Closes json's two documented fidelity limits (iteration 5 strictness):
- field_class gains WOB_FIELD_BOOL (a plain `Bool` field) and
WOB_FIELD_NIL_BOOL (a `?Bool`: WO_NIL_SCALAR nil + bool encoding) — the
kind byte alone cannot tell a Bool slot from an Int slot, so the metadata
carries it. Emitter writes them (field_class_meta); loader whitelists
them; json.c encodes `true`/`false` (and `null` for a ?Bool nil), decode's
null/omitted-key pre-write covers NIL_BOOL.
- A JSON number with a fraction or exponent is MALFORMED for an Int field:
the checked decode (`json.decode(t) as T`) yields nil for the whole
document instead of silently truncating 3.7 to 3 — the language has no
float, and corrupting data quietly was the one thing a "checked decode"
must never do. Floats stay representable through a raw `json.Value` field.
- corpus: run/json-bool-fidelity pins the round-trip (true/false both ways,
?Bool null both ways, fraction AND exponent rejected).
- Board's two known-gap entries struck; format doc's field_class marker list
extended.
Verified: oop-e2e 87/0; runtime test + test-iso OK; woc-test 540/0;
log-watcher 7/0; employee 8/0.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
