Feature check is not properly done at trigger level

[kate-goldenring]

I have a spin application with 1 HTTP triggered component and 1 MQTT component. The HTTP component uses internal service chaining but not the MQTT one. Regardless, when i go to run the app, I get the error:

Error: This application requires the following features that are not available in this version of the 'mqtt' trigger: local_service_chaining A trigger exited unexpectedly. Terminating.

[kate-goldenring]

We seem to declare host requirements on the app level, yet assess them on the trigger level.

[kate-goldenring]

This was also an issue with previous versions of Spin (confirmed with 2.7), possibly since the service chaining feature was added.

the work arounds are:

1. use self requests instead
2. run without the mqtt trigger using spin up --component-id ...

The issue appears to be because we are assessing the app's host requirements on a trigger level:

spin/crates/trigger/src/cli.rs

Line 185 in 2a9bf7c

if let Err(unmet) = app.ensure_needs_only(&T::supported_host_requirements()) {

One solution would be to place host_requirements under LockedComponent instead of LockedApp, scoping the requirements to a component.