fix(esp32): add connected-STA self-ping CSI traffic source (#954) (#985)

The ESP32 CSI engine only produces CSI for received OFDM frames (L-LTF/
HT-LTF). On a quiet network — or on a display-enabled build where the
#893 MGMT->MGMT+DATA promiscuous upgrade is skipped (has_display=true) —
the only CSI-eligible frames are sparse beacons (often non-OFDM DSSS),
so wifi_csi_callback can starve to yield=0pps -> DEGRADED -> motion=0
(#521, #954).

Fix (additive): pin a ~50 Hz OFDM unicast floor by pinging the STA's own
DHCP gateway. The router's ICMP echo replies are OFDM frames destined to
this station and drive the CSI engine regardless of promiscuous filter
state or ambient traffic. Mirrors Espressif's esp-csi csi_recv_router
reference. Promiscuous capture (#396/#893) is left fully intact so
multistatic/multi-node sensing still hears other stations' frames.

Reconciles PR #955 (which removed promiscuous entirely and conflicted
with the already-shipped #893 DATA-capture path) into an additive change
on current main.

Verified on ESP32-S3 (N16R8, COM8), ESP-IDF v5.4:
  Promiscuous mode enabled (MGMT-only, RuView#396)
  self-ping started -> 192.168.1.1 @50Hz (CSI OFDM source, fix #521/#954)
  CSI cb #1: len=128 rssi=-40 ch=5
  adaptive_ctrl: state=6 yield=13-19pps motion=1.00 presence>0  (SENSE_ACTIVE)
DEGRADED cleared; CSI yield stable ~15 pps over 60 s.

Co-authored-by: Meraj <merajmehrabi@gmail.com>

firmware/esp32-csi-node/main/csi_collector.c

@@ -23,6 +23,9 @@
 #include "esp_wifi.h"
 #include "esp_timer.h"
 #include "sdkconfig.h"
+#include "esp_netif.h"          /* #954: STA gateway lookup for self-ping CSI source */
+#include "ping/ping_sock.h"     /* #954: esp_ping gateway traffic generator */
+#include "lwip/ip_addr.h"       /* #954: ip_addr_t target for esp_ping */
 
 /* ADR-060: Access the global NVS config for MAC filter and channel override. */
 extern nvs_config_t g_nvs_config;
@@ -365,6 +368,67 @@ static void wifi_promiscuous_cb(void *buf, wifi_promiscuous_pkt_type_t type)
     (void)type;
 }
 
+/* ---- RuView#521/#954: connected-STA CSI traffic source (additive) ----
+ *
+ * The ESP32 CSI engine only produces CSI for received OFDM frames (L-LTF/HT-LTF).
+ * On a quiet network — or on a display-enabled build where the #893 MGMT->MGMT+DATA
+ * promiscuous upgrade is skipped (has_display=true) — the only CSI-eligible frames
+ * are sparse beacons (often non-OFDM DSSS), so wifi_csi_callback can starve to
+ * yield=0pps -> DEGRADED -> motion/presence=0 (#521, #954).
+ *
+ * This guarantees a ~50 Hz OFDM unicast floor by pinging the STA's own gateway:
+ * the router's ICMP echo replies are OFDM frames destined to this station, which
+ * drive the CSI engine regardless of promiscuous filter state or ambient traffic.
+ * It is ADDITIVE — promiscuous capture (#396/#893) is left fully intact so
+ * multistatic/multi-node sensing still hears other stations' frames. Mirrors
+ * Espressif's esp-csi csi_recv_router reference.
+ */
+static esp_ping_handle_t s_self_ping = NULL;
+static void csi_ping_cb_noop(esp_ping_handle_t hdl, void *args) { (void)hdl; (void)args; }
+
+static void csi_start_self_ping(void)
+{
+    if (s_self_ping != NULL) {
+        return;  /* already running */
+    }
+
+    esp_netif_t *sta = esp_netif_get_handle_from_ifkey("WIFI_STA_DEF");
+    esp_netif_ip_info_t ip;
+    if (sta == NULL || esp_netif_get_ip_info(sta, &ip) != ESP_OK || ip.gw.addr == 0) {
+        ESP_LOGW(TAG, "self-ping: no gateway IP yet; CSI relies on ambient frames (#954)");
+        return;
+    }
+
+    char gw_str[16];
+    esp_ip4addr_ntoa(&ip.gw, gw_str, sizeof(gw_str));
+
+    ip_addr_t target;
+    memset(&target, 0, sizeof(target));
+    ipaddr_aton(gw_str, &target);
+
+    esp_ping_config_t cfg = ESP_PING_DEFAULT_CONFIG();
+    cfg.target_addr     = target;
+    cfg.count           = ESP_PING_COUNT_INFINITE;
+    cfg.interval_ms     = 20;     /* 50 Hz -> ~50 received OFDM replies/sec */
+    cfg.data_size       = 1;
+    cfg.task_stack_size = 4096;
+
+    esp_ping_callbacks_t cbs = {
+        .cb_args         = NULL,
+        .on_ping_success = csi_ping_cb_noop,
+        .on_ping_timeout = csi_ping_cb_noop,
+        .on_ping_end     = csi_ping_cb_noop,
+    };
+
+    if (esp_ping_new_session(&cfg, &cbs, &s_self_ping) == ESP_OK && s_self_ping != NULL) {
+        esp_ping_start(s_self_ping);
+        ESP_LOGI(TAG, "self-ping started -> %s @50Hz (CSI OFDM source, fix #521/#954)", gw_str);
+    } else {
+        ESP_LOGW(TAG, "self-ping: esp_ping_new_session failed");
+        s_self_ping = NULL;
+    }
+}
+
 void csi_collector_set_node_id(uint8_t node_id)
 {
     s_node_id = node_id;
@@ -526,6 +590,11 @@ void csi_collector_init(void)
 
     ESP_LOGI(TAG, "CSI collection initialized (node_id=%u, channel=%u)",
              (unsigned)s_node_id, (unsigned)csi_channel);
+
+    /* RuView#521/#954: start the connected-STA traffic source so the CSI engine
+     * receives a guaranteed OFDM unicast floor even when promiscuous capture is
+     * starved (display builds / quiet networks). Additive to #396/#893. */
+    csi_start_self_ping();
 }
 
 /* Accessor for other modules that need the authoritative runtime node_id. */