feat: streaming hydration support for JSX/SSR in Cloudflare Workers environment

Background / Motivation

When building SSR applications with Hono's JSX renderer on Cloudflare Workers, the current implementation returns a fully rendered HTML string. While this works well for simple pages, it misses the opportunity to leverage HTTP streaming for progressive hydration — a technique that significantly improves perceived load time (Time to First Byte / Largest Contentful Paint).

Modern frameworks like React 18+, Solid Start, and Qwik have demonstrated that streaming SSR with selective hydration can cut LCP by 30–60% on cold starts, which is especially impactful in edge environments where CPU time is limited.

Current Behavior

// Current: blocks until full render is complete
app.get('/', (c) => {
  return c.html(<MyPage />)
})
// → sends entire HTML document as one chunk

There is no built-in way to flush partial HTML to the client while remaining components are still rendering.

Proposed Solution

Add a streamHtml() / renderToReadableStream() helper that returns a ReadableStream and works natively with the Workers runtime:

import { streamHtml } from 'hono/jsx-stream'

app.get('/', (c) => {
  const stream = renderToReadableStream(
    <Suspense fallback={<LoadingShell />}>
      <AsyncDataPage />
    </Suspense>
  )
  return new Response(stream, {
    headers: { 'Content-Type': 'text/html; charset=utf-8' },
  })
})

Key requirements:

• Compatible with workerd / Cloudflare Workers runtime (no Node.js streams)
• Honors <Suspense> boundaries — flushes synchronous subtrees immediately, defers async ones
• Works alongside the existing @hono/react-renderer and native JSX renderer
• Optional: inject inline <script> hydration chunks after async boundaries resolve

Environment

• Runtime: Cloudflare Workers (workerd)
• Hono version: v4.x (latest)
• Renderer: hono/jsx (built-in) and/or @hono/react-renderer

Alternatives Considered

• Using hono/streaming with manual chunked writes — works but requires hand-rolling the HTML structure, no Suspense support
• Wrapping in a Service Worker on the client — adds complexity, defeats the edge-first purpose

Additional Context

This would position Hono as a strong SSR framework for edge-first applications on Workers. Happy to prototype an initial implementation if the team is open to the direction.