- raiseIfErr traps the JS error sentinel (\x01FNERR:) and raises a catchable
PRG runtime error instead of handing back undefined/{error} as data.
- __GET__/__SET__ methods: explicit data read/write with existence +
writability (getter-only/non-writable/non-extensible) checks.
- per-VM lastErr (FN_LASTERROR) so parallel requests don't cross messages.
- capi/napi_errtest.prg exercises the 4 cases via BEGIN SEQUENCE/RECOVER USING.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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