What it means
There are two classes. blocking means a violation ends the command with a non-zero exit; advisory means the violation is reported and the command still succeeds. The class is read at dispatch time and is what routes the finding, so it is a mechanism rather than a label.
How it works
A validator never calls mj_fail directly. It calls mj_doctrine_fail, which reads MJ_DOCTRINE_CLASS — set by the dispatcher from the registry — and emits FAIL for a blocking doctrine and WARN for an advisory one. Only FAIL and DRIFT increment the counter the command turns into its exit code. An unknown class is neither: it is a configuration error, reported as such, and it fails closed rather than defaulting to advisory.
watch is the one command that overrides this, and deliberately. It never blocks work — it reports what has moved and exits 11 to say it found something — so under watch every deviation is drift, advisory ones included.
How to see it
majordomus check # WARN checkpoint … 40m ago, interval 15m → exit 0
# change class: advisory to class: blocking for majordomus.checkpoint-freshness
majordomus check # FAIL checkpoint … 40m ago, interval 15m → exit 10test/cases/17_doctrine_enforcement.sh performs exactly that edit in a throwaway copy of the tool and asserts the exit code moves.
What it does not cover
The class says what a violation costs, not how serious the underlying problem is. There is no severity ladder, and adding one would mean adding a level that neither blocks nor is worth reporting.
Why it exists
Enforcement systems drift toward a middle setting where a rule is nominally enforced and nothing ever fails. Two classes make that impossible to express: a rule either stops the work or it does not, and the registry says which in one word that the code reads.