docs(plan): Phase A4 — multi-cell BSP implementation plan
Five tasks: pre-flight baseline → CellTransit.FindCellSet (3 tests + impl
+ commit) → Transition.CheckOtherCells (6 tests + impl + commit) →
FindEnvCollisions wire-up (1 integration test + commit) → visual verify
at Holtburg inn vestibule → roadmap + handoff doc update.
Each implementation task is TDD: write failing tests, verify red,
implement, verify green, run baseline, commit. Three commits land
A4 in the codebase, fourth commit lands the docs.
Spec: docs/superpowers/specs/2026-05-20-phase-a4-multi-cell-bsp-design.md
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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