Fix E2E test timeout by caching Puppeteer binaries

[rishigupta-3]

Summary

Fixes intermittent E2E nightly test failures caused by Puppeteer Chrome binary download timing out during npm ci.

Changes

• Add Puppeteer binary caching: Cache ~/.cache/puppeteer directory between workflow runs
• Increase timeout: Bump npm ci timeout from 10m to 15m for Linux and macOS
• Smart cache invalidation: Cache key based on package-lock.json hash

Problem

The E2E nightly tests were failing intermittently on macOS (and occasionally Linux) with:

npm error signal SIGTERM
npm error command sh -c node install.mjs

The gtimeout 10m npm ci command was killing the process after 10 minutes while Puppeteer was downloading Chrome binaries (~200MB).

Solution

By caching the Puppeteer binaries, subsequent runs will skip the download entirely (cache hit) or only download if dependencies change. Combined with the increased timeout, this should eliminate the intermittent failures.

Test Plan

• Changes tested locally
• Wait for next scheduled E2E run to verify cache behavior
• Monitor success rate over next few days

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.70%. Comparing base (65a3b1b) to head (5995fdf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
+ Coverage   89.69%   89.70%   +0.01%     
==========================================
  Files         146      146              
  Lines       14482    14482              
  Branches      983      984       +1     
==========================================
+ Hits        12989    12990       +1     
+ Misses       1472     1471       -1     
  Partials       21       21              

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