ESM to CommonJS lowering

Scope

Translates ESM syntax to CommonJS when target: 'commonjs' with transformSyntax enabled.
Assumes Node 22.21+ runtime with __filename/__dirname shims supplied by the host (matches package engines).
Keeps optional live-binding behavior via liveBindings (strict/loose/off).
Top-level await (TLA) handling is controlled by topLevelAwait: 'error' | 'wrap' | 'preserve' when lowering to CommonJS.
Optional import.meta.main gating via importMetaMain: 'shim' | 'warn' | 'error'.

import statements become require calls; side-effect imports become bare require() calls.
Default imports use the bundler-style helper __interopDefault = mod => (mod && mod.__esModule ? mod.default : mod) when cjsDefault: 'auto'; otherwise they can target module.exports or .default directly per option.
Namespace imports bind to the full require result; named imports destructure from the same binding.
Re-exporting a default (export { default as x } from) routes through the interop helper to match bundler behavior for CJS sources.
When the interop helper is emitted, exports.__esModule = true is also seeded for downstream consumers.

Local named exports emit to exports.<name> (or bracket access) with Object.defineProperty getters when liveBindings: 'strict'; snapshot assignment is used for loose/off.
export default writes to module.exports = <expr> in the common case; when TLA is present and allowed (wrap/preserve), default exports write to exports.default = <expr> so the exports object stays stable for async wrapping.
export * from lowers to a for...in over the required module, skipping default, guarding on hasOwnProperty, and defining getters to mirror live bindings.
Named re-exports from another module (export { foo as bar } from) use getters when liveBindings: 'strict', otherwise snapshot assignment; default re-exports still use the interop helper.

topLevelAwait: 'error' (default) throws during transform when a TLA is found while targeting CommonJS.
topLevelAwait: 'wrap' wraps the entire CJS output in const __tla = (async () => { ...; return module.exports; })(); and attaches __tla to both module.exports and the resolved value. Consumers can await require('./file').__tla for readiness.
topLevelAwait: 'preserve' runs the lowered code inside an immediately-invoked async function but does not attach a promise; consumers must rely on the natural scheduling of async effects.
In both allowed modes, default exports write to exports.default instead of replacing module.exports to keep the exports object consistent while async initialization completes.
Fixture: test/fixtures/topLevelAwait.mjs plus tests in test/module.ts cover both wrap and preserve behaviors.

import.meta.url → require("node:url").pathToFileURL(__filename).href
import.meta.filename → __filename
import.meta.dirname → __dirname
import.meta.resolve → require.resolve
import.meta.main → configurable: default shim to process.argv[1] === __filename; with importMetaMain: 'warn' a warning is embedded for Node <22.18/24.2; with importMetaMain: 'error' the transform throws on those runtimes.
Bare import.meta becomes module so property accesses stay valid in CJS output.

test/fixtures/esmDefault.mjs: default import from the CJS provider, re-exported as default for interop checks (default import yields the CJS module object).
test/fixtures/esmNamed.mjs: named import and aliasing from the CJS provider, re-exported for assertions.
test/fixtures/esmNamespace.mjs: namespace import shape from the CJS provider, re-exported as ns.
test/fixtures/esmReexport.mjs: named + star re-exports from the CJS provider (includes live binding passthrough).
test/fixtures/liveReexport.mjs: re-export from a mutating CJS source; exercised when liveBindings: 'strict' to verify getter-based live bindings.
test/fixtures/esmProvider.cjs: CJS source exposing default/named exports plus a mutating live counter for binding checks (interval is unref()ed; tests wait ≥30ms to observe changes).