fix(gateway): allow the native WebView origin via CORS

The packaged native app (Capacitor) serves the bundled SPA from a localhost scheme, so its Connect calls to erudit-game.ru are cross-origin. The gateway had no CORS handling, so the preflight OPTIONS returned 405 with no Access-Control-Allow-Origin and the WebView blocked every RPC — a native build could never reach the gateway and stayed stuck offline (the native online path was never exercised on-device; on-device D was airplane-mode only). Add a CORS middleware that answers the preflight and sets the response headers for the native localhost origins (https/http/capacitor://localhost); web is same-origin and untouched. Fixes the native emulator 'starts offline, can't go online' report.

gateway/internal/connectsrv/cors.go

@@ -0,0 +1,47 @@
+package connectsrv
+
+import "net/http"
+
+// nativeWebViewOrigins are the browser Origins of the packaged native apps. Capacitor serves the
+// bundled SPA from a localhost scheme, so its Connect calls to the gateway are cross-origin; the web
+// app is same-origin and needs no entry. Requests carry Authorization, so the allowlist reflects the
+// exact origin rather than "*".
+var nativeWebViewOrigins = map[string]bool{
+	"https://localhost":     true, // Capacitor Android (default https scheme)
+	"http://localhost":      true, // Capacitor with the http scheme
+	"capacitor://localhost": true, // Capacitor iOS default scheme
+}
+
+// withNativeCORS answers the CORS preflight and adds the CORS response headers for the packaged
+// native apps' cross-origin calls to the Connect edge. Without it the WebView blocks every RPC on the
+// preflight (the gateway otherwise returns 405 with no Access-Control-Allow-Origin), so a native
+// build can never reach the gateway and stays stuck offline. Same-origin (web) and any non-native
+// origin are untouched.
+func withNativeCORS(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		origin := r.Header.Get("Origin")
+		if nativeWebViewOrigins[origin] {
+			h := w.Header()
+			h.Set("Access-Control-Allow-Origin", origin)
+			h.Add("Vary", "Origin")
+			h.Set("Access-Control-Allow-Credentials", "true")
+			// The client interceptor reads the soft-tier update signal off the response.
+			h.Set("Access-Control-Expose-Headers", "X-Update-Recommended")
+			if r.Method == http.MethodOptions {
+				h.Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
+				// Reflect the requested headers (the origin is already allowlisted): the Connect client
+				// sends Connect-Protocol-Version / Connect-Timeout-Ms plus X-Client-Version and
+				// Authorization, and the exact set varies by call.
+				if reqHeaders := r.Header.Get("Access-Control-Request-Headers"); reqHeaders != "" {
+					h.Set("Access-Control-Allow-Headers", reqHeaders)
+				} else {
+					h.Set("Access-Control-Allow-Headers", "Content-Type, Connect-Protocol-Version, X-Client-Version, Authorization")
+				}
+				h.Set("Access-Control-Max-Age", "86400")
+				w.WriteHeader(http.StatusNoContent)
+				return
+			}
+		}
+		next.ServeHTTP(w, r)
+	})
+}