skill-source
An advisory: it explains, and blocks nothing, on a write to an installed skill copy rather than to its source.
What it catches
A write to an installed skill copy rather than to its source.
Seeing it
A verdict names its rule in brackets, which is how you got here:
advise [skill-source]: ...
magus describe rule skill-source prints the same entry at a terminal, and
magus describe rules lists every rule this workspace enforces.