Venv.apply refused the whole graph when any secondary profile's
config.yaml was unreadable, so one broken sibling config failed every
update. Update syncs now leave that profile's plugins out of the union,
report it (stderr + receipt warning), and build the rest; the profile's
plugins rejoin on the next sync once its config is fixed. Boot currency
already skips broken secondaries, so the result reads as current.
Ordinary syncs keep refusing to shrink the recorded graph.
cae75f0ead