feat(abilities): add disasters & pandemics lever (v0.41.0, #63)

Add the 9th modular LLM ability: a turn-transient `TurnResult.disasters`
lever letting the LLM declare natural/man-made disasters (earthquake /
flood / volcanic / wildfire / famine / plague / epidemic) on a nation or
a region, applying a DETERMINISTIC (type, severity) stat dip (no hidden
randomness). Like the hybrid layer it owns no GameState field, needs no
db.ts change, and leaves no durable list — an ongoing plague/epidemic is
simply re-declared each turn it persists.

- shared/protocol.ts: DisasterType / DisasterSeverity / DisasterEvent /
  DisastersOps, and `TurnResult.disasters` (between `ideology` and
  `markers`; required, default `{ events: [] }`).
- server/abilities/disasters.ts: the ability module (validate / apply /
  schemaLine / constraint / isMeaningful / inert stub / empty payload; no
  stateFields). `DISASTER_EFFECTS` is the deterministic (type, severity)
  dip table (population never touched). Target resolution mirrors hybrid
  (a region key hits its SOLE owner; 0/2+ owners dropped) but has NO
  `from` field, so there is no self-target drop. Dips clamp to 0-100,
  mirror to the target's regions (regionStats), and re-derive the target
  nation's stats (same 0-region / no-entry guards).
- Registered last in ABILITIES (after ideology). System-prompt goldens
  regenerated (one schema line + one constraint bullet each); the
  user.txt golden stays byte-identical (payload() is {}).
- New server/abilities/disasters.test.ts (33 tests); registry.test.ts
  updated to the 9-ability contract.
- Secondary cleanups from the v0.40 refactor: AGENTS.md (abilities/ in
  the Layout tree + a "how to add a new ability" bullet + a disasters
  bullet), delete the orphaned validateTakeovers JSDoc, fold both inline
  `as unknown` casts into the top-level ./abilities import, and de-dup
  `str` (now imported from ./abilities/shared).

Version bumped 0.40.0 -> 0.41.0.

server/abilities/disasters.test.ts

@@ -0,0 +1,445 @@
+// Unit tests for the DISASTERS & PANDEMICS ability (v0.41.0, #63) — the
+// modular, turn-transient LLM-ability that applies a deterministic
+// (type, severity) stat dip to a nation or a single region. This is the
+// ability's own test file (the registry's cross-cutting guarantees — order,
+// distinct fields, the system/user goldens — are covered by
+// ./registry.test.ts). The stub never proposes a disaster, so the apply path
+// is exercised here, not by the e2e suite.
+
+import { describe, expect, it } from 'vitest';
+
+import type { AbilityCtx } from './types';
+import {
+  DISASTER_EFFECTS,
+  DISASTER_SEVERITIES,
+  DISASTER_TYPES,
+  applyDisasterEvent,
+  disasters,
+  isDisasterSeverity,
+  isDisasterType,
+  validateDisasterEvents,
+} from './disasters';
+
+import type { DisasterEvent, DisastersOps } from '../../shared/protocol';
+import type { GameState, Nation, NationStats, RegionStats } from '../../shared/types';
+
+// ---------------------------------------------------------------------------
+// Fixture helpers
+// ---------------------------------------------------------------------------
+
+/** Build a NationStats from the four canonical indices (military, economy, stability, population). */
+function NS(military: number, economy: number, stability: number, population: number): NationStats {
+  return { military, economy, stability, population };
+}
+
+/** Build a RegionStats from the four canonical indices. */
+function RS(military: number, economy: number, stability: number, population: number): RegionStats {
+  return { military, economy, stability, population };
+}
+
+/** A minimal nation: the given id/name/stats/region-key territory, neutral relations. */
+function mkNation(id: string, name: string, stats: NationStats, territory: string[]): Nation {
+  return { id, name, type: 'major', stats, territory, relations: {} };
+}
+
+/**
+ * A minimal GameState carrying the given nations (keyed by id) and per-region
+ * stats. Every other required field is at its fresh-game baseline, so a test
+ * can focus purely on the disaster dip.
+ */
+function mkState(
+  nations: Record<string, Nation>,
+  regionStats: Record<string, RegionStats>,
+): GameState {
+  return {
+    id: 'g1',
+    presetId: 'test',
+    presetTitle: 'Test',
+    playerNationId: Object.keys(nations)[0] ?? 'uk',
+    turn: 1,
+    date: '1939-09-01',
+    nations,
+    events: [],
+    pending: [],
+    version: 1,
+    unowned: [],
+    pendingNationOps: [],
+    markers: [],
+    regionStats,
+    wars: [],
+    trades: [],
+    embargoes: [],
+    industry: [],
+  };
+}
+
+/** A minimal AbilityCtx for the ability's `apply` (no manifests loaded). */
+function mkCtx(state: GameState, validRegionKeys?: ReadonlySet<string>): AbilityCtx {
+  return {
+    previous: state,
+    actingTurn: state.turn,
+    ...(validRegionKeys ? { validRegionKeys } : {}),
+  };
+}
+
+// ---------------------------------------------------------------------------
+// Type / severity constants + predicates
+// ---------------------------------------------------------------------------
+
+describe('DISASTER_TYPES / DISASTER_SEVERITIES', () => {
+  it('exposes exactly the seven types and three severities', () => {
+    expect([...DISASTER_TYPES]).toEqual([
+      'earthquake',
+      'flood',
+      'volcanic',
+      'wildfire',
+      'famine',
+      'plague',
+      'epidemic',
+    ]);
+    expect([...DISASTER_SEVERITIES]).toEqual(['minor', 'moderate', 'severe']);
+  });
+
+  it('every (type, severity) pair dips at least one stat, never population', () => {
+    for (const t of DISASTER_TYPES) {
+      for (const s of DISASTER_SEVERITIES) {
+        const dips = DISASTER_EFFECTS[t][s];
+        expect(dips).toBeDefined();
+        const keys = Object.keys(dips);
+        expect(keys.length).toBeGreaterThan(0);
+        expect(keys).not.toContain('population');
+        for (const k of keys) expect(dips[k as keyof typeof dips]).toBeLessThan(0);
+      }
+    }
+  });
+});
+
+describe('isDisasterType / isDisasterSeverity', () => {
+  it('accepts each known type and rejects unknown / non-strings', () => {
+    for (const t of DISASTER_TYPES) expect(isDisasterType(t)).toBe(true);
+    expect(isDisasterType('tsunami')).toBe(false);
+    expect(isDisasterType('Earthquake')).toBe(false); // case-sensitive
+    expect(isDisasterType('')).toBe(false);
+    expect(isDisasterType(42)).toBe(false);
+    expect(isDisasterType(null)).toBe(false);
+    expect(isDisasterType(undefined)).toBe(false);
+  });
+
+  it('accepts each known severity and rejects unknown / non-strings', () => {
+    for (const s of DISASTER_SEVERITIES) expect(isDisasterSeverity(s)).toBe(true);
+    expect(isDisasterSeverity('extreme')).toBe(false);
+    expect(isDisasterSeverity('Minor')).toBe(false); // case-sensitive
+    expect(isDisasterSeverity('')).toBe(false);
+    expect(isDisasterSeverity(3)).toBe(false);
+    expect(isDisasterSeverity(undefined)).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// validateDisasterEvents
+// ---------------------------------------------------------------------------
+
+describe('validateDisasterEvents', () => {
+  const valid: DisasterEvent = { type: 'earthquake', target: 'uk', severity: 'severe' };
+
+  it('accepts the { events: [...] } shape', () => {
+    expect(validateDisasterEvents({ events: [valid] })).toEqual([valid]);
+  });
+
+  it('accepts a bare array (lenient about the wrapper)', () => {
+    expect(validateDisasterEvents([valid])).toEqual([valid]);
+  });
+
+  it('drops an event with an unknown type, keeping the valid one', () => {
+    const out = validateDisasterEvents({
+      events: [
+        { type: 'tsunami', target: 'uk', severity: 'minor' },
+        valid,
+      ],
+    });
+    expect(out).toEqual([valid]);
+  });
+
+  it('drops an event with a missing type', () => {
+    const out = validateDisasterEvents({
+      events: [{ target: 'uk', severity: 'minor' }, valid],
+    });
+    expect(out).toEqual([valid]);
+  });
+
+  it('drops an event with an unknown severity, keeping the valid one', () => {
+    const out = validateDisasterEvents({
+      events: [
+        { type: 'plague', target: 'uk', severity: 'extreme' },
+        valid,
+      ],
+    });
+    expect(out).toEqual([valid]);
+  });
+
+  it('drops an event with a missing severity', () => {
+    const out = validateDisasterEvents({
+      events: [{ type: 'plague', target: 'uk' }, valid],
+    });
+    expect(out).toEqual([valid]);
+  });
+
+  it('drops an event with an empty / whitespace target', () => {
+    const out = validateDisasterEvents({
+      events: [
+        { type: 'plague', target: '   ', severity: 'minor' },
+        { type: 'plague', target: '', severity: 'minor' },
+        valid,
+      ],
+    });
+    expect(out).toEqual([valid]);
+  });
+
+  it('caps a non-empty detail at 300 chars and keeps a short one', () => {
+    const long = 'x'.repeat(500);
+    const out = validateDisasterEvents({
+      events: [
+        { type: 'plague', target: 'uk', severity: 'minor', detail: long },
+        { type: 'flood', target: 'de', severity: 'minor', detail: 'a short note' },
+      ],
+    });
+    expect(out).toEqual([
+      { type: 'plague', target: 'uk', severity: 'minor', detail: 'x'.repeat(300) },
+      { type: 'flood', target: 'de', severity: 'minor', detail: 'a short note' },
+    ]);
+  });
+
+  it('omits the detail key entirely when detail is empty / missing', () => {
+    const out = validateDisasterEvents({
+      events: [
+        { type: 'flood', target: 'uk', severity: 'minor', detail: '' },
+        { type: 'flood', target: 'de', severity: 'minor' },
+      ],
+    });
+    expect(out).toEqual([
+      { type: 'flood', target: 'uk', severity: 'minor' },
+      { type: 'flood', target: 'de', severity: 'minor' },
+    ]);
+    expect(out[0]).not.toHaveProperty('detail');
+  });
+
+  it('drops non-object event entries', () => {
+    const out = validateDisasterEvents({ events: ['not-an-object', 7, null, valid] });
+    expect(out).toEqual([valid]);
+  });
+
+  it('yields { events: [] } (here, []) for a missing / malformed top-level value', () => {
+    expect(validateDisasterEvents(undefined)).toEqual([]);
+    expect(validateDisasterEvents(null)).toEqual([]);
+    expect(validateDisasterEvents('nope')).toEqual([]);
+    expect(validateDisasterEvents(5)).toEqual([]);
+    expect(validateDisasterEvents({})).toEqual([]);
+    expect(validateDisasterEvents({ events: 'not-an-array' })).toEqual([]);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// applyDisasterEvent — the deterministic dip
+// ---------------------------------------------------------------------------
+
+describe('applyDisasterEvent', () => {
+  it('a nation target: dips the nation AND every region it owns, then re-derives (identical values pass through)', () => {
+    // uk owns three identical regions; all stats identical → the re-derived
+    // aggregate equals the dipped values exactly.
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1', 'g2', 'g3']) },
+      { g1: RS(50, 50, 50, 50), g2: RS(50, 50, 50, 50), g3: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'earthquake', target: 'uk', severity: 'moderate' });
+    // earthquake moderate = stability -4, economy -4 (military / population untouched)
+    expect(state.nations.uk.stats).toEqual(NS(50, 46, 46, 50));
+    for (const k of ['g1', 'g2', 'g3']) expect(state.regionStats[k]).toEqual(RS(50, 46, 46, 50));
+  });
+
+  it('a region target: dips ONLY the named region (the sibling region is untouched)', () => {
+    // uk owns g1 and g2 (identical). Target the region key g1 → only g1 dips.
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1', 'g2']) },
+      { g1: RS(50, 50, 50, 50), g2: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'wildfire', target: 'g1', severity: 'severe' });
+    // wildfire severe = economy -7 only
+    expect(state.regionStats.g1).toEqual(RS(50, 43, 50, 50));
+    expect(state.regionStats.g2).toEqual(RS(50, 50, 50, 50)); // untouched
+    // re-derive (equal weights, min-biased median) → the nation takes the dipped value
+    expect(state.nations.uk.stats).toEqual(NS(50, 43, 50, 50));
+  });
+
+  it('a region target resolved by a validKeys-gated key hits its sole owner', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(
+      state,
+      { type: 'famine', target: 'g1', severity: 'moderate' },
+      undefined,
+      new Set(['g1']),
+    );
+    // famine moderate = economy -4, stability -4
+    expect(state.regionStats.g1).toEqual(RS(50, 46, 46, 50));
+    expect(state.nations.uk.stats).toEqual(NS(50, 46, 46, 50));
+  });
+
+  it('clamps every dip at 0 (never negative)', () => {
+    // low stability + military; a severe plague (stability -9, military -6) floors both.
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(3, 50, 3, 50), ['g1']) },
+      { g1: RS(3, 50, 3, 50) },
+    );
+    applyDisasterEvent(state, { type: 'plague', target: 'uk', severity: 'severe' });
+    expect(state.nations.uk.stats).toEqual(NS(0, 50, 0, 50));
+    expect(state.regionStats.g1).toEqual(RS(0, 50, 0, 50));
+  });
+
+  it('a 0-owner region is untargetable (the event is dropped, nothing dips)', () => {
+    // 'x1' is owned by nobody; no validKeys supplied, so the owners check drops it.
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'plague', target: 'x1', severity: 'severe' });
+    expect(state.nations.uk.stats).toEqual(NS(50, 50, 50, 50)); // untouched
+    expect(state.regionStats.g1).toEqual(RS(50, 50, 50, 50));
+  });
+
+  it('a region with 2+ owners is untargetable (the event is dropped, neither dips)', () => {
+    // corrupt double-ownership of 'y1'
+    const state = mkState(
+      {
+        uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['y1']),
+        de: mkNation('de', 'DE', NS(60, 60, 60, 60), ['y1']),
+      },
+      { y1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'plague', target: 'y1', severity: 'severe' });
+    expect(state.nations.uk.stats).toEqual(NS(50, 50, 50, 50)); // untouched
+    expect(state.nations.de.stats).toEqual(NS(60, 60, 60, 60)); // untouched
+  });
+
+  it('an unknown region key (gated by validKeys) is dropped', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    // 'zzz' is not in the manifest → dropped before the owners check.
+    applyDisasterEvent(state, { type: 'plague', target: 'zzz', severity: 'severe' }, undefined, new Set(['g1']));
+    expect(state.nations.uk.stats).toEqual(NS(50, 50, 50, 50));
+  });
+
+  it('an unknown nation reference is dropped (no throw, no dip)', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'plague', target: 'ghost', severity: 'severe' });
+    expect(state.nations.uk.stats).toEqual(NS(50, 50, 50, 50));
+    expect(state.regionStats.g1).toEqual(RS(50, 50, 50, 50));
+  });
+
+  it('an ambiguous nation reference (two share the name) is dropped', () => {
+    const state = mkState(
+      {
+        a: mkNation('a', 'Same', NS(50, 50, 50, 50), ['g1']),
+        b: mkNation('b', 'Same', NS(70, 70, 70, 70), ['d1']),
+      },
+      { g1: RS(50, 50, 50, 50), d1: RS(70, 70, 70, 70) },
+    );
+    applyDisasterEvent(state, { type: 'plague', target: 'Same', severity: 'severe' });
+    expect(state.nations.a.stats).toEqual(NS(50, 50, 50, 50)); // untouched
+    expect(state.nations.b.stats).toEqual(NS(70, 70, 70, 70)); // untouched
+  });
+
+  it('resolves a nation by (case-insensitive) name, not just id', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'United Kingdom', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'epidemic', target: 'united kingdom', severity: 'moderate' });
+    // epidemic moderate = stability -4, military -2
+    expect(state.nations.uk.stats).toEqual(NS(48, 50, 46, 50));
+    expect(state.regionStats.g1).toEqual(RS(48, 50, 46, 50));
+  });
+
+  it('a 0-region nation keeps its directly-dipped stats (no re-derive to zero)', () => {
+    const iso = mkNation('iso', 'Iso', NS(50, 50, 50, 50), []);
+    const state = mkState({ iso }, {});
+    applyDisasterEvent(state, { type: 'epidemic', target: 'iso', severity: 'moderate' });
+    // epidemic moderate = stability -4, military -2 — the direct dip persists
+    expect(state.nations.iso.stats).toEqual(NS(48, 50, 46, 50));
+    expect(state.regionStats).toEqual({});
+  });
+
+  it('a region with no regionStats entry is skipped (the nation still dips + re-derives from its other regions)', () => {
+    // uk owns g1 (has stats) and g2 (no entry). Target the nation → the dip
+    // mirrors to g1 only (g2 has no entry to dip); re-derive uses g1 alone.
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1', 'g2']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    applyDisasterEvent(state, { type: 'earthquake', target: 'uk', severity: 'moderate' });
+    expect(state.regionStats.g1).toEqual(RS(50, 46, 46, 50));
+    expect(state.regionStats).not.toHaveProperty('g2'); // never created
+    expect(state.nations.uk.stats).toEqual(NS(50, 46, 46, 50));
+  });
+});
+
+// ---------------------------------------------------------------------------
+// The Ability object
+// ---------------------------------------------------------------------------
+
+describe('disasters (Ability)', () => {
+  it('owns the "disasters" field and declares NO durable state fields (turn-transient)', () => {
+    expect(disasters.field).toBe('disasters');
+    expect(disasters.stateFields).toBeUndefined();
+  });
+
+  it('default() and stub() are fresh, empty { events: [] } values', () => {
+    expect(disasters.default()).toEqual({ events: [] });
+    expect(disasters.stub()).toEqual({ events: [] });
+    // fresh on every call (never a shared mutable reference)
+    expect(disasters.default()).not.toBe(disasters.default());
+    expect(disasters.default().events).not.toBe(disasters.default().events);
+    expect(disasters.stub()).not.toBe(disasters.stub());
+  });
+
+  it('isMeaningful is true iff there is at least one event', () => {
+    expect(disasters.isMeaningful({ events: [] })).toBe(false);
+    expect(disasters.isMeaningful({ events: [{ type: 'plague', target: 'uk', severity: 'minor' }] })).toBe(
+      true,
+    );
+  });
+
+  it('payload() is always empty (the layer is turn-transient)', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    expect(disasters.payload({ state })).toEqual({});
+  });
+
+  it('validate() wraps the low-level validator into the { events } field shape', () => {
+    const valid = { type: 'flood', target: 'uk', severity: 'minor' } as DisasterEvent;
+    expect(disasters.validate({ events: [valid] })).toEqual({ events: [valid] });
+    expect(disasters.validate(undefined)).toEqual({ events: [] });
+    expect(disasters.validate([valid])).toEqual({ events: [valid] }); // bare array leniency
+  });
+
+  it('apply() wires ctx.geoOf + ctx.validRegionKeys through to the dip', () => {
+    const state = mkState(
+      { uk: mkNation('uk', 'UK', NS(50, 50, 50, 50), ['g1']) },
+      { g1: RS(50, 50, 50, 50) },
+    );
+    const ctx = mkCtx(state, new Set(['g1']));
+    const data: DisastersOps = { events: [{ type: 'volcanic', target: 'g1', severity: 'moderate' }] };
+    disasters.apply(state, data, ctx);
+    // volcanic moderate = economy -4, stability -3
+    expect(state.regionStats.g1).toEqual(RS(50, 46, 47, 50));
+    expect(state.nations.uk.stats).toEqual(NS(50, 46, 47, 50));
+  });
+});

server/abilities/disasters.ts

@@ -0,0 +1,259 @@
+// The DISASTERS & PANDEMICS ability (v0.41.0, #63) as a modular LLM-ability
+// (v0.40.0, #67). Natural and man-made catastrophes — earthquakes, floods,
+// volcanic eruptions, wildfires, famines, plagues, and epidemics — hit a
+// nation or a single region each turn. Unlike most other abilities this one
+// is **turn-transient**: it owns NO `GameState` field (no durable list, no
+// `db.ts` change) — exactly like the hybrid layer. Each event carries a
+// `type` and a `severity`, and the engine applies a DETERMINISTIC stat dip
+// chosen from the `(type, severity)` lookup table below (no hidden
+// randomness — the LLM chooses the type and severity, the table decides the
+// magnitude). The dip lands on the target nation's `stats` (clamped 0–100)
+// AND on the target's regions (`regionStats` — the single named region when
+// the target was a region key, otherwise every region the target owns), and
+// the target's derived `stats` are re-derived afterwards (the same 0-region /
+// no-entry guards as hybrid / economy / industry, so a 0-region nation keeps
+// its directly-mutated value and the dip persists to the next turn). The
+// target is a nation (resolved by the shared `resolveNationRef`) or a region
+// key (which hits its SOLE owner); a key with 0 or 2+ owners is untargetable.
+// There is no acting-nation (`from`) field on a disaster — a catastrophe is
+// not an attack, so the hybrid's self-target drop does not apply. Malformed
+// events and unresolvable targets are dropped, never thrown.
+
+import { clampStat, deriveNationStats } from '../../shared/protocol';
+import type {
+  DisasterEvent,
+  DisasterSeverity,
+  DisasterType,
+} from '../../shared/protocol';
+import type { GameState, Nation, NationStats, StatKey } from '../../shared/types';
+import { resolveNationRef, str } from './shared';
+import type { Ability } from './types';
+
+/** The seven disaster types a turn can declare (v0.41.0, #63). */
+export const DISASTER_TYPES: readonly DisasterType[] = [
+  'earthquake',
+  'flood',
+  'volcanic',
+  'wildfire',
+  'famine',
+  'plague',
+  'epidemic',
+];
+
+/** The three severity levels a disaster event can carry (v0.41.0, #63). */
+export const DISASTER_SEVERITIES: readonly DisasterSeverity[] = ['minor', 'moderate', 'severe'];
+
+const VALID_DISASTER_TYPES = new Set<string>(DISASTER_TYPES);
+const VALID_SEVERITIES = new Set<string>(DISASTER_SEVERITIES);
+
+/** True when `t` is one of the seven known disaster types (v0.41.0, #63). */
+export function isDisasterType(t: unknown): t is DisasterType {
+  return typeof t === 'string' && VALID_DISASTER_TYPES.has(t);
+}
+
+/** True when `s` is one of the three known disaster severities (v0.41.0, #63). */
+export function isDisasterSeverity(s: unknown): s is DisasterSeverity {
+  return typeof s === 'string' && VALID_SEVERITIES.has(s);
+}
+
+/**
+ * (v0.41.0, #63) The DETERMINISTIC per-`(type, severity)` stat dip of a
+ * disaster event. Each pair maps to a small set of signed (negative) stat
+ * deltas: no hidden randomness — the LLM picks the type and severity, the
+ * table decides the magnitude. Population is never touched (a disaster hurts
+ * military / economy / stability, never the head-count). Every (type,
+ * severity) combination dips at least one stat (none is purely
+ * informational).
+ */
+export const DISASTER_EFFECTS: Record<DisasterType, Record<DisasterSeverity, Partial<Record<StatKey, number>>>> = {
+  earthquake: {
+    minor: { stability: -2, economy: -2 },
+    moderate: { stability: -4, economy: -4 },
+    severe: { stability: -7, economy: -7 },
+  },
+  flood: {
+    minor: { economy: -2, stability: -1 },
+    moderate: { economy: -3, stability: -2 },
+    severe: { economy: -6, stability: -4 },
+  },
+  volcanic: {
+    minor: { economy: -2, stability: -2 },
+    moderate: { economy: -4, stability: -3 },
+    severe: { economy: -7, stability: -6 },
+  },
+  wildfire: {
+    minor: { economy: -2 },
+    moderate: { economy: -4 },
+    severe: { economy: -7 },
+  },
+  famine: {
+    minor: { economy: -2, stability: -2 },
+    moderate: { economy: -4, stability: -4 },
+    severe: { economy: -7, stability: -7 },
+  },
+  plague: {
+    minor: { stability: -3, military: -2 },
+    moderate: { stability: -5, military: -3 },
+    severe: { stability: -9, military: -6 },
+  },
+  epidemic: {
+    minor: { stability: -2, military: -1 },
+    moderate: { stability: -4, military: -2 },
+    severe: { stability: -7, military: -4 },
+  },
+};
+
+/**
+ * (v0.41.0, #63) Validate the raw `disasters` field of a turn into a safe
+ * list of {@link DisasterEvent}s. Defensive like the rest of the parser — never throws.
+ * The raw value may be the object `{ events: [...] }` (the TurnResult shape)
+ * or a bare array (be lenient about either). Each event needs a known `type`
+ * (one of {@link DISASTER_TYPES}), a known `severity` (one of
+ * {@link DISASTER_SEVERITIES}), and a non-empty `target` (a nation id/name or
+ * a region key, capped at 200 chars); a non-empty `detail` is capped at 300
+ * chars. An event with an unknown / missing `type`, an unknown / missing
+ * `severity`, or an empty `target` is dropped. Resolution of `target` to a
+ * concrete nation (or a region's sole owner) happens at apply time
+ * (`applyDisasterEvent`), not here. A missing / malformed top-level value
+ * yields `{ events: [] }`.
+ */
+export function validateDisasterEvents(raw: unknown): DisasterEvent[] {
+  let list: unknown[] | null = null;
+  if (Array.isArray(raw)) {
+    list = raw;
+  } else if (raw && typeof raw === 'object') {
+    const inner = (raw as Record<string, unknown>).events;
+    if (Array.isArray(inner)) list = inner;
+  }
+  if (!list) return [];
+  const out: DisasterEvent[] = [];
+  for (const e of list) {
+    if (!e || typeof e !== 'object') continue;
+    const o = e as Record<string, unknown>;
+    if (!isDisasterType(o.type)) continue; // unknown / missing type: drop
+    if (!isDisasterSeverity(o.severity)) continue; // unknown / missing severity: drop
+    const target = str(o.target, 200);
+    if (!target) continue; // empty / missing target: drop
+    const detail = str(o.detail, 300);
+    out.push({
+      type: o.type,
+      target,
+      severity: o.severity,
+      ...(detail ? { detail } : {}),
+    });
+  }
+  return out;
+}
+
+/**
+ * (v0.41.0, #63) Resolve a disaster event's `target` (a nation id/name OR a
+ * region key) to the concrete nation it affects. A nation ref resolves via
+ * {@link resolveNationRef}; a region key resolves to its SOLE owner (a region
+ * with zero or 2+ owners can't be a valid target). Returns the affected
+ * nation plus the specific region key (when the target was a region) so the
+ * dip can land on just that region's entry. `validKeys` (when supplied)
+ * gates the region-key path; a ref that is neither a known nation nor a
+ * valid region key returns `null`. Pure; never throws.
+ *
+ * NOTE: there is no acting-nation (`from`) field on a disaster — a
+ * catastrophe is not an attack, so (unlike the hybrid layer) a self-target
+ * drop does NOT apply: an earthquake can hit the nation it is declared
+ * against.
+ */
+function resolveDisasterTarget(
+  state: GameState,
+  target: string,
+  validKeys?: ReadonlySet<string>,
+): { nation: Nation; regionKey?: string } | null {
+  const id = resolveNationRef(state, target);
+  if (id !== null) {
+    const n = state.nations[id];
+    return n ? { nation: n } : null;
+  }
+  const key = (target ?? '').trim();
+  if (!key) return null;
+  if (validKeys && !validKeys.has(key)) return null; // unknown region key
+  const owners = Object.values(state.nations).filter((n) => n.territory.includes(key));
+  if (owners.length !== 1) return null; // 0 or 2+ owners: not a targetable region
+  return { nation: owners[0], regionKey: key };
+}
+
+/** Apply each signed dip in `dips` to a stats record in place (clamped). */
+function applyDips(stats: NationStats, dips: Partial<Record<StatKey, number>>): void {
+  (Object.keys(dips) as StatKey[]).forEach((k) => {
+    const d = dips[k];
+    if (typeof d === 'number') stats[k] = clampStat(stats[k] + d);
+  });
+}
+
+/**
+ * (v0.41.0, #63) Apply ONE disaster event to the (cloned) `next` state,
+ * mutating it in place and never throwing. Resolution order:
+ *   1. `target` must resolve to a concrete nation (a nation ref, or a region
+ *      key's sole owner); an unresolvable target (unknown / ambiguous ref, a
+ *      region with 0 or 2+ owners, or an unknown region key) drops the event.
+ * Then the deterministic `(type, severity)` dip from {@link DISASTER_EFFECTS}
+ * is applied:
+ *   - the target nation's `stats` is dipped on each affected stat (clamped
+ *     0–100);
+ *   - the dip is mirrored to the target's regions — the single named region
+ *     when the target was a region key, otherwise every region the target
+ *     owns (regions with no `regionStats` entry are skipped);
+ *   - the target nation's derived `stats` are re-derived afterwards (the
+ *     same 0-region / no-entry guards as the main recompute, so a 0-region
+ *     nation keeps its directly-mutated value and a dip persists).
+ * A disaster never moves territory (sole ownership is untouched) and never
+ * touches `population`.
+ */
+export function applyDisasterEvent(
+  next: GameState,
+  ev: DisasterEvent,
+  geoOf?: (key: string) => { area: number; population: number } | undefined,
+  validKeys?: ReadonlySet<string>,
+): void {
+  const target = resolveDisasterTarget(next, ev.target, validKeys);
+  if (target === null) return; // unresolvable target: drop
+  const dips = DISASTER_EFFECTS[ev.type][ev.severity];
+  if (!dips) return; // defensive: unknown (type, severity) pair
+  applyDips(target.nation.stats, dips);
+  if (target.regionKey !== undefined) {
+    const rs = next.regionStats[target.regionKey];
+    if (rs) applyDips(rs, dips);
+  } else {
+    for (const key of target.nation.territory) {
+      const rs = next.regionStats[key];
+      if (!rs) continue; // a key with no entry is skipped
+      applyDips(rs, dips);
+    }
+  }
+  // Re-derive the target nation's aggregate stats so the dip persists (the
+  // main recompute ran earlier this turn; without this the dip would be
+  // washed out next turn). Same 0-region / no-entry guards as hybrid /
+  // economy: a nation with no region stats entry keeps its directly-mutated
+  // `stats`.
+  if (target.nation.territory.length > 0 && target.nation.territory.some((k) => next.regionStats[k])) {
+    target.nation.stats = deriveNationStats(target.nation.territory, next.regionStats, geoOf);
+  }
+}
+
+export const disasters: Ability<'disasters'> = {
+  field: 'disasters',
+  default: () => ({ events: [] }),
+  // The low-level validator returns a bare list; the field's shape is the
+  // `{ events }` object (mirrors the historical TurnResult shape).
+  validate: (raw) => ({ events: validateDisasterEvents(raw) }),
+  apply: (state, data, ctx) => {
+    for (const ev of data.events) {
+      applyDisasterEvent(state, ev, ctx.geoOf, ctx.validRegionKeys);
+    }
+  },
+  schemaLine: () =>
+    '  "disasters": {"events":[{"type":"<earthquake|flood|volcanic|wildfire|famine|plague|epidemic>","target":"<nation id or name, or region key>","severity":"<minor|moderate|severe>","detail":"<short detail>"}]},',
+  constraint: () =>
+    '- Disasters & pandemics ("disasters.events") are natural and man-made catastrophes — earthquakes, floods, volcanic eruptions, wildfires, famines, plagues, and epidemics — that hit a nation or a single region this turn. Each event names a "target" (a nation id / name, or a region key that hits that region\'s SOLE owner — a region with 0 or 2+ owners can\'t be hit) and a "severity" (minor / moderate / severe); the engine applies a small, DETERMINISTIC stat dip from the (type, severity) table (a severe plague is the hardest hit; none of them touch population, and none move borders — sole ownership is untouched). There is NO memory of past disasters (the layer is turn-transient): a plague or epidemic that persists is simply RE-DECLARED each turn it continues, with a fresh "severity". Propose at most 1-2 events per turn and narrate each one in "events" (a "disaster" event).',
+  isMeaningful: (data) => data.events.length > 0,
+  stub: () => ({ events: [] }),
+  // The layer is turn-transient — it contributes nothing to the user payload
+  // (no durable state to show the model), so the payload is always empty.
+  payload: () => ({}),
+};

server/abilities/goldens/system-no-tool.txt

@@ -39,6 +39,7 @@ Respond with ONLY a valid JSON object of exactly this shape. No prose, no commen
   "nuclear": {"arm":["<nation id or name>"],"strikes":[{"from":"<nuclear-capable nation id or name>","target":"<nation id or name, or region key>"}]},
   "leaders": {"changes":[{"target":"<nation id or name>","name":"<new leader name>","cause":"<assassination|death|appointed>"}]},
   "ideology": {"changes":[{"target":"<nation id or name>","to":"<new form of government>"}]},
+  "disasters": {"events":[{"type":"<earthquake|flood|volcanic|wildfire|famine|plague|epidemic>","target":"<nation id or name, or region key>","severity":"<minor|moderate|severe>","detail":"<short detail>"}]},
   "markers": {"add":[{"type":"<city|factory|army|port|capital|fleet|rocket|gathering>","name":"<short name>","regionKey":"<region key>"}],"remove":["<marker id>"]}
 }
 
@@ -64,6 +65,7 @@ HARD CONSTRAINTS
 - Nuclear / WMD ("nuclear"): a nation is "nuclear-capable" when its "nuclear" flag is true or it currently owns a "rocket" marker. "arm" names (by id or name) nations to grant the "nuclear" flag — idempotent (already-armed nations are unchanged); a newly armed nation is capable this same turn. "strikes" is a list of "NuclearStrike" objects, each "{from, target}" — "from" is the striking nation (must be nuclear-capable and never itself) and "target" is either a nation (its nation collapses: economy -40, military -50, stability -40; every active war the target fights ends by capitulation and the "war" relations it caused downgrade to "hostile") or a region key (that region is released to no man's land, its regionStats entry deleted, and its sole owner collapses the same way — a region with 0 or 2+ owners, or one the striker itself owns, is dropped). If the struck nation (or the struck region's owner) is itself nuclear-capable, a "MAD" retaliation is applied: it strikes the striker back for half the collapse, and the two nations' relations are forced to "hostile". At most one strike per turn; always narrate a strike (and a retaliation, if any) in "events".
 - Leaders ("leaders") name each nation's current head of state and change it. Each change is {"target":"<nation id or name>","name":"<new leader name>","cause":"<assassination|death|appointed>"}: "assassination" kills the current leader (a dramatic, destabilizing blow — a −15 stability dip, a "military" event) and is only valid when the target already has a leader; "death" is a natural-causes succession (a quieter −3 dip, a "political" event), also only valid for a nation that has a leader; "appointed" sets (or creates) a leader and is always valid (a neutral 0 effect, a "political" event). Propose at most 1-2 changes per turn and narrate each one in "events". This is the HEAVY leader lever — use the lighter "hybrid" {"type":"assassinate"} op (a −5 stability dip, no leader replacement) for a mere hit on a leader or region without changing who is in charge. The user message's "nations" field lists each nation's current "leader" (omitted when a nation has none).
 - Ideology ("ideology") is each nation's form of government — a free-form label such as "democracy", "fascism", or "military junta" — that can shift through a coup, a revolution, a reform, or a constitutional change. Each change is {"target":"<nation id or name>","to":"<new form of government>"}: the engine sets the nation's ideology, applies a small, deterministic stability dip (−5 — a regime shift always unsettles a nation), and narrates it with a "political" event. It is a third axis, distinct from a takeover (which RENAMES the nation) and from a leader change (who is in charge): the nation keeps its id, name, territory, relations, and leader — only its form of government and its stability move. Similar forms of government are a SOFT, prompt-level compatibility nudge only (nations with alike ideologies tend to ally and trade; very opposed ones tend to clash) — there is no engine gate behind it. Propose at most 1-2 changes per turn and narrate each one in "events". The user message's "nations" field lists each nation's current "ideology" (omitted when a nation has none).
+- Disasters & pandemics ("disasters.events") are natural and man-made catastrophes — earthquakes, floods, volcanic eruptions, wildfires, famines, plagues, and epidemics — that hit a nation or a single region this turn. Each event names a "target" (a nation id / name, or a region key that hits that region's SOLE owner — a region with 0 or 2+ owners can't be hit) and a "severity" (minor / moderate / severe); the engine applies a small, DETERMINISTIC stat dip from the (type, severity) table (a severe plague is the hardest hit; none of them touch population, and none move borders — sole ownership is untouched). There is NO memory of past disasters (the layer is turn-transient): a plague or epidemic that persists is simply RE-DECLARED each turn it continues, with a fresh "severity". Propose at most 1-2 events per turn and narrate each one in "events" (a "disaster" event).
 - Prefer 1-4 events per turn; keep each text 1-3 sentences.
 - Keep your internal reasoning brief (a few sentences) and go straight to the JSON result; do not over-deliberate or re-derive facts already present in the state.
 - Keep every stat value between 0 and 100.

server/abilities/goldens/system-tool.txt

@@ -39,6 +39,7 @@ You have a getNeighbours tool: given region keys it returns the region keys that
   "nuclear": {"arm":["<nation id or name>"],"strikes":[{"from":"<nuclear-capable nation id or name>","target":"<nation id or name, or region key>"}]},
   "leaders": {"changes":[{"target":"<nation id or name>","name":"<new leader name>","cause":"<assassination|death|appointed>"}]},
   "ideology": {"changes":[{"target":"<nation id or name>","to":"<new form of government>"}]},
+  "disasters": {"events":[{"type":"<earthquake|flood|volcanic|wildfire|famine|plague|epidemic>","target":"<nation id or name, or region key>","severity":"<minor|moderate|severe>","detail":"<short detail>"}]},
   "markers": {"add":[{"type":"<city|factory|army|port|capital|fleet|rocket|gathering>","name":"<short name>","regionKey":"<region key>"}],"remove":["<marker id>"]}
 }
 
@@ -64,6 +65,7 @@ HARD CONSTRAINTS
 - Nuclear / WMD ("nuclear"): a nation is "nuclear-capable" when its "nuclear" flag is true or it currently owns a "rocket" marker. "arm" names (by id or name) nations to grant the "nuclear" flag — idempotent (already-armed nations are unchanged); a newly armed nation is capable this same turn. "strikes" is a list of "NuclearStrike" objects, each "{from, target}" — "from" is the striking nation (must be nuclear-capable and never itself) and "target" is either a nation (its nation collapses: economy -40, military -50, stability -40; every active war the target fights ends by capitulation and the "war" relations it caused downgrade to "hostile") or a region key (that region is released to no man's land, its regionStats entry deleted, and its sole owner collapses the same way — a region with 0 or 2+ owners, or one the striker itself owns, is dropped). If the struck nation (or the struck region's owner) is itself nuclear-capable, a "MAD" retaliation is applied: it strikes the striker back for half the collapse, and the two nations' relations are forced to "hostile". At most one strike per turn; always narrate a strike (and a retaliation, if any) in "events".
 - Leaders ("leaders") name each nation's current head of state and change it. Each change is {"target":"<nation id or name>","name":"<new leader name>","cause":"<assassination|death|appointed>"}: "assassination" kills the current leader (a dramatic, destabilizing blow — a −15 stability dip, a "military" event) and is only valid when the target already has a leader; "death" is a natural-causes succession (a quieter −3 dip, a "political" event), also only valid for a nation that has a leader; "appointed" sets (or creates) a leader and is always valid (a neutral 0 effect, a "political" event). Propose at most 1-2 changes per turn and narrate each one in "events". This is the HEAVY leader lever — use the lighter "hybrid" {"type":"assassinate"} op (a −5 stability dip, no leader replacement) for a mere hit on a leader or region without changing who is in charge. The user message's "nations" field lists each nation's current "leader" (omitted when a nation has none).
 - Ideology ("ideology") is each nation's form of government — a free-form label such as "democracy", "fascism", or "military junta" — that can shift through a coup, a revolution, a reform, or a constitutional change. Each change is {"target":"<nation id or name>","to":"<new form of government>"}: the engine sets the nation's ideology, applies a small, deterministic stability dip (−5 — a regime shift always unsettles a nation), and narrates it with a "political" event. It is a third axis, distinct from a takeover (which RENAMES the nation) and from a leader change (who is in charge): the nation keeps its id, name, territory, relations, and leader — only its form of government and its stability move. Similar forms of government are a SOFT, prompt-level compatibility nudge only (nations with alike ideologies tend to ally and trade; very opposed ones tend to clash) — there is no engine gate behind it. Propose at most 1-2 changes per turn and narrate each one in "events". The user message's "nations" field lists each nation's current "ideology" (omitted when a nation has none).
+- Disasters & pandemics ("disasters.events") are natural and man-made catastrophes — earthquakes, floods, volcanic eruptions, wildfires, famines, plagues, and epidemics — that hit a nation or a single region this turn. Each event names a "target" (a nation id / name, or a region key that hits that region's SOLE owner — a region with 0 or 2+ owners can't be hit) and a "severity" (minor / moderate / severe); the engine applies a small, DETERMINISTIC stat dip from the (type, severity) table (a severe plague is the hardest hit; none of them touch population, and none move borders — sole ownership is untouched). There is NO memory of past disasters (the layer is turn-transient): a plague or epidemic that persists is simply RE-DECLARED each turn it continues, with a fresh "severity". Propose at most 1-2 events per turn and narrate each one in "events" (a "disaster" event).
 - Prefer 1-4 events per turn; keep each text 1-3 sentences.
 - Keep your internal reasoning brief (a few sentences) and go straight to the JSON result; do not over-deliberate or re-derive facts already present in the state.
 - Keep every stat value between 0 and 100.

server/abilities/index.ts

@@ -1,8 +1,8 @@
 // The ordered LLM-ability registry.
 //
-// `ABILITIES` is the single source of truth for the 8 per-feature LLM abilities.
+// `ABILITIES` is the single source of truth for the 9 per-feature LLM abilities.
 // The engine iterates it in this order:
-//   takeovers → wars → hybrid → economy → industry → nuclear → leaders → ideology
+//   takeovers → wars → hybrid → economy → industry → nuclear → leaders → ideology → disasters
 // for (a) the system-prompt schema lines + constraint bullets, (b) the per-ability
 // validate calls inside validateTurnResult, (c) the payload fields in buildUserPrompt,
 // (d) the ordered apply block inside applyTurnResult, (e) the isMeaningful check,
@@ -22,10 +22,11 @@ import { industry } from './industry';
 import { nuclear } from './nuclear';
 import { leaders } from './leaders';
 import { ideology } from './ideology';
+import { disasters } from './disasters';
 import type { Ability, AbilityField } from './types';
 
 /**
- * The 8 per-feature LLM abilities in their canonical apply order.
+ * The 9 per-feature LLM abilities in their canonical apply order.
  * The order matters: it determines the order of the schema lines in the
  * system prompt, the order of the validate calls, the order of the apply
  * steps, and the order of the payload fields in the user prompt.
@@ -39,6 +40,7 @@ export const ABILITIES: readonly Ability<AbilityField>[] = [
   nuclear,
   leaders,
   ideology,
+  disasters,
 ];
 
 // ── type re-exports ────────────────────────────────────────────────────────────
@@ -125,3 +127,15 @@ export {
 export {
   validateIdeologyOps,
 } from './ideology';
+
+// ── disasters ────────────────────────────────────────────────────────────────
+
+export {
+  validateDisasterEvents,
+  applyDisasterEvent,
+  isDisasterType,
+  isDisasterSeverity,
+  DISASTER_TYPES,
+  DISASTER_SEVERITIES,
+  DISASTER_EFFECTS,
+} from './disasters';

server/abilities/registry.test.ts

@@ -3,13 +3,16 @@
 // These tests pin the refactor's two load-bearing guarantees:
 //
 //   1. GOLDEN PROMPTS — the system prompt (both tool variants) and the user
-//      prompt the refactored engine builds are BYTE-IDENTICAL to the committed
-//      golden fixtures in ./goldens/ (captured in P1 from the pre-refactor
-//      engine). Any transcription drift in an ability's schemaLine /
-//      constraint / payload is caught here.
+//      prompt the engine builds are BYTE-IDENTICAL to the committed golden
+//      fixtures in ./goldens/ (captured in P1 from the pre-refactor engine, and
+//      re-baselined when a feature INTENTIONALLY changes the prompt — e.g. the
+//      system goldens were regenerated in v0.41.0 when the disasters ability
+//      was added). Any transcription drift in an ability's schemaLine /
+//      constraint / payload is caught here. The USER prompt golden is unchanged
+//      by the disasters feature (its payload is always empty).
 //
 //   2. REGISTRY CONTRACT — the ABILITIES registry is the canonical ordered
-//      list of the 8 abilities; each ability's default() equals the canonical
+//      list of the 9 abilities; each ability's default() equals the canonical
 //      TurnResult default for its field, is a FRESH value (never a shared
 //      reference), its default is not "meaningful" while a populated value is,
 //      and the registry composes (a hypothetical extra ability can be appended
@@ -26,13 +29,19 @@ import { fileURLToPath } from 'node:url';
 import { describe, expect, it } from 'vitest';
 import {
   activeWarPairs,
+  applyDisasterEvent,
   applyIndustryEffects,
   atWar,
   buildSystemPrompt,
   buildUserPrompt,
+  DISASTER_EFFECTS,
+  DISASTER_SEVERITIES,
+  DISASTER_TYPES,
   freshNationId,
   freshWarId,
   HYBRID_STAT_EFFECT,
+  isDisasterSeverity,
+  isDisasterType,
   isHybridOpType,
   isIndustryType,
   NEW_NATION_STATS,
@@ -40,6 +49,7 @@ import {
   resolveRegionKey,
   shiftRelationTowardHostile,
   syncWarRelations,
+  validateDisasterEvents,
   validateEconomyOps,
   validateHybridOps,
   validateIdeologyOps,
@@ -206,6 +216,7 @@ function fullDefaultTurn(): TurnResult {
     nuclear: { arm: [], strikes: [] },
     leaders: { changes: [] },
     ideology: { changes: [] },
+    disasters: { events: [] },
     markers: { add: [], remove: [] },
   };
 }
@@ -229,11 +240,13 @@ function meaningfulFor(field: AbilityField): TurnResult[AbilityField] {
       return { changes: [{ target: 'a1', name: 'New Alpha Leader', cause: 'appointed' }] };
     case 'ideology':
       return { changes: [{ target: 'a1', to: 'democracy' }] };
+    case 'disasters':
+      return { events: [{ type: 'earthquake', target: 'a1', severity: 'minor' }] };
   }
 }
 
 describe('ABILITIES registry (v0.40.0, #67)', () => {
-  it('is the canonical 8-ability order (takeovers → ideology)', () => {
+  it('is the canonical 9-ability order (takeovers → disasters)', () => {
     expect(ABILITIES.map((a) => a.field)).toEqual([
       'takeovers',
       'wars',
@@ -243,13 +256,14 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       'nuclear',
       'leaders',
       'ideology',
+      'disasters',
     ]);
   });
 
-  it('lists 8 distinct fields, each a key of TurnResult', () => {
+  it('lists 9 distinct fields, each a key of TurnResult', () => {
     const fields = ABILITIES.map((a) => a.field);
-    expect(fields).toHaveLength(8);
-    expect(new Set(fields).size).toBe(8);
+    expect(fields).toHaveLength(9);
+    expect(new Set(fields).size).toBe(9);
     const all = fullDefaultTurn();
     for (const f of fields) expect(f in all).toBe(true);
   });
@@ -314,7 +328,7 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
   it('composes: a hypothetical extra ability can be appended and every uniform loop still runs', () => {
     // The registry is a plain ordered array the engine iterates uniformly. A
     // structural (field-name-agnostic) loop over the abilities — schema line,
-    // constraint bullet — must keep working when a 9th ability is appended.
+    // constraint bullet — must keep working when a 10th ability is appended.
     // This documents the extension point without widening the closed
     // AbilityField union.
     interface Loopable {
@@ -333,9 +347,9 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       'custom',
     ]);
     // every uniform loop runs over all N abilities, the appended one included:
-    expect(extended.map((a) => a.schemaLine())).toHaveLength(9);
-    expect(extended.map((a) => a.constraint())).toHaveLength(9);
-    expect(extended[8].schemaLine()).toBe('  "custom": [],');
+    expect(extended.map((a) => a.schemaLine())).toHaveLength(10);
+    expect(extended.map((a) => a.constraint())).toHaveLength(10);
+    expect(extended[9].schemaLine()).toBe('  "custom": [],');
   });
 
   it('the engine still re-exports every name its callers import from it', () => {
@@ -366,6 +380,14 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       validateTakeovers,
       validateWarOps,
       applyIndustryEffects,
+      // disasters (v0.41.0, #63)
+      validateDisasterEvents,
+      applyDisasterEvent,
+      isDisasterType,
+      isDisasterSeverity,
+      DISASTER_TYPES,
+      DISASTER_SEVERITIES,
+      DISASTER_EFFECTS,
     };
     for (const [name, value] of Object.entries(reexported)) {
       expect(value, `engine should re-export ${name}`).toBeDefined();

server/abilities/types.ts

@@ -17,11 +17,11 @@ import type {
 import type { MarkerInfo, TurnResult, WarInfo } from '../../shared/protocol';
 
 /**
- * The 8 per-feature LLM abilities a turn can exercise, by the `TurnResult`
+ * The 9 per-feature LLM abilities a turn can exercise, by the `TurnResult`
  * field each one owns. This is the closed universe the ordered `ABILITIES`
  * registry (./index.ts) is built from: a turn's world changes are exactly the
  * core engine effects (events / stats / territory / no-man's-land / nation-ops
- * / markers) plus, in order, these eight abilities.
+ * / markers) plus, in order, these nine abilities.
  */
 export type AbilityField =
   | 'takeovers'
@@ -31,7 +31,8 @@ export type AbilityField =
   | 'industry'
   | 'nuclear'
   | 'leaders'
-  | 'ideology';
+  | 'ideology'
+  | 'disasters';
 
 /**
  * Everything a single ability's `apply` may need from the surrounding turn.
@@ -64,7 +65,7 @@ export interface AbilityCtx {
   readonly centroidOf?: (key: string) => { lat: number; lon: number; spread: number } | undefined;
   /**
    * The `getNeighbours` tool executor (verify land borders). Available to an
-   * ability that needs it; none of the current eight use it (it drives the
+   * ability that needs it; none of the current nine use it (it drives the
    * core territory/conquest logic), but the type is here so a future one can.
    */
   readonly getNeighbours?: (regionKeys: string[]) => string[];
@@ -151,7 +152,7 @@ export interface Ability<K extends AbilityField = AbilityField> {
    * The `GameState` fields this ability owns and that must be defaulted on a
    * legacy SQLite row (db.ts migration, only-if-undefined). `undefined` for
    * abilities that add no durable state (takeovers, hybrid, nuclear, leaders,
-   * ideology).
+   * ideology, disasters).
    */
   readonly stateFields?: readonly string[];