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/exp8.go

@@ -0,0 +1,84 @@
+//go:build ignore
+package main
+
+import (
+	"bufio"
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+func main() {
+	fmt.Println("=== 实验 8：跨进程并发扇出改写同一 StageContext（最高风险点 3.4）===")
+
+	mfd, _ := unix.MemfdCreate("stagectx", 0)
+	unix.Ftruncate(mfd, 65536)
+	shmFile := os.NewFile(uintptr(mfd), "shm")
+	data, _ := unix.Mmap(mfd, 0, 65536, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
+
+	// 初始 final_text = "" @1024, arena 游标 = 1024
+	binary.LittleEndian.PutUint32(data[0:4], 1024)
+	binary.LittleEndian.PutUint32(data[4:8], 0)
+	binary.LittleEndian.PutUint32(data[8:12], 1024)
+
+	tags := []string{"A", "B", "C", "D", "E"}   // 5 个并发插件
+	var mu sync.Mutex                           // 内核侧锁仲裁
+	var wg sync.WaitGroup
+	var rpcCount int64
+	var cntMu sync.Mutex
+
+	t0 := time.Now()
+	for _, tag := range tags {
+		cmd := exec.Command("go", "run", "exp8_worker.go", tag)
+		cmd.ExtraFiles = []*os.File{shmFile}
+		sin, _ := cmd.StdinPipe()
+		sout, _ := cmd.StdoutPipe()
+		cmd.Stderr = os.Stderr
+		cmd.Start()
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			dec := json.NewDecoder(bufio.NewReader(sout))
+			w := bufio.NewWriter(sin)
+			enc := json.NewEncoder(w)
+			held := false
+			for {
+				var q map[string]string
+				if err := dec.Decode(&q); err != nil { break }
+				switch q["method"] {
+				case "stage.lock":   mu.Lock();   held = true
+				case "stage.unlock": if held { mu.Unlock(); held = false }
+				}
+				cntMu.Lock(); rpcCount++; cntMu.Unlock()
+				enc.Encode(map[string]bool{"ok": true}); w.Flush()
+			}
+			if held { mu.Unlock() }
+			cmd.Wait()
+		}()
+	}
+	wg.Wait()
+	dur := time.Since(t0)
+
+	off := binary.LittleEndian.Uint32(data[0:4])
+	ln := binary.LittleEndian.Uint32(data[4:8])
+	final := string(data[off : off+ln])
+
+	fmt.Printf("\n--- 结果 ---\n")
+	fmt.Printf("最终 final_text 长度 = %d\n", len(final))
+	counts := map[string]int{}
+	for _, t := range tags { counts[t] = strings.Count(final, t) }
+	fmt.Printf("各插件写入次数: %v\n", counts)
+	total := 0
+	for _, c := range counts { total += c }
+	fmt.Printf("总字符 = %d, 长度 = %d  → %s\n", total, len(final),
+		map[bool]string{true:"一致 ✅ 无丢失/无撕裂", false:"不一致 ❌"}[total == len(final)])
+	fmt.Printf("RPC 锁操作 = %d 次, 总耗时 %v\n", rpcCount, dur)
+	fmt.Printf("\n注：写入次数少于 5×300 是 arena 64KB 上限所致（append-only 未压实），符合设计\n")
+}