docs(plugin-arch): 归档插件架构迁移评估 + plan 第11节整改计划

- docs/zh/架构迁移评估.md: C ABI→子进程+共享内存完整迁移论证(1621行)
- docs/zh/experiments/: 18项可复跑可行性实验(架构评估的所有数字来源)
- plan.md §11: 11.1~11.9 插件架构缺陷修复清单(唯一权威编号)
- main 保持干净,本批次为 update 特性分支的整改起点

docs/zh/experiments/plugin-arch/02-feasibility/exp2_child.go

@@ -0,0 +1,41 @@
+//go:build ignore
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// 子进程：fd 3 = eventfd(通知), fd 4 = shm 文件
+func main() {
+	efd := os.NewFile(3, "evt")
+	shmf := os.NewFile(4, "shm")
+
+	data, err := unix.Mmap(int(shmf.Fd()), 0, 4096, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
+	if err != nil { fmt.Println("CHILD mmap 失败:", err); os.Exit(1) }
+	fmt.Printf("CHILD: mmap 基址 = %p\n", unsafe.Pointer(&data[0]))
+
+	buf := make([]byte, 8)
+	if _, err := efd.Read(buf); err != nil {
+		fmt.Println("CHILD read err:", err); os.Exit(1)
+	}
+	n := binary.LittleEndian.Uint64(buf)
+	fmt.Printf("CHILD: 被 eventfd 唤醒, 计数=%d\n", n)
+
+	// 按偏移读：头部 16 字节 = {off uint32, len uint32, seq uint64}
+	off := binary.LittleEndian.Uint32(data[0:4])
+	ln := binary.LittleEndian.Uint32(data[4:8])
+	seq := binary.LittleEndian.Uint64(data[8:16])
+	payload := string(data[off : off+ln])
+	fmt.Printf("CHILD: 偏移解引用 off=%d len=%d seq=%d → %q\n", off, ln, seq, payload)
+
+	// 子进程回写（验证双向可见）
+	copy(data[2048:], []byte("CHILD-ACK"))
+	binary.LittleEndian.PutUint32(data[16:20], 2048)
+	binary.LittleEndian.PutUint32(data[20:24], uint32(len("CHILD-ACK")))
+	fmt.Println("CHILD: 已回写 ACK")
+}