Rune previously threw the instant any non-finite number materialized, which
killed the program before the model's own guard could run — so idiomatic code
like parseInt(x) || 0, Number(x) then Number.isNaN(x), averages, and counters
crashed mid-expression. Real JS (and a real-engine sandbox) let these values
flow and rely on JSON serialization to turn them into null at the edge.
- copyIn no longer rejects non-finite numbers, so NaN/Infinity exist as ordinary
in-sandbox intermediates and defensive guards can run.
- copyOut normalizes non-finite numbers to null as a value leaves the sandbox;
final return and tool-call arguments both funnel through it, so one check pins
both boundaries (matching JSON.stringify, which produces null anyway).
- NaN/Infinity are now bindable identifiers (e.g. reduce(max, -Infinity)).
Extends rune-parity.test.ts (guards run, non-finite -> null out incl. nested, a
direct copyOut unit test) and updates rune.md.
Aiden Cline
e06a099a88