[gbradham]

Summary

• See the arena: Session Review finds each session's drawn arena and outlines it on the video. It looks for a saved <session>_arena.json beside the session or its video, then for the batch's pose_calibration.json. A new Arena menu (Draw arena… / Load arena…) saves one beside the session. A new Arena transport toggle shows or hides the outline and grid.
• Grid: Range tab → Exploration → Grid (Off, 2×2 … 20×20), remembered in settings. Cells are laid out in floor centimetres and mapped through the arena homography, so under a tilted camera every cell is the same patch of floor. Round and plus-maze arenas count only cells whose centre is on the floor.
• Exploration statistic: cells entered, % explored and the time to enter every cell over the selected range. Visited cells are shaded on the video. The numbers are also new epoch-table metrics and appear in the CSV exports for every session in the cohort.

New Qt-free module: glider/analysis/behavior/exploration.py.

Notes

• A cell counts as entered after a single scored frame of the body centre inside it. There is no minimum time in the cell yet.
• Live recordings don't save the arena corners, so they need "Draw arena…" once.

Test plan

• tests/unit/analysis/behavior/test_exploration.py: geometry, perspective, coverage counts, window limits, finding the arena file and the batch calibration
• TestArenaGrid in tests/unit/gui/behavior/test_analysis_window.py: inspector numbers, grid change, Off, missing arena, cohort rows and metric catalog, saving, painting
• Session Review, analysis and onboarding suites: 2449 passed; ruff and black clean
• Try it on a real cohort with a drawn arena