Client not always unregistered when removing its iframe

[danielwiehl]

Describe the bug

It turned out that sometimes clients are not unregistered when removing their iframe.

To Reproduce

Steps to reproduce the behavior:

1. Open Testing App of the SCION Microfrontend Platform: https://scion-microfrontend-platform-testing-app.vercel.app
2. Open the DevTools (DevTools toggle button in the upper right corner)
3. Close the DevTools
4. See the warning logged to the console after one minute that a stale client was detected

Or for a testing app microfrontend:

1. Open Testing App of the SCION Microfrontend Platform: https://scion-microfrontend-platform-testing-app.vercel.app
2. Open the DevTools (DevTools toggle button in the upper right corner)
3. Load the router page into the left outlet: https://scion-microfrontend-platform-testing-app1-v1-0-0-rc-12.vercel.app/#/outlet-router
   3.1. Enter 'devtools' into the outlet field
   3.2. Enter 'https://scion-microfrontend-platform-testing-app3-v1-0-0-rc-12.vercel.app/#/publish-message' into the URL field
   3.3. Click 'Navigate'
4. Close the DevTools
5. See the warning logged to the console after one minute that a stale client was detected

Analysis

The unload handler of the MicrofrontendPlatformStopper is invoked and the disconnect message published to the broker. However, the broker never receives the disconnect message. Listening to the pagehide event also leads to the same result.

Expected behavior

The client is disposed when removing its iframe.

Environment

• SCION Microfrontend Platform version: 1.0.0-rc.12
• Browser: Chrome 108.0.5359.125