- _exchange_spacing/_exchange_centers (two more per-level lists, only read
for levels that have a boundary) become _BlockedBoundary.spacing/centers.
- _level_blocks dropped: remap_finest reads each layout's own .block.
- _device_boundaries -> _boundaries: the record holds host geometry, tables,
Jets and device handles, so 'device' was misleading (the old host-only
_boundaries list no longer exists). Tests migrated mechanically.
Remaining per-level lists (_layouts, _level_cfgs, _leaf, _state, _boundaries)
are the immutable construction plan, built before the memory preflight and
kept after close; _levels holds device handles only and is cleared on close.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
