Automatic middleware tracing

[nicohrubec]

docs

Solution brainstorm: Hook into the build process to automatically wrap any middleware calls with spans.

Tests: Update the tests that check that middleware emits correct spans. Since we already added manual instrumentation wrappers for this we just need to update the test applications to remove the manual wrapping and then this should still work.

[linear]

JS-1194

[nicohrubec]

From initial testing it seems that adding a middleware doesn't change the information we have available in the server entry point, i.e. our existing wrapper for the server entry point won't be enough to instrument this. Instead, we will need some other type of mechanism to instrument this. There is many ways to set middleware in tss applications. For instance, there is three types of tss middleware and each needs to be enabled in a different place in tss applications. Therefore, I think adding additional API for manual wrapping of these places would be lots of friction and people would probably just not do it. Alternatively, I think the way to go here is to go with automatic instrumentation via a custom otel integration that hooks into relevant tss API. Concretely, this should be:

• createFileRoute -> server -> middleware for request middleware
• createServerFn.middleware() for server function middleware
• createStart -> requestMiddleware() for global middleware