 		if len(intermediate) == 0 && len(P) > 0 {
 			ip.handleWinKey(P)
+			return
+		}
+	case '~':
+		if len(intermediate) == 0 && len(P) >= 2 {
+			mod := calcModifier(P[1])
+			if ks, ok := csiAllKeys[csiParamMode{M: mode, P: P0}]; ok {
+				ip.post(NewEventKey(ks.Key, 0, mod))
+				return
+			}
+			if P0 == 27 && len(P) > 2 {
+				if P[2] < ' ' || P[2] == 0x7F {
+					ip.post(NewEventKey(Key(P[2]), 0, mod))
+				} else {
+					ip.post(NewEventKey(KeyRune, rune(P[2]), mod))
+				}
+				return
+			}
 		}
 	}
 
@@ -824,7 +841,6 @@ func (ip *inputProcessor) handleCsi(mode rune, params []byte, intermediate []byt
 		ip.post(NewEventKey(k, 0, calcModifier(P[1])))
 		return
 	}
-
 	// if we got here we just swallow the unknown sequence
 }
 

tscreen.go

@@ -24,7 +24,6 @@ import (
 	"io"
 	"maps"
 	"os"
-	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -320,13 +319,12 @@ func (t *tScreen) prepareExtendedOSC() {
 	}
 
 	if t.enableCsiU == "" && t.ti.XTermLike {
-		if runtime.GOOS == "windows" {
-			t.enableCsiU = "\x1b[?9001h"
-			t.disableCsiU = "\x1b[?9001l"
-		} else {
-			t.enableCsiU = "\x1b[>1u"
-			t.disableCsiU = "\x1b[<u"
-		}
+		// three advanced keyboard protocols:
+		// - xterm modifyOtherKeys (uses CSI 27 ~ )
+		// - kitty csi-u (uses CSI u)
+		// - win32-input-mode (uses CSI _)
+		t.enableCsiU = "\x1b[>4;2m" + "\x1b[>1u" + "\x1b[9001h"
+		t.disableCsiU = "\x1b[9001l" + "\x1b[<u" + "\x1b[>4;0m"
 	}
 }