In dev, accessing a path not in `src/routes` causes the event.platform property to be undefined

[yutak23]

Describe the bug

It is similar to the following issue, but differs in essence.
#10389

The PR allows the platform property to be emulated even in dev/preview, but when requesting a path that does not exist (which should be 404), the platform property is undefined.

I think the reason for this error is that event.platform is emulated only under the condition that if (route) is true.
I believe that this problem can be solved by implementing an implementation that emulates event.platform only for DEV.
https://github.com/sveltejs/kit/blob/%40sveltejs/kit%402.5.18/packages/kit/src/runtime/server/respond.js#L216

Reproduction

1. Implement as follows.

// src/hooks.server.js
import { sveltekitSessionHandle } from 'svelte-kit-sessions';
import { sequence } from '@sveltejs/kit/hooks';
import KvStore from 'svelte-kit-connect-cloudflare-kv';
import { SESSION_SECRET } from '$env/static/private';
...
/** @type {import('@sveltejs/kit').Handle} */
const sessionHandle = async ({ event, resolve }) => {
	// https://kit.svelte.dev/docs/adapter-cloudflare#bindings
	const store = new KvStore({ client: event.platform.env.SESSION_NAMESPACE });
	const sveltekitSession = sveltekitSessionHandle({
		secret: SESSION_SECRET,
		saveUninitialized: true,
		cookie: {
			maxAge: 60 * 60 * 24 * 14, // 14 days
			secure: !dev,
			sameSite: 'lax'
		},
		store
	});

	return sveltekitSession({ event, resolve });
};

export const handle = sequence(sessionHandle, ...);

2. Create wrangler.toml as follows

kv_namespaces = [
  { binding = "SESSION_NAMESPACE", id = "<ignored>", preview_id = "<ignored>" },
]

3. Set svelte.config.js as follows

// svelte.config.js
import adapter from '@sveltejs/adapter-cloudflare';

/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		adapter: adapter({
			routes: {
				include: ['/*'],
				exclude: ['<all>']
			}
		}),
	}
};

export default config;

4. npx vite dev
5. Access paths that are not defined, e.g. /not_found
6. error occur

TypeError: Cannot read properties of undefined (reading 'env')
    at sessionHandle (/home/study/workspace/pj/src/hooks.server.js:15:53)
    at apply_handle (/home/study/workspace/pj/node_modules/@sveltejs/kit/src/exports/hooks/sequence.js:85:11)
    at Object.eval [as handle] (/home/study/workspace/pj/node_modules/@sveltejs/kit/src/exports/hooks/sequence.js:74:10)
    at Module.respond (/home/study/workspace/pj/node_modules/@sveltejs/kit/src/runtime/server/respond.js:323:40)

Logs

No response

System Info

System:
    OS: Linux 5.14 AlmaLinux 9.3 (Shamrock Pampas Cat)
    CPU: (2) x64 Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
    Memory: 3.67 GB / 7.49 GB
    Container: Yes
    Shell: 5.1.8 - /bin/bash
  Binaries:
    Node: 18.20.2 - ~/.nodebrew/current/bin/node
    Yarn: 1.22.22 - ~/.nodebrew/current/bin/yarn
    npm: 10.5.0 - ~/.nodebrew/current/bin/npm
  npmPackages:
    @sveltejs/adapter-cloudflare: ^4.7.0 => 4.7.0 
    @sveltejs/kit: ^2.5.18 => 2.5.18 
    @sveltejs/vite-plugin-svelte: ^3.1.1 => 3.1.1 
    svelte: ^4.2.18 => 4.2.18 
    vite: ^5.3.5 => 5.3.5

Severity

serious, but I can work around it

Additional Information

No response

[eltigerchino]

duplicate of #12512