feat: expose host print function to Node.js API

[simongdavies]

Add setHostPrintFn() to SandboxBuilder allowing Node.js callers to receive guest console.log/print output via a callback.

• New setHostPrintFn(callback) method on SandboxBuilder (NAPI layer)
• Uses ThreadsafeFunction in blocking mode for synchronous print semantics
• Supports method chaining (returns this)
• Added to lib.js sync wrapper list for error code extraction
• 4 new vitest tests: chaining, single log, multiple logs, consumed error
• index.d.ts auto-generated by napi build with correct TypeScript types

[Copilot]

Pull request overview

This PR exposes guest console.log/print output to Node.js consumers by adding a setHostPrintFn() callback hook on SandboxBuilder, wiring it through the NAPI layer and JS error-enrichment wrapper, and validating behavior via new Vitest tests.

Changes:

• Add SandboxBuilder.setHostPrintFn() to the Rust NAPI layer using a blocking ThreadsafeFunction<String> to preserve synchronous print semantics.
• Add a custom lib.js wrapper for setHostPrintFn that catches exceptions thrown by the user’s callback to avoid unhandled errors.
• Add Vitest coverage for chaining, single/multi log delivery, callback replacement, callback-throw resilience, and consumed-builder errors.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/js-host-api/src/lib.rs	Adds the NAPI set_host_print_fn method that registers a host print callback into the underlying sandbox builder.
src/js-host-api/lib.js	Wraps setHostPrintFn to catch callback exceptions and keep error-code enrichment behavior consistent.
src/js-host-api/tests/sandbox.test.js	Adds tests ensuring host print callback semantics and builder lifecycle behavior.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

This test asserts on secondMessages immediately after await loaded.callHandler(...), but the print wrapper defers the user callback via Promise.resolve().then(...) (see other tests here that yield with setTimeout(0)). Without a yield/flush here, this can be timing-dependent and flaky; add the same flush before the assertions (or make the print wrapper synchronous).

[Copilot]

The typeof callback !== 'function' branch is redundant/misleading: because the native signature expects a ThreadsafeFunction, non-callables will be rejected by napi argument conversion before Rust validation can run, so you won’t get a project-specific [ERR_*] code either way. Consider validating and throwing a clear JS error here, or remove the branch/comment to avoid implying the Rust layer will handle non-functions.

Suggested change

	// Forward non-function values to the native method for consistent
	// validation errors (the Rust layer rejects non-callable arguments).
	return origSetHostPrintFn.call(this, callback);
	throw new TypeError(
	`SandboxBuilder.setHostPrintFn expects a function, received ${typeof callback}`
	);