Extend site state validator to ensure that multi-key listener strateg…

[gabordozsa]

…y is immutable (#2411)

Fixes #2411

[nluaces]

By using the reload type set to auto:
skupper system install --reload-type=auto
I can modify the strategy from the input resources, and it will be modified in the runtime resources as well.
I think the issue is that this validation is not done in the Refresh method that updates the site changes without restarting the router:

https://github.com/gabordozsa/skupper/blob/a12a254e5017d5f99ada2a9befca160c1ce54712/internal/nonkube/compat/site_state_renderer.go#L382

[gabordozsa]

By using the reload type set to auto: skupper system install --reload-type=auto I can modify the strategy from the input resources, and it will be modified in the runtime resources as well. I think the issue is that this validation is not done in the Refresh method that updates the site changes without restarting the router:

@nluaces I added the validation to theRefresh()method, too.

It works for me now: runtime will not pick up the strategy change from the input dir. However, I did not see any error message in the system-controller log. Is that okay?

[nluaces]

@gabordozsa I have tried your last changes and I think it works as expected:

2026/04/30 15:22:28 INFO Resource has been created: /output/namespaces/west/input/resources/multikey.yaml component=input.resource.handler namespace=west
2026/04/30 15:22:28 ERROR Failed to refresh site state: invalid multikeylistener: my-backend-multikey - strategy cannot be changed component=input.resource.handler namespace=west

I've got this from the system-controller log.