markdown links parsed anchor targets twice more and probed existence
without a cache; translation pairing reparsed every document after link
normalization and globbed four times; the README model-experience and
limitations checks parsed each README three times; type equivalence
parsed all 1,835 documents; Session format references reparsed each pair
four times. Each gate now parses a document once: links and anchors come
from one tree, pairing reuses the original tree when every rewritten
destination keeps the block structure and falls back to a full reparse
otherwise, the README checks share one tree, a text prefilter skips
documents that cannot hold a source-equivalence fence, and the
persistence renderer passes its trees on. Outputs are byte-identical on
the repository, and seeded faults are reported identically.
Refs #5852
