Flatland: a minimal 2D artificial-life world engine (pure, process-free).

The instrument for the Flatland / ALife convergence front (faber-ecosystem PLAN_FLATLAND.md, exp058). A toroidal WxW grid holding plants (food cells) and avatars (evolved networks). This module is PURE physics -- sensing, movement, distance, nearest-object -- with no episode loop, no energy accounting and no randomness; the caller (the exp058 runner, later a scape adapter) owns those.

Held IDENTICAL to the 057 pursuit-evasion grid on purpose (DESIGN gate, 2026-07-23): same 9x9 torus, same 4-way argmax movement, same shortest-wrap RELATIVE-POSITION sensing modality (NOT DXNN2 range/ray sensors -- deferred as a confound). The ONLY thing Flatland adds over 057 is the energy economy (plants + eating + death), which lives in the caller. So a later coupling difference is attributable to the ecology, not the sensing.

Sensor vector (5 floats), same modality for every avatar: [OppDX, OppDY, PlantDX, PlantDY, EnergyFrac] where Opp* is the shortest-wrap signed delta to the opponent (0 if none), Plant* the delta to the nearest plant (0 if none), each normalised by W div 2, and EnergyFrac = Energy / E0.

Move codes: 0=North (y-1), 1=East (x+1), 2=South (y+1), 3=West (x-1).