fix: resolve CSI terminator, snapshot resize, and escape UTF-8 bugs

Address three PR review findings: isCSITerminator missed the full
ECMA-48 range (0x40-0x7E), causing ~-terminated sequences like function
keys to consume subsequent content. The Strip() regex had the same gap.

- Expand isCSITerminator to full 0x40-0x7E range and add ~ to Strip regex
- Handle pty.Setsize error on snapshot temporary resize
- Use utf8.DecodeRuneInString for multi-byte runes in escape.Interpret
- Add tests for tilde-terminated CSI, UTF-8 escape, and look-ahead

Author: schovi

internal/ansi/clear_test.go

@@ -1274,6 +1274,17 @@ func TestFrameDetector_CursorJumpTopLookAhead(t *testing.T) {
 			t.Error("should NOT truncate when only cursor positioning/control follows")
 		}
 	})
+
+	t.Run("jump followed by tilde-terminated CSI then content - truncation fires", func(t *testing.T) {
+		d := NewFrameDetector(TruncationStrategy{CursorJumpTop: true})
+
+		d.Process(buildRows(1, 20))
+
+		result := d.Process([]byte(cursorPos(1) + "\x1b[15~hello world"))
+		if !result.Truncate {
+			t.Error("should truncate when content follows after tilde-terminated sequence")
+		}
+	})
 }
 
 func TestFrameDetector_CursorHomeLookAhead(t *testing.T) {

internal/ansi/strip.go

@@ -8,7 +8,7 @@ import (
 )
 
 var ansiPatterns = []*regexp.Regexp{
-	regexp.MustCompile(`\x1b\[[0-9;]*[A-Za-z]`),             // CSI sequences (colors, cursor, etc)
+	regexp.MustCompile(`\x1b\[[0-9;]*[A-Za-z~]`),            // CSI sequences (colors, cursor, etc)
 	regexp.MustCompile(`\x1b\][^\x07\x1b]*(?:\x07|\x1b\\)`), // OSC sequences
 	regexp.MustCompile(`\x1b[()][AB012]`),                    // Character set selection
 	regexp.MustCompile(`\x1b[=>]`),                           // Keypad modes
@@ -455,7 +455,7 @@ func parseEraseDisplay(s string, i int) (mode, end int, ok bool) {
 }
 
 func isCSITerminator(c byte) bool {
-	return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '@' || c == '`'
+	return c >= 0x40 && c <= 0x7E
 }
 
 // hasPrintableAhead checks if printable content follows within maxBytes,

internal/ansi/strip_test.go

@@ -345,6 +345,21 @@ func TestStrip(t *testing.T) {
 			input:    "\x1b[1;1Hhello world\x1b[2;1Hrow2\x1b[1;6H\x1b[1J",
 			expected: "      world\nrow2",
 		},
+		{
+			name:     "function key escape sequences",
+			input:    "before\x1b[15~after",
+			expected: "beforeafter",
+		},
+		{
+			name:     "delete key escape sequence",
+			input:    "text\x1b[3~more",
+			expected: "textmore",
+		},
+		{
+			name:     "cursor positioning with tilde-terminated sequences mixed in",
+			input:    "\x1b[1;1H\x1b[15~hello",
+			expected: "hello",
+		},
 	}
 
 	for _, tt := range tests {

internal/daemon/server.go

@@ -651,7 +651,9 @@ func (s *Server) handleSnapshot(req Request) Response {
 
 	tempCols := clampUint16(meta.Cols + 1)
 	tempRows := clampUint16(meta.Rows + 1)
-	pty.Setsize(ptmx, &pty.Winsize{Cols: tempCols, Rows: tempRows})
+	if err := pty.Setsize(ptmx, &pty.Winsize{Cols: tempCols, Rows: tempRows}); err != nil {
+		return Response{Success: false, Error: fmt.Sprintf("temporary resize for snapshot: %v", err)}
+	}
 	if cmd != nil && cmd.Process != nil {
 		cmd.Process.Signal(syscall.SIGWINCH)
 	}

internal/escape/escape.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 )
 
 // Interpret processes escape sequences in a string.
@@ -82,8 +83,9 @@ func Interpret(s string) (string, error) {
 			i += 2
 
 		default:
-			result.WriteByte(s[i+1])
-			i += 2
+			r, size := utf8.DecodeRuneInString(s[i+1:])
+			result.WriteRune(r)
+			i += 1 + size
 		}
 	}
 

internal/escape/escape_test.go

@@ -44,6 +44,7 @@ func TestInterpret_UnknownSequences(t *testing.T) {
 		{"slash", `\/`, "/"},
 		{"at sign", `\@`, "@"},
 		{"hash", `\#`, "#"},
+		{"multi-byte UTF-8 after backslash", `\é`, "é"},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {