Round-7 blocker-1 residual: the PyYAML-absent line-parser fallback in
detect-platform.sh (_strip_scalar) returned a stringified scalar for
UNQUOTED YAML values that PyYAML's implicit resolver types as a
non-string (int/null/bool/float/timestamp). That bypassed _accept's
isinstance(str) guard and could surface a garbage credential (e.g.
"12345", "null", "true") where the PyYAML path resolves NO token and
fails closed -- violating the module invariant that the fallback is only
ever MORE conservative than PyYAML, never less.
Root cause fix: mirror PyYAML 6.0.3's SafeLoader implicit resolver. An
unquoted plain scalar matching the null/bool/int/float/timestamp forms
now returns None (fail closed); a quoted scalar is always a string and is
accepted verbatim (quote-stripped) as before. Quoted-string handling,
scope-aware attribution, indentation, and inline-comment stripping are
unchanged. The predicate was fuzzed against real PyYAML over ~800k random
tokens with zero fail-open divergences.
Extends the forced-PyYAML-absence parser-equivalence harness with
token: 12345/null/~/yes/true/3.14 (each fails closed identically to
PyYAML) and token: "12345"/'abc' (quoted literals still accepted).
Blockers 2/3/4 (port-bound host, origin+full-path URL pin, review-body
binding) are untouched.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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