Add tests for SSE log context propagation across fiber boundaries

[jsxs0]

Summary

Add tests for the log context capture/restore cycle in SSE::Application, where parent fiber log tags are saved during initialization and restored in the child fiber spawned by start_stream.

Context

While working on the SSE specs for #248 and #264, I noticed that every aspect of SSE::Application now has dedicated test coverage: graceful shutdown (#261), connection cleanup for raw streams (#248), single-value streams (#264). But the context propagation itself had none.

The capture happens at initialization:

@log_tags, @log_context = Fiber[:__rage_logger_tags], Fiber[:__rage_logger_context]

The restore happens in the streaming fiber:

Fiber.schedule do
  Fiber[:__rage_logger_tags], Fiber[:__rage_logger_context] = @log_tags, @log_context

This is the mechanism that ensures log correlation survives the fiber boundary. Without it, a streaming response loses its request ID and any custom log context.

Test plan

4 tests covering:

• Capture from parent fiber on initialization

• Restore in child fiber for enumerator streams

• Restore in child fiber for proc streams

• Nil context handled gracefully

  bundle exec rspec spec/sse/ -- 57 examples, 0 failures

[rsamoilov]

🚀