Document request-scoped MySQL cleanup

src/lib/mysql-connector.h

@@ -33,8 +33,10 @@ struct MySQL {
 	DValue query(String q, StringMap params);
 	DValue get_pending_result();
 
-	// Unregisters from the request's connection tracking, so stack-allocated
-	// instances cannot leave dangling pointers behind for request cleanup.
+	// Unregisters from request connection tracking, so stack-allocated instances
+	// cannot leave dangling pointers behind for request cleanup. Heap handles
+	// returned by mysql_connect() are also request-owned and auto-closed at the
+	// end of the request if user code does not call mysql_disconnect() first.
 	~MySQL() { disconnect(); }
 
 };