Pass non-HTML data from Component to Layout in SSR?

[datvm]

Similar to this question on SO: https://stackoverflow.com/questions/79677250/pass-parameters-from-a-component-to-a-layout-in-blazor-web-app-with-server-sta

I'm using .NET 8 Blazor Web App with static rendering. In MVC/Razor Pages, a page could pass variables (such as a bool) to the layout using ViewBag or similar mechanics, allowing the layout to conditionally show or hide parts of the UI, or in my case, add a class name to the tag.

In Blazor, I tried to implement something similar to HeadContent/HeadOutlet by using: a shared service, Cascading Parameters; I even have an event and call StateHasChanged when the property is set but it's not reflected in the layout.

There is one exception: if a HeadOutlet access that shared variable, the content is up-to-date.

How does HeadOutlet do that? Can I somehow change the content of Layout from a Component and notify SSR to match?

[datvm]

Surprisingly, for some reason, wrapping everything inside a SectionContent helps!

<SectionOutlet SectionName="Test" />

<SectionContent SectionName="Test">
    <CascadingValue Value="layoutModel">
        <PageTitle>@(layoutModel.Title ?? "NO TITLE")</PageTitle>

        <PageHeader />

        <div>
            Title: @(layoutModel.Title)
            @(layoutModel.Wide)
        </div>
    </CascadingValue>
</SectionContent>

The content is up-to-date with the value set by the Component!