Re-vendor tooling and docs-sync equivalents read the pin docs/VENDORED.txt
(available at 0.5.0 and later) instead of naming the doc set themselves, so
a new doctrine file reaches every consumer at its next ordinary pin bump
with zero list edits. A hardcoded list propagates nothing and its
staleness is silent: docs-sync --check asserts byte-identity for the files
the list names and says nothing about one it omits.
What makes reading the manifest sufficient rather than merely better is
the self-guard this PR adds, tagged unreleased until the first tag carries
it, per the RELEASES.md paragraph above it.
Refs #251
