Cache repeated npm module loader filesystem work

[noise64]

• related to GOL-348
• related to GOL-350
• caches missing package.json reads within one outer CommonJS resolution graph, clearing the negative set when the graph ends and after guest filesystem mutations
• caches successful module-loader realpaths for one QuickJS runtime while keeping CommonJS and ESM cache domains separate
• preserves symlink flags, retries failures, and leaves public node:fs realpath uncached
• retains aggregate prototype results in Markdown and only the final reviewed raw P2/P3 report pair

Results

The final candidate was measured with three serial, fresh-state, cold local-registry samples of npm --version, npm view, and npm ci on both P2 and P3. The physical call counts were identical on both targets.

Command	Missing package.json reads	Physical loader realpaths
npm --version	204 → 96 (−52.9%)	426 → 78 (−81.7%)
npm view	1,768 → 596 (−66.3%)	3,545 → 477 (−86.5%)
npm ci	2,645 → 847 (−68.0%)	5,007 → 616 (−87.7%)

Final cold local-registry timing medians:

Target / command	Wall	Process CPU
P2 npm --version	0.582s	0.570s
P2 npm view	3.963s	3.923s
P2 npm ci	6.974s	6.944s
P3 npm --version	0.592s	0.590s
P3 npm view	4.376s	4.233s
P3 npm ci	7.965s	7.533s

Timings are observational and can vary between runs. The reconciled physical filesystem call counts are the comparison invariant. All 60 final samples succeeded, every ci installed both pinned packages, local HTTP request counts matched expectations, and no trace overflow occurred.

Full methodology, aggregate prototype tables, and final raw-report links are in 2026-09-21-cache-experiments.md.

Correctness boundaries

• failed realpaths remain uncached and retryable
• public node:fs realpath APIs remain uncached and observe filesystem changes
• guest filesystem mutations invalidate relevant missing-metadata entries
• --preserve-symlinks bypasses both loader caches; --preserve-symlinks-main bypasses CommonJS main canonicalization
• CommonJS and ESM realpath caches use separate domains
• Wizer initialization cannot populate loader filesystem caches
• relative CommonJS inputs resolve against process.cwd() before native cache lookup

Validation

• complete GitHub P2/P3 runtime and node-compat matrix
• all-target build and Clippy
• ten-lane P2/P3 skeleton Clippy matrix
• focused P2/P3 loader-cache runtime coverage and npm install/isolation cases
• DTS goldenfile regeneration and verification
• module-loader architecture checks and manual benchmark guards
• Prettier, ESLint, and TypeScript compilation
• post-push Claude exact-SHA review: clear