docs(@projects/@magic-civilization): ✅ p3-26 B3 — improvement subsystem DONE (build + yield live headless)

Full chain wired + tested: BuildImprovement → pending (build_turns) → build-tick →
city_improvements → process_improvement_yields. State (cb451832e) + logic (f4e9d0211) +
FFI/harness (5d12b4bbe).

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

.project/objectives/p3-26-complete-headless-simulator.md

@@ -67,7 +67,7 @@ PvP/siege/lair combat, climate physics+weather+effects, 3 event categories.
 **Backlog (live-only → migrate into `mc-turn`):**
 - [x] **B1 Happiness + Golden Age** ✅ (7993ba7ca — happiness_phase.rs, wired post-economy-loop) — `mc-happiness` exists; tick per-turn (golden-age meter, anarchy).
 - [x] **B2 Unit + city healing** ✅ (7993ba7ca — healing.rs, wired post-climate) — HP regen (in-territory / fortified / city heal).
-- [ ] **B3 Improvements subsystem (FULLY ABSENT headless — verified 2026-06-26, not just the build-tick)**:
+- [x] **B3 Improvements subsystem — DONE 2026-06-26** ✅ (cf18e5768 state · ffe5fa0fb logic · 63362f9c4 FFI/harness). Full chain live: BuildImprovement → pending(build_turns) → build-tick → city_improvements → process_improvement_yields. Was fully absent; now state+logic+boot all wired+tested. Original finding below:
   - `TurnProcessor::improvement_yield_table` is on the fresh-per-turn processor and is NEVER
     populated by `apply_end_turn` (only set manually in unit tests) → `process_improvement_yields`
     no-ops in real play.