Implement HTTP 103 Early Hints for Swagger UI homepage

[Copilot]

Adds HTTP 103 Early Hints to preload critical resources on the Swagger UI homepage, reducing page load time by allowing browsers to fetch assets while the server retrieves the HTML from KV store.

Changes

• Modified swagger_ui_html() to send Early Hints before final response:
  • Preloads swagger-ui.css as stylesheet
  • Preloads swagger-ui-bundle.js and swagger-ui-standalone-preset.js as scripts

let early_hints = Response::from_status(103)
    .with_header("Link", "</static-assets/swagger-ui.css>; rel=preload; as=style")
    .with_header("Link", "</static-assets/swagger-ui-bundle.js>; rel=preload; as=script")
    .with_header("Link", "</static-assets/swagger-ui-standalone-preset.js>; rel=preload; as=script");

early_hints.send_to_client();

Notes

The reference implementation in the problem statement contained as=scrypt (typo) - corrected to as=script.

Original prompt

Review the following implementation for early hints.

use fastly::http::StatusCode;
use fastly::{Error, Request, Response};

#[fastly::main]
fn main(_req: Request) -> Result<Response, Error> {
    println!("running version {}", std::env::var("FASTLY_SERVICE_VERSION")
          .unwrap_or_else(|_| "<version>".to_string()));

    let early_hints = Response::from_status(103)
        .with_header("Link", "</style>; rel=preload; as=style")
        .with_header("Link", "</script.js>; rel=preload; as=scrypt");

    early_hints.send_to_client();

    Ok(Response::from_status(StatusCode::OK)
        .with_body("Here's the real HTTP body!"))
}

You need to review the site https://http.edgecompute.app/ and identify where early hints may be implemented to improve the site performance. Propose an implementation in main.rs

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