`consume.read_sources` reads both YAML forms. This library's three copies of
the line-oriented frontmatter grammar read only the flow one, and on a block
sequence they return the key with an EMPTY value -- not a `KeyError` a
consumer can catch, an address that disappears.
Measured 2026-09-12 over four bundles a producer ships, denominator = files
carrying a frontmatter block: 2 756 of 2 757, 446 of 447, 1 133 of 1 134 and
270 of 271 concept files lose the address through the flat readers, while
PyYAML 6.0.3 and the pinned guard 1.4.0 both read it on 100 % of the same
files.
The bar is dict EQUALITY against two independent readers rather than "it
parses". The two disagree on one axis and it is named rather than averaged:
the guard keeps a leaf's quotes verbatim, PyYAML decodes them, and this
library follows `read_sources`' K3-22 rule.
Red: 13 failed, 12 passed. The 12 are the known-positive controls and the
known-negatives the fix may not move -- the nested-`title:` substitution trap
above all, plus the flow form, an absent key, and a shape `read_sources`
refuses.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
