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/exp3_child.go

@@ -0,0 +1,31 @@
+//go:build ignore
+package main
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"time"
+)
+
+type req struct{ ID int `json:"id"`; Method string `json:"method"` }
+type resp struct{ ID int `json:"id"`; OK bool `json:"ok"` }
+
+func main() {
+	in := bufio.NewReader(os.Stdin)
+	out := bufio.NewWriter(os.Stdout)
+	enc, dec := json.NewEncoder(out), json.NewDecoder(in)
+
+	const N = 20000
+	t0 := time.Now()
+	for i := 0; i < N; i++ {
+		enc.Encode(req{ID: i, Method: "stage.lock"})
+		out.Flush()
+		var r resp
+		if err := dec.Decode(&r); err != nil { fmt.Fprintln(os.Stderr, "dec:", err); return }
+	}
+	d := time.Since(t0)
+	fmt.Fprintf(os.Stderr, "CHILD: %d 次 lock RPC 往返 用时 %v, 均摊 %.2f µs/次\n",
+		N, d, float64(d.Microseconds())/float64(N))
+}