Fetch: new Response()/new Request() — instanceof always false and .constructor is undefined (no prototype link) #5433

Summary

x instanceof Response (and instanceof Request) is always false, and x.constructor is undefined, for the native Fetch handles — even for an object freshly created with new Response(...). Field access (.status, .headers, …) works, but the prototype/constructor link is missing, so any code that discriminates a union with instanceof Response misbehaves.

Environment

• perry 0.5.1189, main @ 0cc6ee14c, built from source
• macOS arm64
• No dependencies.

Repro

repro.ts:

const r = new Response('hi', { status: 200 });
console.log('typeof r             :', typeof r);
console.log('r instanceof Response:', r instanceof Response);
console.log('r.constructor?.name  :', (r as any).constructor?.name);
console.log('r.status             :', r.status);

const q = new Request('http://x/');
console.log('q instanceof Request :', q instanceof Request);

perry compile repro.ts -o repro && ./repro

Actual

typeof r             : object
r instanceof Response: false      <-- expected true
r.constructor?.name  : undefined  <-- expected "Response"
r.status             : 200
q instanceof Request : false      <-- expected true

Expected

new Response() instanceof Response === true and r.constructor === Response (matching Node/Bun/browsers), so instanceof-based discrimination works.

Impact

Very common idiom — e.g. a guard that returns either a value or a Response:

const auth = gate(c);            // AuthContext | Response
if (auth instanceof Response) return auth;   // always false under perry
use(auth.user.id);               // falls through, throws on the Response

This is the cause of a class of TypeError: Cannot read properties of undefined we hit across ~25 admin handlers in a Hono app. Workaround is duck-typing ('status' in x / a field-presence type guard). Related to the constructor-binding work in #2608/#2640.