diff --git a/backend/cmd/scert-nginx/main_linux.go b/backend/cmd/scert-nginx/main_linux.go
new file mode 100644
index 0000000..a394a47
--- /dev/null
+++ b/backend/cmd/scert-nginx/main_linux.go
@@ -0,0 +1,69 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"net"
+	"os"
+	"os/signal"
+	"strconv"
+	"syscall"
+
+	"git.pcux.cn/xuans/Scert/backend/internal/nginxactivation"
+)
+
+func inheritedListener(expectedPath string) (*net.UnixListener, error) {
+	if os.Getenv("LISTEN_PID") != strconv.Itoa(os.Getpid()) || os.Getenv("LISTEN_FDS") != "1" {
+		return nil, errors.New("必须由单个 systemd Unix socket 启动激活服务")
+	}
+	file := os.NewFile(3, "activation-socket")
+	if file == nil {
+		return nil, errors.New("激活 socket 描述符不存在")
+	}
+	defer file.Close()
+	listener, err := net.FileListener(file)
+	if err != nil {
+		return nil, err
+	}
+	unixListener, ok := listener.(*net.UnixListener)
+	if !ok {
+		_ = listener.Close()
+		return nil, errors.New("激活器拒绝非 Unix 监听器")
+	}
+	unixListener.SetUnlinkOnClose(false)
+	if unixListener.Addr().Network() != "unix" || unixListener.Addr().String() != expectedPath {
+		_ = unixListener.Close()
+		return nil, errors.New("激活 socket 与固定策略不匹配")
+	}
+	return unixListener, nil
+}
+
+func run(ctx context.Context, path string) error {
+	if os.Geteuid() != 0 {
+		return errors.New("独立 Nginx 激活服务必须由 root 启动")
+	}
+	policy, err := nginxactivation.LoadPolicy(path)
+	if err != nil {
+		return fmt.Errorf("读取受信激活策略失败：%w", err)
+	}
+	listener, err := inheritedListener(policy.SocketPath)
+	if err != nil {
+		return err
+	}
+	defer listener.Close()
+	service := nginxactivation.LocalService{Rotation: policy.Rotation(), AllowedUID: *policy.AllowedUID}
+	return service.Serve(ctx, listener)
+}
+
+func main() {
+	path := flag.String("policy", "/etc/scert-nginx/policy.json", "root 管理的独立激活策略文件")
+	flag.Parse()
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, *path); err != nil {
+		fmt.Fprintln(os.Stderr, "Nginx 本地激活服务启动或运行失败：", err)
+		os.Exit(1)
+	}
+}
diff --git a/backend/internal/nginxactivation/client_linux.go b/backend/internal/nginxactivation/client_linux.go
new file mode 100644
index 0000000..bf65097
--- /dev/null
+++ b/backend/internal/nginxactivation/client_linux.go
@@ -0,0 +1,144 @@
+package nginxactivation
+
+import (
+	"context"
+	"errors"
+	"net"
+	"os"
+	"path/filepath"
+	"syscall"
+	"time"
+)
+
+var ErrLocalOperation = errors.New("本地 Nginx 激活操作未完成，请核对事务状态")
+
+// Client 只能连接受保护的本地 Unix socket；生产调用方必须指定 root 的 UID 0。
+type Client struct {
+	SocketPath string
+	ServiceUID uint32
+}
+
+func (c Client) Ready(ctx context.Context) (ReadyState, error) {
+	result, err := c.call(ctx, request{Action: "ready"})
+	if err != nil {
+		return ReadyState{}, err
+	}
+	if result.Ready == nil {
+		return ReadyState{}, errors.New("本地激活服务没有返回就绪状态")
+	}
+	return *result.Ready, nil
+}
+
+func (c Client) State(ctx context.Context) (State, error) {
+	result, err := c.call(ctx, request{Action: "state"})
+	if err != nil {
+		return State{}, err
+	}
+	if result.State == nil {
+		return State{}, errors.New("本地激活服务没有返回事务状态")
+	}
+	return *result.State, nil
+}
+
+func (c Client) Stage(ctx context.Context, chain, key []byte) (string, error) {
+	result, err := c.call(ctx, request{Action: "stage", Chain: chain, Key: key})
+	if err == nil && !validID(result.ID) {
+		return "", errors.New("本地激活服务返回无效事务编号")
+	}
+	return result.ID, err
+}
+
+func (c Client) Commit(ctx context.Context, id string) error {
+	_, err := c.call(ctx, request{Action: "commit", ID: id})
+	return err
+}
+
+func (c Client) Reconcile(ctx context.Context, id string) (State, error) {
+	result, err := c.call(ctx, request{Action: "reconcile", ID: id})
+	if result.State != nil {
+		return *result.State, err
+	}
+	if err != nil {
+		return State{}, err
+	}
+	return State{}, errors.New("本地激活服务没有返回恢复结果")
+}
+
+func (c Client) call(ctx context.Context, message request) (response, error) {
+	message.Version = protocolVersion
+	if !validRequest(message) {
+		return response{}, errors.New("本地激活请求无效")
+	}
+	if err := validateSocket(c.SocketPath, c.ServiceUID); err != nil {
+		return response{}, err
+	}
+	ctx, cancel := context.WithTimeout(ctx, 95*time.Second)
+	defer cancel()
+	connection, err := (&net.Dialer{}).DialContext(ctx, "unix", c.SocketPath)
+	if err != nil {
+		return response{}, err
+	}
+	defer connection.Close()
+	unixConnection, ok := connection.(*net.UnixConn)
+	if !ok {
+		return response{}, errors.New("本地激活连接类型无效")
+	}
+	uid, err := peerUID(unixConnection)
+	if err != nil || uid != c.ServiceUID {
+		return response{}, errors.New("本地激活服务身份不可信")
+	}
+	stop := context.AfterFunc(ctx, func() { _ = connection.Close() })
+	defer stop()
+	deadline, _ := ctx.Deadline()
+	if err := connection.SetDeadline(deadline); err != nil {
+		return response{}, err
+	}
+	if err := writeFrame(connection, message); err != nil {
+		return response{}, errors.Join(err, ctx.Err())
+	}
+	var result response
+	if err := readFrame(connection, &result); err != nil {
+		return response{}, errors.Join(err, ctx.Err())
+	}
+	if result.Version != protocolVersion {
+		return response{}, errors.New("本地激活协议版本不匹配")
+	}
+	if result.Code != "ok" {
+		return result, ErrLocalOperation
+	}
+	return result, nil
+}
+
+func validateSocket(path string, uid uint32) error {
+	if !filepath.IsAbs(path) || filepath.Clean(path) != path || path == "/" {
+		return errors.New("激活 socket 必须使用规范绝对路径")
+	}
+	info, err := os.Lstat(path)
+	if err != nil {
+		return err
+	}
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok || info.Mode()&os.ModeSocket == 0 || stat.Uid != uid || info.Mode().Perm()&0o117 != 0 {
+		return errors.New("激活 socket 类型、所有者或权限不可信")
+	}
+	return validateTrustedParents(filepath.Dir(path), uid)
+}
+
+func validateTrustedParents(path string, uid uint32) error {
+	for ; ; path = filepath.Dir(path) {
+		info, err := os.Lstat(path)
+		if err != nil {
+			return err
+		}
+		stat, ok := info.Sys().(*syscall.Stat_t)
+		if !ok || !info.IsDir() || (stat.Uid != uid && stat.Uid != 0) {
+			return errors.New("激活策略父目录的类型或所有者不可信")
+		}
+		if info.Mode().Perm()&0o022 != 0 && !(stat.Uid == 0 && info.Mode()&os.ModeSticky != 0) {
+			return errors.New("激活策略父目录允许非受信用户写入")
+		}
+		if filepath.Dir(path) == path {
+			return nil
+		}
+	}
+}
diff --git a/backend/internal/nginxactivation/ipc_linux.go b/backend/internal/nginxactivation/ipc_linux.go
new file mode 100644
index 0000000..eef5cc5
--- /dev/null
+++ b/backend/internal/nginxactivation/ipc_linux.go
@@ -0,0 +1,153 @@
+package nginxactivation
+
+import (
+	"context"
+	"errors"
+	"net"
+	"sync"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+const operationTimeout = 60 * time.Second
+
+// LocalService 只接受内核认证的指定 UID，不依赖请求提供的身份。
+// 监听器由受信启动器提供；本服务不创建 TCP 入口或删除 socket 文件。
+type LocalService struct {
+	Rotation   Rotation
+	AllowedUID uint32
+}
+
+func peerUID(connection *net.UnixConn) (uint32, error) {
+	raw, err := connection.SyscallConn()
+	if err != nil {
+		return 0, err
+	}
+	var credentials *unix.Ucred
+	var socketErr error
+	if err := raw.Control(func(fd uintptr) {
+		credentials, socketErr = unix.GetsockoptUcred(int(fd), unix.SOL_SOCKET, unix.SO_PEERCRED)
+	}); err != nil {
+		return 0, err
+	}
+	if socketErr != nil {
+		return 0, socketErr
+	}
+	if credentials == nil || credentials.Pid <= 0 {
+		return 0, errors.New("本地激活连接缺少内核身份")
+	}
+	return credentials.Uid, nil
+}
+
+func (s LocalService) Serve(ctx context.Context, listener *net.UnixListener) error {
+	if listener == nil {
+		return errors.New("本地激活服务缺少 Unix 监听器")
+	}
+	if s.Rotation.Reloader == nil {
+		return errors.New("本地激活策略未初始化")
+	}
+	listener.SetUnlinkOnClose(false)
+	defer listener.Close()
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+	stop := context.AfterFunc(ctx, func() { _ = listener.Close() })
+	defer stop()
+	var workers sync.WaitGroup
+	defer workers.Wait()
+	capacity := make(chan struct{}, 4)
+	for {
+		connection, err := listener.AcceptUnix()
+		if err != nil {
+			cancel()
+			if errors.Is(err, net.ErrClosed) && ctx.Err() != nil {
+				return nil
+			}
+			return err
+		}
+		select {
+		case capacity <- struct{}{}:
+			workers.Add(1)
+			go func() {
+				defer workers.Done()
+				defer func() { <-capacity }()
+				s.handle(ctx, connection)
+			}()
+		default:
+			_ = connection.Close()
+		}
+	}
+}
+
+func (s LocalService) handle(ctx context.Context, connection *net.UnixConn) {
+	defer connection.Close()
+	uid, err := peerUID(connection)
+	if err != nil || uid != s.AllowedUID {
+		return
+	}
+	_ = connection.SetReadDeadline(time.Now().Add(3 * time.Second))
+	stop := context.AfterFunc(ctx, func() { _ = connection.Close() })
+	defer stop()
+	var message request
+	if err := readFrame(connection, &message); err != nil || !validRequest(message) {
+		_ = connection.SetWriteDeadline(time.Now().Add(time.Second))
+		_ = writeFrame(connection, response{Version: protocolVersion, Code: "invalid_request"})
+		return
+	}
+	operationCtx, cancel := context.WithTimeout(ctx, operationTimeout)
+	defer cancel()
+	result := s.execute(operationCtx, message)
+	// 私钥不写入日志、错误或响应，处理结束后清理请求缓冲。
+	clear(message.Key)
+	_ = connection.SetWriteDeadline(time.Now().Add(3 * time.Second))
+	_ = writeFrame(connection, result)
+}
+
+func validRequest(message request) bool {
+	if message.Version != protocolVersion {
+		return false
+	}
+	switch message.Action {
+	case "ready", "state":
+		return message.ID == "" && len(message.Chain) == 0 && len(message.Key) == 0
+	case "stage":
+		return message.ID == "" && len(message.Chain) > 0 && len(message.Chain) <= 1<<20 && len(message.Key) > 0 && len(message.Key) <= 64<<10
+	case "commit", "reconcile":
+		return validID(message.ID) && len(message.Chain) == 0 && len(message.Key) == 0
+	default:
+		return false
+	}
+}
+
+func (s LocalService) execute(ctx context.Context, message request) response {
+	result := response{Version: protocolVersion, Code: "ok"}
+	var err error
+	switch message.Action {
+	case "ready":
+		value, readyErr := s.Rotation.Ready(ctx)
+		err = readyErr
+		if err == nil {
+			result.Ready = &value
+		}
+	case "state":
+		value, stateErr := s.Rotation.State(ctx)
+		err = stateErr
+		if err == nil {
+			result.State = &value
+		}
+	case "stage":
+		result.ID, err = s.Rotation.Stage(ctx, message.Chain, message.Key)
+	case "commit":
+		err = s.Rotation.Commit(ctx, message.ID)
+	case "reconcile":
+		value, reconcileErr := s.Rotation.Reconcile(ctx, message.ID)
+		err = reconcileErr
+		if value.ID != "" {
+			result.State = &value
+		}
+	}
+	if err != nil {
+		result.Code = "operation_failed"
+	}
+	return result
+}
diff --git a/backend/internal/nginxactivation/ipc_linux_test.go b/backend/internal/nginxactivation/ipc_linux_test.go
new file mode 100644
index 0000000..c238ead
--- /dev/null
+++ b/backend/internal/nginxactivation/ipc_linux_test.go
@@ -0,0 +1,167 @@
+package nginxactivation
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"net"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func startLocalService(t *testing.T, rotation Rotation, allowed uint32) (Client, context.CancelFunc, <-chan error) {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "activation.sock")
+	listener, err := net.ListenUnix("unix", &net.UnixAddr{Name: path, Net: "unix"})
+	if err != nil { t.Fatal(err) }
+	listener.SetUnlinkOnClose(false)
+	if err := os.Chmod(path, 0o600); err != nil { t.Fatal(err) }
+	ctx, cancel := context.WithCancel(context.Background())
+	done := make(chan error, 1)
+	service := LocalService{Rotation: rotation, AllowedUID: allowed}
+	go func() { done <- service.Serve(ctx, listener) }()
+	t.Cleanup(cancel)
+	return Client{SocketPath: path, ServiceUID: uint32(os.Geteuid())}, cancel, done
+}
+
+func stopLocalService(t *testing.T, cancel context.CancelFunc, done <-chan error) {
+	t.Helper()
+	cancel()
+	select {
+	case err := <-done:
+		if err != nil { t.Fatal(err) }
+	case <-time.After(5 * time.Second):
+		t.Fatal("本地激活服务未及时退出")
+	}
+}
+
+func TestLocalServiceRoundTrip(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid()))
+	defer stopLocalService(t, cancel, done)
+	ctx := context.Background()
+	if ready, err := client.Ready(ctx); err != nil || ready.Hostname != testHostname {
+		t.Fatal("就绪查询失败", ready, err)
+	}
+	id, err := client.Stage(ctx, f.candidate.chain, f.candidate.key)
+	if err != nil { t.Fatal(err) }
+	state, err := client.State(ctx)
+	if err != nil || state.ID != id || state.Status != "staged" {
+		t.Fatalf("事务查询失败：%+v, %v", state, err)
+	}
+	f.upstream.active.Store(&f.candidate.pair)
+	if err := client.Commit(ctx, id); err != nil { t.Fatal(err) }
+	state, err = client.State(ctx)
+	if err != nil || state.Status != "committed" { t.Fatal(state, err) }
+	if state, err := client.Reconcile(ctx, id); err != nil || state.Status != "committed" {
+		t.Fatal(state, err)
+	}
+	if err := client.Commit(ctx, id); !errors.Is(err, ErrLocalOperation) {
+		t.Fatal("重复提交应要求查询已知终态", err)
+	}
+}
+
+func TestLocalServiceRejectsUnauthorizedPeer(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid())+1)
+	defer stopLocalService(t, cancel, done)
+	ctx, stop := context.WithTimeout(context.Background(), time.Second)
+	defer stop()
+	if _, err := client.Stage(ctx, f.candidate.chain, f.candidate.key); err == nil {
+		t.Fatal("未授权 UID 不应调用激活器")
+	}
+	if state, err := f.rotation.State(context.Background()); err != nil || state.Status != "idle" {
+		t.Fatal("未授权调用改变了事务", state, err)
+	}
+}
+
+func TestLocalServiceRejectsUnsafeMessages(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid()))
+	defer stopLocalService(t, cancel, done)
+	for _, message := range []request{
+		{Version: 1, Action: "exec"},
+		{Version: 2, Action: "state"},
+		{Version: 1, Action: "commit", ID: "../../config"},
+		{Version: 1, Action: "state", Key: []byte("secret")},
+		{Version: 1, Action: "stage", Chain: []byte("pem")},
+	} {
+		connection, err := net.Dial("unix", client.SocketPath)
+		if err != nil { t.Fatal(err) }
+		_ = connection.SetDeadline(time.Now().Add(time.Second))
+		if err := writeFrame(connection, message); err != nil { t.Fatal(err) }
+		var result response
+		err = readFrame(connection, &result)
+		_ = connection.Close()
+		if err != nil || result.Code != "invalid_request" {
+			t.Fatal("无效请求没有被拒绝", result, err)
+		}
+	}
+	connection, err := net.Dial("unix", client.SocketPath)
+	if err != nil { t.Fatal(err) }
+	defer connection.Close()
+	_ = connection.SetDeadline(time.Now().Add(time.Second))
+	var header [4]byte
+	binary.BigEndian.PutUint32(header[:], maxFrameSize+1)
+	if _, err := connection.Write(header[:]); err != nil { t.Fatal(err) }
+	var result response
+	if err := readFrame(connection, &result); err != nil || result.Code != "invalid_request" {
+		t.Fatal("超限帧没有立即拒绝", result, err)
+	}
+	state, err := f.rotation.State(context.Background())
+	if err != nil || state.Status != "idle" { t.Fatal(state, err) }
+}
+
+func TestLocalServiceLostStageResponseCanReconcile(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid()))
+	defer stopLocalService(t, cancel, done)
+	connection, err := net.Dial("unix", client.SocketPath)
+	if err != nil { t.Fatal(err) }
+	if err := writeFrame(connection, request{Version: 1, Action: "stage", Chain: f.candidate.chain, Key: f.candidate.key}); err != nil {
+		t.Fatal(err)
+	}
+	_ = connection.Close()
+	ctx, stop := context.WithTimeout(context.Background(), 3*time.Second)
+	defer stop()
+	var state State
+	for {
+		state, err = client.State(ctx)
+		if err == nil && state.Status == "staged" { break }
+		if ctx.Err() != nil { t.Fatal("丢失响应后未找到暂存事务", state, err) }
+		time.Sleep(10*time.Millisecond)
+	}
+	state, err = client.Reconcile(ctx, state.ID)
+	if err != nil || state.Status != "rolled_back" { t.Fatal(state, err) }
+}
+
+func TestLocalServiceShutdownClosesStalledClients(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid()))
+	connection, err := net.Dial("unix", client.SocketPath)
+	if err != nil { t.Fatal(err) }
+	defer connection.Close()
+	if _, err := connection.Write([]byte{0}); err != nil { t.Fatal(err) }
+	stopLocalService(t, cancel, done)
+	if _, err := os.Lstat(client.SocketPath); err != nil {
+		t.Fatal("服务停止不应删除托管 socket", err)
+	}
+}
+
+func TestLocalClientRejectsUntrustedSocket(t *testing.T) {
+	f := newRotationFixture(t)
+	client, cancel, done := startLocalService(t, f.rotation, uint32(os.Geteuid()))
+	defer stopLocalService(t, cancel, done)
+	wrong := client
+	wrong.ServiceUID++
+	if _, err := wrong.State(context.Background()); err == nil { t.Fatal("不应信任错误所有者") }
+	link := filepath.Join(filepath.Dir(client.SocketPath), "link.sock")
+	if err := os.Symlink(client.SocketPath, link); err != nil { t.Fatal(err) }
+	wrong = client
+	wrong.SocketPath = link
+	if _, err := wrong.State(context.Background()); err == nil { t.Fatal("不应连接符号链接") }
+	if err := os.Chmod(client.SocketPath, 0o666); err != nil { t.Fatal(err) }
+	if _, err := client.State(context.Background()); err == nil { t.Fatal("不应连接公开可写 socket") }
+}
diff --git a/backend/internal/nginxactivation/policy_linux.go b/backend/internal/nginxactivation/policy_linux.go
new file mode 100644
index 0000000..069cfd4
--- /dev/null
+++ b/backend/internal/nginxactivation/policy_linux.go
@@ -0,0 +1,131 @@
+package nginxactivation
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// Policy 必须由 root 独立维护，不能复用 Scert 可写的应用配置。
+type Policy struct {
+	Version int `json:"version"`
+	AllowedUID *uint32 `json:"allowed_uid"`
+	SocketPath string `json:"socket_path"`
+	Directory string `json:"directory"`
+	Hostname string `json:"hostname"`
+	ProxyAddress string `json:"proxy_address"`
+	UpstreamAddress string `json:"upstream_address"`
+	NginxBinary string `json:"nginx_binary"`
+	NginxConfig string `json:"nginx_config"`
+	NginxPrefix string `json:"nginx_prefix"`
+}
+
+func LoadPolicy(path string) (Policy, error) {
+	return loadPolicy(path, 0)
+}
+
+func loadPolicy(path string, owner uint32) (Policy, error) {
+	var policy Policy
+	data, err := readTrustedPolicy(path, owner)
+	if err != nil {
+		return policy, err
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&policy); err != nil {
+		return policy, err
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		return policy, errors.New("激活策略包含多余内容")
+	}
+	if policy.Version != 1 || policy.AllowedUID == nil || *policy.AllowedUID == 0 {
+		return policy, errors.New("激活策略版本或非特权调用者 UID 无效")
+	}
+	if !filepath.IsAbs(policy.SocketPath) || filepath.Clean(policy.SocketPath) != policy.SocketPath || policy.SocketPath == "/" || len(policy.SocketPath) > 107 {
+		return policy, errors.New("激活 socket 路径无效")
+	}
+	if err := validateDirectory(policy.Directory); err != nil {
+		return policy, err
+	}
+	rotation := policy.Rotation()
+	if err := errors.Join(rotation.Proxy.validate(), rotation.Upstream.validate()); err != nil {
+		return policy, err
+	}
+	if policy.ProxyAddress == policy.UpstreamAddress {
+		return policy, errors.New("代理和上游不能使用同一地址")
+	}
+	if err := validateOwnedFile(policy.NginxBinary, owner, true); err != nil {
+		return policy, err
+	}
+	if err := validateOwnedFile(policy.NginxConfig, owner, false); err != nil {
+		return policy, err
+	}
+	if !filepath.IsAbs(policy.NginxPrefix) || filepath.Clean(policy.NginxPrefix) != policy.NginxPrefix {
+		return policy, errors.New("Nginx 前缀必须是规范绝对目录")
+	}
+	if err := validateTrustedParents(policy.NginxPrefix, owner); err != nil {
+		return policy, err
+	}
+	return policy, nil
+}
+
+func (p Policy) Rotation() Rotation {
+	return Rotation{
+		Directory: p.Directory,
+		Proxy: Endpoint{Address: p.ProxyAddress, Hostname: p.Hostname},
+		Upstream: Endpoint{Address: p.UpstreamAddress, Hostname: p.Hostname},
+		Reloader: CommandReloader{Binary: p.NginxBinary, Config: p.NginxConfig, Prefix: p.NginxPrefix},
+	}
+}
+
+func validateOwnedFile(path string, owner uint32, executable bool) error {
+	if !filepath.IsAbs(path) || filepath.Clean(path) != path {
+		return errors.New("激活策略文件必须使用规范绝对路径")
+	}
+	if err := validateTrustedParents(filepath.Dir(path), owner); err != nil {
+		return err
+	}
+	info, err := os.Lstat(path)
+	if err != nil {
+		return err
+	}
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok || !info.Mode().IsRegular() || stat.Uid != owner || stat.Nlink != 1 || info.Mode().Perm()&0o022 != 0 {
+		return errors.New("激活策略文件类型、所有者或写权限不可信")
+	}
+	if executable && (info.Mode().Perm()&0o100 == 0 || info.Mode()&(os.ModeSetuid|os.ModeSetgid) != 0) {
+		return errors.New("Nginx 可执行文件权限无效")
+	}
+	return nil
+}
+
+func readTrustedPolicy(path string, owner uint32) ([]byte, error) {
+	if err := validateOwnedFile(path, owner, false); err != nil {
+		return nil, err
+	}
+	file, err := os.OpenFile(path, os.O_RDONLY|unix.O_NOFOLLOW|unix.O_NONBLOCK, 0)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	info, err := file.Stat()
+	if err != nil {
+		return nil, err
+	}
+	stat, ok := info.Sys().(*syscall.Stat_t)
+	if !ok || !info.Mode().IsRegular() || stat.Uid != owner || stat.Nlink != 1 || info.Mode().Perm()&0o022 != 0 || info.Size() > 16<<10 {
+		return nil, errors.New("激活策略文件不可信或超过限制")
+	}
+	data, err := io.ReadAll(io.LimitReader(file, (16<<10)+1))
+	if err != nil || len(data) > 16<<10 {
+		return nil, errors.New("读取激活策略失败或超过限制")
+	}
+	return data, nil
+}
diff --git a/backend/internal/nginxactivation/protocol.go b/backend/internal/nginxactivation/protocol.go
new file mode 100644
index 0000000..1d05135
--- /dev/null
+++ b/backend/internal/nginxactivation/protocol.go
@@ -0,0 +1,84 @@
+package nginxactivation
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"io"
+)
+
+const protocolVersion = 1
+const maxFrameSize = 2 << 20
+
+type request struct {
+	Version int    `json:"version"`
+	Action  string `json:"action"`
+	ID      string `json:"id,omitempty"`
+	Chain   []byte `json:"chain,omitempty"`
+	Key     []byte `json:"key,omitempty"`
+}
+
+type response struct {
+	Version int         `json:"version"`
+	Code    string      `json:"code"`
+	ID      string      `json:"id,omitempty"`
+	State   *State      `json:"state,omitempty"`
+	Ready   *ReadyState `json:"ready,omitempty"`
+}
+
+// 固定长度前缀避免依赖连接 EOF；先校验上限再分配请求缓冲。
+func readFrame(reader io.Reader, value any) error {
+	var header [4]byte
+	if _, err := io.ReadFull(reader, header[:]); err != nil {
+		return err
+	}
+	length := binary.BigEndian.Uint32(header[:])
+	if length == 0 || length > maxFrameSize {
+		return errors.New("本地激活消息大小无效")
+	}
+	data := make([]byte, int(length))
+	if _, err := io.ReadFull(reader, data); err != nil {
+		return err
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(value); err != nil {
+		return err
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		return errors.New("本地激活消息包含多余内容")
+	}
+	return nil
+}
+
+func writeFrame(writer io.Writer, value any) error {
+	data, err := json.Marshal(value)
+	if err != nil {
+		return err
+	}
+	if len(data) == 0 || len(data) > maxFrameSize {
+		return errors.New("本地激活消息超过限制")
+	}
+	var header [4]byte
+	binary.BigEndian.PutUint32(header[:], uint32(len(data)))
+	if err := writeAll(writer, header[:]); err != nil {
+		return err
+	}
+	return writeAll(writer, data)
+}
+
+func writeAll(writer io.Writer, data []byte) error {
+	for len(data) > 0 {
+		n, err := writer.Write(data)
+		if err != nil {
+			return err
+		}
+		if n <= 0 || n > len(data) {
+			return io.ErrShortWrite
+		}
+		data = data[n:]
+	}
+	return nil
+}
diff --git a/backend/internal/nginxactivation/protocol_test.go b/backend/internal/nginxactivation/protocol_test.go
new file mode 100644
index 0000000..e2cc9eb
--- /dev/null
+++ b/backend/internal/nginxactivation/protocol_test.go
@@ -0,0 +1,71 @@
+package nginxactivation
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"io"
+	"testing"
+)
+
+func framedBytes(data []byte) []byte {
+	framed := make([]byte, 4, len(data)+4)
+	binary.BigEndian.PutUint32(framed, uint32(len(data)))
+	return append(framed, data...)
+}
+
+func TestLocalProtocolBoundsAndSchema(t *testing.T) {
+	oversized := make([]byte, 4)
+	binary.BigEndian.PutUint32(oversized, maxFrameSize+1)
+	for _, data := range [][]byte{
+		{}, {0, 0}, {0, 0, 0, 0}, oversized,
+		{0, 0, 0, 10, '{'},
+		framedBytes([]byte(`{"version":1,"action":"state","command":"nginx"}`)),
+		framedBytes([]byte(`{"version":1,"action":"state"}{}`)),
+		framedBytes([]byte(`[]`)),
+	} {
+		var message request
+		if err := readFrame(bytes.NewReader(data), &message); err == nil {
+			t.Fatalf("不应接受消息 %q", data)
+		}
+	}
+	want := request{Version: 1, Action: "stage", Chain: []byte("certificate"), Key: []byte("private")}
+	var stream bytes.Buffer
+	if err := writeFrame(&stream, want); err != nil {
+		t.Fatal(err)
+	}
+	var got request
+	if err := readFrame(&stream, &got); err != nil || got.Action != want.Action || !bytes.Equal(got.Key, want.Key) || !bytes.Equal(got.Chain, want.Chain) {
+		t.Fatalf("消息往返不一致：%+v, %v", got, err)
+	}
+	if err := writeFrame(io.Discard, request{Chain: make([]byte, maxFrameSize)}); err == nil {
+		t.Fatal("不应编码超过上限的帧")
+	}
+}
+
+type partialWriter struct { bytes.Buffer }
+
+func (w *partialWriter) Write(data []byte) (int, error) {
+	if len(data) > 2 {
+		data = data[:2]
+	}
+	return w.Buffer.Write(data)
+}
+
+type stalledWriter struct{}
+
+func (stalledWriter) Write([]byte) (int, error) { return 0, nil }
+
+func TestLocalProtocolHandlesShortWrites(t *testing.T) {
+	writer := &partialWriter{}
+	if err := writeFrame(writer, response{Version: 1, Code: "ok"}); err != nil {
+		t.Fatal(err)
+	}
+	var reply response
+	if err := readFrame(&writer.Buffer, &reply); err != nil || reply.Code != "ok" {
+		t.Fatal("短写导致响应丢失", err)
+	}
+	if err := writeFrame(stalledWriter{}, reply); !errors.Is(err, io.ErrShortWrite) {
+		t.Fatal("无进展写入应退出", err)
+	}
+}
diff --git a/backend/internal/nginxactivation/reconcile_linux.go b/backend/internal/nginxactivation/reconcile_linux.go
new file mode 100644
index 0000000..b8c9a9a
--- /dev/null
+++ b/backend/internal/nginxactivation/reconcile_linux.go
@@ -0,0 +1,130 @@
+package nginxactivation
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"os"
+)
+
+func leafHash(der []byte) string {
+	hash := sha256.Sum256(der)
+	return hex.EncodeToString(hash[:])
+}
+
+func transactionState(current transaction) State {
+	return State{ID: current.ID, Status: current.Status, PreviousHash: leafHash(current.PreviousLeaf), CandidateHash: leafHash(current.CandidateLeaf)}
+}
+
+func (r Rotation) State(ctx context.Context) (State, error) {
+	root, lock, err := r.open(ctx)
+	if err != nil {
+		return State{}, err
+	}
+	defer root.Close()
+	defer lock.Close()
+	current, err := readTransaction(root)
+	if errors.Is(err, os.ErrNotExist) {
+		return State{Status: "idle"}, nil
+	}
+	if err != nil {
+		return State{}, err
+	}
+	return transactionState(current), nil
+}
+
+// Ready 在申请前核对固定策略、双层入口、专用材料和 Nginx 配置。
+func (r Rotation) Ready(ctx context.Context) (ReadyState, error) {
+	root, lock, err := r.open(ctx)
+	if err != nil {
+		return ReadyState{}, err
+	}
+	defer root.Close()
+	defer lock.Close()
+	current, err := readTransaction(root)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return ReadyState{}, err
+	}
+	if err == nil && (current.Status == "pending" || current.Status == "staged") {
+		return ReadyState{}, errors.New("管理证书仍有未完成事务")
+	}
+	leaf, err := r.Proxy.Check(ctx, nil)
+	if err != nil {
+		return ReadyState{}, err
+	}
+	if _, err := r.Upstream.Check(ctx, leaf); err != nil {
+		return ReadyState{}, err
+	}
+	include, err := readRegular(root, includeName, 4096)
+	if err != nil {
+		return ReadyState{}, err
+	}
+	if err := verifyIncludeMaterial(root, include, leaf); err != nil {
+		return ReadyState{}, err
+	}
+	if err := r.Reloader.Check(ctx); err != nil {
+		return ReadyState{}, err
+	}
+	if err := requireInclude(root, include); err != nil {
+		return ReadyState{}, err
+	}
+	return ReadyState{Hostname: r.Proxy.Hostname, ProxyAddress: r.Proxy.Address, UpstreamAddress: r.Upstream.Address, LeafHash: leafHash(leaf)}, nil
+}
+
+// Reconcile 仅根据严格验证的实际上游完成未决事务，不推断配置保存是否成功。
+// 上游不可用、外部改动或证书不属于事务时保留记录，交由协调者处理后重试。
+func (r Rotation) Reconcile(ctx context.Context, id string) (State, error) {
+	root, lock, err := r.open(ctx)
+	if err != nil {
+		return State{}, err
+	}
+	defer root.Close()
+	defer lock.Close()
+	current, err := readTransaction(root)
+	if err != nil {
+		return State{}, err
+	}
+	if id == "" || id != current.ID {
+		return State{}, errors.New("恢复事务编号不匹配")
+	}
+	state := transactionState(current)
+	if current.Status == "committed" || current.Status == "rolled_back" {
+		return state, nil
+	}
+	upstream, err := r.Upstream.Check(ctx, nil)
+	if err != nil {
+		return state, err
+	}
+	if bytes.Equal(upstream, current.PreviousLeaf) {
+		if err := r.rollback(ctx, root, current); err != nil {
+			return state, err
+		}
+		current.Status = "rolled_back"
+		return transactionState(current), nil
+	}
+	if !bytes.Equal(upstream, current.CandidateLeaf) {
+		return state, errors.New("上游证书不属于未决事务，拒绝自动恢复")
+	}
+	if err := requireInclude(root, current.CandidateInclude); err != nil {
+		return state, err
+	}
+	if err := verifyIncludeMaterial(root, current.CandidateInclude, current.CandidateLeaf); err != nil {
+		return state, err
+	}
+	if err := r.Proxy.Wait(ctx, current.CandidateLeaf); err != nil {
+		return state, err
+	}
+	if _, err := r.Upstream.Check(ctx, current.CandidateLeaf); err != nil {
+		return state, err
+	}
+	if err := requireInclude(root, current.CandidateInclude); err != nil {
+		return state, err
+	}
+	current.Status = "committed"
+	if err := saveTransaction(root, current); err != nil {
+		return state, err
+	}
+	return transactionState(current), nil
+}
diff --git a/backend/internal/nginxactivation/reconcile_linux_test.go b/backend/internal/nginxactivation/reconcile_linux_test.go
new file mode 100644
index 0000000..25c9995
--- /dev/null
+++ b/backend/internal/nginxactivation/reconcile_linux_test.go
@@ -0,0 +1,81 @@
+package nginxactivation
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestRotationReadyAndState(t *testing.T) {
+	f := newRotationFixture(t)
+	ctx := context.Background()
+	state, err := f.rotation.State(ctx)
+	if err != nil || state.Status != "idle" {
+		t.Fatalf("空事务状态错误：%+v, %v", state, err)
+	}
+	ready, err := f.rotation.Ready(ctx)
+	if err != nil || ready.LeafHash != leafHash(f.old.pair.Certificate[0]) || ready.Hostname != testHostname || ready.UpstreamAddress != f.upstream.Address {
+		t.Fatalf("就绪状态错误：%+v, %v", ready, err)
+	}
+	if _, err := f.rotation.Stage(ctx, f.candidate.chain, f.candidate.key); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.rotation.Ready(ctx); err == nil {
+		t.Fatal("未决事务不能通过申请前检查")
+	}
+	state, err = f.rotation.State(ctx)
+	if err != nil || state.Status != "staged" || state.CandidateHash != leafHash(f.candidate.pair.Certificate[0]) || state.PreviousHash != ready.LeafHash {
+		t.Fatalf("候选事务状态错误：%+v, %v", state, err)
+	}
+}
+
+func TestRotationReconcileUsesActualUpstream(t *testing.T) {
+	for _, scenario := range []string{"old", "candidate", "pending-candidate", "unrelated", "unavailable", "external-include", "wrong-id"} {
+		t.Run(scenario, func(t *testing.T) {
+			f := newRotationFixture(t)
+			ctx := context.Background()
+			id, err := f.rotation.Stage(ctx, f.candidate.chain, f.candidate.key)
+			if err != nil {
+				t.Fatal(err)
+			}
+			expected := "committed"
+			f.upstream.active.Store(&f.candidate.pair)
+			switch scenario {
+			case "old":
+				f.upstream.active.Store(&f.old.pair)
+				expected = "rolled_back"
+			case "pending-candidate":
+				current := f.assertStatus(t, "staged")
+				current.Status = "pending"
+				root, err := os.OpenRoot(f.rotation.Directory)
+				if err != nil { t.Fatal(err) }
+				defer root.Close()
+				if err := saveTransaction(root, current); err != nil { t.Fatal(err) }
+			case "unrelated":
+				other := f.authority.issue(t, testHostname, time.Now().Add(-time.Hour), time.Now().Add(72*time.Hour))
+				f.upstream.active.Store(&other.pair)
+			case "unavailable":
+				f.upstream.server.Close()
+			case "external-include":
+				writeTestFile(t, filepath.Join(f.rotation.Directory, includeName), []byte("# 外部修改\n"))
+			case "wrong-id":
+				id = "00000000000000000000000000000000"
+			}
+			state, err := f.rotation.Reconcile(ctx, id)
+			if scenario == "unrelated" || scenario == "unavailable" || scenario == "external-include" || scenario == "wrong-id" {
+				if err == nil { t.Fatal("无法确认的状态不应完成恢复") }
+				f.assertStatus(t, "staged")
+				return
+			}
+			if err != nil || state.Status != expected {
+				t.Fatalf("恢复结果错误：%+v, %v", state, err)
+			}
+			f.assertStatus(t, expected)
+			if _, err := f.rotation.Reconcile(ctx, id); err != nil {
+				t.Fatal("重复恢复应返回终态", err)
+			}
+		})
+	}
+}
diff --git a/backend/internal/nginxactivation/status.go b/backend/internal/nginxactivation/status.go
new file mode 100644
index 0000000..a1c504c
--- /dev/null
+++ b/backend/internal/nginxactivation/status.go
@@ -0,0 +1,16 @@
+package nginxactivation
+
+// State 不包含文件路径、私钥或完整配置，可通过受保护的本地协议返回。
+type State struct {
+	ID            string `json:"id,omitempty"`
+	Status        string `json:"status"`
+	PreviousHash  string `json:"previous_hash,omitempty"`
+	CandidateHash string `json:"candidate_hash,omitempty"`
+}
+
+type ReadyState struct {
+	Hostname     string `json:"hostname"`
+	ProxyAddress string `json:"proxy_address"`
+	UpstreamAddress string `json:"upstream_address"`
+	LeafHash     string `json:"leaf_hash"`
+}