chore: cache npm downloads in the cross-language workflow

[AmaadMartin]

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Link to Issue or Description of Change

1. Link to an existing issue (if applicable):
   Closes: #issue_number
   Related: #issue_number
2. Or, if no issue exists, describe the change:

Problem: The run-tests job in .github/workflows/cross-language-integration.yml invokes actions/setup-node@v6 with no with: block at all, so the cache input is unset. With cache unset the action performs neither a cache restore before the job nor a cache save in its post step, and the job's npm install therefore does a full cold resolve plus a full tarball download of the entire workspace dependency tree on every push to main and every pull request — on macos-latest, the most expensive runner class in use here.

setup-node's automatic caching cannot rescue this. Its package-manager-cache input defaults to true, but auto-caching only engages when package.json declares packageManager or devEngines.packageManager. Verified against this checkout: grep -rn --include=package.json -E '"(packageManager|devEngines|engines)"' . across the root and every workspace (core/, dev/, integrations/) returns zero matches, so the auto-detect path never fires. Corroborating the state of the repo today, grep -rn "cache" .github/ also returned zero matches — no workflow here caches anything.

This is a CI-efficiency defect, not a correctness defect: the job produces the right answer, just slowly and with avoidable registry traffic.

Solution: Set the cache input explicitly. Two added lines, one file, zero deletions:

      - name: Use Node.js
        uses: actions/setup-node@v6
        with:
          cache: npm

Why this shape, and what was deliberately not added:

• No cache-dependency-path. This is an npm-workspaces repo ("workspaces": ["core", "dev", "integrations"]), so there is exactly one lockfile — package-lock.json at the repository root (find . -maxdepth 3 -name package-lock.json confirms no nested lockfiles). setup-node scans the workspace root for it automatically, making the input redundant configuration.
• No node-version / node-version-file. There is no .nvmrc, no .node-version, and no engines field anywhere in this repo, so node-version-file would hard-fail the step. Pinning the Node version is a separate decision and is deliberately out of scope for this PR.
• No hand-rolled actions/cache step and no restore-keys fallbacks. setup-node's built-in handling is the whole point of the change.
• npm install is left as-is (not "improved" to npm ci), and the Go setup, build, and test steps are untouched. Same triggers, same runner, same pass/fail semantics.

Cache key shape produced by setup-node (node-cache-${RUNNER_OS}-${os.arch()}-${packageManager}-${hashFiles(lockfile)}), which on this job resolves to:

node-cache-macOS-<arch>-npm-<sha256 of package-lock.json>

Because the job runs on macos-latest only, exactly one cache entry is ever produced by this workflow — negligible against the repository's Actions cache budget. There are no npm restore-keys, so a lockfile change rotates to a clean miss rather than restoring a stale partial cache.

Scope / collision check: Before implementing, I listed all open PRs on this fork (gh pr list --state open --limit 100) and diffed the file lists of every plausibly adjacent CI change (#296, #250, #245, #237, #235, #204, #207). #296 (ci: cache npm downloads in the validation workflow) makes the analogous change in .github/workflows/validation.yaml; the remaining CI PRs also only touch validation.yaml. No open PR touches cross-language-integration.yml, so there is no collision and nothing to stack on. This PR deliberately does not touch validation.yaml — that would conflict with #296.

Release impact: none. The commit and this PR are titled chore: on purpose — this repo runs release-please ("release-type": "node"), and a feat:/fix: title on a CI-only change would open a release PR and bump every workspace version for no product change. chore: is not a release-triggering conventional-commit type.

Revert: delete the two added lines.

Testing Plan

Please describe the tests that you ran to verify your changes. This is required for all PRs that are not small documentation or typo fixes.

Unit Tests:
[ ] I have added or updated unit tests for my change.
[x] All unit tests pass locally.

No unit test was added, deliberately. The deliverable is two lines of GitHub Actions YAML; there is no executable unit under test, and a test asserting on the contents of a workflow file would be pure churn. No application code is added or changed, so no JS test suite exercises this diff. The verification burden is carried by static checks plus the live CI run.

Static checks run locally on the pushed commit:

1. YAML parses

   $ python3 -c "import yaml; yaml.safe_load(open('.github/workflows/cross-language-integration.yml')); print('yaml ok')"
   yaml ok
   

2. The key is set exactly where intended, and only there

   $ python3 -c "import yaml; s=yaml.safe_load(open('.github/workflows/cross-language-integration.yml'))['jobs']['run-tests']['steps'][1]; print(s)"
   {'name': 'Use Node.js', 'uses': 'actions/setup-node@v6', 'with': {'cache': 'npm'}}
   

   with s['uses'] == 'actions/setup-node@v6', s['with']['cache'] == 'npm' and set(s['with']) == {'cache'} all asserting cleanly.
3. Proof the check can fail (negative control). The same assertion run against the unfixed file from main (git show main:.github/workflows/cross-language-integration.yml) fails, so the check has real signal rather than passing vacuously:

   {'name': 'Use Node.js', 'uses': 'actions/setup-node@v6'}
       assert s['with']['cache'] == 'npm'
              ~^^^^^^^^
   KeyError: 'with'
   

4. The diff is minimal

   $ git diff --stat main
    .github/workflows/cross-language-integration.yml | 2 ++
    1 file changed, 2 insertions(+)
   

   git diff --name-only main lists only that one file.
5. No forbidden inputs crept in

   $ grep -nE "node-version|cache-dependency-path" .github/workflows/cross-language-integration.yml
   (no output)
   

6. validation.yaml is untouched — it appears in neither git status nor the diff.
7. No lockfile churn. npm install --dry-run --ignore-scripts resolved cleanly against the unchanged lockfile (added 1163 packages) and git status --porcelain afterwards showed only the workflow file. (--ignore-scripts was needed only because this sandbox has no node_modules, so the repo's husky prepare script is not installed locally; it is unrelated to this change.)

Manual End-to-End (E2E) Tests:

The live CI run on this PR is the end-to-end test — the change only has observable behaviour on a GitHub-hosted runner. Reproduce it with:

1. gh pr checks <pr-number> --watch --fail-fast, and confirm the Cross-Language Tests workflow's run-tests job passes. (The validation workflow also defines a job named run-tests, so two similarly named checks appear — identify them by workflow name.)
2. gh run view <run-id> --log on the first run: the Use Node.js step should report a miss and the post step should report a save.
3. gh run rerun <run-id> without touching package-lock.json, then read the re-run log: Use Node.js should report a restore from the same key, and the post step should decline to re-save. A re-run of the same PR (rather than a second PR) is required because a pull_request-triggered cache is scoped to that PR's merge ref.

Observed results on this PR (macos-latest, arm64, Node v24.18.0 / npm 11.16.0 as provisioned by the runner). Both attempts of the Cross-Language Tests run-tests job concluded success:

	Attempt 1 (cold)	Attempt 2 (re-run, lockfile unchanged)
Use Node.js cache line	npm cache is not found	Cache restored from key: node-cache-macOS-arm64-npm-56fcdc8f564da454e69438f0c13d07bf1025685b0519cecdc64092109b985331
Post Use Node.js	Cache saved with the key: node-cache-macOS-arm64-npm-56fcdc8f564da454e69438f0c13d07bf1025685b0519cecdc64092109b985331 (~85 MB / 88,878,655 B)	Cache hit occurred on the primary key node-cache-macOS-arm64-npm-56fcdc8f…b985331, not saving cache.
Use Node.js step duration	1s	4s (restore + extract of the 85 MB archive)
Install dependencies	added 1089 packages, and audited 1093 packages in 16s	added 1089 packages, and audited 1093 packages in 18s

The restore/save cycle works exactly as designed, and the key is stable across the two attempts.

Honest caveat on the timings: this sample shows no wall-clock win. npm install self-reported 16s cold vs 18s warm, and the Use Node.js step itself grew by ~3s to restore and extract the 85 MB archive — so the cached run was marginally slower end to end, not faster. I am reporting the measurement rather than the expectation. Two things to note when weighing it: a single before/after pair on a hosted runner is dominated by runner-to-runner variance at this scale (a ~16s step), and the durable benefit of the cache is that ~85 MB of tarballs no longer come from the registry on every push and PR — which is registry-traffic and registry-availability insurance, not a speed claim. If a reviewer considers avoided registry traffic insufficient justification for the added restore step on this particular job, that is a reasonable reason to decline this PR; I would rather surface that than assert a speedup the logs do not support.

Two warnings appear in the run annotations. Both are pre-existing and unrelated to this change — they are emitted by the Setup Go step, are present on unmodified main, and do not fail the job: Restore cache failed: Dependencies file is not found in … Supported file pattern: go.sum (actions/setup-go's own default caching, which finds no root go.sum), and the actions/setup-go@v5 Node 20 deprecation notice. Fixing either is out of scope here.

The validation workflow was unaffected, as intended: its run-tests legs passed on ubuntu-latest, macos-latest and windows-latest.

Checklist

[x] I have read the CONTRIBUTING.md document.
[x] I have performed a self-review of my own code.
[x] I have commented my code, particularly in hard-to-understand areas.
[ ] I have added tests that prove my fix is effective or that my feature works.
[x] New and existing unit tests pass locally with my changes.