Step 6: downstream_client() no longer sends X-Request-Id, and request_id
is gone from the internal request bodies, models, function signatures
and log lines; correlation now travels as traceparent. The gateway's
public request_id stays (the contract tests require it) but is now the
trace ID, 32 hex digits and still a valid UUID, so the value the
frontend shows can be pasted into Tempo.
Step 7: delete tests/test_no_observability.py. It guarded the Phase 0
"no observability" state, which Phase 3 ends by design.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>