Fix flaky test tests/site_chat/test_prospect_data.py::test_no_activity_row_keeps_the_erased_persons_data

The merge lane saw `tests/site_chat/test_prospect_data.py::test_no_activity_row_keeps_the_erased_persons_data` fail and then pass on a rerun of the same tree. - Test: `tests/site_chat/test_prospect_data.py::test_no_activity_row_keeps_the_erased_persons_data` - Tree: `6af3d7e68231ec7081ae78d074aeed9b9d602832` - Lane task: 10219 - Flake record: 01a177a9-3ed6-77eb-9e6b-6d4ba6d840ab Make it deterministic; do not delete it unless it tests nothing.

Fixed flake: capture rows' random hex console_session could spell "ada", and the scan raced the fire-and-forget capture. Test now waits for its 3 rows (captured_writes + user_id scope) and matches erased data exactly. Quick gate green; PR #6979 queued. Memory: none applied.