fix: register the Semaphore service worker when hydration finishes after load

[soamdesai-tfh]

Summary

The Semaphore service worker was never registered in next dev, and could be skipped in production on slow hydration.

src/pages/_app.tsx registered /sw.js from an inline next/script tag. With the default afterInteractive strategy that script runs after React hydration and only attaches a window load listener. When hydration finishes after load has already fired, the listener never runs, so:

• /sw.js is never registered and /semaphore/semaphore.wasm + .zkey are never cached,
• retryDownload() in src/lib/utils.ts hangs on navigator.serviceWorker.ready,
• the "Downloading Semaphore" chip never clears.

Changes

• src/lib/register-service-worker.ts (new): registers immediately when document.readyState === "complete", otherwise waits for load with a once listener, and returns a cleanup that removes the pending listener. Registration failures are logged with the script URL and consequence, never swallowed.
• src/pages/_app.tsx: calls the helper from a dedicated effect and drops the inline <Script>. No inline script means no CSP nonce is needed for registration. getInitialProps / pageProps.nonce are intentionally left in place: next build reports that this getInitialProps opts every route out of Automatic Static Optimization, so removing it is a separate decision.
• tests/register-service-worker.test.ts (new): five node:test cases covering the immediate branch, the deferred branch, cleanup, the rejection path, and browsers without service worker support.
• .eslintrc.json: "root": true, in its own commit. Checkouts nested inside another copy of the repo made ESLint cascade into the parent config and fail on a conflicting tailwindcss plugin. No effect in CI; easy to drop if unwanted.

Verification

Before the fix, in next dev with public/sw.js generated: page hydrated, document.readyState === "complete", inline #sw script element present, getRegistrations() empty, no caches, chip stuck.

After the fix, from a clean state (worker unregistered, caches deleted):

Check	next dev	next build + next start
navigator.serviceWorker.getRegistrations()	1 registration, /sw.js, activated	1 registration, /sw.js, activated
semaphore-cache contents	wasm + zkey	wasm + zkey
"Downloading Semaphore" chip	gone	gone
Console errors / CSP violations	none	none; CSP header enforced, 0 inline scripts without a nonce

pnpm lint, pnpm typecheck, pnpm test (25/25), pnpm spellcheck and pnpm build all pass.

Notes

• public/sw.js is gitignored and generated by pnpm build; for dev, run pnpm exec workbox injectManifest workbox-config.cjs first.
• Pre-existing and not addressed here: public/service-worker.js configures ExpirationPlugin({ maxEntries: 1 }) on a cache that must hold two files, so one entry is likely evicted after the first proof and re-downloaded on later visits.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
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