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[docs] Document concrete Eventing.Subscribe<T> requirement #1533

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David Pine (IEvangelist) merged 1 commit into from
Aug 20, 2026
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[docs] Document concrete Eventing.Subscribe<T> requirement #1533

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9 changes: 9 additions & 0 deletions src/frontend/src/content/docs/app-host/eventing.mdx
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Expand Up @@ -113,6 +113,15 @@ builder.Eventing.Subscribe<AfterResourcesCreatedEvent>(
callbacks like `onResourceReady`.
</Aside>

<Aside type="caution">
`Eventing.Subscribe<T>()` requires `T` to be a concrete event type.
Subscribing to an interface or abstract class throws an `ArgumentException`.
For `IDistributedApplicationEvent`, the exception message is
`Cannot subscribe to interface or abstract type 'IDistributedApplicationEvent'. Subscribe to a concrete event type instead.`
Use a concrete event type such as `BeforeStartEvent` or
`AfterResourcesCreatedEvent`.
</Aside>

When the AppHost is run, by the time the Aspire dashboard is displayed, you should see the following log output in the console:

```plaintext {2,12} data-disable-copy
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