Per spec FR1 + Phase 1.4 + architecture feedback (data != view):
- Data classes DiffHunk, DiffFile -> src/patch_modal.py (alongside PendingPatch; all patch-domain data)
- Operations parse_diff/parse_hunk_header/get_line_color/apply_patch_to_file (called by gui_2) -> src/gui_2.py
- GUI is a pure view; data lives elsewhere; no new files per AGENTS.md
Tests: tests/test_diff_viewer.py imports from src.gui_2 (parse_diff/apply_patch_to_file) and src.patch_modal (DiffFile/DiffHunk).
- Create src/patch_modal.py with PatchModalManager class
- Manage patch approval workflow: request, apply, reject
- Provide singleton access via get_patch_modal_manager()
- Add 8 unit tests for modal manager