`next/dynamic`: CSS imported by dynamically loaded components not applied

[james-elicx]

This issue was created by an agent analysing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-05-22).

Problem

When a component is loaded via next/dynamic, the CSS it imports (global, CSS modules) is not injected into the page. Components fail to become visible (zero size due to missing styles), causing all 4 tests in the suite to time out waiting for elements.

waiting for locator('#server') to be visible — CSS for dynamic component never injected

Estimated Impact

~4 test failures across the deploy suite.

Affected Test Suites

• test/e2e/app-dir/next-dynamic-css/next-dynamic-css.test.ts (4 failures)

Recommendation

1. Reproduce first in vinext's own test suite. Add a next/dynamic import of a component that imports a CSS module and assert the rendered text is visible (i.e. CSS was applied).

2. Inject the dynamic component's CSS on load. When the dynamic chunk loads, append its associated CSS to the document. Use Vite's CSS asset metadata.

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Part of #1328.

[james-elicx]

Triage update (agent investigation): reproduced and root-caused (not fixed on main). vinext delegates client-component CSS to @vitejs/plugin-rsc, which only preinits CSS for registered client references ('use client' modules in the rsc graph). A module reached only via a runtime import() inside a client component (the next/dynamic case) is not a registered client reference and is not in the rsc graph, so neither transformRscCssExport nor vite-rsc's client-reference CSS preinit fires for it — its extracted chunk CSS is never emitted as a <link>/preinit at SSR time.

Correctly fixing this needs per-dynamic-boundary chunk→CSS resolution (build manifest in prod + dev collectCss) and SSR-time link/preinit emission keyed on rendered boundaries — the exact machinery already being built in #1594 (dynamic-preload-metadata.ts + lazy-chunks.ts + DynamicPreloadChunks, closes #1516). Recommend resolving #1515 by extending #1594's dynamic-boundary emission to include stylesheets, rather than a parallel localized patch (which would risk CSS double-emit/ordering regressions). Deferred as not-a-small-isolated-patch.