perf: startup and cache micro-optimizations

[Divkix]

Closes #437

Summary

• Cache hasMdxFiles() result per root directory — avoids redundant recursive filesystem walks when config() fires per Vite environment (RSC/SSR/Client = 3+ times)
• Cache resolvePostcssStringPlugins() result per project root — skips repeated existsSync checks across 17 PostCSS config file candidates on each config() invocation
• Replace byte-by-byte base64 encode/decode in KV cache handler with Buffer APIs for significantly faster serialization
• Pass pre-normalized URL to nodeToWebRequest() in App Router prod server — eliminates redundant normalizePath call in the RSC handler for pathological URLs

Test plan

• 9 new tests in tests/startup-cache.test.ts — MDX scan caching (5) and PostCSS config caching (4)
• 3 new edge-case tests in tests/kv-cache-handler.test.ts — 1 MiB buffer, null bytes, all 256 byte values
• 5 new tests in tests/node-to-web-request.test.ts — urlOverride parameter behavior
• All 33 kv-cache-handler tests pass
• Typecheck (tsgo --noEmit) clean
• Lint (oxlint) clean
• Format (oxfmt --check) clean

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/vinext@436

commit: 34c85a6

[Copilot]

Pull request overview

This PR targets startup-time performance by caching expensive filesystem operations during repeated Vite config() invocations, and by reducing overhead in request normalization and KV cache serialization.

Changes:

• Add module-level caches for MDX directory scanning and PostCSS string-plugin resolution.
• Optimize KV cache ArrayBuffer base64 serialization/deserialization using Buffer.
• Allow passing a pre-normalized URL into nodeToWebRequest() and add coverage for the new behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/vinext/src/index.ts	Adds per-root caches for MDX scanning and PostCSS plugin resolution; exports internals for tests.
packages/vinext/src/cloudflare/kv-cache-handler.ts	Switches base64 encode/decode to Buffer and adds input validation before decoding.
packages/vinext/src/server/prod-server.ts	Adds urlOverride support to nodeToWebRequest() and passes a pre-normalized URL from the App Router server path.
tests/startup-cache.test.ts	New tests covering MDX scan caching and PostCSS resolution caching behaviors.
tests/node-to-web-request.test.ts	New tests covering nodeToWebRequest() urlOverride semantics.
tests/kv-cache-handler.test.ts	Adds edge-case ArrayBuffer base64 roundtrip tests (large buffers, null bytes, all byte values).

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[Copilot]

BASE64_RE only checks the alphabet/padding characters but doesn’t enforce base64 structural validity (e.g., length multiple of 4 / disallowing length % 4 === 1). Because Buffer.from(str, "base64") is permissive, some malformed inputs made of valid characters can decode without throwing, which would bypass the “corrupted entry => cache miss” logic. Consider tightening validation (e.g., a stricter regex or explicit length/padding checks) so invalid base64 reliably triggers the safeBase64ToArrayBuffer() null path.

[Copilot]

The spy is manually restored at the end of the test, but if an assertion throws before reaching mockRestore(), the spy can leak into later tests. Consider wrapping the spy in a try/finally (or adding an afterEach(() => vi.restoreAllMocks()) for the suite) to guarantee cleanup on failures.

Suggested change

	// Second call — should use cache, no filesystem reads
	const result2 = hasMdxFiles(tmpDir, appDir, null);
	expect(result2).toBe(true);
	expect(readdirSpy).not.toHaveBeenCalled();
	readdirSpy.mockRestore();
	try {
	// Second call — should use cache, no filesystem reads
	const result2 = hasMdxFiles(tmpDir, appDir, null);
	expect(result2).toBe(true);
	expect(readdirSpy).not.toHaveBeenCalled();
	} finally {
	readdirSpy.mockRestore();
	}

[Copilot]

Similar to the MDX caching test, this spy is restored only on the happy path. If an assertion fails before mockRestore(), the spy remains active and may affect subsequent tests. Consider using try/finally around the spy or an afterEach(() => vi.restoreAllMocks()) cleanup.

[Copilot]

This spy cleanup has the same failure-path leak risk as the other existsSync spy above (mockRestore() won’t run if an assertion throws first). Using try/finally around the spy (or afterEach restoreAllMocks) would make the test isolation more robust.

Suggested change

	// Second call — should use cache
	const result2 = await resolvePostcssStringPlugins(dir);
	expect(result2).toBeUndefined();
	expect(existsSpy).not.toHaveBeenCalled();
	existsSpy.mockRestore();
	try {
	// Second call — should use cache
	const result2 = await resolvePostcssStringPlugins(dir);
	expect(result2).toBeUndefined();
	expect(existsSpy).not.toHaveBeenCalled();
	} finally {
	existsSpy.mockRestore();
	}