Constant FN_ID_TEST_INVOKE_TWO_SERIAL 

pub const FN_ID_TEST_INVOKE_TWO_SERIAL: u32 = 0x100;

Javm scheduler probe: runs two top-level invokes through one in-guest KernelScheduler (call_loop::run_two_for_test). Payload is two raw InvokePackets concatenated; output is rkyv-encoded [InvocationResult; 2].