feature-implement

# Implement and test 1. **Implement the design.** Keep the change focused on the requirements. Follow the repository's conventions in `CLAUDE.md`, including framework-owned instructions, database query names, deprecation notes, and comment style. 2. **Test it.** Read `tests/README.md` and `tests/_helpers/README.md`, then the nearest existing scenario. Reuse or extend existing coverage before adding setup. Put input matrices at the lowest reliable layer; add E2E only for a distinct process, transport, or browser boundary. - Map every covered CUJ to at least one test that exercises the new behavior. There is no fail-before proof for new behavior, but each test must fail if the feature were removed; a test that only passes is not coverage. - Run the directly affected test modules and focused checks. Do not run the full repository suite locally; CI owns that. - Check environment-derived defaults with ambient variables populated, so a test does not pass only because of the local environment. 3. **Assess the impact.** Load `otto-impact-assessment` and apply it to the full diff. Record the results in the handoff's `impact_assessment` and `test_audit`. If a requirement turns out to be infeasible, stop building it, mark its CUJs not covered with the reason, and continue with the rest. Then load `feature-demo`.