Two bugs in the folded-thinking rendering path:
1. Cache invalidation: changing folded_thinking did not invalidate cached
cell renders because the cell revision stayed the same. Now track
folded_cells in the cache and force re-render when it changes.
2. Index mapping: in the slow path (with collapsed cells), the cache idx
is a filtered position, but folded_cells uses original virtual indices.
Add original_index_map parameter to ensure_split so fold lookups
resolve correctly.
Added two regression tests:
- folded_thinking_cache_invalidation: verifies fold/unfold triggers re-render
- folded_thinking_with_collapsed_cells_uses_original_indices: verifies
correct fold behavior when collapsed_cells filtering is active
Hu Qiantao
b35b97ca6d