docs(@projects/@magic-civilization): 🏛️ p3-29 — Rail-1 turn unification objective (the real DRY fix)

Owner flagged the duplication: live game runs GDScript turn orchestration (turn_processor.gd
_process_* + EcologyState.tick) while headless runs mc-turn::step — two turn orchestrations.
This session built mc-turn::step into the complete single source of truth; p3-29 is the capstone:
switch turn_manager to GdTurnProcessor.step (bridge already exists at lib.rs:6354), render the
TurnResult for UI, delete the GDScript orchestration. HIGH-STAKES live-game rewrite — needs a
render proof before merge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.project/objectives/p3-29-rail1-turn-unification.md

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+---
+id: p3-29
+title: Rail-1 turn unification — live game calls the Rust turn, delete GDScript orchestration
+priority: p3
+scope: game1
+owner: warcouncil
+status: open
+updated_at: 2026-06-27
+---
+
+## Summary
+
+**The DRY / Rail-1 violation (verified 2026-06-27).** There are TWO turn orchestrations:
+- LIVE: `turn_manager.gd` → `turn_processor.gd::_process_*` (GDScript) + `EcologyState.tick` +
+  `WorldsimState` — GDScript orchestrating the turn.
+- HEADLESS: `GdPlayerApi` → `mc_turn::TurnProcessor::step` (Rust).
+
+The system *math* lives once in the Rust crates (DRY). The turn *orchestration* is duplicated —
+and the p3-26/p3-27 work this session added happiness/healing/improvements/recipes/equipment/
+ecology to `mc-turn` while the live game still runs its GDScript copies (e.g. `EcologyState.tick`
+duplicates the new Rust `ecology_phase`). This session BUILT `mc-turn::step` into the complete
+single source of truth; this objective is the capstone that makes it actually single.
+
+The bridge already exists: `GdTurnProcessor::step(GdGameState)` (api-gdext/src/lib.rs:6354) runs
+`mc_turn::TurnProcessor::step` on the LIVE game's state. The live turn just doesn't call it.
+
+## Acceptance
+
+- [ ] `turn_manager.gd` runs the turn via `GdTurnProcessor.step(GameState)` instead of the
+  per-player `proc._process_*` loop.
+- [ ] The returned `TurnResult` is rendered to UI (EventBus signals: chronicle, combat log,
+  flora succession, notifications) — GDScript translates the result, emits no sim logic.
+- [ ] `turn_processor.gd::_process_*` orchestration + the duplicate `EcologyState.tick` deleted
+  (or reduced to UI-only translation).
+- [ ] WorldsimState/terraform: either ported into `mc-turn` (preferred, completes Rail-1) or
+  kept as the one remaining GDScript-driven pass with a tracked carve-out.
+- [ ] **Render proof**: a `scenes/tests/` proof scene + screenshot showing the live game plays
+  a turn correctly through the Rust step (UI parity with the old GDScript turn).
+- [ ] GUT green; headless `mc-turn` already proven (it IS the step being adopted).
+
+## Notes
+
+Created 2026-06-27 after the owner flagged that "headless runs every system the live game does"
+is duplication, not DRY. HIGH-STAKES: rewrites the playable game's turn loop — must not merge
+without the render proof (Rail UI rule + phase-gate). Sequence: (1) audit what the GDScript loop
+emits vs `TurnResult`; (2) wire turn_manager → GdTurnProcessor.step behind the result-render;
+(3) delete the GDScript orchestration; (4) render-proof on apricot/plum. This is the true
+Rail-1 finish line — bigger than B7 (per-building queues), which becomes moot once the live
+game runs the Rust turn (which has the model the unified turn will use).