FLX-2105: golden update without a reason and a changelog row

Family: plan/replay binding (the 2000 band)

Moving a golden baseline is a deliberate act (KERNEL-SPEC §10): --update-golden requires --reason, and the new baseline must be recorded as a GOLDEN-CHANGELOG.md row naming the components that moved. Without both, a silent regression and an intended change look the same in the history.

Look it up offline

$ fluxsim explain FLX-2105

Every code is listed in the error index.