test(workerd): reproduce stacked content-encoding decode gap

[james-elicx]

Summary

• add a framework-free Workerd reproduction with a deterministic local Node origin
• compare a single gzip control with a genuinely double-gzipped gzip, gzip response
• include encodeResponseBody: "manual" and Node native Fetch as behavioral controls
• document observed versus expected output and the suspected Workerd source seam

Observed

With Wrangler 4.124.0, the single-gzip response decodes to JSON. The default stacked response remains encoded, begins with gzip magic bytes (1f8b), and fails JSON parsing exactly like explicit manual mode. Node native Fetch decodes both responses successfully.

Validation

• node --check origin.mjs worker.js node-baseline.mjs
• local origin + wrangler dev + curl reproduction
• node node-baseline.mjs
• npx --yes wrangler@4.124.0 deploy --dry-run

Draft handoff for the Workerd runtime team; no vinext, Next.js, OpenNext, cache backend, account, or deployment is involved.

[pkg-pr-new]

Open in StackBlitz

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npm i https://pkg.pr.new/vinext@2986

commit: 83051d3

[github-actions]

Example	Preview	Production	Original
app-router-cloudflare	preview	production
pages-router-cloudflare	preview	production
app-router-playground	preview	production	original
realworld-api-rest	preview	production
nextra-docs-template	preview	production
benchmarks	preview	production
hackernews	preview	production	original
workers-cache	preview	production
web	preview	production

[github-actions]

Performance benchmarks

Compared 83051d3 against base b663d4b using alternating same-runner rounds. Next.js was unchanged and skipped.

0 improved · 0 regressed · 6 within ±1.5%

Scenario	Framework	Baseline	Current	Change
Client bundle size (gzip)	vinext	140.3 KB	140.3 KB	⚫ 0.0%
Client entry size (gzip)	vinext	127.7 KB	127.7 KB	⚫ 0.0%
Dev server cold start	vinext	3.21 s	3.22 s	⚫ +0.3%
Production build time	vinext	3.63 s	3.61 s	⚫ -0.5%
RSC entry closure size (gzip)	vinext	115.5 KB	115.5 KB	⚫ -0.0%
Server bundle size (gzip)	vinext	196.7 KB	196.7 KB	⚫ -0.0%

View detailed results and traces

_{🟢 improvement · 🔴 regression · ⚫ change below 1.5% · paired base/head}