fix: read version-specific h3 exports via runtime key

[CodeDredd]

Problem

1.0.0 breaks downstream Nuxt builds on h3 v1:

"toResponse" is not exported by node_modules/.pnpm/h3@1.15.11/node_modules/h3/dist/index.mjs,
imported by node_modules/.pnpm/h3-compression@1.0.0_h3@1.15.11/node_modules/h3-compression/dist/index.mjs

Root cause

helper.ts accessed the version-specific h3 symbols as namespace members — h3.toResponse (v2-only) and h3.send (v1-only). Our own dist keeps those as runtime member access, but when a downstream bundler (Nuxt → Nitro → Rollup) re-bundles dist/index.mjs, Rollup resolves h3.toResponse against the actually-installed h3@1.15.11, finds no such export, and converts it into a failing static named import. The same breaks in reverse for send under h3 v2.

Fix

Read version-specific symbols through a runtime key so no bundler can fold them into a static named import:

function h3Export<T>(name: string): T | undefined {
  return (h3 as Record<string, unknown>)[name] as T | undefined
}
const send = h3Export<...>('send')
const toResponse = h3Export<...>('toResponse')

Built output now emits h3[name] instead of h3.toResponse, so Rollup keeps import * as h3 with runtime indexing.

Test

test/dist-bundling.test.ts Rollup-bundles the built dist/index.mjs against a stub h3 that — like any single h3 major — exports neither send nor toResponse, and asserts there are no MISSING_EXPORT warnings. Verified it catches the regression: the old h3.toResponse pattern produces exactly "toResponse" is not exported by ...; the fixed pattern produces none. Version-independent, so it runs in every CI matrix cell.

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