The rollup took the highest fix version across a component's advisories. That
is wrong whenever an advisory is patched on more than one release branch.
nanoid is the case that exposed it. Both advisories against it are fixed on two
branches - 3.3.16 and 5.1.16, 3.3.18 and 5.1.6 - and the rollup recommended
5.1.16 with a MAJOR warning. But nanoid is transitive, pulled in by postcss at
`^3.3.11`, a range no 5.x release can satisfy. The recommendation was not merely
a bigger job than necessary, it was unreachable: the actual target is 3.3.18, a
patch inside the existing range.
Per advisory the target is now the lowest published fix above the version in
use; per component it is the highest of those, since one upgrade has to satisfy
every advisory against it. Fixes on older branches are skipped rather than
offered as a downgrade - axios advisories list 0.30.x fixes that would have been
a downgrade from 1.13.2.
This also gives the MAJOR label meaning. It now fires only when no fix exists on
the current branch, rather than whenever some branch happened to be higher.
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