The dynamic /i18n/[locale] route handler answered with Next's default
Cache-Control (private, max-age=0, must-revalidate) and no validator —
its immutable-cache header was overridden, so a non-PWA browser would
re-download the full catalog on every hard load. Static public/ files
keep an ETag (repeat loads revalidate to a 304) and the service
worker's cache-first rule covers the offline relaunch; the ?v= build
key the layout appends busts both per deploy.
scripts/generate-i18n-boot.mjs writes public/i18n/<locale>.js for all
six locales as a prebuild/predev step (the sw-version.js pattern);
output is gitignored. The route handler is removed.
Measured on a production build, authenticated DE session: dashboard
document 522 KB raw / 139 KB gz -> 170 KB raw / 24.6 KB gz; the DE
catalog moves into a one-time 119 KB gz cached asset.
H2
The measured first-load gap on / was never the server: FCP painted the
SSR shell at ~1.8 s but LCP landed at ~5.5 s (mobile-throttled) because
the tiles waited for JS download + hydrate + a CLIENT-side snapshot
fetch — while /api/dashboard/snapshot answers in ~8 ms server-side.
src/app/page.tsx is now a thin RSC wrapper: it runs the same cached
snapshot read the API route uses (extracted to
src/lib/dashboard/snapshot-read.ts, one shared SWR cell for both
readers) and hands the result to TanStack via HydrationBoundary +
dehydrate, so the first HTML carries real tile data and the mounted
cell starts warm (staleTime 60 s, refetchOnMount false — no double
fetch). Query keys come only from the central factory
(dashboardSnapshot(locale) + the dashboardWidgets seed the client cell
already performs); the payload is JSON-round-tripped so the hydrated
shape is byte-equal to the wire shape. Fail-soft: no session or any
builder error renders the page exactly as before. The 1,727-line client
page moves unchanged to src/app/page-client.tsx; no component-tree
rewrite.
Companion: the documented bundle tooling was dead on Turbopack
(ANALYZE=1 silent no-op, bundle-report read a webpack-only JSON), so
H2/H3-class regressions shipped invisibly. scripts/check-bundle-budget.mjs
derives per-route gzip totals from the Turbopack client-reference
manifests + rootMainFiles, prints the report (pnpm bundle-report), and
enforces bundle-budget.json (pnpm bundle-check): per-route caps,
total-client-JS cap, a recharts-duplication guard (fingerprint count
must stay 1), and a catalog guard (no message catalog referenced by any
route manifest). Wired into the existing e2e workflow after next build.
H4
Marc-André Bombeck