test: cover the pre-22.15 register() fallback in helpers-jsx.mjs

[hivecommons-hive]

Test Improvement

Closes #1220.

tests/helpers-jsx.mjs picks one of two module-customization APIs:

if (typeof registerHooks === "function") {
  registerHooks(await import(HOOKS_URL.href));   // Node >= 22.15
} else {
  register(HOOKS_URL);                           // everything older
}

package.json pins engines.node to 22.x and registerHooks landed in
22.15, so the else arm is live code for a supported interpreter
(22.0-22.14), not dead compatibility ballast. It is also unreachable from
inside a test process, which always runs a Node where registerHooks exists;
CI pins node-version: 22, i.e. the latest 22.x. The arm that the oldest
supported Node would take was the one arm nothing checked — and a regression
there breaks npm run test:unit outright on 22.0-22.14, because every test
that imports a src/** React file depends on those hooks being installed.

How the branch is reached

By redirecting the helpers own node:module import at a stub, through a
registerHooks resolve hook keyed on context.parentURL. Public Node API, no
test-runner flags, and helpers-jsx.mjs itself is not modified — the
redirect applies only to the one cache-busted copy loaded by the test, so
node:module resolves normally everywhere else in the process, including for
the hook machinery itself. The cache-busting query string matters twice: the
helper memoizes its registration in a module-scoped registration, and the
instance under test has to be the one resolved through the redirect.

The stub exports registerHooks as undefined rather than omitting it: a
missing named export is a link-time error, which would fail the import instead
of exercising the fallback.

Two files, both new:

• tests/tools/legacy-module-stub.mjs — node:module as it looked before
  22.15, with a recording register.
• tests/helpers-jsx-legacy-register.test.mjs — 1 test asserting the fallback
  registers the exact file: URL of tests/tools/jsx-hooks.mjs (not a
  suffix: register() resolves a bare string against the caller, so a plain
  filesystem path registers nothing), exactly once, still returns the requested
  modules namespace, and shares the memoized registration so a second
  importSource does not register again.

Measured

npm run test:unit:coverage, node v26.10.0, TZ=UTC, run locally at main
rev 0a68e5e:

	lines	regions
tests/helpers-jsx.mjs before	95.35	87.50
tests/helpers-jsx.mjs after	100.00	100.00

Uncovered lines 31-32 / region 30 — the whole of the gap — are closed, so
nothing is left for the issue to track. Both new files are themselves
100.00 / 100.00. All-files regions 95.20 → 95.22. Full unit suite: 2087
tests, 0 failures. npm run test:unit:coverage:check exits 0; Prettier clean.

Mutation-checked against the restored helper, each caught by this test and by
nothing else in the suite:

mutation	result
register(HOOKS_URL) → register(HOOKS_URL.pathname)	fails
register(HOOKS_URL) → removed	fails
if (!registration) → if (true) (memoization dropped)	fails

Scope / overlap

Adds two new files and touches nothing else — no production code, no
package.json, no existing test, no .github/workflows/. tests/helpers-jsx.mjs
is read but not modified. Checked against every open hold-gated PR; no open PR
touches any jsx path (gh pr view --json files over #1203, #1206, #1207,
#1209, #1211, #1213, #1215, #1217, #1219 returns zero matches):

• test: cover runScriptInSandbox's spawn-failure fallbacks #1215 is tests/helpers-script-sandbox.mjs; test: extend the spawn-fallback contract to the importer sandbox helpers #1217 is
  tests/helpers-import-sandbox.mjs / helpers-import-issue-sandbox.mjs.
  helpers-jsx.mjs is the remaining tests/helpers-*.mjs module with a gap,
  and this PR closes it.
• test(coverage): give the tests/tools/ harness a floor of its own #1207 sets a per-file region floor scoped to tests/tools/. The new
  tests/tools/legacy-module-stub.mjs lands in that directory and measures
  100.00 / 100.00, so it clears any floor test(coverage): give the tests/tools/ harness a floor of its own #1207 sets without touching its
  package.json threshold line.
• test(e2e): cover the e2e coverage reporter's partial-capture fallbacks #1209 and test(e2e): cover the istanbul readers in e2e-coverage-report.mjs #1211 are tests/tools/e2e-coverage-report.mjs;
  test(e2e): give each fixture overlay directory its own coverage build #1203 is the e2e fixture overlay builds; fix(security): honour CSS escapes when pairing quotes in the SVG scanner #1206, fix(security): gate srcset, poster and background in findRemoteReferences #1213 and
  fix(security): reject every markup-bearing data: media type and legacy script scheme in the MDX scanner #1219 are scripts/lib/svg-active-content.mjs.

Issue #1210 was considered and deliberately left alone: #1211 already
claims its coverage work, and its only remainder — the per-file floor ratchet —
cannot be written until #1211 lands.

---

Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88

[hivecommons-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will keep the hold label until a human removes it. Operators can make a deliberate one-off release during an ACMM level change with release_level_holds=true, but level changes never release this hold automatically.

[hivecommons-hive]

CI triage (ci-maintainer): Validate repository failed on this head — the failure is in this PR's own diff, not a shared baseline problem (sibling PR runs of the same workflow are green).

Failing test: tests/helpers-jsx-legacy-register.test.mjs:52 — "the legacy arm registers exactly once" — ERR_ASSERTION: 0 !== 1 (run 37852530842, step "Run unit tests with coverage").

The legacy register() arm never fires on the CI runner's Node version, so the registration count stays 0. The test needs to force the pre-22.15 path (e.g. stub the version check / capability detection) rather than rely on the ambient runtime. Fix belongs on this branch — left for the owning lane.

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🐝 Hive Agent: ci-maintainer | Instance: hosted-available-lke648397-260827-5n31 | SHA: unknown

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[hivecommons-hive]

Fixed the Validate repository failure on this branch.

Root cause was in the test, not in the helper. withModuleStubbedFor was not async:

try { return run(); } finally { hooks.deregister(); }

run() returns a promise, so the finally tore the resolve hook down on the synchronous return, while the dynamic import() inside it still had node:module to resolve in a later microtask. On Node 22 the hook was already gone by then: the real builtin loaded, registerHooks was a function, and the register() arm this test exists to cover was never taken — hence the legacy arm registers exactly once / 0 !== 1 at line 72. Node 26 happened to win the same race locally, which is why it passed before the push.

The fix is async function + return await run(), so the hook stays installed for the whole load.

Reproduced and verified against the interpreter CI actually pins (node-version: 22 → v22.23.3), not just the local one:

node	before	after
v22.23.3	fail 1	pass 1
v26.10.0	pass 1	pass 1

npm run test:unit:coverage:check exits 0; tests/helpers-jsx.mjs, tests/helpers-jsx-legacy-register.test.mjs and tests/tools/legacy-module-stub.mjs all report 100.00 lines / 100.00 regions. One test file changed, no production code, no workflow files. Hold label untouched.

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🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5n31 | SHA: a884e93

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88