Adds the transport-agnostic pipeline orchestrator. Each step implements
async validate + process; the runner wraps both in a Timer, writes
per-step entries to response.metadata.timings, and aborts on the first
IXException by writing response.error.
- Step exposes a step_name property (defaults to class name) so tests and
logs label steps consistently.
- Timer is a plain context manager that appends one {step, elapsed_seconds}
entry on exit regardless of whether the body raised, so the timeline
stays reconstructable for failed steps.
- 9 unit tests cover ordering, skip-on-false, IXException in validate vs.
process, timings populated for every executed step, and shared-response
mutation across steps. Non-IX exceptions propagate.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
