The conformance number was measured against a lossy oracle: the JSON
projection (in.json) discards anchors, tags, and scalar styles, and exists
for only about half the cases, so "passing" often meant only "parse did not
throw". Measured against the official suite's own test.event event streams,
the true exact conformance is 254 of 308 valid cases (40 emit a wrong event
stream, 14 false-reject), well below the JSON-proxy figure.
Add a canonical-event gate (Tests/CanonicalEventConformanceTests.swift) that
serializes the parser's events into the yaml-test-suite yeast format and
compares them exactly to each case's test.event, checking anchors, tags,
scalar styles, flow vs block, and explicit document markers, for every valid
case. The gate records the gap set and fails on any regression or unrecorded
fix. All 402 test.event files are vendored alongside their inputs.
To make the comparison exact, the parser Event model now records whether a
document boundary was explicit (documentStart/documentEnd carry an `explicit`
flag), distinguishing `---`/`...` from an implicit boundary. This resolves 89
cases that were previously correct but unverifiable without normalization.
No parser behavior changed; this is measurement and model fidelity. The 40
wrong-event and 14 false-reject cases are the real remaining gaps, to be fixed
against this gate.
