新增: 会话分叉功能，优化增量扫描缓存

- 会话分叉: 按 c 键从历史会话分叉，支持带方向提示
- 启动自动加载历史记录
- 增量扫描: 缓存内存化、目录 modTime 跳过、已删除条目裁剪
- 刷新按钮复用 onTabSwitch 单一入口

internal/util.go

@@ -0,0 +1,134 @@
+package internal
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"math/big"
+	"runtime"
+	"strings"
+	"unicode/utf16"
+	"unicode/utf8"
+)
+
+// 平台信息（启动时确定）
+var (
+	isWindows  = runtime.GOOS == "windows"
+	platformKey = runtime.GOOS + "-" + runtime.GOARCH
+)
+
+// toWinPath 将路径中的 / 替换为 \
+func toWinPath(s string) string {
+	return strings.ReplaceAll(s, "/", "\\")
+}
+
+// --- 字符串宽度 ---
+
+func stringWidth(s string) int {
+	w := 0
+	for _, r := range s {
+		w += runeWidth(r)
+	}
+	return w
+}
+
+func runeWidth(r rune) int {
+	if r >= 0x1100 &&
+		(r <= 0x115F || r == 0x2329 || r == 0x232A ||
+			(r >= 0x2E80 && r <= 0xA4CF && r != 0x303F) ||
+			(r >= 0xAC00 && r <= 0xD7A3) ||
+			(r >= 0xF900 && r <= 0xFAFF) ||
+			(r >= 0xFE10 && r <= 0xFE19) ||
+			(r >= 0xFE30 && r <= 0xFE6F) ||
+			(r >= 0xFF01 && r <= 0xFF60) ||
+			(r >= 0xFFE0 && r <= 0xFFE6) ||
+			(r >= 0x20000 && r <= 0x2FFFD) ||
+			(r >= 0x30000 && r <= 0x3FFFD)) {
+		return 2
+	}
+	return 1
+}
+
+func padRightByWidth(s string, targetW int) string {
+	w := stringWidth(s)
+	if w >= targetW {
+		return s
+	}
+	return s + strings.Repeat(" ", targetW-w)
+}
+
+func truncateByWidth(s string, maxW int) string {
+	w := 0
+	for i := 0; i < len(s); {
+		r, size := utf8.DecodeRuneInString(s[i:])
+		rw := runeWidth(r)
+		if w+rw > maxW {
+			return s[:i]
+		}
+		w += rw
+		i += size
+	}
+	return s
+}
+
+func wrapByWidth(s string, maxW int) []string {
+	if maxW <= 0 || s == "" {
+		return []string{s}
+	}
+	var lines []string
+	for s != "" {
+		cut := truncateByWidth(s, maxW)
+		lines = append(lines, cut)
+		s = s[len(cut):]
+	}
+	return lines
+}
+
+func fitWidth(s string, w int) string {
+	return padRightByWidth(truncateByWidth(s, w), w)
+}
+
+// --- 视口 ---
+
+func viewport(cursor, total, height int) (int, int) {
+	if total <= height {
+		return 0, total
+	}
+	half := height / 2
+	start := cursor - half
+	if start < 0 {
+		start = 0
+	}
+	end := start + height
+	if end > total {
+		end = total
+		start = end - height
+		if start < 0 {
+			start = 0
+		}
+	}
+	return start, end
+}
+
+func padLinesTo(lines []string, w, target int) string {
+	for len(lines) < target {
+		lines = append(lines, strings.Repeat(" ", w))
+	}
+	return strings.Join(lines, "\n")
+}
+
+// --- Windows Terminal ---
+
+func encodePSCommand(script string) string {
+	u16 := utf16.Encode([]rune(script))
+	b := make([]byte, len(u16)*2)
+	for i, r := range u16 {
+		b[i*2] = byte(r)
+		b[i*2+1] = byte(r >> 8)
+	}
+	return base64.StdEncoding.EncodeToString(b)
+}
+
+func randRange(min, max int) int {
+	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
+	return min + int(n.Int64())
+}