[mdns] Fix RP2040 mDNS not restarting after WiFi reconnect (#14737)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/mdns/mdns_component.h

@@ -129,6 +129,10 @@ class MDNSComponent final : public Component {
 #endif
 #ifdef USE_MDNS_STORE_SERVICES
   StaticVector<MDNSService, MDNS_SERVICE_COUNT> services_{};
+#endif
+#ifdef USE_RP2040
+  bool was_connected_{false};
+  bool initialized_{false};
 #endif
   void compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUNT> &services, char *mac_address_buf);
 };

esphome/components/mdns/mdns_rp2040.cpp

@@ -36,12 +36,32 @@ static void register_rp2040(MDNSComponent *, StaticVector<MDNSService, MDNS_SERV
 }
 
 void MDNSComponent::setup() {
-  this->setup_buffers_and_register_(register_rp2040);
-  // Schedule MDNS.update() via set_interval() instead of overriding loop().
-  // This removes the component from the per-iteration loop list entirely,
-  // eliminating virtual dispatch overhead on every main loop cycle.
-  // See MDNS_UPDATE_INTERVAL_MS comment in mdns_component.h for safety analysis.
-  this->set_interval(MDNS_UPDATE_INTERVAL_MS, []() { MDNS.update(); });
+  // RP2040's LEAmDNS library registers a LwipIntf::stateUpCB() callback to restart
+  // mDNS when the network interface reconnects. However, stateUpCB() is stubbed out
+  // in arduino-pico's LwipIntfCB.cpp because the original ESP8266 implementation used
+  // schedule_function() which doesn't exist in arduino-pico, and the callback can't
+  // safely run directly since netif status callbacks fire from IRQ context
+  // (PICO_CYW43_ARCH_THREADSAFE_BACKGROUND) while _restart() allocates UDP sockets.
+  //
+  // Workaround: defer MDNS.begin() and service registration until the network is
+  // connected (has an IP), then call notifyAPChange() on subsequent reconnects to
+  // restart mDNS probing and announcing — all from main loop context so it's
+  // thread-safe.
+  this->set_interval(MDNS_UPDATE_INTERVAL_MS, [this]() {
+    bool connected = network::is_connected();
+    if (connected && !this->was_connected_) {
+      if (!this->initialized_) {
+        this->setup_buffers_and_register_(register_rp2040);
+        this->initialized_ = true;
+      } else {
+        MDNS.notifyAPChange();
+      }
+    }
+    this->was_connected_ = connected;
+    if (this->initialized_) {
+      MDNS.update();
+    }
+  });
 }
 
 void MDNSComponent::on_shutdown() {

esphome/components/wifi/__init__.py

@@ -563,13 +563,6 @@ async def to_code(config):
         cg.add_library("ESP8266WiFi", None)
     elif CORE.is_rp2040:
         cg.add_library("WiFi", None)
-        # RP2040's mDNS library (LEAmDNS) relies on LwipIntf::stateUpCB() to restart
-        # mDNS when the network interface reconnects. However, this callback is disabled
-        # in the arduino-pico framework. As a workaround, we block component setup until
-        # WiFi is connected via can_proceed(), ensuring mDNS.begin() is called with an
-        # active connection. This define enables the loop priority sorting infrastructure
-        # used during the setup blocking phase.
-        cg.add_define("USE_LOOP_PRIORITY")
 
     if CORE.is_esp32:
         if config[CONF_ENABLE_BTM] or config[CONF_ENABLE_RRM]:

esphome/components/wifi/wifi_component.cpp

@@ -2109,20 +2109,6 @@ void WiFiComponent::retry_connect() {
   }
 }
 
-#ifdef USE_RP2040
-// RP2040's mDNS library (LEAmDNS) relies on LwipIntf::stateUpCB() to restart
-// mDNS when the network interface reconnects. However, this callback is disabled
-// in the arduino-pico framework. As a workaround, we block component setup until
-// WiFi is connected, ensuring mDNS.begin() is called with an active connection.
-
-bool WiFiComponent::can_proceed() {
-  if (!this->has_sta() || this->state_ == WIFI_COMPONENT_STATE_DISABLED || this->ap_setup_) {
-    return true;
-  }
-  return this->is_connected_();
-}
-#endif
-
 void WiFiComponent::set_reboot_timeout(uint32_t reboot_timeout) { this->reboot_timeout_ = reboot_timeout; }
 bool WiFiComponent::is_connected_() const {
   return this->state_ == WIFI_COMPONENT_STATE_STA_CONNECTED &&

esphome/components/wifi/wifi_component.h

@@ -437,10 +437,6 @@ class WiFiComponent : public Component {
 
   void retry_connect();
 
-#ifdef USE_RP2040
-  bool can_proceed() override;
-#endif
-
   void set_reboot_timeout(uint32_t reboot_timeout);
 
   bool is_connected() const { return this->connected_; }