[Bug]: WebSocketRoute crashes with KeyNotFoundException when a close event omits `code`/`reason` during Browser.CloseAsync with a connected mock route

[KrzysFR]

Version

1.61.0

Steps to reproduce

using Microsoft.Playwright;

using var pw = await Playwright.CreateAsync();
var browser = await pw.Chromium.LaunchAsync(new() { Headless = true });
var context = await browser.NewContextAsync();

await context.RouteAsync("**/*", route => route.FulfillAsync(new()
{
    Status = 200,
    ContentType = "text/html",
    Body = "<script>new WebSocket('wss://mock.local/ws');</script>",
}));

// mock server: never calls ConnectToServerAsync
await context.RouteWebSocketAsync("**/ws", ws => ws.OnMessage(frame => ws.Send(frame.Text)));

var page = await context.NewPageAsync();
await page.GotoAsync("https://mock.local/");
await page.WaitForTimeoutAsync(500); // let the WS connect

await browser.CloseAsync(); // <- throws

Expected behavior

Browser.CloseAsync() should not throw in this case.

Actual behavior

Unhandled exception. System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
   at System.Text.Json.JsonElement.GetProperty(String propertyName)
   at Microsoft.Playwright.Core.WebSocketRoute.OnMessage(String method, JsonElement serverParams) in /_/src/Playwright/Core/WebSocketRoute.cs:line 99
   at Microsoft.Playwright.Transport.Connection.Dispatch(PlaywrightServerMessage message)
   ...
   at Microsoft.Playwright.Core.Browser.CloseAsync(BrowserCloseOptions options)

Additional context

Analysis

In the wire protocol, the closePage / closeServer events of WebSocketRoute carry optional
code and reason — the TypeScript client types the handlers accordingly
(packages/playwright-core/src/client/network.ts):

private _onServerClose?: (code: number | undefined, reason: string | undefined) => any;

But WebSocketRoute.OnMessage in the .NET binding reads them with the throwing accessor for both
events, in both the handler branch and the forwarding branch :

serverParams.GetProperty("code").GetInt32()
serverParams.GetProperty("reason").GetString()
serverParams.GetProperty("wasClean").GetBoolean()

When the browser (or page/context) is closed while a mocked WebSocket is still connected the close
event arrives without code/reason, JsonElement.GetProperty throws and the exception escapes
through Connection.Dispatch, failing the in-flight Browser.CloseAsync() call.

It should probably use TryGetProperty with null/default value fallback instead ?

Workaround

For now, I track live IWebSocketRoute instances and close them explicitly with a code before tearing down
pages/context/browser:

await ws.CloseAsync(new() { Code = 1000, Reason = "teardown" });

Environment

- Operating System: [Windows 11]
- CPU: [x64]
- Browser: [Chromium]
- .NET Version (TFM): [net10.0]