* perf: cache startup filesystem scans, optimize base64 and path normalization
- Cache hasMdxFiles() result per root directory to avoid redundant
recursive filesystem walks when config() fires per Vite environment
- Cache resolvePostcssStringPlugins() result per project root to skip
repeated existsSync checks across 17 PostCSS config file candidates
- 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 to eliminate redundant path normalization in the RSC handler
* fix: validate base64 structural length and improve test spy cleanup
Add length % 4 check to base64ToArrayBuffer to reject structurally
invalid base64 strings that pass the character-set regex but produce
empty/truncated buffers via Buffer.from(). Replace manual mockRestore()
calls with afterEach(vi.restoreAllMocks) to prevent spy leaks on
assertion failure.
* fix: address bonk review comments — composite mdx cache key, postcss comment order, hoist test import
* fix: cache Promise in resolvePostcssStringPlugins to prevent concurrent scan race; add POST urlOverride test
* fmt
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Co-authored-by: James <james@eli.cx>
Divanshu Chauhan (divkix)