[web_server] Address review: tighter socket auto-load, flash cost in the log, fallback compile test

esphome/components/web_server/__init__.py

@@ -53,9 +53,14 @@ def AUTO_LOAD() -> list[str]:
     # ota.web_server's dependency on web_server_base would not be satisfied in time.
     auto_load = ["json", "web_server_base"]
     # The AP mode DNS server (web_server_base/dns_server_esp32_idf) uses socket; only
-    # configs with a WiFi access point can end up in AP mode.
+    # configs with a WiFi access point can end up in AP mode. CORE.raw_config is set
+    # after package merging, so a wifi block from a package is visible here.
     wifi = CORE.raw_config.get(CONF_WIFI) if CORE.raw_config else None
-    if CORE.is_esp32 and (not isinstance(wifi, dict) or CONF_AP in wifi):
+    if (
+        CORE.is_esp32
+        and wifi is not None
+        and (not isinstance(wifi, dict) or CONF_AP in wifi)
+    ):
         auto_load.append("socket")
     return auto_load
 
@@ -384,7 +389,8 @@ def _final_validate_ap_mode(config: ConfigType) -> None:
         if CONF_LOCAL not in config:
             _LOGGER.info(
                 "WiFi is AP only: embedding the web interface in the firmware "
-                "(local: true) and serving it as a captive portal on the access point. "
+                "(local: true, roughly 13 KB of flash for version 2, 78 KB for "
+                "version 3) and serving it as a captive portal on the access point. "
                 "Set 'local: false' to load it from the internet instead."
             )
     elif wifi_is_ap_only(wifi_config) and not serve_local(config, wifi_config):

esphome/components/web_server/web_server.cpp

@@ -452,9 +452,11 @@ void WebServer::handle_not_found_(AsyncWebServerRequest *request) {
   // to the real page. A redirect rather than the page itself, because the interface resolves
   // its /events and REST paths relative to the page URL.
   if (this->dns_.is_running() && request->method() == HTTP_GET) {
-    char location[7 + network::IP_ADDRESS_BUFFER_SIZE];
+    // Captive mode requires port 80 (enforced at validation), so no port suffix is needed.
+    char location[7 + network::IP_ADDRESS_BUFFER_SIZE + 1];
     size_t pos = buf_append_str(location, sizeof(location), 0, "http://");
     wifi::global_wifi_component->wifi_soft_ap_ip().str_to(location + pos);
+    buf_append_str(location, sizeof(location), strlen(location), "/");
     request->redirect(location);
     return;
   }

tests/components/web_server/common-ap-fallback.yaml

@@ -0,0 +1,11 @@
+# STA with AP fallback plus local: true opts the fallback into captive AP mode; exercises
+# the runtime start (fallback branch in wifi loop) and end (on STA connect) paths.
+wifi:
+  ssid: MySSID
+  password: password1
+  ap:
+    ssid: "ESPHome-Test"
+    password: "Test1234!"
+
+web_server:
+  local: true

tests/components/web_server/test-ap-fallback.esp32-idf.yaml

@@ -0,0 +1,2 @@
+packages:
+  web_server: !include common-ap-fallback.yaml