## Investigation Found that this functionality is already implemented. The E2E tests for updating milestone project assignment were previously added in commit 2674e45 (TRCKR-647). ### Tests verified on master: tests/e2e/test_update_milestone_project_assignment.py **Test coverage (7 passing, 1 skipped):** - test_assign_milestone_to_project_from_none - PASSED - test_change_milestone_project_to_different_project - PASSED - test_clear_milestone_project_to_none - SKIPPED (known backend bug) - test_project_assignment_preserves_other_fields - PASSED - test_project_dropdown_shows_available_projects - PASSED - test_project_dropdown_searchable - PASSED - test_project_assignment_escape_cancels - PASSED - test_click_outside_closes_project_dropdown - PASSED The skipped test has a documented backend bug where PATCH /api/milestones/{id} does not handle project_id=null. ### Conclusion This issue appears to be a duplicate of TRCKR-647. All required E2E tests already exist and pass.