Faithful Go port of the C++ fivenode Require() mechanism: persistent node
sidecar + JSON handle protocol (require→handle, call→method with auto-await
Promise, end), driven by pure-Go glue (os/exec + stdio). No C/CGO, not
`node -e` string eval. NODE_PATH points at the app's node_modules.
PRG: FN_REQUIRE / FN_CALL / FN_END / FN_LASTERROR.
Replaces the earlier nodertl (NODE_EVAL string-eval), removed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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