`respec` invocation fails with exit code 127 on every build (v2.12.5 and v2.13.0)

[marcoscaceres]

The respec build step fails on every CI run for w3c/gamepad going back to at least 2026-02-13, both on pull_request and on push to gh-pages. The annotation is:

Command `respec -s "http://localhost:3000/index.html?gitRevision=<SHA>" \
  -o "index.html.built.html" --verbose -t 20 -e` failed with exit code: 127.

Exit 127 means respec is not on PATH when src/build.ts invokes it as a bare command:

https://github.com/w3c/spec-prod/blob/v2.13.0/src/build.ts#L102-L120

Versions confirmed broken

Pin	Run
w3c/spec-prod@v2 (= v2.13.0)	https://github.com/w3c/gamepad/actions/runs/25891886076
w3c/spec-prod@v2.12.5	https://github.com/w3c/gamepad/actions/runs/25893348176

Same identical failure under both. Also reproduces on push to gh-pages (https://github.com/w3c/gamepad/actions/runs/25892690820), so it's not PR-specific.

In w3c/gamepad, this has been failing on every PR run and every gh-pages push since at least 2026-02-13.

Local baseline passes

Running ReSpec locally against the same source with the same flags exits 0:

npx respec --localhost --haltonerror -s index.html -o /dev/null
# exit 0, 0 errors, only no-unused-dfns warnings

So the spec content is fine — the failure is in how the action installs or locates the respec binary.

Reproducing workflow

jobs:
  ci:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: w3c/spec-prod@v2
        with:
          VALIDATE_INPUT_MARKUP: true

Working hypothesis (please verify)

Looking at the action source (v2.13.0):

• src/setup.ts calls install("respec", PUPPETEER_ENV) for the ReSpec toolchain
• install() in src/utils.ts runs pnpm add respec in ACTION_DIR, then restores the original package.json and pnpm-lock.yaml to fake --no-save (workaround for Update to package.json breaks multi-spec builds #213 / fix: correctly reset pnpm-lock.yaml after package install #218)
• src/build.ts then calls await sh('respec ...'). I checked both PUPPETEER_ENV (src/constants.ts) and sh (src/utils.ts) and neither touches PATH — sh uses child_process.exec with { ...process.env, ...execOptions.env }. So the respec lookup falls through to whatever PATH the action runner inherits from pnpm/action-setup and actions/setup-node.

If pnpm add respec is silently failing or the resulting binary isn't on PATH under newer pnpm (the major jump to 10.x landed in #210, with further bumps in #217 and #225), the downstream respec lookup gets exit 127 with no upstream error surfaced.

Suggested debugging

1. Make the install() helper throw on a non-zero exit from pnpm add instead of silently returning the output
2. Log the pnpm add stdout/stderr when the subsequent respec command fails

Happy to test fixes or run additional reproducers.