Self-host ECharts runtime asset

[miohtama]

Why

ECharts was loaded from jsDelivr at runtime, which makes chart rendering depend on a third-party CDN hostname that may be blocked by Malaysian ISPs or other network filters. Serving the runtime as a first-party build asset keeps the lazy-loading behaviour while making the script available through the normal frontend deployment and Cloudflare proxy.

Lessons learnt

SvelteKit emits ?url package assets under /_app/immutable/assets/ with content-hashed filenames and long-lived immutable cache headers. The built Node adapter returns cache-control: public,max-age=31536000,immutable for the emitted ECharts bundle, so Cloudflare can cache it safely as a first-party static asset.

Summary

• Add echarts@5.6.0 as a dependency and load echarts/dist/echarts.min.js through Vite instead of jsDelivr.
• Add resolveEChartsScriptUrl() as the single helper for changing the runtime location later.
• Reuse the shared ECharts runtime loader from the diagnostics page.
• Add an integration assertion that the ECharts runtime is same-origin, immutable, and served from /_app/immutable/assets/.
• Document the first-party ECharts asset and static cache header behaviour.