Embedded JavaScript sandbox and host API for lanekeep rules.

The embedded QuickJS runtime, the capability-restricted host API, the TypeScript stripping step, and the module loader.

The sandbox boundary lives here. Rule code reaches exactly the functions this crate exposes and nothing else: no ambient filesystem, no process, no network, no clock, no randomness. Those globals are not restricted, they are absent.

Every addition to the host API widens the trust boundary and bumps the API version that feeds the cache key.

How absence is achieved

Two mechanisms, and the first is much stronger than the second.

Not installed. The engine's optional intrinsics are opted into rather than opted out of, so Date, Performance and WeakRef are never created. There is no original for a rule to reach: nothing to patch, nothing to restore, no prototype chain leading back.

Deleted at startup. Math.random lives among the non-optional base objects, so it has to go afterwards. This is weaker in principle — deletion can be undone if a reference escapes — but a rule that defines its own Math.random has written deterministic code, which is all this needs to guarantee.

Anything a host function does not offer, a rule cannot do. fs, process, fetch, setTimeout and friends were never part of this engine to begin with, which is asserted rather than assumed.

What is here so far

The sandbox and its budgets. The host API, TypeScript stripping and the module loader arrive in later milestones.