Merge pull request 'feat(#60): nuclear/WMD — capability flag + strikes (region → no-man's-land, nation collapse + war capitulation, MAD retaliation) (v0.37.0)' (#71) from feat/60-nuclear-wmd into master

CHANGELOG.md

@@ -2,6 +2,23 @@
 
 All notable changes to **History** are listed here, newest first.
 
+## v0.37.0 — 2026-10-15 19:15
+- **#60: Nuclear / WMD — a per-nation `nuclear` capability flag + a `TurnResult.nuclear` lever (`arm` + `strikes`) with deterministic strikes and MAD retaliation.** A nation is *nuclear-capable* when its `nuclear` flag is `true` **or** it currently owns a `rocket` marker (a launch site is an arsenal). The model can **arm** nations (grant the flag — idempotent; a newly-armed nation is capable the same turn, since `arm` is applied before `strikes`) and fire **strikes** (`{ from, target }`). The engine is **fully deterministic (no hidden randomness)** and **additive** (a `db.ts` change is not needed — `nuclear` is an optional `Nation` field; a pre-v0.37 row loads with the flag absent).
+  - **Capability (`shared/protocol.ts`).** `isNuclearCapable(nation, markers)` — exported pure helper: `nation.nuclear === true` **or** it owns a `rocket` marker (`marker.type === 'rocket' && marker.ownerNationId === nation.id`). Markers supply the *pre-turn* rocket set, so a rocket placed this turn makes the owner capable from the *next* turn.
+  - **Types (`shared/types.ts`).** `Nation.nuclear?: boolean` (optional; `undefined`/absent = not armed; default `false` behavior).
+  - **Protocol (`shared/protocol.ts`).** New `NuclearStrike` (`{ from; target }` — `from` is the striking nation, `target` is a nation ref or a region key) and `NuclearOps` (`{ arm: string[]; strikes: NuclearStrike[] }`); `TurnResult.nuclear` is **required**, placed between `industry` and `markers`, default `{ arm: [], strikes: [] }`. New exported `NuclearStatKey` (`'economy' | 'military' | 'stability'`) and the two deterministic collapse tables: **`NUCLEAR_COLLAPSE = { economy: −40, military: −50, stability: −40 }**` (a full strike's effect on the struck nation / region owner) and **`NUCLEAR_RETALIATION = { economy: −20, military: −25, stability: −20 }`**` (the half-strength MAD backfire).
+  - **Engine (`server/engine.ts`).**
+    - `validateNuclearOps(raw)` — new exported, defensive validator (never throws): a missing/malformed object yields `{ arm: [], strikes: [] }`; `arm` entries are non-empty strings (≤120 chars) deduped; a strike needs a non-empty `from` **and** `target` (≤120) and is **dropped when it targets itself** (same ref, case-insensitive) — a self-strike is a no-op, never thrown.
+    - `applyNuclearOps(next, ops, state, geoOf?, validKeys?, regionNameOf?, actingTurn?)` — new exported, the load-bearing nuclear block. **`arm` first** (idempotent; a resolve miss or a self-arm is a no-op), then **`strikes`** in order: resolve `from` (an unresolvable or non-capable striker is **dropped** — capability checked against the *pre-turn* marker set plus any flag granted this turn); a `target` that is a **nation** collapses it (the `NUCLEAR_COLLAPSE` deltas applied to its `stats` and every region it owns, each affected nation's derived stats re-derived, 0-region / no-entry guards as elsewhere), ends **every active war it fights** by **capitulation** (`endWarsBetween` captures the active pairs *before* ending so a war declared+ended the same turn is handled), and downgrades the now-inactive `war` relations to `hostile`; a `target` that is a **region key** releases it to no man's land (a key with 0 or 2+ owners, or one the striker itself owns, is **dropped**), deletes its `regionStats` entry, and collapses its **sole owner** the same way. **MAD**: if the struck nation (or the struck region's sole owner) is itself nuclear-capable, it retaliates against the striker for the half-strength `NUCLEAR_RETALIATION` (clamped, mirrored, re-derived) and the two nations' relations are forced to `hostile` (`forceHostile` — both directions, unless already `war`). Each strike and each retaliation appends a dramatic **`military`** event (`war` is not a valid `EventType`). Sole ownership is never broken by a strike (a region is released, not re-claimed) and the block never throws.
+    - `applyTurnResult` — the nuclear block runs **after `industry` and before `markers`** (order: events → relations → territory → stateChanges → recompute → wars → hybrid → economy → industry → **nuclear** → markers → nationOps); it passes the *original* (pre-turn) `state` for the capability marker set and the current `regionNameOf` for event text.
+    - `isMeaningful` — a non-empty `nuclear.arm` or `nuclear.strikes` makes a turn meaningful.
+    - `validateTurnResult` — initializes and validates `nuclear` (default `{ arm: [], strikes: [] }`).
+    - `buildSystemPrompt` — documents the `nuclear` field and a constraint bullet (the capability rule; `arm` is idempotent; a strike hits a nation or a region; the collapse + capitulation + MAD outcomes; at most one strike per turn, always narrated) in both tool and plain modes.
+    - `buildUserPrompt` — new optional `nuclear` param (`Record<string, boolean>`, the per-nation capability map); when provided, each `state.nations` entry in the payload is stamped with its `nuclear` capability; when undefined the key is omitted entirely (stub / no-capability prompt stays byte-identical). `runTurn` always supplies the map (computed from `isNuclearCapable` over `state.markers`).
+  - **Stub (`server/stub.ts`).** `deterministicTurn` always returns `nuclear: { arm: [], strikes: [] }` — the stub **never** arms a nation or fires a strike, so the e2e (CI, `LLM_STUB=1`) is unaffected and the nuclear path is covered by unit tests only.
+  - **Tests.** 29 new unit tests: `isNuclearCapable` (flag / own rocket / non-rocket / other's rocket / null owner); `validateNuclearOps` (well-formed, `arm` dedupe, missing `from`/`target`, self-target drop, malformed top-level); `applyTurnResult` nuclear (arm idempotency across turns, arm+strike same turn, region strike → release + stats deleted + owner collapse + no MAD + the single `military` event, nation strike + pre-existing war → capitulation + hostile, nation strike + same-turn declare → capitulation + hostile, MAD on a capable nation target, MAD on a capable region owner, rocket-marker-only capability, non-capable striker dropped, 2+-owner region dropped, 0-owner/unowned region dropped, self-target dropped, malformed strikes never throw); `isMeaningful` (arm / strike); `buildUserPrompt` (per-nation capability stamped when the map is given, omitted when undefined); and two `db.test.ts` round-trips (a legacy row with no flag loads with it absent; a set flag round-trips through save/load).
+- **Version** bumped `0.36.0 → 0.37.0`.
+
 ## v0.36.0 — 2026-10-15 18:17
 - **#59: Resources & Industry — per-region synthesized resource profiles + a per-region industry-project lever with a deterministic per-turn economy boost.** Every prior lever moved borders, dipped stats one-shot, or proposed a player-confirmed change; this version adds a **resource abundance layer** (every sub-region gets a synthesized 4-value profile) and a **development lever**: the model can build industry projects (oil facilities, iron mines, food operations, factories) in individual regions, and every committed turn each active project pays its region's sole owner a small, deterministic economy gain scaled by the region's `industry` resource value. The engine is **fully deterministic (no hidden randomness)**: the resource profiles are a pure function of the region key (FNV-1a) scaled by an area factor, and the per-turn effect is a fixed, clamped, mirrored, re-derived stat adjustment.
   - **Manifest (`public/region-resources.json`, new).** 1,800 entries — region key → `{ oil, iron, food, industry }` (each 0–1, 2dp) — built by the new turf-free, deterministic, **idempotent** `scripts/build-region-resources.mjs` (`npm run build:region-resources`): per resource, `(fnv1a32(`${key}\u0000${resource}`) & 0x3fff) / 0x4000` → [0,1), times an area factor `1 + 0.2·min(1, log10(1+area)/8)` (max ≈1.2) from `region-geo.json` (missing geo / zero area → pure hash), clamped to 1, keys sorted, byte-identical re-run. Pinned by `scripts/build-region-resources.test.ts` (key-set equality vs `region-keys.json`, sorted order, per-entry shape, spot-checked values, determinism via a re-run).

package.json

@@ -1,6 +1,6 @@
 {
   "name": "history",
-  "version": "0.36.0",
+  "version": "0.37.0",
   "private": true,
   "type": "module",
   "description": "AI-driven alternate-history simulator — the LLM is the world engine (Pax Historia style).",

server/db.test.ts

@@ -178,6 +178,28 @@ describe('openDb', () => {
     db.close();
   });
 
+  it('(v0.37.0 #60) a legacy row saved before the nation nuclear flag existed loads with it absent (not capable)', () => {
+    const db = openDb(':memory:');
+    // makeState has no nation.nuclear field — a pre-v0.37 save. The flag is
+    // optional and not re-stamped by load, so an absent flag stays absent.
+    db.save(makeState('legacy'));
+    const loaded = db.load('legacy');
+    expect(loaded).not.toBeNull();
+    expect(loaded!.nations.uk.nuclear).toBeUndefined();
+    db.close();
+  });
+
+  it('(v0.37.0 #60) a set nation nuclear flag round-trips through save/load', () => {
+    const db = openDb(':memory:');
+    const s = makeState('nuc');
+    s.nations.uk.nuclear = true; // armed (e.g. by a turn's nuclear.arm op)
+    db.save(s);
+    const loaded = db.load('nuc');
+    expect(loaded).not.toBeNull();
+    expect(loaded!.nations.uk.nuclear).toBe(true);
+    db.close();
+  });
+
   it('delete removes a game by id and reports absence otherwise', () => {
     const db = openDb(':memory:');
     db.save(makeState('a'));

server/engine.test.ts

@@ -1,15 +1,19 @@
 import { describe, expect, it } from 'vitest';
-import type { GameState, MarkerType, Nation, NationStats, Preset, RelationStatus, RegionStats, RoundItem, War } from '../shared/types';
+import type { GameState, MapMarker, MarkerType, Nation, NationStats, Preset, RelationStatus, RegionStats, RoundItem, War } from '../shared/types';
 import {
   CONQUEST_MILITARY_MARGIN,
   makeEvent,
   markerId,
   MAX_MARKERS,
   seedRegionStats,
+  isNuclearCapable,
+  NUCLEAR_COLLAPSE,
+  NUCLEAR_RETALIATION,
   type HybridOp,
   type MarkerInfo,
   type MarkerSpec,
   type NationOp,
+  type NuclearStrike,
   type TurnResult,
 } from '../shared/protocol';
 import type { LlmClient, ToolDefinition, WireMessage } from './llm';
@@ -45,6 +49,7 @@ import {
   validateHybridOps,
   validateIndustryOps,
   validateMarkerOps,
+  validateNuclearOps,
   validateNationOps,
   validateRegionChanges,
   validateTakeovers,
@@ -563,7 +568,7 @@ describe('validateNationOps (v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'France', to: 'French Republic' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [{ kind: 'rename', nationRef: 'France', to: 'French Republic' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     });
     expect(withOps).not.toBeNull();
     expect(withOps!.nationOps).toEqual([{ kind: 'rename', nationRef: 'France', to: 'French Republic' }]);
@@ -585,7 +590,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     });
     expect(next.nations.de.name).toBe('DE'); // still the old name
     expect(next.pendingNationOps).toEqual([{ kind: 'rename', nationRef: 'de', to: 'Reich' }]);
@@ -606,7 +611,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'us', to: 'USA' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] }, // new proposal this turn
+      nationOps: [{ kind: 'rename', nationRef: 'us', to: 'USA' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] }, // new proposal this turn
     });
     expect(next.pendingNationOps).toEqual([
       { kind: 'rename', nationRef: 'de', to: 'Reich' }, // the old one survived
@@ -625,7 +630,7 @@ describe('applyTurnResult (nation-op proposals, v0.23 #16 P4a)', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     });
     expect(next.pendingNationOps).toEqual([{ kind: 'rename', nationRef: 'de', to: 'Reich' }]);
   });
@@ -1082,7 +1087,7 @@ describe('applyTurnResult', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     };
     applyTurnResult(state, result);
     expect(JSON.stringify(state)).toBe(snapshot);
@@ -1099,7 +1104,7 @@ describe('applyTurnResult', () => {
       relations: [],
       territoryChanges: [],
       unowned: [],
-      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
     expect(next.pending).toEqual([]);
@@ -1122,7 +1127,7 @@ describe('applyTurnResult', () => {
       // is not a real key at all. Both are proposed as a gain by DE.
       territoryChanges: [{ nation: 'de', gain: ['wales-bbbb', 'not-a-region-xyz'], lose: [] }],
       unowned: [],
-      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result, new Set(['wales-bbbb']));
     // the valid key was gained (taken from its sole previous owner); the bogus one was ignored
@@ -1148,7 +1153,7 @@ describe('applyTurnResult', () => {
       // released (not in state.unowned), so it does not enter GameState.unowned.
       territoryChanges: [{ nation: 'de', gain: ['POL', 'wales-bbbb'], lose: [] }],
       unowned: [],
-      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result); // no validKeys -> nothing filtered
     expect(next.nations.de.territory).toContain('wales-bbbb');
@@ -1166,7 +1171,7 @@ describe('applyTurnResult (sole-ownership invariants, v0.21 #16 P2)', () => {
     regionChanges: [],
     relations: [],
     unowned: [],
-    nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+    nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
   };
 
   it('a double claim (two different gainers, one key) is rejected: the key stays with its original owner', () => {
@@ -1256,7 +1261,7 @@ describe('applyTurnResult (no man\'s land, v0.22 #16 P3)', () => {
     relations: [],
     territoryChanges: [],
     unowned: [],
-    nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+    nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
   };
 
   it('a release removes the key from its sole owner and marks it in GameState.unowned', () => {
@@ -1371,7 +1376,7 @@ describe('applyTurnResult (no man\'s land, v0.22 #16 P3)', () => {
 
   it('a lone release is meaningful (it survives the retry/nudge path)', () => {
     expect(
-      isMeaningful({ date: 'x', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: ['GBR'], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] } }),
+      isMeaningful({ date: 'x', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: ['GBR'], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] } }),
     ).toBe(true);
   });
 
@@ -1678,9 +1683,9 @@ describe('buildSystemPrompt (tool mode, v0.21 #16 P2)', () => {
 
 describe('isMeaningful', () => {
   it('is true with an event, false when everything is empty', () => {
-    expect(isMeaningful({ date: 'x', events: [{ nation: 'uk', type: 'military', title: 't', text: 'b', outcome: 'neutral' }], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] } })).toBe(true);
+    expect(isMeaningful({ date: 'x', events: [{ nation: 'uk', type: 'military', title: 't', text: 'b', outcome: 'neutral' }], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] } })).toBe(true);
-    expect(isMeaningful({ date: 'x', events: [], stateChanges: [{ nation: 'uk', stat: 'military', op: 'set', value: 5 }], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] } })).toBe(true);
+    expect(isMeaningful({ date: 'x', events: [], stateChanges: [{ nation: 'uk', stat: 'military', op: 'set', value: 5 }], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] } })).toBe(true);
-    expect(isMeaningful({ date: 'x', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] } })).toBe(false);
+    expect(isMeaningful({ date: 'x', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [], unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] } })).toBe(false);
   });
 
   it('(v0.23 #16 P4a) a turn that only proposes a nation-op is meaningful (it survives the retry/nudge path)', () => {
@@ -1693,7 +1698,7 @@ describe('isMeaningful', () => {
         relations: [],
         territoryChanges: [],
         unowned: [],
-        nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+        nationOps: [{ kind: 'rename', nationRef: 'de', to: 'Reich' }], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
       }),
     ).toBe(true);
   });
@@ -1713,6 +1718,7 @@ describe('isMeaningful', () => {
         wars: { declare: [], end: [] },
         hybrid: { ops: [] },
         economy: { trade: [], embargo: [] }, industry: { projects: [] },
+        nuclear: { arm: [], strikes: [] },
         markers: { add: [{ type: 'city', name: 'Lyon', regionKey: 'rhone-rhne' }], remove: [] },
       }),
     ).toBe(true);
@@ -1733,6 +1739,7 @@ describe('isMeaningful', () => {
         wars: { declare: [], end: [] },
         hybrid: { ops: [] },
         economy: { trade: [], embargo: [] }, industry: { projects: [] },
+        nuclear: { arm: [], strikes: [] },
         markers: { add: [], remove: [] },
       }),
     ).toBe(true);
@@ -1755,6 +1762,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1787,6 +1795,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1810,6 +1819,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1836,6 +1846,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1861,6 +1872,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     });
     expect(validated!.takeovers).toEqual([]);
@@ -1886,6 +1898,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1909,6 +1922,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1930,6 +1944,7 @@ describe('takeovers (regime change, v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
     const next = applyTurnResult(state, result);
@@ -1963,6 +1978,7 @@ describe('markers (point placement, v0.27 #44)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [mk('city', 'Strasbourg', 'moselle-rygy')], remove: [] },
     };
     const next = applyTurnResult(state, result, undefined, centroidOf);
@@ -1987,13 +2003,13 @@ describe('markers (point placement, v0.27 #44)', () => {
     const add = [mk('city', 'Strasbourg', 'moselle-rygy')];
     const first = applyTurnResult(state, {
       date: '1939-09-03', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [],
-      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add, remove: [] },
+      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add, remove: [] },
     }, undefined, centroidOf);
     expect(first.markers).toHaveLength(1);
     // a second turn proposes the exact same marker again
     const second = applyTurnResult(first, {
       date: '1939-09-05', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [],
-      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add, remove: [] },
+      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add, remove: [] },
     }, undefined, centroidOf);
     expect(second.markers).toHaveLength(1);
     expect(second.markers[0].id).toBe(first.markers[0].id); // stable id, no second copy
@@ -2019,6 +2035,7 @@ describe('markers (point placement, v0.27 #44)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: {
         add: [
           { type: 'city', name: 'Good', regionKey: 'moselle-rygy' }, // valid + centroid → kept
@@ -2065,6 +2082,7 @@ describe('markers (point placement, v0.27 #44)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: {
         add: [
           { type: 'city', name: 'NewA', regionKey: 'new-a' },
@@ -2090,7 +2108,7 @@ describe('markers (point placement, v0.27 #44)', () => {
     ];
     const next = applyTurnResult(state, {
       date: '1939-09-03', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [],
-      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [idA, 'zzzz-not-there'] },
+      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [idA, 'zzzz-not-there'] },
     }, undefined, centroidOf);
     expect(next.markers).toHaveLength(1);
     expect(next.markers[0].id).toBe(idB); // only A removed; the bogus id was a no-op
@@ -2106,14 +2124,14 @@ describe('markers (point placement, v0.27 #44)', () => {
     // 1) uk releases the region → the marker becomes ownerless
     const released = applyTurnResult(state, {
       date: '1939-09-03', events: [], stateChanges: [], regionChanges: [], relations: [], territoryChanges: [],
-      unowned: ['moselle-rygy'], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      unowned: ['moselle-rygy'], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     }, undefined, centroidOf);
     expect(released.markers[0].ownerNationId).toBeNull();
     // 2) de re-claims the region → the marker's owner follows to de
     const reclaimed = applyTurnResult(released, {
       date: '1939-09-05', events: [], stateChanges: [], regionChanges: [], relations: [],
       territoryChanges: [{ nation: 'de', gain: ['moselle-rygy'], lose: [] }],
-      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, markers: { add: [], remove: [] },
+      unowned: [], nationOps: [], takeovers: [], wars: { declare: [], end: [] }, hybrid: { ops: [] }, economy: { trade: [], embargo: [] }, industry: { projects: [] }, nuclear: { arm: [], strikes: [] }, markers: { add: [], remove: [] },
     }, undefined, centroidOf);
     expect(reclaimed.markers[0].ownerNationId).toBe('de');
   });
@@ -2182,6 +2200,7 @@ describe('markers (point placement, v0.27 #44)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [{ type: 'city', name: 'Strasbourg', regionKey: 'moselle-rygy' }], remove: [] },
     });
     const { state } = await runTurn({
@@ -2275,6 +2294,7 @@ function mkTurnResult(partial: Partial<TurnResult>): TurnResult {
     hybrid: partial.hybrid ?? { ops: [] },
     economy: partial.economy ?? { trade: [], embargo: [] },
     industry: partial.industry ?? { projects: [] },
+    nuclear: partial.nuclear ?? { arm: [], strikes: [] },
     markers: partial.markers ?? { add: [], remove: [] },
   };
 }
@@ -2999,6 +3019,7 @@ describe('validateTakeovers (v0.32.0 #54)', () => {
       wars: { declare: [], end: [] },
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] }, industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     });
     expect(withTakeovers).not.toBeNull();
@@ -3386,6 +3407,7 @@ describe('isMeaningful — wars (v0.33.0 #56)', () => {
         wars: { declare: [{ sides: ['a', 'b'] }], end: [] },
         hybrid: { ops: [] },
         economy: { trade: [], embargo: [] }, industry: { projects: [] },
+        nuclear: { arm: [], strikes: [] },
         markers: { add: [], remove: [] },
       }),
     ).toBe(true);
@@ -3406,6 +3428,7 @@ describe('isMeaningful — wars (v0.33.0 #56)', () => {
         wars: { declare: [], end: [{ id: 'w1', outcome: 'armistice' }] },
         hybrid: { ops: [] },
         economy: { trade: [], embargo: [] }, industry: { projects: [] },
+        nuclear: { arm: [], strikes: [] },
         markers: { add: [], remove: [] },
       }),
     ).toBe(true);
@@ -3426,6 +3449,7 @@ describe('isMeaningful — wars (v0.33.0 #56)', () => {
         wars: { declare: [], end: [] },
         hybrid: { ops: [] },
         economy: { trade: [], embargo: [] }, industry: { projects: [] },
+        nuclear: { arm: [], strikes: [] },
         markers: { add: [], remove: [] },
       }),
     ).toBe(false);
@@ -4349,3 +4373,274 @@ describe('runTurn — industry (v0.36.0 #59)', () => {
     expect(state.industry).toEqual([]);
   });
 });
+
+// --- Nuclear / WMD (v0.37.0, #60) -------------------------------------------
+
+describe('isNuclearCapable (v0.37.0 #60)', () => {
+  const marker = (id: string, type: MarkerType, ownerNationId: string | null): MapMarker =>
+    ({ id, type, name: 'site', regionKey: 'g1', lat: 0, lon: 0, ownerNationId, placedTurn: 1 });
+  const n = (id: string, nuclear?: boolean): Nation =>
+    nuclear ? { ...mkNation(id, NS(50, 50, 50, 50), []), nuclear } : mkNation(id, NS(50, 50, 50, 50), []);
+
+  it('is true when the nuclear flag is set', () => {
+    expect(isNuclearCapable(n('uk', true), [])).toBe(true);
+  });
+  it('is true when the nation owns a rocket marker (a launch site is an arsenal)', () => {
+    expect(isNuclearCapable(n('uk'), [marker('m1', 'rocket', 'uk')])).toBe(true);
+  });
+  it('is false when the flag is unset and no rocket marker is owned', () => {
+    expect(isNuclearCapable(n('uk'), [marker('m1', 'city', 'uk')])).toBe(false);
+  });
+  it('a rocket marker owned by another nation does not confer capability', () => {
+    expect(isNuclearCapable(n('uk'), [marker('m1', 'rocket', 'de')])).toBe(false);
+  });
+  it('a rocket marker with a null owner does not confer capability', () => {
+    expect(isNuclearCapable(n('uk'), [marker('m1', 'rocket', null)])).toBe(false);
+  });
+});
+
+describe('validateNuclearOps (v0.37.0 #60)', () => {
+  it('accepts well-formed arm + strikes', () => {
+    const out = validateNuclearOps({ arm: ['uk'], strikes: [{ from: 'uk', target: 'de' }] });
+    expect(out).toEqual({ arm: ['uk'], strikes: [{ from: 'uk', target: 'de' }] });
+  });
+  it('dedupes arm refs and drops empty / non-string entries', () => {
+    const out = validateNuclearOps({ arm: ['uk', 'uk', '', '   ', 'de', null, 5] as unknown[] });
+    expect(out.arm).toEqual(['uk', 'de']);
+  });
+  it('drops a strike missing a from or a target', () => {
+    const out = validateNuclearOps({
+      strikes: [
+        { target: 'de' } as unknown as NuclearStrike, // no from
+        { from: 'uk' } as unknown as NuclearStrike, // no target
+        'not-an-object' as unknown as NuclearStrike,
+        null as unknown as NuclearStrike,
+        { from: 'uk', target: 'g1' }, // valid
+      ],
+    });
+    expect(out.strikes).toEqual([{ from: 'uk', target: 'g1' }]);
+  });
+  it('drops a self-target (from === target, case-insensitive)', () => {
+    const out = validateNuclearOps({ strikes: [{ from: 'UK', target: 'uk' }, { from: 'uk', target: 'de' }] });
+    expect(out.strikes).toEqual([{ from: 'uk', target: 'de' }]);
+  });
+  it('a missing / malformed top-level object yields { arm: [], strikes: [] }', () => {
+    expect(validateNuclearOps(undefined)).toEqual({ arm: [], strikes: [] });
+    expect(validateNuclearOps(null)).toEqual({ arm: [], strikes: [] });
+    expect(validateNuclearOps('nope')).toEqual({ arm: [], strikes: [] });
+    expect(validateNuclearOps({})).toEqual({ arm: [], strikes: [] });
+    expect(validateNuclearOps({ arm: 'x', strikes: 'y' })).toEqual({ arm: [], strikes: [] });
+  });
+});
+
+describe('applyTurnResult — nuclear ops (v0.37.0 #60)', () => {
+  // uk starts nuclear-capable (the flag); de is not. Each owns one region.
+  const base = (): GameState => {
+    const uk: Nation = { ...mkNation('uk', NS(50, 50, 50, 50), ['g1']), nuclear: true };
+    const de: Nation = { ...mkNation('de', NS(50, 50, 50, 50), ['d1']) };
+    return mkTurnState({ uk, de }, { g1: RS(50, 50, 50, 50), d1: RS(50, 50, 50, 50) });
+  };
+
+  it('arming a nation sets its nuclear flag (idempotent across turns)', () => {
+    const next = applyTurnResult(base(), mkTurnResult({ nuclear: { arm: ['uk', 'de'], strikes: [] } }));
+    expect(next.nations.uk.nuclear).toBe(true);
+    expect(next.nations.de.nuclear).toBe(true);
+    const next2 = applyTurnResult(next, mkTurnResult({ nuclear: { arm: ['uk'], strikes: [] } }));
+    expect(next2.nations.uk.nuclear).toBe(true);
+    expect(next2.nations.de.nuclear).toBe(true); // unchanged
+  });
+
+  it('a nation that arms this turn is capable and can strike in the same turn', () => {
+    const s = base();
+    delete (s.nations.uk as { nuclear?: boolean }).nuclear; // start unarmed
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: ['uk'], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.nations.uk.nuclear).toBe(true);
+    expect(next.unowned).toContain('d1'); // the armed-this-turn strike landed
+  });
+
+  it('a region strike releases the region, deletes its stats, and collapses the owner', () => {
+    const next = applyTurnResult(base(), mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.nations.de.territory).toEqual([]);
+    expect(next.unowned).toContain('d1');
+    expect(next.regionStats['d1']).toBeUndefined();
+    expect(next.regionStats['g1']).toBeDefined();
+    expect(next.nations.de.stats.economy).toBe(50 + NUCLEAR_COLLAPSE.economy);
+    expect(next.nations.de.stats.military).toBe(50 + NUCLEAR_COLLAPSE.military);
+    expect(next.nations.de.stats.stability).toBe(50 + NUCLEAR_COLLAPSE.stability);
+    expect(next.nations.de.stats.population).toBe(50);
+    // de is not capable → no MAD, the striker is unharmed
+    expect(next.nations.uk.stats.military).toBe(50);
+    expect(next.nations.uk.stats.economy).toBe(50);
+    expect(next.events).toHaveLength(1);
+    expect(next.events[0].type).toBe('military');
+    expect(next.events[0].title).toBe('Nuclear strike on d1');
+  });
+
+  it('a nation strike devastates the target and ends a shared war in capitulation (relation → hostile)', () => {
+    const s = base();
+    s.wars = [{ id: 'w1', sides: ['uk', 'de'], declaredTurn: 1, declaredDate: '1939-09-01', status: 'active' }];
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'de' }] },
+    }));
+    expect(next.nations.de.stats.military).toBe(50 + NUCLEAR_COLLAPSE.military);
+    expect(next.wars.find((w) => w.id === 'w1')?.status).toBe('capitulation');
+    expect(next.nations.uk.relations.de).toBe('hostile');
+    expect(next.nations.de.relations.uk).toBe('hostile');
+    // de is not capable → no MAD
+    expect(next.nations.uk.stats.military).toBe(50);
+  });
+
+  it('a nation strike ends a war declared in the same turn (the sync-then-end ordering)', () => {
+    const next = applyTurnResult(base(), mkTurnResult({
+      wars: { declare: [{ sides: ['uk', 'de'] }], end: [] },
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'de' }] },
+    }));
+    const w = next.wars.find((w) => w.sides.includes('uk') && w.sides.includes('de'));
+    expect(w?.status).toBe('capitulation');
+    expect(next.nations.uk.relations.de).toBe('hostile');
+    expect(next.nations.de.relations.uk).toBe('hostile');
+  });
+
+  it('a strike on a nuclear-capable target triggers a MAD retaliation on the striker', () => {
+    const s = base();
+    s.nations.de.nuclear = true; // the target is capable
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'de' }] },
+    }));
+    expect(next.nations.de.stats.military).toBe(50 + NUCLEAR_COLLAPSE.military);
+    expect(next.nations.uk.stats.military).toBe(50 + NUCLEAR_RETALIATION.military);
+    expect(next.nations.uk.stats.economy).toBe(50 + NUCLEAR_RETALIATION.economy);
+    expect(next.nations.uk.stats.stability).toBe(50 + NUCLEAR_RETALIATION.stability);
+    expect(next.nations.uk.relations.de).toBe('hostile');
+    expect(next.nations.de.relations.uk).toBe('hostile');
+    expect(next.events).toHaveLength(2);
+    expect(next.events.some((e) => e.title === 'MAD retaliation')).toBe(true);
+  });
+
+  it('a region strike on a nuclear-capable owner triggers a MAD retaliation', () => {
+    const s = base();
+    s.nations.de.nuclear = true; // the owner of d1 is capable
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.unowned).toContain('d1');
+    expect(next.nations.de.stats.military).toBe(50 + NUCLEAR_COLLAPSE.military);
+    expect(next.nations.uk.stats.military).toBe(50 + NUCLEAR_RETALIATION.military);
+    expect(next.nations.uk.relations.de).toBe('hostile');
+    expect(next.nations.de.relations.uk).toBe('hostile');
+    expect(next.events).toHaveLength(2);
+  });
+
+  it('a nation with a rocket marker (not the flag) can strike', () => {
+    const s = base();
+    delete (s.nations.uk as { nuclear?: boolean }).nuclear; // no flag
+    s.markers = [{ id: 'm1', type: 'rocket', name: 'site', regionKey: 'g1', lat: 0, lon: 0, ownerNationId: 'uk', placedTurn: 1 }];
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.unowned).toContain('d1');
+  });
+
+  it('a strike by a non-nuclear-capable nation is dropped (never thrown)', () => {
+    const s = base();
+    delete (s.nations.uk as { nuclear?: boolean }).nuclear;
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.nations.de.territory).toEqual(['d1']);
+    expect(next.unowned).toEqual([]);
+    expect(next.nations.de.stats.military).toBe(50);
+    expect(next.events).toHaveLength(0);
+  });
+
+  it('a strike on a region with two or more owners is dropped (never thrown)', () => {
+    const s = base();
+    s.nations.uk.territory = ['g1', 'd1']; // d1 now has two owners (uk, de)
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.unowned).toEqual([]);
+    expect(next.nations.de.stats.military).toBe(50);
+    expect(next.events).toHaveLength(0);
+  });
+
+  it('a strike on an unowned (no-man\'s-land) region is dropped (nothing to devastate)', () => {
+    const s = base();
+    s.nations.de.territory = []; // d1 has zero owners
+    s.unowned = ['d1'];
+    delete s.regionStats['d1'];
+    const next = applyTurnResult(s, mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'd1' }] },
+    }));
+    expect(next.unowned).toEqual(['d1']);
+    expect(next.nations.uk.stats.military).toBe(50);
+    expect(next.events).toHaveLength(0);
+  });
+
+  it('a strike whose target is the striker itself is dropped (never thrown)', () => {
+    const next = applyTurnResult(base(), mkTurnResult({
+      nuclear: { arm: [], strikes: [{ from: 'uk', target: 'uk' }] },
+    }));
+    expect(next.nations.uk.stats.military).toBe(50);
+    expect(next.events).toHaveLength(0);
+  });
+
+  it('never throws on malformed strikes (unknown from, unknown target, empty strings)', () => {
+    const next = applyTurnResult(base(), mkTurnResult({
+      nuclear: {
+        arm: [],
+        strikes: [
+          { from: 'ghost', target: 'de' },
+          { from: 'uk', target: 'nowhere' },
+          { from: 'uk', target: '' },
+        ],
+      },
+    }));
+    expect(next.nations.de.stats.military).toBe(50);
+    expect(next.events).toHaveLength(0);
+  });
+});
+
+describe('isMeaningful — nuclear (v0.37.0 #60)', () => {
+  it('a turn with only an arm op or a strike is meaningful', () => {
+    expect(isMeaningful(mkTurnResult({ nuclear: { arm: ['uk'], strikes: [] } }))).toBe(true);
+    expect(isMeaningful(mkTurnResult({ nuclear: { arm: [], strikes: [{ from: 'uk', target: 'de' }] } }))).toBe(true);
+  });
+  it('a turn with empty nuclear ops and nothing else is not meaningful', () => {
+    expect(isMeaningful(mkTurnResult({ nuclear: { arm: [], strikes: [] } }))).toBe(false);
+  });
+});
+
+describe('buildUserPrompt — nuclear capability (v0.37.0 #60)', () => {
+  const state = (): GameState =>
+    mkTurnState(
+      {
+        uk: { ...mkNation('uk', NS(50, 50, 50, 50), ['g1']), nuclear: true },
+        de: mkNation('de', NS(50, 50, 50, 50), ['d1']),
+      },
+      { g1: RS(50, 50, 50, 50), d1: RS(50, 50, 50, 50) },
+    );
+
+  it('stamps each nation\'s nuclear capability when the map is provided', () => {
+    const out = JSON.parse(
+      buildUserPrompt(state(), [], undefined, undefined, [], [], undefined, undefined, undefined, undefined, undefined, undefined, {
+        uk: true,
+        de: false,
+      }),
+    );
+    expect(out.state.nations.uk.nuclear).toBe(true);
+    expect(out.state.nations.de.nuclear).toBe(false);
+  });
+
+  it('omits the nuclear capability entirely when the map is undefined', () => {
+    const out = JSON.parse(
+      buildUserPrompt(state(), [], undefined, undefined, [], [], undefined, undefined, undefined, undefined, undefined, undefined),
+    );
+    expect(out.state.nations.uk).not.toHaveProperty('nuclear');
+    expect(out.state.nations.de).not.toHaveProperty('nuclear');
+  });
+});

server/engine.ts

@@ -33,9 +33,12 @@ import {
   HYBRID_OP_TYPES,
   isDateLike,
   isMarkerType,
+  isNuclearCapable,
   makeEvent,
   markerId,
   MAX_MARKERS,
+  NUCLEAR_COLLAPSE,
+  NUCLEAR_RETALIATION,
   nationForPrompt,
   type EconomyEmbargoOp,
   type EconomyOps,
@@ -46,6 +49,8 @@ import {
   type MarkerInfo,
   type MarkerSpec,
   type NationOp,
+  type NuclearOps,
+  type NuclearStatKey,
   type RegionStatChange,
   type Takeover,
   type TurnEventSpec,
@@ -237,6 +242,7 @@ export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): s
     '  "hybrid": {"ops":[{"type":"<spy|sabotage|assassinate|cyber|economic|information|proxy>","from":"<nation id or name>","target":"<nation id or name, or region key>","detail":"<short detail>","outcome":"<success|exposed>"}]},',
     '  "economy": {"trade":[{"a":"<nationId>","b":"<nationId>","lift":<true|false>}],"embargo":[{"from":"<nationId>","target":"<nationId>","lift":<true|false>}]},',
     '  "industry": {"projects":[{"regionKey":"<region key>","type":"<oil|iron|food|industry>"}]},',
+    '  "nuclear": {"arm":["<nation id or name>"],"strikes":[{"from":"<nuclear-capable nation id or name>","target":"<nation id or name, or region key>"}]},',
     '  "markers": {"add":[{"type":"<city|factory|army|port|capital|fleet|rocket|gathering>","name":"<short name>","regionKey":"<region key>"}],"remove":["<marker id>"]}',
     '}',
     '',
@@ -259,6 +265,7 @@ export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): s
     '- Covert / hybrid ops ("hybrid.ops") are non-kinetic operations — spies, sabotage, assassination attempts, cyberattacks, economic pressure, disinformation, and proxy support. Unlike territory they NEVER move borders: a successful op applies a small, deterministic effect (a small dip in the target\'s economy / stability / military for sabotage / assassinate / cyber / economic, or a relation nudge toward hostile for information / proxy), while an "exposed" op backfires (no effect, and the actor\'s relation with the target sours by one step toward hostile). "target" may be a nation id / name or a region key (a region key hits that region\'s sole owner). Keep each detail short, propose at most a few per turn, and narrate each op in "events".',
     '- Economy ("economy") is the trade & embargo layer: a bilateral trade (trade: {"a":"..","b":".."}) gives BOTH parties a small, deterministic economy gain every turn, while a unilateral embargo (embargo: {"from":"..","target":".."}) lowers only the TARGET\'s economy every turn. Omit "lift" to declare / impose, and set "lift":true to end or lift an existing one (the user message\'s "trades"/"embargoes" fields list what is currently active). Propose at most 1-2 operations per turn and narrate each one in "events". Trades and embargoes between nations at war are suspended automatically by the engine.',
     '- Industry ("industry") is the per-resource development lever: each project is a building in one region you (or a nation) controls — {"regionKey":"<region key>","type":"<oil|iron|food|industry>"} (an oil facility, an iron mine, a food operation, or a factory). Every committed turn each active project gives its region\'s owner a small, deterministic economy gain, the bigger the region\'s industry profile (see the "resources" field). A region holds at most one project — do not re-declare one on a region that already has one (the user message\'s "industry" field lists what is already built). Propose at most 1-2 new projects per turn and narrate each one in "events".',
+    '- 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".',
   '- 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.',
@@ -351,6 +358,15 @@ export function buildUserPrompt(
    * can reference them. Omitted entirely when undefined.
    */
   industryProjects?: IndustryProject[],
+  /**
+   * (v0.37.0, #60) Each nation's nuclear capability (nation id -> boolean),
+   * computed by the caller via `isNuclearCapable` (the nation's `nuclear` flag
+   * OR a current `rocket` marker). When defined, each nation in the `state.
+   * nations` map is stamped with `nuclear: true|false` so the model knows who
+   * can arm/strike and who can MAD-retaliate. Omitted entirely (no `nuclear`
+   * key on any nation) when undefined.
+   */
+  nuclear?: Record<string, boolean>,
 ): string {
   const player = state.nations[state.playerNationId];
   const playerName = player?.name ?? state.playerNationId;
@@ -440,7 +456,10 @@ export function buildUserPrompt(
       date: state.date,
       playerNationId: state.playerNationId,
       nations: Object.fromEntries(
-        Object.entries(state.nations).map(([id, n]) => [id, nationForPrompt(n)]),
+        Object.entries(state.nations).map(([id, n]) => [
+          id,
+          nuclear ? { ...nationForPrompt(n), nuclear: nuclear[id] ?? false } : nationForPrompt(n),
+        ]),
       ),
       recentEvents: state.events.slice(-5).map((e) => ({
         turn: e.turn,
@@ -611,6 +630,7 @@ export function validateTurnResult(
     hybrid: { ops: [] },
     economy: { trade: [], embargo: [] },
     industry: { projects: [] },
+    nuclear: { arm: [], strikes: [] },
     markers: { add: [], remove: [] },
   };
 
@@ -729,6 +749,14 @@ export function validateTurnResult(
   // is kept). Refs stay raw and the effect is deterministic at apply time.
   result.industry = validateIndustryOps(o.industry);
 
+  // (v0.37, #60) Nuclear / WMD ops: `arm` grants an arsenal to the named
+  // nations and `strikes` are nuclear strikes fired this turn. Refs stay raw
+  // here (resolved against the real state at apply time, like wars / hybrid
+  // ops); an unresolvable ref, a non-capable striker, or an invalid region is
+  // dropped at apply time, never thrown. Applied directly by applyTurnResult
+  // (after industry, before markers).
+  result.nuclear = validateNuclearOps(o.nuclear);
+
   // (v0.27, #44) Map-marker ops: new placements (validated here) and
   // removals by stable id. Applied by applyTurnResult after the territory
   // moves (a new marker's owner is the region's post-turn owner).
@@ -1031,6 +1059,40 @@ export function validateIndustryOps(raw: unknown): IndustryOps {
   return out;
 }
 
+/**
+ * (v0.37, #60) Validate the raw `nuclear` object of a turn into a safe
+ * {@link NuclearOps}. Defensive like the rest of the parser — never throws.
+ * `arm`: non-empty nation refs (capped at 120 chars), deduped; a ref is
+ * resolved (id or name) at APPLY time, so an unknown ref is dropped there, not
+ * here. `strikes`: each needs a non-empty `from` (the striking nation ref) and
+ * a non-empty `target` (a nation ref OR a region key), each capped at 120
+ * chars; a self-target (`from` and `target` the same ref) is dropped here. A
+ * missing / malformed top-level object yields `{ arm: [], strikes: [] }`.
+ */
+export function validateNuclearOps(raw: unknown): NuclearOps {
+  const out: NuclearOps = { arm: [], strikes: [] };
+  if (!raw || typeof raw !== 'object' || Array.isArray(raw)) return out;
+  const o = raw as Record<string, unknown>;
+  if (Array.isArray(o.arm)) {
+    for (const e of o.arm) {
+      const s = typeof e === 'string' ? e.trim() : '';
+      if (s && !out.arm.includes(s)) out.arm.push(s.slice(0, 120));
+    }
+  }
+  if (Array.isArray(o.strikes)) {
+    for (const e of o.strikes) {
+      if (!e || typeof e !== 'object') continue;
+      const s = e as Record<string, unknown>;
+      const from = str(s.from, 120);
+      const target = str(s.target, 120);
+      if (!from || !target) continue;
+      if (from.toLowerCase() === target.toLowerCase()) continue; // self-target: drop
+      out.strikes.push({ from, target });
+    }
+  }
+  return out;
+}
+
 /**
  * (v0.33.0, #56) The UNORDERED pairs of belligerents of a set of ACTIVE
  * wars: a war with sides [a, b, c] contributes the pairs {a,b}, {a,c},
@@ -1556,6 +1618,300 @@ export function applyIndustryEffects(
   }
 }
 
+// --- Nuclear / WMD (v0.37, #60): the WMD lever --------------------------------
+//
+// A nuclear strike is a DETERMINISTIC devastation (no hidden randomness): the
+// LLM decides which nuclear-capable nation strikes and what it targets; the
+// engine decides the size of the effect (NUCLEAR_COLLAPSE / NUCLEAR_RETALIATION
+// in protocol.ts). This block runs AFTER the industry effects and BEFORE the
+// marker owner-recompute, because a region strike RELEASES its region to no
+// man's land, which changes the final ownership the markers depend on.
+//
+//   ARM: each `arm` ref (id or name) is resolved and that nation's `nuclear`
+//        flag is set to true (idempotent; an unresolvable ref is dropped).
+//        Arming runs first, so a nation that arms AND strikes this turn is
+//        capable.
+//
+//   STRIKE: each strike is validated independently (never throws):
+//     (a) `from` must resolve to a nuclear-capable nation (the `nuclear` flag
+//         or a rocket marker), else dropped.
+//     (b) The target is a NATION (a ref resolving to a distinct nation) or a
+//         REGION (a region key / name with a SOLE owner that is not the
+//         striker):
+//         - a nation target: the target's economy / military / stability are
+//           devastated (NUCLEAR_COLLAPSE, mirrored to its regions); if `from`
+//           and the target are on opposite sides of an active war, that war
+//           ends in `capitulation` and the warring relation falls back to
+//           hostile; if the target is nuclear-capable, the striker suffers a
+//           half-strength MAD retaliation.
+//         - a region target: the region is released to no man's land (its
+//           regionStats entry leaves the table), its former owner is
+//           devastated (NUCLEAR_COLLAPSE), and if that owner is nuclear-capable
+//           the striker suffers a half-strength MAD retaliation.
+//     (c) every applied strike appends a dramatic event (the EXISTING `military`
+//         category — no new category is invented), and a MAD strike appends an
+//         extra "MAD retaliation" event.
+//
+//   After all strikes, every affected nation's derived stats are re-derived
+//   (the same 0-region / no-entry guards as the main recompute), so the
+//   collapse persists and the sole-ownership invariant is untouched.
+
+/** The three stats a nuclear strike collapses (population is never touched). */
+const NUCLEAR_STATS: NuclearStatKey[] = ['economy', 'military', 'stability'];
+
+/**
+ * Devastate one nation's stats AND every region it owns (mirroring the
+ * collapse into `regionStats`, like the economy / hybrid layers), clamped to
+ * 0–100. Never throws.
+ */
+function collapseNationStats(
+  next: GameState,
+  nationId: string,
+  collapse: Record<NuclearStatKey, number>,
+): void {
+  const n = next.nations[nationId];
+  if (!n) return;
+  for (const k of NUCLEAR_STATS) {
+    const d = collapse[k];
+    n.stats[k] = clampStat(n.stats[k] + d);
+    for (const key of n.territory) {
+      const rs = next.regionStats[key];
+      if (rs) rs[k] = clampStat(rs[k] + d);
+    }
+  }
+}
+
+/**
+ * Release a region key to no man's land, reusing the turn's release semantics:
+ * the key leaves its SOLE owner's territory, is marked in `GameState.unowned`,
+ * and its `regionStats` entry is deleted. A key with 0 or 2+ owners (or an
+ * already-unowned key) is left untouched. Never throws.
+ */
+function releaseRegionToNoMansLand(next: GameState, key: string): void {
+  if (next.unowned.includes(key)) return; // already no man's land
+  const owners = Object.values(next.nations).filter((n) => n.territory.includes(key));
+  if (owners.length !== 1) return; // 0 or 2+ owners: not releasable
+  next.nations[owners[0]!.id].territory = next.nations[owners[0]!.id].territory.filter(
+    (k) => k !== key,
+  );
+  next.unowned.push(key);
+  delete next.regionStats[key];
+}
+
+/**
+ * End every ACTIVE war whose sides include both `a` and `b` (a nuclear
+ * capitulation), then downgrade the `war` relation of every pair that is no
+ * longer covered by an active war back to `hostile` (the war → relation sync).
+ * Capturing the active pairs immediately BEFORE the end keeps this correct for
+ * a war declared and ended in the SAME turn (where the start-of-turn `prev`
+ * that `syncWarRelations` uses would not contain it). Never throws.
+ */
+function endWarsBetween(next: GameState, a: string, b: string): void {
+  const before = activeWarPairs(next.wars);
+  let ended = false;
+  for (const w of next.wars) {
+    if (w.status === 'active' && w.sides.includes(a) && w.sides.includes(b)) {
+      w.status = 'capitulation';
+      ended = true;
+    }
+  }
+  if (!ended) return;
+  const after = activeWarPairs(next.wars);
+  for (const key of before) {
+    if (after.has(key)) continue; // still covered by another active war
+    const [x, y] = key.split('\u0000');
+    const nx = next.nations[x];
+    const ny = next.nations[y];
+    if (!nx || !ny) continue;
+    if (nx.relations[y] === 'war' || ny.relations[x] === 'war') {
+      nx.relations[y] = 'hostile';
+      ny.relations[x] = 'hostile';
+    }
+  }
+}
+
+/**
+ * Force the relation between two nations to `hostile` in BOTH directions —
+ * the aftermath of a MAD exchange. A `war` relation is never downgraded (the
+ * war entity owns it while active — e.g. a region strike that devastates one
+ * warring side without ending the war). Never throws.
+ */
+function forceHostile(next: GameState, a: string, b: string): void {
+  const na = next.nations[a];
+  const nb = next.nations[b];
+  if (!na || !nb) return;
+  if (na.relations[b] !== 'war') na.relations[b] = 'hostile';
+  if (nb.relations[a] !== 'war') nb.relations[a] = 'hostile';
+}
+
+/**
+ * Apply a turn's nuclear ops to the (cloned) `next` state, mutating it in
+ * place and never throwing. See the section comment above for the full
+ * contract. `state` is the ORIGINAL (pre-turn) state — its `markers` supply the
+ * "owns a rocket" half of nuclear capability (a rocket marker placed this very
+ * turn makes its owner capable only from the next turn, while a nation that
+ * ARMS this turn is capable immediately, since arming runs first).
+ */
+export function applyNuclearOps(
+  next: GameState,
+  ops: NuclearOps,
+  state: GameState,
+  geoOf?: (key: string) => { area: number; population: number } | undefined,
+  validKeys?: ReadonlySet<string>,
+  regionNameOf?: (key: string) => string | undefined,
+  actingTurn?: number,
+): void {
+  if (ops.arm.length === 0 && ops.strikes.length === 0) return;
+  const turn = actingTurn ?? next.turn;
+  const markers = state.markers ?? [];
+  const capable = (id: string): boolean => {
+    const n = next.nations[id];
+    return n ? isNuclearCapable(n, markers) : false;
+  };
+
+  // (1) ARM: set the nuclear flag (idempotent); unresolvable refs are dropped.
+  for (const ref of ops.arm) {
+    const id = resolveNationRef(next, ref);
+    if (id === null) continue;
+    const n = next.nations[id];
+    if (!n) continue;
+    n.nuclear = true;
+  }
+
+  const affected = new Set<string>();
+  const regionDisplay = (key: string): string => regionNameOf?.(key) ?? key;
+
+  // (2) STRIKES: each validated independently against the post-arm state.
+  for (const strike of ops.strikes) {
+    const fromId = resolveNationRef(next, strike.from);
+    if (fromId === null) continue; // unknown / ambiguous striker: drop
+    const from = next.nations[fromId];
+    if (!from) continue;
+    if (!capable(fromId)) continue; // a non-capable nation cannot strike
+    if (fromId === resolveNationRef(next, strike.target)) continue; // self: drop
+
+    // Resolve the target: a NATION (a ref resolving to a distinct nation) or a
+    // REGION (a region key / name with a sole owner that is not the striker).
+    let target:
+      | { kind: 'nation'; nation: Nation }
+      | { kind: 'region'; key: string; owner: Nation }
+      | null = null;
+    const tid = resolveNationRef(next, strike.target);
+    if (tid !== null) {
+      const tn = next.nations[tid];
+      if (tn) target = { kind: 'nation', nation: tn };
+    } else {
+      const rk = validKeys
+        ? resolveRegionKey(strike.target, validKeys, regionNameOf ?? (() => undefined))
+        : (strike.target.trim() || null);
+      if (rk !== null) {
+        const owners = Object.values(next.nations).filter((n) => n.territory.includes(rk));
+        if (owners.length === 1 && owners[0]!.id !== fromId) {
+          target = { kind: 'region', key: rk, owner: owners[0]! };
+        }
+        // a 0/2+-owner region, or a region the striker owns (self), is dropped
+      }
+    }
+    if (target === null) continue; // unresolvable target: drop
+
+    if (target.kind === 'nation') {
+      // Devastate the target nation.
+      collapseNationStats(next, target.nation.id, NUCLEAR_COLLAPSE);
+      affected.add(target.nation.id);
+      // A strike on a nation at war with the striker ends that war in
+      // capitulation (the relation then falls back to hostile).
+      endWarsBetween(next, fromId, target.nation.id);
+      // MAD: a nuclear-capable target strikes back at half strength and the
+      // two nations end the exchange at least hostile.
+      if (capable(target.nation.id)) {
+        collapseNationStats(next, fromId, NUCLEAR_RETALIATION);
+        affected.add(fromId);
+        forceHostile(next, fromId, target.nation.id);
+        next.events.push(
+          makeEvent(
+            {
+              nation: fromId,
+              type: 'military',
+              title: 'MAD retaliation',
+              text: `${target.nation.name} launches a retaliatory nuclear strike against ${from.name}; mutual assured destruction devastates ${from.name} in turn.`,
+              outcome: 'failure',
+            },
+            turn,
+            next.date,
+          ),
+        );
+      }
+      next.events.push(
+        makeEvent(
+          {
+            nation: fromId,
+            type: 'military',
+            title: `Nuclear strike on ${target.nation.name}`,
+            text: `${from.name} devastates ${target.nation.name} with a nuclear strike; the target's economy, military and stability collapse.`,
+            outcome: 'success',
+          },
+          turn,
+          next.date,
+        ),
+      );
+    } else {
+      // Devastate the region: release it to no man's land, then devastate its
+      // former owner.
+      const owner = target.owner;
+      releaseRegionToNoMansLand(next, target.key);
+      collapseNationStats(next, owner.id, NUCLEAR_COLLAPSE);
+      affected.add(owner.id);
+      // MAD: a nuclear-capable owner strikes back at half strength and the
+      // two nations end the exchange at least hostile.
+      if (capable(owner.id)) {
+        collapseNationStats(next, fromId, NUCLEAR_RETALIATION);
+        affected.add(fromId);
+        forceHostile(next, fromId, owner.id);
+        next.events.push(
+          makeEvent(
+            {
+              nation: fromId,
+              type: 'military',
+              title: 'MAD retaliation',
+              text: `${owner.name} launches a retaliatory nuclear strike against ${from.name} in response to the devastation of ${regionDisplay(
+                target.key,
+              )}; mutual assured destruction devastates ${from.name} in turn.`,
+              outcome: 'failure',
+            },
+            turn,
+            next.date,
+          ),
+        );
+      }
+      next.events.push(
+        makeEvent(
+          {
+            nation: fromId,
+            type: 'military',
+            title: `Nuclear strike on ${regionDisplay(target.key)}`,
+            text: `${from.name} obliterates ${regionDisplay(
+              target.key,
+            )} with a nuclear strike, reducing the region to no man's land and devastating its former owner, ${owner.name}.`,
+            outcome: 'success',
+          },
+          turn,
+          next.date,
+        ),
+      );
+    }
+  }
+
+  // (3) RE-DERIVE: every affected nation's aggregate stats (the same 0-region /
+  // no-entry guards as the main recompute), so the collapse persists.
+  for (const id of affected) {
+    const n = next.nations[id];
+    if (!n) continue;
+    if (n.territory.length === 0) continue; // 0-region guard: no regions to aggregate
+    if (!n.territory.some((k) => next.regionStats[k])) continue; // no entry: keep n.stats
+    n.stats = deriveNationStats(n.territory, next.regionStats, geoOf);
+  }
+}
+
 /**
  * A turn is "meaningful" if it produced at least an event, a stat change, a stat change, a
  * no-man's-land release (v0.22 #16 P3: a release is a real world change even
@@ -1588,6 +1944,10 @@ export function isMeaningful(result: TurnResult): boolean {
     // (v0.36, #59) an industry project built this turn is a real world change
     // (the active project list moved).
     result.industry.projects.length > 0 ||
+    // (v0.37, #60) a nation arming a nuclear arsenal or a nuclear strike fired
+    // this turn is a real world change.
+    result.nuclear.arm.length > 0 ||
+    result.nuclear.strikes.length > 0 ||
     // (v0.27, #44) a marker placed or removed this turn is a real world change.
     result.markers.add.length > 0 ||
     result.markers.remove.length > 0
@@ -2002,6 +2362,16 @@ export function applyTurnResult(
   applyIndustryOps(next, result.industry, validKeys);
   applyIndustryEffects(next, resourceOf, geoOf);
 
+  // --- Nuclear / WMD (v0.37, #60): the WMD lever ---
+  //
+  // Placed AFTER the industry/economy effects (both move stats) and BEFORE the
+  // markers block (a region strike releases its region to no man's land, which
+  // changes the FINAL ownership the marker owner-recompute depends on). See
+  // applyNuclearOps for the full contract (arm, strike, MAD, re-derive).
+  // `state` (the original pre-turn state) supplies the markers used for the
+  // rocket-marker half of nuclear capability.
+  applyNuclearOps(next, result.nuclear, state, geoOf, validKeys, regionNameOf, actingTurn);
+
   // --- Map markers (v0.27, #44) ---
   //
   // Markers are anchored to a region key and are processed against the FINAL
@@ -2528,6 +2898,12 @@ export async function runTurn(opts: {
             deriveNationResources(n.territory, resourceOf, geoOf),
           ]),
         );
+  // (v0.37.0, #60) each nation's nuclear capability (its `nuclear` flag OR a
+  // current `rocket` marker), so the model knows who can arm/strike and who
+  // can MAD-retaliate. Always emitted (computed from the PRE-turn markers).
+  const nuclearCapability = Object.fromEntries(
+    Object.values(state.nations).map((n) => [n.id, isNuclearCapable(n, state.markers ?? [])]),
+  );
   const user = buildUserPrompt(
     state,
     items,
@@ -2547,6 +2923,8 @@ export async function runTurn(opts: {
     // resource.
     nationResources,
     state.industry ?? [],
+    // (v0.37.0, #60) per-nation nuclear capability (flag or rocket marker).
+    nuclearCapability,
   );
   const nudge =
     'Your previous output was invalid. Respond with ONLY the JSON object described above for this batch — no prose, no fences.';
@@ -2604,6 +2982,7 @@ export async function runTurn(opts: {
       hybrid: { ops: [] },
       economy: { trade: [], embargo: [] },
       industry: { projects: [] },
+      nuclear: { arm: [], strikes: [] },
       markers: { add: [], remove: [] },
     };
   }

server/stub.ts

@@ -13,7 +13,13 @@ export interface StubPayload {
     turn: number;
     date: string;
     playerNationId: string;
-    nations: Record<string, { stats: Record<string, number>; territory?: string[] }>;
+    // `nuclear` (v0.37.0, #60) is the per-nation nuclear capability stamped by
+    // the engine (its `nuclear` flag OR a `rocket` marker); the stub ignores
+    // it — it never arms or strikes (see deterministicTurn).
+    nations: Record<
+      string,
+      { stats: Record<string, number>; territory?: string[]; nuclear?: boolean }
+    >;
   };
   /** The raw pending round the engine emitted (one entry per queued item). */
   pending?: RoundItem[];
@@ -141,6 +147,11 @@ function truncate(s: string, n: number): string {
  * (v0.36.0, #59) The stub likewise NEVER declares an industry project (it
  * always returns `industry: { projects: [] }`) — the per-region industry
  * path is covered by unit tests only, keeping the e2e assertions untouched.
+ *
+ * (v0.37.0, #60) The stub likewise NEVER arms a nation or fires a nuclear
+ * strike (it always returns `nuclear: { arm: [], strikes: [] }`) — the
+ * nuclear / WMD path is covered by unit tests only, keeping the e2e
+ * assertions untouched.
  */
 export function deterministicTurn(p: StubPayload): TurnResult {
   const state = p.state;
@@ -212,6 +223,7 @@ export function deterministicTurn(p: StubPayload): TurnResult {
     hybrid: { ops: [] }, // the stub never runs hybrid/covert ops (see doc comment)
     economy: { trade: [], embargo: [] }, // the stub never touches trades/embargoes (see doc comment)
     industry: { projects: [] }, // the stub never declares industry projects (see doc comment)
+    nuclear: { arm: [], strikes: [] }, // the stub never arms or strikes (see doc comment)
     markers: { add: [], remove: [] }, // the stub never touches markers (see doc comment)
   };
 }

shared/protocol.ts

@@ -7,6 +7,7 @@ import type {
   EventType,
   GameState,
   IndustryProject,
+  MapMarker,
   MarkerType,
   Nation,
   NationStats,
@@ -433,6 +434,90 @@ export interface IndustryOps {
   projects: IndustryProject[];
 }
 
+/**
+ * (v0.37, #60) A single nuclear strike. `from` names the striking nation
+ * (id or name — it must be **nuclear-capable**, see `isNuclearCapable`);
+ * `target` names what is struck — either a **region key** (the region is
+ * devastated to no man's land and its former owner devastated) or a
+ * **nation** (id or name — the target's economy / military / stability are
+ * devastated; if the striker and the target are on opposite sides of an
+ * active war, that war ends in `capitulation`).
+ */
+export interface NuclearStrike {
+  /** The striking nation (id or name). Must be nuclear-capable. */
+  from: string;
+  /** The struck target: a region key, or a nation (id or name). */
+  target: string;
+}
+
+/**
+ * (v0.37, #60) The turn's NUCLEAR operations, nested under
+ * `TurnResult.nuclear`. `arm` names the nations (id or name) that declare a
+ * nuclear arsenal this turn (idempotent — arming an already-armed nation is a
+ * no-op; an unresolvable ref is dropped); `strikes` are the nuclear strikes
+ * fired this turn (at most one per turn in the prompt contract; each is
+ * validated independently — an invalid `from` or `target` is dropped, never
+ * thrown). A strike on a nuclear-capable target (or the owner of a struck
+ * region) triggers a smaller "MAD" retaliation on the striker. Required;
+ * default `{ arm: [], strikes: [] }`.
+ */
+export interface NuclearOps {
+  /** Nation refs (id or name) arming a nuclear arsenal this turn. */
+  arm: string[];
+  /** The nuclear strikes fired this turn. */
+  strikes: NuclearStrike[];
+}
+
+// --- Nuclear / WMD effect math (v0.37, #60) ----------------------------------
+//
+// A nuclear strike is a DETERMINISTIC, devastating stat collapse — there is no
+// hidden randomness (the LLM decides WHO strikes and WHAT is targeted; the
+// engine decides the size of the effect). The two magnitude tables below are
+// the single source of truth for the collapse: a full strike devastates a
+// nation (or the former owner of a devastated region) by `NUCLEAR_COLLAPSE`,
+// while a "MAD" retaliation (fired when a nuclear-capable nation is struck)
+// devastates the STRIKER by half that, `NUCLEAR_RETALIATION`. Both dip the
+// three war-relevant stats only (population is untouched); each value is the
+// signed per-turn delta the engine clamps against 0–100.
+
+/** The stats a nuclear strike collapses (population is never touched). */
+export type NuclearStatKey = 'economy' | 'military' | 'stability';
+
+/**
+ * (v0.37, #60) The deterministic stat collapse a FULL nuclear strike inflicts
+ * on its target (a struck nation, or the former owner of a devastated region):
+ * a heavy dip in economy / military / stability. Shared so the engine and the
+ * unit tests agree on the exact magnitudes.
+ */
+export const NUCLEAR_COLLAPSE: Record<NuclearStatKey, number> = {
+  economy: -40,
+  military: -50,
+  stability: -40,
+};
+
+/**
+ * (v0.37, #60) The deterministic stat collapse of a "MAD" RETALIATION — fired
+ * automatically when a nuclear-capable nation (or the owner of a devastated
+ * region) is struck — which hits the STRIKER at half the full collapse.
+ */
+export const NUCLEAR_RETALIATION: Record<NuclearStatKey, number> = {
+  economy: NUCLEAR_COLLAPSE.economy / 2,
+  military: NUCLEAR_COLLAPSE.military / 2,
+  stability: NUCLEAR_COLLAPSE.stability / 2,
+};
+
+/**
+ * (v0.37, #60) Whether a nation is **nuclear-capable** — i.e. able to fire a
+ * nuclear strike and subject to MAD retaliation: its `nuclear` flag is set, OR
+ * it owns a `rocket` marker (a launch site is an arsenal). A legacy nation
+ * without the flag is not nuclear unless it has a rocket marker. Pure +
+ * shared (used by the engine and the unit tests).
+ */
+export function isNuclearCapable(nation: Nation, markers: readonly MapMarker[]): boolean {
+  if (nation.nuclear === true) return true;
+  return markers.some((m) => m.ownerNationId === nation.id && m.type === 'rocket');
+}
+
 /** The exact JSON object the world-simulator LLM must return for a turn. */
 export interface TurnResult {
   date: string;
@@ -537,6 +622,21 @@ export interface TurnResult {
    * untouched. Required; default `{ projects: [] }`.
    */
   industry: IndustryOps;
+  /**
+   * (v0.37, #60) Nuclear / WMD ops — the LLM's nuclear lever. `arm` names
+   * the nations that declare a nuclear arsenal this turn (idempotent);
+   * `strikes` are the nuclear strikes fired this turn (at most one per turn
+   * in the prompt contract). A strike may target a **region** (devastated to
+   * no man's land, its former owner devastated) or a **nation** (its economy
+   * / military / stability devastated; a strike that lands on a nation
+   * warring with the striker ends that war in capitulation). A strike on a
+   * nuclear-capable target (or the owner of a struck region) triggers a
+   * smaller, automatic "MAD" retaliation on the striker. Only
+   * nuclear-capable nations (the `Nation.nuclear` flag set, or owning a
+   * `rocket` marker) may strike. Applied directly by `applyTurnResult`,
+   * never queued. Required; default `{ arm: [], strikes: [] }`.
+   */
+  nuclear: NuclearOps;
   /**
    * (v0.27, #44) Map-marker ops this turn. `add` places new named markers
    * (the engine positions each at its region's centroid + a small

shared/types.ts

@@ -72,6 +72,14 @@ export interface Nation {
   stats: NationStats;
   territory: string[];
   relations: Record<string, RelationStatus>;
+  /**
+   * Whether the nation controls nuclear weapons (v0.37, #60). Optional — a
+   * legacy game loaded from SQLite has no flag, which means "not nuclear".
+   * A nation is *nuclear-capable* (for the `nuclear` lever and MAD
+   * retaliation) when this is `true` OR it owns a `rocket` marker (see
+   * `isNuclearCapable` in `protocol.ts`).
+   */
+  nuclear?: boolean;
 }
 
 /** Categories a narrative event can take. */