docs(#145): implementation plan — cell-relative physics frame (7 slices)
Bite-sized, TDD-structured 7-slice plan for subagent-driven execution:
(1) Position/Frame types + GetBlockOffset, (2) PhysicsBody carries
Position, (3) membership via AdjustToOutside — closes the cascade,
(4) inter-tick collision state cell-relative + validate_transition
lockstep, (5) wire off Position, (6) _liveCenter render-only, (7)
teleport velocity-idle. Conformance via transform-on-read.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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