docs(@projects/@magic-civilization): 📊 p3-26 B8 7/12 (plague) + p3-27 fauna-disease-is-unwired finding

- B8 events now 7/12 (plague terrain blight added).
- Recorded that mc_ecology's disease system is config-only (no applier, only a validate-bin
  caller) — fauna plague/pandemic are a feature to write, not just wiring.

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

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

@@ -72,7 +72,7 @@ PvP/siege/lair combat, climate physics+weather+effects, 3 event categories.
 - [ ] **B5 Loot decay** — `mc-city` items; (disabled in live too).
 - [ ] **B6 Equipment/crafting** — `mc-city/recipes.rs`; add headless Craft action + tick (was gap 3).
 - [ ] **B7 Per-building queues** — dual-city-model unification (was gap 4).
-- [~] **B8 event categories — 6/12 live** ✅ wildfire/drought/volcanic/seismic/impact/tsunami (a18e1394b). Remaining: solar/glacial (need solar_forcing/glacial_forcing physics consumption); plague/pandemic/marine (need biosphere [[p3-27 ...]]); magical→G3.
+- [~] **B8 event categories — 7/12 live** ✅ wildfire/drought/volcanic/seismic/impact/tsunami (a18e1394b) + plague terrain-blight (4be44db3a). Remaining: solar/glacial (need solar_forcing/glacial_forcing physics consumption); pandemic+marine fauna-side + the fauna disease mechanism itself (see [[p3-27-biosphere-headless]]); magical→G3.
 - [ ] **Biosphere cluster → see [[p3-27 ...]]** (ecology population + flora succession + marine).
 
 Sequencing: B1/B2/B3 (self-contained turn-glue) parallelizable as separate modules; B6/B7

.project/objectives/p3-27-biosphere-headless.md

@@ -73,3 +73,19 @@ plague/pandemic/marine events.
 Tests: deterministic — seed a population + minimal real config (`config::load_real_config`
 test helper), tick via the phase, assert populations evolve + a flora transition applies +
 continuation JSON round-trips.
+
+## Finding 2026-06-26: the fauna disease system is config-only (unwired)
+
+While wiring bio-targeting events, discovered `mc_ecology::events` is **scaffolding without an
+applier**: it exposes `EventCategory`/`EventTierData` + `load_event_categories` (parses
+plague.json/pandemic.json/ecological.json) and `from_json`, but has **no function that applies
+disease mortality to `tile_populations`**. Its only caller is `mc-sim/src/bin/disease_validate.rs`
+(a config validator). It is NOT invoked by `EcologyEngine::process_step`, the headless turn, or
+the live game. So fauna plague/pandemic are unimplemented everywhere — a real feature to write,
+not just headless wiring:
+- Add `apply_disease(&mut tile_populations, &EventCategory, tier, density, rng)` to mc-ecology
+  (density-frequency from pandemic.json; mortality from tier data).
+- Drive it from `process_ecology_phase` (mc-player-api) using boot-loaded disease configs +
+  the same continuation-state persistence.
+The **terrain** side of plague (quality/biome blight) IS done as a mc-climate event category
+(4be44db3a); pandemic's terrain/T3-city-population side remains.