Summary

Handlers can now return eventStream instead of return eventStream.send().

EventStream extends HTTPResponse, so the existing toResponse →
prepareResponseBody branch (val instanceof HTTPResponse) renders it as the
response directly — streaming the readable side with the SSE headers. No
core / response.ts changes were needed.

app.get("/sse", (event) => {
  const eventStream = createEventStream(event);
  const interval = setInterval(() => eventStream.push("Hello world"), 1000);
  eventStream.onClosed(() => clearInterval(interval));
  return eventStream; // previously: return eventStream.send()
});

Details

• EventStream extends HTTPResponse: the transform stream is created before
  super() so its readable side becomes the response body, with status: 200
  and the SSE headers passed to super().
• Extracted an eventStreamHeaders(event) helper shared by the direct-return
  path and setEventStreamHeaders().
• send() is kept and fully backward-compatible (still stages headers on
  event.res and returns the readable), so return eventStream.send() keeps
  working.
• Prepared event.res.headers still merge in as before; HEAD / null-body
  handling comes for free via the HTTPResponse path.

Tests

• Added a regression test asserting the direct-return path streams events with
  text/event-stream and status 200 (runs in both web + node matrix).
• Updated docs/examples (return eventStream).
• Full suite green: 1610 passed, no type errors.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • SSE handlers can now return event streams directly for simpler streaming responses.
  • Added centralized SSE header handling to standardize response headers.

• Bug Fixes

  • Improved event stream response initialization and streaming behavior while keeping existing push/cleanup behavior.

• Documentation

  • Updated SSE guides and examples to show handlers returning the event stream directly.

• Tests

  • Added an SSE test covering direct event stream returns and verification of multiple streamed messages.