Add client registry and CLIENT_INFO UART command on master.

Track ESP-NOW slaves in a shared registry and respond to CLIENT_INFO
with protobuf ClientInfoResponse; ESP-NOW path upserts registry entries.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/client_registry.c

@@ -0,0 +1,104 @@
+#include "client_registry.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/idf_additions.h"
+#include <string.h>
+
+typedef struct {
+  client_info_t info;
+  bool active;
+} client_slot_t;
+
+static client_slot_t s_clients[CLIENT_REGISTRY_MAX];
+
+static uint32_t now_ms(void) {
+  return (uint32_t)(xTaskGetTickCount() * portTICK_PERIOD_MS);
+}
+
+static bool mac_equal(const uint8_t *a, const uint8_t *b) {
+  return memcmp(a, b, CLIENT_MAC_LEN) == 0;
+}
+
+void client_registry_init(void) { memset(s_clients, 0, sizeof(s_clients)); }
+
+const client_info_t *
+client_registry_find_by_mac(const uint8_t mac[CLIENT_MAC_LEN]) {
+  if (mac == NULL) {
+    return NULL;
+  }
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && mac_equal(s_clients[i].info.mac, mac)) {
+      return &s_clients[i].info;
+    }
+  }
+  return NULL;
+}
+
+esp_err_t client_registry_upsert(const uint8_t mac[CLIENT_MAC_LEN], uint32_t id,
+                                 uint32_t version, bool available, bool used,
+                                 bool *out_is_new) {
+  if (mac == NULL) {
+    return ESP_ERR_INVALID_ARG;
+  }
+
+  uint32_t ts = now_ms();
+  client_slot_t *slot = NULL;
+  bool is_new = false;
+
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && mac_equal(s_clients[i].info.mac, mac)) {
+      slot = &s_clients[i];
+      break;
+    }
+  }
+
+  if (slot == NULL) {
+    for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+      if (!s_clients[i].active) {
+        slot = &s_clients[i];
+        slot->active = true;
+        memcpy(slot->info.mac, mac, CLIENT_MAC_LEN);
+        is_new = true;
+        break;
+      }
+    }
+    if (slot == NULL) {
+      return ESP_ERR_NO_MEM;
+    }
+  }
+
+  slot->info.id = id;
+  slot->info.version = version;
+  slot->info.available = available;
+  slot->info.used = used;
+  slot->info.last_ping = ts;
+  slot->info.last_success_ping = ts;
+
+  if (out_is_new != NULL) {
+    *out_is_new = is_new;
+  }
+  return ESP_OK;
+}
+
+size_t client_registry_count(void) {
+  size_t n = 0;
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active) {
+      n++;
+    }
+  }
+  return n;
+}
+
+const client_info_t *client_registry_at(size_t index) {
+  size_t n = 0;
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (!s_clients[i].active) {
+      continue;
+    }
+    if (n == index) {
+      return &s_clients[i].info;
+    }
+    n++;
+  }
+  return NULL;
+}