refactor(lint): add eslint-plugin-baseline-js for browser compatibility

[overbalance]

What problem is this solving?

Adds automated checking for Web API browser compatibility, ensuring SDK code only uses APIs that are "widely available" (30+ months across all major browsers).

Short description of changes

• Add eslint-plugin-baseline-js with type-aware parsing for source files
• Add standalone eslint config for compiled output to catch non-baseline APIs from dependencies
• Reorganize lint/check scripts: sdk:check = sdk:check:tsc + sdk:check:eslint
• Simplify validate-sdk.js by removing redundant AST-based baseline analysis
• Retain es-check on compiled output as syntax verification safety net
• Remove unused scripts/build.js
• Split CI validate-build job into separate SDK/CLI build and validate steps

Testing

• Verified eslint catches non-baseline APIs in source (e.g., navigator.scheduling)
• Verified es-check catches ES version violations (private fields in ES6, using in ES2022)
• Verified eslint on dist catches non-baseline APIs from bundled dependencies
• All existing tests pass

[github-actions]

Chrome DevTools Protocol Tracing (Script: 102.49ms, Heap: 13.09MB)

	Number of Requests	Size of Requests	Script Duration	Task Duration	Heap Used Size
Requests	+3 requests	+29.68 KB
Page Loaded			+14.00 ms	+8.19 ms	+0.91 MB
Generate 100 fetch requests			+16.26 ms	+77.12 ms	+1.73 MB
Generate 100 XHR requests			+40.11 ms	+112.22 ms	+2.31 MB
Click 100 buttons and generate 100 logs			+24.11 ms	+29.03 ms	+2.92 MB
Throw a 100 exceptions			+0.81 ms	+11.52 ms	+2.17 MB
End Session			+7.21 ms	+21.24 ms	+3.05 MB
Total	+3 requests	+29.68 KB	+102.49 ms	+259.31 ms	+13.09 MB

Lighthouse (Script Eval: 46.40ms)

	Difference	Description
Total Blocking Time	0 ms	Difference in Total Blocking Time: Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds. Learn more about the Total Blocking Time metric.
Main Thread Time	+60.83 ms	Difference in Main Thread Time: Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this. Learn how to minimize main-thread work
Script Evaluation Time	+46.40 ms	Difference in Script Evaluation Time: Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this. Learn how to reduce Javascript execution time.

Platform Tests (vite-7 gzip: 47.99KB)

vite-7 Platform Tests

	Total Uncompressed Size	Total Gzip Size
vite-7 - esnext	+164.67 KB	+47.99 KB
vite-7 - es2015	+171.51 KB	+49.67 KB

vite-otel-latest Platform Tests

	Total Uncompressed Size	Total Gzip Size
vite-otel-latest - esnext	+163.74 KB	+49.69 KB
vite-otel-latest - es2015	+170.50 KB	+51.32 KB

webpack-5 Platform Tests

	Total Uncompressed Size	Total Gzip Size
webpack-5 - esnext	+121.11 KB	+43.18 KB
webpack-5 - es2015	+122.22 KB	+44.65 KB

[jpmunz]

confirming this is not adding new functionality correct? The idea is to keep the same validation we had before but leverage eslint-plugin-baseline-js instead of our custom code?

[jpmunz]

is this needed given the ignoreFeatures in eslint.dist.config.js?

[overbalance]

Yes because comments are stripped out of compiled output.

[jpmunz]

I'm not sure I follow, if this was removed the rule still triggers even though ignoreFeatures: ['compression-streams', 'proto'] is set? What is ignoreFeatures then configuring?

[overbalance]

eslint.config.js validates source code (which doesn't ignore features, hence the disable comments) and eslint.dist.config.js is used to validate compiled output. The IIFE file is stripped of comments so it was more convenient to add ignoreFeatures for all files in the dist folder.

[jpmunz]

ah ok I understand now, thanks!

[jpmunz]

this is pretty long ago for the plugin to not take it into account, is it updated regularly?

[overbalance]

I wrote this poorly. CS was added to all browsers thirty months ago but only became "widely available" in November 2025. I'll revise.