Rewrite handle_test_affected_paths from a canned always-success stub to a
live handler mirroring Build's handle_test_and_repair (A5): derive mock
inputs once via start_schema/generate_mock_inputs and persist a TestInput
(reused on retest), run run_draft (degrading to a synthesized failed Run on
exception), and mint a real immutable Run. Pass -> edit.review with a green
TestResultCard + summary. Fail -> real diagnose/propose_repair, stage
fc.diagnosis/staged_repair/risk, emit a red TestResultCard + ErrorCard (+
ChangeSetCard when intents are proposed) -> edit.await_repair (the B1 gate).
No auto-apply; apply_repair still runs only inside handle_await_repair's
approve_repair branch.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>