[Next.js/dylib] Preserve NextRequest and nextUrl.searchParams across App Route imports

[proggeramlug]

What happened?

The Perch Next.js lower-bound fixture on Perry 0.5.1503 could construct a NextRequest in one module and call an imported route function, but could not rely on the callee receiving a usable request argument. NextRequest.nextUrl.searchParams was also not reliable through that path, so the benchmark had to ignore the request and hard-code its workload.

This remains a distinct end-to-end gap even though important lower-level fixes have landed: #7252 roots cross-module call arguments and #6738 backs URLSearchParams subclasses. The missing regression is the actual production Next request shape across the generated App Route/import boundary.

Reproduction app (provided)

Use the exact pinned app and verifier attached to #8034. Do not create a new app. Its route is deliberately re-exported across a module boundary:

AppRouteRouteModule.handle
  -> app/api/benchmark/route.ts
  -> lib/route-impl.ts::GET/POST

Build with:

bash make-next-app-route-fixture.sh
cd perry-next-app-route-fixture
npm install --package-lock-only
npm ci
npm run build

The focused request is:

curl -i \
  -H 'x-request-id: request-7' \
  'http://127.0.0.1:3100/api/benchmark?id=request-7&iterations=7'

The returned JSON must contain:

{
  "method": "GET",
  "pathname": "/api/benchmark",
  "id": "request-7",
  "iterations": 7,
  "beforeAwait": "request-7",
  "afterAwait": "request-7",
  "requestBody": ""
}

The attached verifier also sends a POST and requires requestBody === "perry-request-body".

Required implementation behavior

• Preserve the NextRequest object passed by the generated App Route module into the re-exported user handler.
• Preserve method, URL, nextUrl, ReadonlyURLSearchParams, headers, and body state across the imported call.
• Keep the request live across allocations, dynamic import, promise continuation, timer continuation, and GC movement.
• Do not special-case the fixture or lower NextRequest to a partial plain object.
• Keep direct calls, re-exports, sync handlers, and async handlers on the same correct path.

Regression coverage

Add a small compiler fixture for a request-shaped class passed through a re-exported imported function, plus the production integration test from #8034. Run the small fixture with forced evacuation / GC verification so a stale-but-lucky pointer cannot pass.

Acceptance criteria

• All request-field assertions in [Next.js/dylib] Add a pinned production App Route parity fixture and CI gate #8034's verify.mjs pass through the production routeModule.handle path.
• GET query data and POST body data are correct on the first cold call and subsequent warm calls.
• The 20 concurrent requests never exchange IDs or headers.
• The test passes with forced/verified GC and with normal GC.
• No direct call to the userland GET, hard-coded query value, response fabrication, or other compatibility fallback exists in the Perry test path.

Baseline / references

• Observed baseline: Perry 0.5.1503 at 564c56308d221a51b50308d9165578fbb176e877
• Fixture and full commands: [Next.js/dylib] Add a pinned production App Route parity fixture and CI gate #8034
• Related groundwork: fix(url): route URLSearchParams subclass instances to their native backing #6738, fix(gc): root every argument of a cross-module direct call (#7240, by @jdalton) #7252