feat: use Chromium as a true WASM driver — fix Leg 2, add Playwright, explore sandbox isolation

[iheitlager]

Summary

Leg 2 (leg2_pyodide_chromium) is misnamed — it loads Pyodide directly in Node.js via loadPyodide() and never uses Puppeteer or Chromium. The puppeteer dependency in package.json is unused.

This issue tracks making Leg 2 honest and progressively exploring Chromium as a real WASM runtime driver.

Tasks

Phase 1: Fix Leg 2 — True Puppeteer-driven Pyodide

• Rewrite harness.js to actually launch headless Chrome via Puppeteer
• Load Pyodide inside the browser page (not Node.js)
• Proxy HTTP requests through page.evaluate() into the browser's Pyodide
• Keep the current Node.js-only version as leg2a (rename) for comparison
• Add the real Chromium variant as leg2b
• Benchmark both — measure the overhead of Chrome as the WASM host vs bare Node.js

Phase 2: Playwright experiment

• Create a new leg using Playwright instead of Puppeteer
• Compare API ergonomics, startup time, and reliability
• Playwright is the more modern/maintained choice for 2026

Phase 3: Chrome as a sandbox

• Explore using browser contexts as isolation boundaries
• Per-request WASM sandboxes (fresh BrowserContext per request, or context pooling)
• This is closer to real serverless patterns (Cloudflare Workers, Fermyon)
• Measure isolation overhead vs shared-context approach

Hypotheses to add

#	Hypothesis
H8	Pyodide-in-Chrome has higher cold start and memory than Pyodide-in-Node due to browser overhead
H9	Warm request latency comparable — Chrome's V8 and Node's V8 run WASM at similar speed
H10	Browser context isolation adds measurable per-request overhead but provides security guarantees
H11	Playwright and Puppeteer have comparable performance for this use case

Learning goals

• Understand Puppeteer/Playwright APIs for headless browser automation
• Learn CDP (Chrome DevTools Protocol) concepts under the hood
• Explore the browser as a compute sandbox (not just a rendering engine)
• Compare Node.js-as-WASM-host vs Chrome-as-WASM-host patterns

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🤖 Analysis by Claude