feat(js): add a CommonJS entry point for the synchronous API

[konard]

Summary

command-stream@0.18.0 published a single ESM specifier, so a CommonJS host could not use the synchronous API:

$ node -e 'require("command-stream")'
Error [ERR_REQUIRE_ESM]: require() of ES Module .../command-stream/src/$.mjs not supported.

await import('command-stream') works but is asynchronous by definition, which makes it unusable at a synchronous launch-time probe boundary — exactly where ProcessRunner.sync() is most useful.

This PR publishes src/$.cjs under the require export condition. It loads the existing ESM module graph through require(esm) and re-exports the callable $ with every named export attached to it.

Fixes #189

Root cause

js/package.json declared only the ESM entry:

"main": "src/$.mjs",
"exports": { ".": "./src/$.mjs" }

There is no require condition, so Node resolves require('command-stream') straight to the .mjs file. On runtimes without require(esm) that throws ERR_REQUIRE_ESM; on Node.js >= 20.19 / >= 22.12 it resolves, but to a module namespace object, which is not callable — loaded`echo hi` fails with TypeError: loaded is not a function.

Approach

src/$.cjs is a thin wrapper rather than a bundled CJS build. That keeps a single module instance, so require() and import() share the same virtualCommands registry, shell settings and cleanup state — no dual-package hazard, and no build step:

const namespace = require('./$.mjs');          // require(esm)

function $(...args) {
  return namespace.$(...args);                 // forwards, never mutates the ESM `$`
}
// every named export is then attached to `$`, plus `default`, `$` and `__esModule`

Runtimes without require(esm) support now get an actionable message instead of ERR_REQUIRE_ESM:

command-stream: require() of this package needs a runtime with require(esm) support - Node.js >= 20.19.0 or >= 22.12.0 (running v18.20.4). Upgrade Node.js, or load the package with await import('command-stream').

Reproduction

js/experiments/repro-189-commonjs-require.mjs installs the package into a throwaway sandbox and reports what a CommonJS host observes:

$ node js/experiments/repro-189-commonjs-require.mjs

Before (Node.js v20.20.2, package.json without the require condition):

typeof require result: object
callable as a tagged template: false
TypeError: loaded is not a function
exit status: 1

After:

typeof require result: function
callable as a tagged template: true
sync probe: "sync-probe\n" code: 0
exit status: 0

Usage

const $ = require('command-stream');
const { ProcessRunner, shell } = require('command-stream');

const probe = $({ mirror: false, capture: true })`git --version`.sync();
if (probe.code === 0) {
  console.log(probe.stdout.trim());
}

js/examples/commonjs-launch-probe.cjs demonstrates the issue's real-world use case (synchronous launch-time availability probes) and runs under both node and bun.

Tests

• js/tests/commonjs-entry.test.mjs — 9 tests: manifest wiring, in-process require() shape (callable $, default, __esModule, named exports), a real .sync() call through the CJS entry, require()/import() returning the identical ProcessRunner/shell objects, and that the ESM $ is left unpolluted. Three of them spawn a real node process resolving the bare specifier command-stream from a sandbox.
• js/tests/node-commonjs-entry.mjs — node --test suite so the CI Node.js matrix (20, 22, 24) exercises require('command-stream') end to end; skips itself on runtimes without require(esm).
• js/tests/commonjs-sandbox.mjs — shared sandbox helper used by both suites and the experiment.
• .github/workflows/js.yml — the Node.js compatibility job now loads src/$.cjs with require() and runs the new node --test suite.

$ bun test js/tests/commonjs-entry.test.mjs
 9 pass, 0 fail, 33 expect() calls

$ node --test js/tests/node-commonjs-entry.mjs
 pass 1, fail 0

Full suite: 808 pass, 5 skip, 0 fail across 59 files. eslint ., prettier --check . and jscpd . are clean.

CI on this branch is green after merging main (0.18.2). The Node.js matrix
confirms the entry point on every supported version:

Job	Runtime	Result
node on ubuntu-latest	v20.20.2	CommonJS entry loads successfully in Node.js 20
node on ubuntu-latest	v22.23.1	CommonJS entry loads successfully in Node.js 22
node on ubuntu-latest	v24.18.0	CommonJS entry loads successfully in Node.js 24

The new node --test suite passes on all three.

Merge with main (0.18.2)

main advanced while this PR was open, which produced three conflicts:

• js/package.json — main added a ./process-runner subpath export (feat(js): expose lightweight ProcessRunner entry #194).
  The merged exports map keeps that subpath alongside the new require /
  import conditions for .. The subpath deliberately keeps its plain string
  target: it exposes only the named export ProcessRunner, which require(esm)
  already returns directly, so it needs no CommonJS wrapper —
  require('command-stream/process-runner').ProcessRunner is a function.
• js/README.md — both additions kept: the upstream "Lightweight
  ProcessRunner entry point" subsection and this PR's "Module Formats" section.
• .gitkeep — accepted the upstream deletion (100be07).

src/$.cjs enumerates the ESM namespace at load time rather than listing exports,
so the exports main added to $.mjs are re-exported automatically with no change
to the wrapper.

Changes

File	Change
js/src/$.cjs	New CommonJS entry point
js/package.json	main / module / exports conditions for require and import
js/README.md	New "Module Formats (ESM and CommonJS)" section + a CJS synchronous example
js/eslint.config.js	Lint **/*.cjs as CommonJS scripts
js/.changeset/commonjs-entry-point.md	minor release

No existing behaviour changes: the ESM entry point, its exports and every existing test are untouched.

Language parity

Labelled parity-exempt: this is a JavaScript module-resolution change (package.json export conditions and a CommonJS entry point). CommonJS has no counterpart in the Rust crate, so there is no equivalent change to make under rust/src/**. No runtime behaviour of the library itself changed.

[konard]

Working session summary

Done. PR #193 is pushed, updated and marked ready for review: #193

Root cause

js/package.json declared only the ESM specifier — "main": "src/$.mjs", "exports": { ".": "./src/$.mjs" }. With no require condition, Node resolves require('command-stream') straight to the .mjs file: ERR_REQUIRE_ESM on runtimes without require(esm), and on Node ≥ 20.19 a module namespace object that isn't callable as $.

Fix

js/src/$.cjs is now published under the require condition. It loads the same ESM graph through require(esm), so require() and import() share one instance (no dual-package hazard — verified by asserting require().ProcessRunner === (await import()).ProcessRunner), and exports a forwarding $ with every named export attached, so the ESM $ is never mutated. Runtimes without require(esm) get an actionable error instead of ERR_REQUIRE_ESM.

Evidence

js/experiments/repro-189-commonjs-require.mjs (sandbox resolving the bare specifier), Node v20.20.2 — before: typeof require result: object, callable as a tagged template: false, TypeError: loaded is not a function, exit 1. After: typeof … function, callable … true, sync probe: "sync-probe\n" code: 0, exit 0.

Verification

• bun test js/tests/commonjs-entry.test.mjs → 9 pass / 0 fail
• node --test js/tests/node-commonjs-entry.mjs → 1 pass
• Full suite bun test js/tests/ → 804 pass, 5 skip, 0 fail across 57 files (the 28 earlier failures were a missing jq in this container; they pass after installing it)
• eslint ., prettier --check ., jscpd . clean
• CI green: lint, changeset check, Bun on ubuntu/macos/windows, and the Node matrix — raw job logs confirm "CommonJS entry loads successfully in Node.js 20 / 22 / 24" and the new node --test suite passing on all three.

One CI note worth flagging: the "JS/Rust source parity" job failed because js/src/** changed without rust/src/**. CommonJS has no counterpart in the Rust crate, so I added the repo's documented escape hatch, the parity-exempt label (used the same way on merged PRs #181/#184/#186), and explained it in the PR body; the job now reports skipping. If a maintainer would rather see a Rust-side change, that decision is theirs to reverse.

Also included: js/examples/commonjs-launch-probe.cjs (the issue's launch-probe use case, runs under both node and bun), a README "Module Formats" section, an ESLint block for **/*.cjs, and a minor changeset.

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[konard]

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