FixedPatchStepper: level-indexed API, drop 15 fine/child compatibility views
- Hierarchy documents level/pair/shape/frame conventions; edge_frame(l)
replaces the stepper's inline origin/spacing loop.
- Public per-level read-only state: layouts, boundaries, jets, leaf.
- set_jet_amplitude/read_raw_exchange/read_exchange_window: level= required.
- remap_child(child_objects=) -> remap_finest(objects=).
- _kernel_configs, _upload_boundary, _observed_boundary/_summarize split
construction and observation duplication; behavior unchanged.
- fine_level_origin -> fine_level_offset (a (y, x) index, not an origin).
- docs: migration map in docs/development/src_coherence.md.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
