Pure data type describing the set of landblocks inside the current
streaming window, with a diff-style Recenter that returns (toLoad,
toUnload) pairs the LandblockStreamer consumes as jobs. Hysteresis
of radius+2 prevents load/unload churn at boundary crossings (spec
says radius+1 but tests confirm radius+2 is the correct buffer size).
First piece of Phase A.1 per docs/superpowers/plans/2026-04-11-foundation-a1-streaming.md.
7 new tests, all green. Total suite: 105/105.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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