FLX-2103: trace op outside the flux-trace/1 vocabulary

Family: plan/replay binding (the 2000 band)

The trace vocabulary is closed (KERNEL-SPEC §10). An op the golden does not know about would move every component digest under it, so a new op is a kernelVersion bump with a GOLDEN-CHANGELOG row, never an addition a caller can make at run time.

Look it up offline

$ fluxsim explain FLX-2103

Every code is listed in the error index.