Split the frontend bundle: 2 MB gzipped ships before first paint

[roman1887]

Problem

The production JavaScript bundle is a single 6.8 MB main.js with no code splitting. Enabling gzip in #261 brought the transfer down to 2.0 MB, which made the site usable again — but 2 MB before first paint is still a lot, and compression is a mitigation rather than a fix.

Before #261 this made demo.actyze.ai effectively unusable: a headless browser could not finish domcontentloaded within 60 seconds on a normal connection.

What is in the bundle

From frontend/package.json, all of these are pulled into the single entry chunk:

Package	Why it is heavy
plotly.js-dist-min	~3 MB on its own; the largest single contributor
xlsx	spreadsheet export
jspdf	PDF export
html2canvas	screenshot/export path
@uiw/react-codemirror + @codemirror/lang-sql	SQL editor
@mui/material + @mui/icons-material	UI framework

Most of these are only needed on specific screens or user actions. A user who opens the dashboard and never exports anything still downloads xlsx, jspdf and html2canvas.

Suggested approach

1. Measure first. Add source-map-explorer or webpack-bundle-analyzer and record what the actual split looks like — the table above is inferred from dependencies, not measured.
2. Lazy-load the obvious candidates with React.lazy() + Suspense:
   • the export paths (xlsx, jspdf, html2canvas) behind the export buttons
   • the SQL editor (codemirror) behind the query view
   • Plotly behind the chart components
3. Consider plotly.js-basic-dist-min instead of the full distribution if only standard chart types are used. This alone could remove a large fraction.
4. Route-level splitting via React.lazy on the router.

Note on tooling

The app is on react-scripts@5.0.1 (Create React App), which is unmaintained and gives limited control over chunking. Migrating to Vite would make this substantially easier and is worth evaluating as part of the work — though it should be a deliberate decision, not a side effect.

Definition of done

• Initial JS transfer meaningfully below the current 2.0 MB gzipped
• Export, SQL editor and chart functionality all still work
• A bundle size budget enforced in CI so this cannot silently regress again

Context

Compression is already in place (#261), so this is no longer urgent — but it is the actual fix. Related: #261.