fix deadlocks and add recovery middleware for http server errors

server/main.go

@@ -11,6 +11,19 @@ import (
 	_ "github.com/go-sql-driver/mysql"
 )
 
+// RecoveryMiddleware catches panics and returns 500
+func RecoveryMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Printf("[PANIC] %v", err)
+				http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			}
+		}()
+		next.ServeHTTP(w, r)
+	})
+}
+
 // getStepManager creates a new StepManager for the given user, loading state from DB
 func getStepManager(userID string) *StepManager {
 	return NewStepManager(userID)
@@ -125,5 +138,5 @@ func main() {
 	// 6. Start Server
 	binding := "0.0.0.0:8080"
 	fmt.Printf("Server starting on http://%s\n", binding)
-	log.Fatal(http.ListenAndServe(binding, nil))
+	log.Fatal(http.ListenAndServe(binding, RecoveryMiddleware(http.DefaultServeMux)))
 }