Add assertion to process method (#1453)

Also adjust clangd so it doesn't bother us with header files about `expected`.

tests/unit/rpc/handlers/FeatureTests.cpp

@@ -23,6 +23,7 @@
 #include "rpc/handlers/Feature.hpp"
 #include "util/Fixtures.hpp"
 
+#include <boost/asio/io_context.hpp>
 #include <boost/json/parse.hpp>
 #include <gtest/gtest.h>
 
@@ -46,3 +47,13 @@ TEST_F(RPCFeatureHandlerTest, AlwaysNoPermissionForVetoed)
         );
     });
 }
+
+TEST(RPCFeatureHandlerDeathTest, ProcessCausesDeath)
+{
+    FeatureHandler handler{};
+    boost::asio::io_context ioContext;
+    boost::asio::spawn(ioContext, [&](auto yield) {
+        EXPECT_DEATH(handler.process(FeatureHandler::Input{"foo"}, Context{yield}), "");
+    });
+    ioContext.run();
+}