Option to load DuckDB WASM from CDN to reduce bundle size

[rernst76]

Description

Add an option to load DuckDB WASM files from jsDelivr CDN instead of bundling them into the build output. This would be controlled by an environment variable (e.g., EVIDENCE_DUCKDB_CDN=true), keeping the current bundled behavior as the default.

The @duckdb/duckdb-wasm library already supports CDN loading natively via getJsDelivrBundles() and selectBundle(), so this would leverage existing, officially supported functionality.

What problem would this solve?

When deploying Evidence sites to Cloudflare Pages, the build fails because DuckDB WASM files exceed Cloudflare's 25MB per-file limit. The WASM files bundled from @duckdb/duckdb-wasm are large enough to push deployments over this limit.

Currently, Evidence bundles DuckDB WASM files directly from node_modules via Vite's ?url imports in @evidence-dev/universal-sql. There's no way to configure Evidence to load these files externally, which makes deployment to size-constrained platforms impossible.

References:

• Cloudflare Pages limits
• DuckDB WASM CDN loading docs
• jsDelivr package

How should it work?

Set an environment variable to enable CDN loading:

  EVIDENCE_DUCKDB_CDN=true npm run build

Under the hood, this would change packages/lib/universal-sql/src/client-duckdb/browser.js from the current bundled approach:

  const DUCKDB_CONFIG = useEh
      ? {
          mainModule: (await import('@duckdb/duckdb-wasm/dist/duckdb-eh.wasm?url')).default,
          mainWorker: (await import('@duckdb/duckdb-wasm/dist/duckdb-browser-eh.worker.js?worker')).default
      }
      : {
          mainModule: (await import('@duckdb/duckdb-wasm/dist/duckdb-mvp.wasm?url')).default,
          mainWorker: (await import('@duckdb/duckdb-wasm/dist/duckdb-browser-mvp.worker.js?worker')).default
      };

To use the library's built-in CDN support:

  import { getJsDelivrBundles, selectBundle } from '@duckdb/duckdb-wasm';

  const JSDELIVR_BUNDLES = getJsDelivrBundles();
  const bundle = await selectBundle(JSDELIVR_BUNDLES);

  const DUCKDB_CONFIG = {
      mainModule: bundle.mainModule,
      mainWorker: bundle.mainWorker
  };

This keeps the default behavior unchanged while giving users an opt-in path for size-constrained deployments.