source-read
An advisory: it explains, and blocks nothing, on an unbounded source read the symbol index has already answered.
What it catches
An unbounded source read the symbol index has already answered.
Seeing it
A verdict names its rule in brackets, which is how you got here:
advise [source-read]: ...
magus describe rule source-read prints the same entry at a terminal, and
magus describe rules lists every rule this workspace enforces.