diff --git a/docs/parliament.md b/docs/parliament.md
index e686c03..e2a4365 100644
--- a/docs/parliament.md
+++ b/docs/parliament.md
@@ -53,13 +53,18 @@ cst-agent --new-project my-app
 
 清空共享上下文、撤销主席与登录票，并停止本机服务。Realm 密钥保留。
 
+## 传输安全
+
+Peer 在 Realm 证书互鉴后做 **临时 X25519 密钥交换**，后续议会上下文同步走
+**XChaCha20-Poly1305**（Monocypher，无需 OpenSSL）。握手前的发现/证书交换仍是明文元数据。
+
 ## Docker 冒烟
 
 ```bash
 bash scripts/docker_parliament_test.sh
 ```
 
-Alpine 内构建，chair↔member 握手。
+Alpine 内构建，chair↔member 握手 + 密封通道。
 
 ## 相关标志
 
diff --git a/include/cst_peer.h b/include/cst_peer.h
index 0f7e7f1..812bbb5 100644
--- a/include/cst_peer.h
+++ b/include/cst_peer.h
@@ -8,17 +8,22 @@
 extern "C" {
 #endif
 
-/* Mutual Realm certificate challenge over TCP (cleartext for now; TLS wrap
- * is the next slice). Same Realm public key required on both sides. */
+/* Mutual Realm certificate challenge over TCP, then ephemeral X25519 +
+ * XChaCha20-Poly1305 (Monocypher) for the session. Same Realm public key
+ * required on both sides. */
 
 typedef struct {
   cst_realm_cert_t remote;
   char host[64];
   int port;
   intptr_t sock; /* open until cst_peer_close */
+  uint8_t aead_key[32];
+  uint64_t send_ctr;
+  uint64_t recv_ctr;
+  int sealed; /* 1 after key exchange */
 } cst_peer_session_t;
 
-/* Dial host:port, prove our cert, verify theirs. 0 on success.
+/* Dial host:port, prove our cert, verify theirs, establish AEAD session.
  * Leaves sock open for post-handshake sync; call cst_peer_close. */
 int cst_peer_dial(const char *host, int port, const cst_realm_cert_t *self,
                   const uint8_t self_sk[64], const uint8_t realm_pk[32],
@@ -33,8 +38,8 @@ int cst_peer_accept(intptr_t listen_sock, const cst_realm_cert_t *self,
 
 void cst_peer_close(cst_peer_session_t *s);
 
-/* After handshake: exchange parliament revision/context. Higher revision wins
- * and is written locally via the callbacks. Returns 0 on success. */
+/* After handshake: exchange parliament revision/context over the sealed
+ * channel. Higher revision wins. Returns 0 on success. */
 typedef struct {
   unsigned long revision;
   char parliament_id[64];
diff --git a/include/cst_version.h b/include/cst_version.h
index a4165ed..bc65884 100644
--- a/include/cst_version.h
+++ b/include/cst_version.h
@@ -3,7 +3,7 @@
 
 #define CST_VERSION_MAJOR 0
 #define CST_VERSION_MINOR 9
-#define CST_VERSION_PATCH 16
+#define CST_VERSION_PATCH 17
 
 #define CST_VERSION_STR_(x) #x
 #define CST_VERSION_STR(x) CST_VERSION_STR_(x)
diff --git a/src/peer_auth.c b/src/peer_auth.c
index 9fe03e8..d6bab2b 100644
--- a/src/peer_auth.c
+++ b/src/peer_auth.c
@@ -223,6 +223,160 @@ static int read_ok(os_socket_t s, int timeout_ms) {
   return ok ? 0 : -1;
 }
 
+static int send_kx_pk(os_socket_t s, const uint8_t pk[32], int timeout_ms) {
+  char hex[65];
+  hex_encode(pk, 32, hex);
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return -1;
+  cJSON_AddNumberToObject(o, "v", 1);
+  cJSON_AddStringToObject(o, "op", "kx");
+  cJSON_AddStringToObject(o, "pk", hex);
+  char *line = cJSON_PrintUnformatted(o);
+  cJSON_Delete(o);
+  if (!line)
+    return -1;
+  int rc = send_line(s, line, timeout_ms);
+  free(line);
+  return rc;
+}
+
+static int read_kx_pk(os_socket_t s, uint8_t pk[32], int timeout_ms) {
+  char *line = recv_line(s, timeout_ms);
+  if (!line)
+    return -1;
+  cJSON *o = cJSON_Parse(line);
+  free(line);
+  if (!o)
+    return -1;
+  const cJSON *op = cJSON_GetObjectItemCaseSensitive(o, "op");
+  const cJSON *p = cJSON_GetObjectItemCaseSensitive(o, "pk");
+  int ok = cJSON_IsString(op) && !strcmp(op->valuestring, "kx") &&
+           cJSON_IsString(p) && hex_decode(p->valuestring, pk, 32) == 0;
+  cJSON_Delete(o);
+  return ok ? 0 : -1;
+}
+
+static int peer_kx(os_socket_t s, int as_client, uint8_t out_key[32],
+                   int timeout_ms) {
+  uint8_t eph_sk[32], eph_pk[32], their_pk[32], shared[32];
+  if (fill_random(eph_sk, 32) != 0)
+    return -1;
+  crypto_x25519_public_key(eph_pk, eph_sk);
+  if (as_client) {
+    if (send_kx_pk(s, eph_pk, timeout_ms) != 0 ||
+        read_kx_pk(s, their_pk, timeout_ms) != 0) {
+      crypto_wipe(eph_sk, sizeof(eph_sk));
+      return -1;
+    }
+  } else {
+    if (read_kx_pk(s, their_pk, timeout_ms) != 0 ||
+        send_kx_pk(s, eph_pk, timeout_ms) != 0) {
+      crypto_wipe(eph_sk, sizeof(eph_sk));
+      return -1;
+    }
+  }
+  crypto_x25519(shared, eph_sk, their_pk);
+  crypto_wipe(eph_sk, sizeof(eph_sk));
+  crypto_blake2b_ctx ctx;
+  crypto_blake2b_init(&ctx, 32);
+  crypto_blake2b_update(&ctx, shared, 32);
+  crypto_blake2b_update(&ctx, (const uint8_t *)"cst-peer-aead-v1", 16);
+  crypto_blake2b_final(&ctx, out_key);
+  crypto_wipe(shared, sizeof(shared));
+  return 0;
+}
+
+static void ctr_nonce(uint8_t nonce[24], uint64_t ctr) {
+  memset(nonce, 0, 24);
+  for (int i = 0; i < 8; i++)
+    nonce[16 + i] = (uint8_t)((ctr >> (56 - 8 * i)) & 0xff);
+}
+
+static int send_sealed(cst_peer_session_t *sess, const void *plain, size_t n,
+                       int timeout_ms) {
+  if (!sess || !sess->sealed || n > 2 * 1024 * 1024)
+    return -1;
+  os_socket_t s = (os_socket_t)sess->sock;
+  uint8_t nonce[24];
+  ctr_nonce(nonce, sess->send_ctr++);
+  uint8_t *cipher = malloc(n ? n : 1);
+  uint8_t mac[16];
+  if (!cipher)
+    return -1;
+  crypto_aead_lock(cipher, mac, sess->aead_key, nonce, NULL, 0,
+                   (const uint8_t *)plain, n);
+  uint32_t body = 24u + (uint32_t)n + 16u;
+  uint8_t hdr[4] = {(uint8_t)(body >> 24), (uint8_t)(body >> 16),
+                    (uint8_t)(body >> 8), (uint8_t)body};
+  int rc = -1;
+  if (os_net_send_all(s, hdr, 4, timeout_ms) == 0 &&
+      os_net_send_all(s, nonce, 24, timeout_ms) == 0 &&
+      (n == 0 || os_net_send_all(s, cipher, n, timeout_ms) == 0) &&
+      os_net_send_all(s, mac, 16, timeout_ms) == 0)
+    rc = 0;
+  free(cipher);
+  return rc;
+}
+
+static int recv_exact(os_socket_t s, void *buf, size_t n, int timeout_ms) {
+  size_t got = 0;
+  while (got < n) {
+    long r = os_net_recv(s, (char *)buf + got, n - got, timeout_ms);
+    if (r <= 0)
+      return -1;
+    got += (size_t)r;
+  }
+  return 0;
+}
+
+static int recv_sealed(cst_peer_session_t *sess, uint8_t **out, size_t *out_n,
+                       int timeout_ms) {
+  *out = NULL;
+  *out_n = 0;
+  if (!sess || !sess->sealed)
+    return -1;
+  os_socket_t s = (os_socket_t)sess->sock;
+  uint8_t hdr[4];
+  if (recv_exact(s, hdr, 4, timeout_ms) != 0)
+    return -1;
+  uint32_t body = ((uint32_t)hdr[0] << 24) | ((uint32_t)hdr[1] << 16) |
+                  ((uint32_t)hdr[2] << 8) | (uint32_t)hdr[3];
+  if (body < 24 + 16 || body > 24 + 16 + 2 * 1024 * 1024)
+    return -1;
+  size_t n = body - 24 - 16;
+  uint8_t nonce[24], mac[16];
+  uint8_t *cipher = malloc(n ? n : 1);
+  uint8_t *plain = malloc(n + 1);
+  if (!cipher || !plain) {
+    free(cipher);
+    free(plain);
+    return -1;
+  }
+  if (recv_exact(s, nonce, 24, timeout_ms) != 0 ||
+      (n && recv_exact(s, cipher, n, timeout_ms) != 0) ||
+      recv_exact(s, mac, 16, timeout_ms) != 0) {
+    free(cipher);
+    free(plain);
+    return -1;
+  }
+  uint8_t expect[24];
+  ctr_nonce(expect, sess->recv_ctr);
+  if (memcmp(nonce, expect, 24) != 0 ||
+      crypto_aead_unlock(plain, mac, sess->aead_key, nonce, NULL, 0, cipher,
+                         n) != 0) {
+    free(cipher);
+    free(plain);
+    return -1;
+  }
+  sess->recv_ctr++;
+  free(cipher);
+  plain[n] = 0;
+  *out = plain;
+  *out_n = n;
+  return 0;
+}
+
 static int handshake_as_client(os_socket_t s, const cst_realm_cert_t *self,
                                const uint8_t self_sk[64],
                                const uint8_t realm_pk[32], int timeout_ms,
@@ -299,6 +453,13 @@ int cst_peer_dial(const char *host, int port, const cst_realm_cert_t *self,
   snprintf(out->host, sizeof(out->host), "%s", host);
   out->port = port;
   out->sock = (intptr_t)s;
+  if (peer_kx(s, 1, out->aead_key, timeout_ms) != 0) {
+    if (err && err_sz)
+      snprintf(err, err_sz, "peer key exchange failed");
+    cst_peer_close(out);
+    return -1;
+  }
+  out->sealed = 1;
   return 0;
 }
 
@@ -330,6 +491,13 @@ int cst_peer_accept(intptr_t listen_sock, const cst_realm_cert_t *self,
   os_net_peer(s, out->host, sizeof(out->host));
   out->port = 0;
   out->sock = (intptr_t)s;
+  if (peer_kx(s, 0, out->aead_key, timeout_ms) != 0) {
+    if (err && err_sz)
+      snprintf(err, err_sz, "peer key exchange failed");
+    cst_peer_close(out);
+    return -1;
+  }
+  out->sealed = 1;
   return 0;
 }
 
@@ -339,10 +507,13 @@ void cst_peer_close(cst_peer_session_t *s) {
   if (s->sock != 0 && s->sock != (intptr_t)OS_SOCKET_BAD)
     os_net_close((os_socket_t)s->sock);
   s->sock = (intptr_t)OS_SOCKET_BAD;
+  crypto_wipe(s->aead_key, sizeof(s->aead_key));
+  s->sealed = 0;
+  s->send_ctr = s->recv_ctr = 0;
 }
 
-static int send_sync_hdr(os_socket_t s, const cst_peer_sync_bundle_t *b,
-                         int timeout_ms) {
+static int send_sync_bundle(cst_peer_session_t *sess,
+                            const cst_peer_sync_bundle_t *b, int timeout_ms) {
   cJSON *o = cJSON_CreateObject();
   if (!o)
     return -1;
@@ -352,30 +523,25 @@ static int send_sync_hdr(os_socket_t s, const cst_peer_sync_bundle_t *b,
   cJSON_AddStringToObject(o, "parliament_id", b->parliament_id);
   cJSON_AddStringToObject(o, "project_id", b->project_id);
   cJSON_AddStringToObject(o, "chair", b->chair_instance);
-  size_t clen = b->context ? strlen(b->context) : 0;
-  cJSON_AddNumberToObject(o, "context_len", (double)clen);
-  char *line = cJSON_PrintUnformatted(o);
+  cJSON_AddStringToObject(o, "context", b->context ? b->context : "");
+  char *txt = cJSON_PrintUnformatted(o);
   cJSON_Delete(o);
-  if (!line)
+  if (!txt)
     return -1;
-  int rc = send_line(s, line, timeout_ms);
-  free(line);
-  if (rc != 0)
-    return -1;
-  if (clen > 0 &&
-      os_net_send_all(s, b->context, clen, timeout_ms) != 0)
-    return -1;
-  return 0;
+  int rc = send_sealed(sess, txt, strlen(txt), timeout_ms);
+  free(txt);
+  return rc;
 }
 
-static int read_sync_hdr(os_socket_t s, cst_peer_sync_bundle_t *b,
-                         int timeout_ms) {
+static int read_sync_bundle(cst_peer_session_t *sess, cst_peer_sync_bundle_t *b,
+                            int timeout_ms) {
   memset(b, 0, sizeof(*b));
-  char *line = recv_line(s, timeout_ms);
-  if (!line)
+  uint8_t *plain = NULL;
+  size_t n = 0;
+  if (recv_sealed(sess, &plain, &n, timeout_ms) != 0)
     return -1;
-  cJSON *o = cJSON_Parse(line);
-  free(line);
+  cJSON *o = cJSON_ParseWithLength((char *)plain, n);
+  free(plain);
   if (!o)
     return -1;
   const cJSON *op = cJSON_GetObjectItemCaseSensitive(o, "op");
@@ -397,51 +563,31 @@ static int read_sync_hdr(os_socket_t s, cst_peer_sync_bundle_t *b,
   if (cJSON_IsString(v))
     snprintf(b->chair_instance, sizeof(b->chair_instance), "%s",
              v->valuestring);
-  size_t clen = 0;
-  v = cJSON_GetObjectItemCaseSensitive(o, "context_len");
-  if (cJSON_IsNumber(v) && v->valuedouble >= 0)
-    clen = (size_t)v->valuedouble;
-  cJSON_Delete(o);
-  if (clen > 2 * 1024 * 1024)
-    return -1;
-  if (clen == 0) {
+  v = cJSON_GetObjectItemCaseSensitive(o, "context");
+  if (cJSON_IsString(v))
+    b->context = strdup(v->valuestring);
+  else
     b->context = strdup("");
-    return b->context ? 0 : -1;
-  }
-  char *ctx = malloc(clen + 1);
-  if (!ctx)
-    return -1;
-  size_t got = 0;
-  while (got < clen) {
-    long r = os_net_recv(s, ctx + got, clen - got, timeout_ms);
-    if (r <= 0) {
-      free(ctx);
-      return -1;
-    }
-    got += (size_t)r;
-  }
-  ctx[clen] = 0;
-  b->context = ctx;
-  return 0;
+  cJSON_Delete(o);
+  return b->context ? 0 : -1;
 }
 
 int cst_peer_sync(cst_peer_session_t *s, cst_peer_sync_bundle_t *local,
                   int timeout_ms, char *err, size_t err_sz) {
   if (err && err_sz)
     err[0] = 0;
-  if (!s || !local || s->sock == (intptr_t)OS_SOCKET_BAD) {
+  if (!s || !local || s->sock == (intptr_t)OS_SOCKET_BAD || !s->sealed) {
     if (err && err_sz)
       snprintf(err, err_sz, "bad peer session");
     return -1;
   }
-  os_socket_t sock = (os_socket_t)s->sock;
-  if (send_sync_hdr(sock, local, timeout_ms) != 0) {
+  if (send_sync_bundle(s, local, timeout_ms) != 0) {
     if (err && err_sz)
       snprintf(err, err_sz, "sync send failed");
     return -1;
   }
   cst_peer_sync_bundle_t remote;
-  if (read_sync_hdr(sock, &remote, timeout_ms) != 0) {
+  if (read_sync_bundle(s, &remote, timeout_ms) != 0) {
     if (err && err_sz)
       snprintf(err, err_sz, "sync recv failed");
     return -1;
diff --git a/tests/test_peer_auth.c b/tests/test_peer_auth.c
index 9df03bd..dfcae6a 100644
--- a/tests/test_peer_auth.c
+++ b/tests/test_peer_auth.c
@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <pthread.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 typedef struct {
@@ -16,6 +17,8 @@ typedef struct {
   uint8_t realm_pk[32];
   int ok;
   char remote_id[64];
+  unsigned long got_rev;
+  char got_ctx[128];
 } srv_t;
 
 static void *server_main(void *p) {
@@ -26,6 +29,18 @@ static void *server_main(void *p) {
                           5000, &sess, err, sizeof(err)) == 0;
   if (s->ok) {
     snprintf(s->remote_id, sizeof(s->remote_id), "%s", sess.remote.instance_id);
+    assert(sess.sealed);
+    cst_peer_sync_bundle_t local = {0};
+    local.revision = 1;
+    snprintf(local.parliament_id, sizeof(local.parliament_id), "parl-s");
+    snprintf(local.project_id, sizeof(local.project_id), "proj");
+    snprintf(local.chair_instance, sizeof(local.chair_instance), "peer-b");
+    local.context = strdup("server-old");
+    assert(cst_peer_sync(&sess, &local, 5000, err, sizeof(err)) == 0);
+    s->got_rev = local.revision;
+    snprintf(s->got_ctx, sizeof(s->got_ctx), "%s",
+             local.context ? local.context : "");
+    free(local.context);
     cst_peer_close(&sess);
   }
   return NULL;
@@ -57,10 +72,24 @@ int main(void) {
   assert(cst_peer_dial("127.0.0.1", port, &ca, ska, realm.pk, 5000, &sess, err,
                        sizeof(err)) == 0);
   assert(!strcmp(sess.remote.instance_id, "peer-b"));
+  assert(sess.sealed);
+  cst_peer_sync_bundle_t local = {0};
+  local.revision = 9;
+  snprintf(local.parliament_id, sizeof(local.parliament_id), "parl-c");
+  snprintf(local.project_id, sizeof(local.project_id), "proj");
+  snprintf(local.chair_instance, sizeof(local.chair_instance), "peer-a");
+  local.context = strdup("client-wins-secret");
+  assert(cst_peer_sync(&sess, &local, 5000, err, sizeof(err)) == 0);
+  /* Client already has higher rev; stays. */
+  assert(local.revision == 9);
+  assert(strstr(local.context, "client-wins-secret"));
+  free(local.context);
   cst_peer_close(&sess);
   pthread_join(th, NULL);
   assert(srv.ok);
   assert(!strcmp(srv.remote_id, "peer-a"));
+  assert(srv.got_rev == 9);
+  assert(strstr(srv.got_ctx, "client-wins-secret"));
 
   /* Foreign realm must fail. */
   cst_realm_keys_t other;