fix(wifi): skip SDK-cached credentials when SSID is already configured (closes #3)

WiFi.begin() without params connects to any SDK-cached network, including
open public hotspots, and then overwrites config.ssid with the wrong SSID.

Now Try 1 (SDK credentials) is only attempted on first boot when no SSID
is configured. Once the user has saved credentials, we go straight to
Try 2 (EEPROM config), so the correct network is always used.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

firmware/clock_ntp_ota_v1.9/wifi_manager.cpp

@@ -67,8 +67,12 @@ void ICACHE_FLASH_ATTR setupWiFi() {
   WiFi.hostname(config.hostname);
   WiFi.mode(WIFI_STA);
 
-  // Try 1: Use WiFi.begin() without params - uses SDK stored credentials
-  Serial.println("Trying SDK-stored credentials...");
+  // Try 1: Use WiFi.begin() without params - only when no SSID is configured.
+  // Skipped if user has a saved SSID: SDK-cached credentials may include open
+  // networks (e.g. public hotspots) that would be preferred over the user's
+  // network, and a successful connect would overwrite config.ssid (issue #3).
+  if (strlen(config.ssid) == 0) {
+    Serial.println("No SSID configured, trying SDK-stored credentials...");
     WiFi.begin();
 
     // SYNCHRONOUS wait for connection (max 10 seconds)
@@ -99,13 +103,14 @@ void ICACHE_FLASH_ATTR setupWiFi() {
       wifiConnState = WIFI_CONN_CONNECTED;
       return;
     }
+  }
 
   // Try 2: If we have EEPROM credentials, try those
   if (strlen(config.ssid) > 0 && strlen(config.password) > 0) {
     Serial.println("\nTrying EEPROM credentials...");
     WiFi.begin(config.ssid, config.password);
 
-    attempts = 0;
+    int attempts = 0;
     while (WiFi.status() != WL_CONNECTED && attempts < 20) {
       showWiFiConnecting(attempts);
       delay(500);

src/clock_ntp_ota_v1.9.ino

@@ -761,9 +761,13 @@ void ICACHE_FLASH_ATTR setupWiFi() {
   // STRATEGY: First try SDK-stored credentials (from WiFiManager), then EEPROM config
   // WiFiManager stores credentials in ESP flash separately from our EEPROM
 
-  // Try 1: Use WiFi.begin() without params - uses SDK stored credentials
-  Serial.println("Trying SDK-stored credentials...");
-  WiFi.begin();  // Uses credentials stored by WiFiManager/SDK
+  // Try 1: Use WiFi.begin() without params - only when no SSID is configured.
+  // Skipped if user has a saved SSID: SDK-cached credentials may include open
+  // networks (e.g. public hotspots) that would be preferred over the user's
+  // network, and a successful connect would overwrite config.ssid (issue #3).
+  if (strlen(config.ssid) == 0) {
+    Serial.println("No SSID configured, trying SDK-stored credentials...");
+    WiFi.begin();
 
     // SYNCHRONOUS wait for connection (max 10 seconds)
     Serial.print("Connecting to WiFi");
@@ -786,16 +790,13 @@ void ICACHE_FLASH_ATTR setupWiFi() {
       Serial.print("DNS: ");
       Serial.println(WiFi.dnsIP());
 
-    // Sync connected SSID to our config
       safeStringCopy(WiFi.SSID(), config.ssid, sizeof(config.ssid));
-    // Note: password stays in SDK storage, we don't have access to it
       saveConfig();
 
-    // Show IP on display
       showIP();
-
       wifiConnState = WIFI_CONN_CONNECTED;
-    return;  // Success!
+      return;
+    }
   }
 
   // Try 2: If we have EEPROM credentials, try those
@@ -803,7 +804,7 @@ void ICACHE_FLASH_ATTR setupWiFi() {
     Serial.println("\nTrying EEPROM credentials...");
     WiFi.begin(config.ssid, config.password);
 
-    attempts = 0;
+    int attempts = 0;
     while (WiFi.status() != WL_CONNECTED && attempts < 20) {
       delay(500);
       Serial.print(".");