Preserve the unsigned range of router RTT jitter

src/routing_layer/etcp_router.c

@@ -1192,7 +1192,8 @@ static void router_handle_ack(struct UTUN_INSTANCE* inst, struct ETCP_ROUTER_CON
         uint16_t new_rtt = get_current_timestamp() - ack_ts;
         int d_rtt = (int)new_rtt - (int)rconn->rtt;
         if (d_rtt < 0) d_rtt = -d_rtt;
-        rconn->rtt_jitter += (int32_t)(((int64_t)d_rtt * 65536 - rconn->rtt_jitter) / 32);
+        int64_t jitter = rconn->rtt_jitter;
+        rconn->rtt_jitter = (uint32_t)(jitter + ((int64_t)d_rtt * 65536 - jitter) / 32);
         rconn->rtt = new_rtt;
     }
     rconn->tx_acked = seq;

src/routing_layer/etcp_router.h

@@ -109,7 +109,7 @@ struct ETCP_ROUTER_CONN {
     uint8_t  svc_id;              // = data[16]
     uint16_t last_dgram_ts;       // последний timestamp датаграммы (rx или tx, timebase 0.1ms)
     uint16_t rtt;                 // измеренный RTT (0.1ms)
-    int32_t  rtt_jitter;          // EMA jitter, fixed-point *65536 (как в ETCP)
+    uint32_t rtt_jitter;          // EWMA |ΔRTT|, беззнаковый fixed-point *65536; монитор показывает удвоенный EWMA
     uint16_t max_inflight;        // настраиваемый рабочий максимум (default=ROUTER_MAX_INFLIGHT)
     uint16_t inflight_limit;      // текущий эффективный лимит (=max_inflight или MINRTT_PROBE_MAX_INFLIGHT)
     uint16_t minrtt;              // скользящее среднее minRTT (0.1ms), default=100 (10ms)

tests/test_etcp_router_unit.c

@@ -642,6 +642,28 @@ static int test_delivery_stats(void) {
     TEARDOWN(); PASS(); return 0;
 }
 
+/* Высокий RTT не должен переполнять fixed-point EWMA jitter в отрицательное значение. */
+static int test_jitter_range(void) {
+    TEST("ACK jitter keeps the full unsigned 16.16 range");
+    struct UASYNC* ua; struct UTUN_INSTANCE inst; etcp_recv_fn recv_cb;
+    SETUP(); debug_set_category_level(DEBUG_CATEGORY_ETCPROUTE, DEBUG_LEVEL_INFO);
+    establish(recv_cb, &inst, TEST_REMOTE_NODE, TEST_SVC_ID, TEST_REMOTE_NODE);
+    struct ETCP_ROUTER_CONN* c = etcp_router_conn_get(&inst, TOPO_GROUP_UTUN, TEST_REMOTE_NODE, TEST_SVC_ID);
+    c->tx_seq = c->tx_sent = 1; c->rtt = 0; c->rtt_jitter = INT32_MAX;
+    struct SVC_ROUTE_HDR ack = {.cmd = ETCP_ID_SVC_ROUTE, .group_id = TOPO_GROUP_UTUN,
+        .src_node_id = TEST_REMOTE_NODE, .dst_node_id = inst.node_id, .svc_id = TEST_SVC_ID, .seq = 1,
+        .reset_id = c->peer_reset_id, .peer_reset_id = c->reset_id, .timestamp = (uint16_t)(get_current_timestamp() - 60000)};
+    if (!ack.timestamp) ack.timestamp = 1;
+    struct ll_entry* e = ll_alloc_lldgram(sizeof(ack)); TESTASSERT(e);
+    memcpy(e->dgram, &ack, sizeof(ack)); e->len = sizeof(ack); recv_cb(&fake_conn, e);
+    uint64_t expected = INT32_MAX + (((int64_t)c->rtt * 65536 - INT32_MAX) / 32);
+    uint64_t measured = (uint64_t)c->rtt_jitter;
+    DEBUG_INFO(DEBUG_CATEGORY_ETCPROUTE, "[regression] RTT=%u jitter=%llu expected=%llu", c->rtt,
+                (unsigned long long)measured, (unsigned long long)expected);
+    TEARDOWN();
+    TESTASSERT(measured == expected && measured > INT32_MAX); PASS(); return 0;
+}
+
 static int test_ack_timer(void) {
     TEST("ACK timer scheduled on data receive");
     struct UASYNC* ua; struct UTUN_INSTANCE inst; etcp_recv_fn recv_cb;
@@ -1574,6 +1596,7 @@ int main(void) {
     test_data_integrity();
     test_ack_receive();
     test_delivery_stats();
+    test_jitter_range();
     test_ack_timer();
     test_send_q();
     test_loopback();