fix: prevent JS asset truncation for files larger than 8KB

[riasvdv]

Summary

• Fixes JS asset serving in LaravelHttpServer::asset() where files >8KB could be silently truncated
• The old code used fread() + ReadableResourceStream which has two bugs: fread() returns at most 8,192 bytes per call inside Amp's event loop, and ReadableResourceStream causes the content-length header to be stripped
• The fix uses file_get_contents() and returns the content as a string body directly, which correctly sets content-length and avoids truncation

The Bug

The asset() method served JS files through this pipeline:

$temporaryContent = fread($file, (int) filesize($filepath));
// ... write to php://temp ...
return new Response(200, [...], new ReadableResourceStream($file));

Three issues:

1. fread() short-read — Inside Amp's non-blocking event loop, fread() returns at most 8,192 bytes per call, not the full file
2. Missing content-length — Response::setBody(ReadableStream) calls removeHeader('content-length'), forcing chunked transfer encoding
3. stream_socket_shutdown() on php://temp — ReadableResourceStream::close() calls stream_socket_shutdown() on non-socket streams (undefined behavior)

This caused Craft CMS Control Panel pages to fail loading because their JS bundles (~50KB+) were truncated to 8KB.

The Fix

fclose($file);
$rawContent = file_get_contents($filepath);
$content = $this->rewriteAssetUrl($rawContent);
$response = new Response(200, [], $content);
$response->setHeader('Content-Type', $contentType);
return $response;

• file_get_contents() reads the entire file regardless of event loop context
• String body → ReadableBuffer → correct content-length header
• No stream cleanup issues

Tests

Three regression tests added:

• serves JS assets as string body instead of stream — Verifies response body is ReadableBuffer (not ReadableResourceStream) via reflection. Fails with old code
• sets content-length header on JS asset responses — Verifies content-length header matches file size. Fails with old code
• serves large JS files completely — End-to-end test via Playwright: creates >8KB JS file, loads it in a page, verifies a marker variable at the end of the file is accessible