feat: nation-op split/merge — apply on confirm (playerPart, fresh ids, relations union) (P4b, #16)

server/engine.test.ts

@@ -4,13 +4,16 @@ import { makeEvent, type NationOp, type TurnResult } from '../shared/protocol';
 import type { LlmClient, ToolDefinition, WireMessage } from './llm';
 import { makeStubLlmClient } from './stub';
 import {
+  applyNationOp,
   applyTurnResult,
   buildSystemPrompt,
   buildUserPrompt,
   confirmNationOp,
+  freshNationId,
   GET_NEIGHBOURS_TOOL,
   isMeaningful,
   makeNeighboursExecutor,
+  NEW_NATION_STATS,
   parseTurnResult,
   playerFrontier,
   queueRoundItem,
@@ -634,7 +637,7 @@ describe('confirmNationOp / rejectNationOp (v0.23 #16 P4a)', () => {
     expect(next!.nations.us.name).toBe('United States');
   });
 
-  it('confirm is a no-op on the world for a P4b-kind op (split/merge) — the op is still removed', () => {
+  it('confirm of a 1-part split is a no-op on the world (fewer than 2 parts) — the op is still removed', () => {
     const state = baseState();
     state.pendingNationOps = [{ kind: 'split', nationRef: 'de', parts: [{ name: 'East' }] }];
     const next = confirmNationOp(state, 0);
@@ -683,18 +686,306 @@ describe('confirmNationOp / rejectNationOp (v0.23 #16 P4a)', () => {
   });
 });
 
-describe('buildSystemPrompt (nationOps contract, v0.23 #16 P4a)', () => {
-  it('both modes contract the nationOps field and the rename proposal rule', () => {
+describe('buildSystemPrompt (nationOps contract, v0.23 #16 P4a; v0.24 #16 P4b)', () => {
+  it('both modes contract the nationOps field with all three op kinds and the proposal rule', () => {
     for (const p of [buildSystemPrompt(preset), buildSystemPrompt(preset, true)]) {
-      // the JSON shape carries the field in both modes
-      expect(p).toMatch(/"nationOps": \[\{"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"\}\]/);
-      // the rule explains that it is a proposal only the player can confirm
+      // the JSON shape carries all three kinds in both modes
+      expect(p).toMatch(/"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"/);
+      expect(p).toMatch(/"kind":"split","nationRef":"<nation id or name>","parts":\[\{"name":"<new name>","territory":\["<region key>"\]\}\]/);
+      expect(p).toMatch(/"kind":"merge","nationRefs":\["<id>","<id>"\],"survivingRef":"<id of the surviving nation>","into":"<new name>"/);
+      // the rule explains that ops are proposals only the player can confirm
       expect(p).toMatch(/PROPOSAL/);
-      expect(p).toMatch(/only takes effect if the player confirms/);
+      expect(p).toMatch(/only take effect if the player confirms/);
+      // and the split/merge shapes are spelt out in the hard constraints
+      expect(p).toMatch(/at least 2 parts/);
+      expect(p).toMatch(/survivingRef" must name one of them/);
     }
   });
 });
 
+describe('freshNationId (v0.24 #16 P4b)', () => {
+  it('returns the first free of n1, n2, ... against the taken set', () => {
+    expect(freshNationId(new Set())).toBe('n1');
+    expect(freshNationId(new Set(['n1']))).toBe('n2');
+    expect(freshNationId(new Set(['n1', 'n2', 'n3']))).toBe('n4');
+    // non-n ids never collide: existing nation ids are irrelevant
+    expect(freshNationId(new Set(['uk', 'de', 'us']))).toBe('n1');
+  });
+});
+
+describe('applyNationOp (split, v0.24 #16 P4b)', () => {
+  /** de owns four regions; the player is uk (so a split of de does not move the pointer). */
+  function splitState(): GameState {
+    const s = baseState();
+    s.nations.de.territory = ['DEU-N', 'DEU-S', 'DEU-E', 'DEU-W'];
+    s.nations.de.relations = { uk: 'ally' };
+    s.nations.uk.relations.de = 'hostile'; // mirror entry, to check the cleanup
+    return s;
+  }
+
+  it('partitions the parent territory: first-wins per key, leftovers to part 0, fresh ids, baseline stats, copied relations, parent removed', () => {
+    const state = splitState();
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'de',
+      parts: [
+        { name: 'East', territory: ['DEU-E', 'DEU-W', 'ZZZ-not-a-key'] },
+        { name: 'West', territory: ['DEU-W', 'DEU-S'] },
+      ],
+    });
+    // the parent is gone and two fresh nations exist (n1, n2 — uk/us/de were taken)
+    expect(state.nations.de).toBeUndefined();
+    expect(Object.keys(state.nations).sort()).toEqual(['n1', 'n2', 'uk', 'us']);
+    const east = state.nations.n1;
+    const west = state.nations.n2;
+    // East claimed DEU-E and DEU-W first (the invalid key is ignored); the
+    // only key no part claimed — DEU-N (DEU-S went to West) — goes to part 0
+    // in the parent's territory order.
+    expect(east.territory).toEqual(['DEU-E', 'DEU-W', 'DEU-N']);
+    // West's DEU-W was already claimed by East; it keeps only DEU-S.
+    expect(west.territory).toEqual(['DEU-S']);
+    // every parent key sits in exactly one part (sole ownership, nothing lost)
+    const all = [...east.territory, ...west.territory].sort();
+    expect(all).toEqual(['DEU-E', 'DEU-N', 'DEU-S', 'DEU-W']);
+    // fresh baseline stats (not the parent's) and inherited form of state
+    expect(east.stats).toEqual(NEW_NATION_STATS);
+    expect(west.stats).toEqual(NEW_NATION_STATS);
+    expect(east.type).toBe('major');
+    expect(west.type).toBe('major');
+    // both parts copied the parent's relations
+    expect(east.relations).toEqual({ uk: 'ally' });
+    expect(west.relations).toEqual({ uk: 'ally' });
+    // the mirror entry for the removed parent is cleaned up
+    expect(state.nations.uk.relations.de).toBeUndefined();
+    expect(state.nations.uk.relations.us).toBe('neutral'); // other entries untouched
+    // the player (uk) is not affected
+    expect(state.playerNationId).toBe('uk');
+  });
+
+  it('an unresolvable nationRef is a no-op (the world is untouched, never throws)', () => {
+    const state = splitState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'zzz-not-a-nation',
+      parts: [{ name: 'East' }, { name: 'West' }],
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('a split named by the parent NAME works (ref resolution, not just id)', () => {
+    const state = splitState();
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'DE', // the name; the id is 'de'
+      parts: [{ name: 'East', territory: ['DEU-E'] }, { name: 'West', territory: ['DEU-W'] }],
+    });
+    expect(state.nations.de).toBeUndefined();
+    expect(state.nations.n1.name).toBe('East');
+    expect(state.nations.n2.name).toBe('West');
+  });
+
+  it('when the parent is the player nation, playerNationId moves to the chosen part (edits.playerPart: default 0, clamped in range)', () => {
+    const state = splitState();
+    state.playerNationId = 'de';
+    applyNationOp(state, {
+      kind: 'split',
+      nationRef: 'de',
+      parts: [{ name: 'East' }, { name: 'West' }, { name: 'Centre' }],
+    });
+    expect(state.playerNationId).toBe('n1'); // default: the first part
+
+    const state2 = splitState();
+    state2.playerNationId = 'de';
+    applyNationOp(
+      state2,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }, { name: 'Centre' }],
+      },
+      { playerPart: 1 },
+    );
+    expect(state2.playerNationId).toBe('n2');
+
+    const state3 = splitState();
+    state3.playerNationId = 'de';
+    applyNationOp(
+      state3,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: 99 }, // clamped down to the last part
+    );
+    expect(state3.playerNationId).toBe('n2');
+
+    const state4 = splitState();
+    state4.playerNationId = 'de';
+    applyNationOp(
+      state4,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: -5 }, // clamped up to the first part
+    );
+    expect(state4.playerNationId).toBe('n1');
+  });
+
+  it('edits.name renames the chosen part (edits.playerPart picks which one)', () => {
+    const state = splitState();
+    applyNationOp(
+      state,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { playerPart: 1, name: 'New West' },
+    );
+    expect(state.nations.n1.name).toBe('East'); // untouched part keeps its name
+    expect(state.nations.n2.name).toBe('New West');
+
+    const state2 = splitState();
+    applyNationOp(
+      state2,
+      {
+        kind: 'split',
+        nationRef: 'de',
+        parts: [{ name: 'East' }, { name: 'West' }],
+      },
+      { name: 'First of the Remnant' }, // no playerPart -> the first part
+    );
+    expect(state2.nations.n1.name).toBe('First of the Remnant');
+    expect(state2.nations.n2.name).toBe('West');
+  });
+
+  it('a 1-part split is a no-op on the world (fewer than 2 parts)', () => {
+    const state = splitState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, { kind: 'split', nationRef: 'de', parts: [{ name: 'East' }] });
+    expect(state).toEqual(before);
+  });
+});
+
+describe('applyNationOp (merge, v0.24 #16 P4b)', () => {
+  /**
+   * de and us will be merged (the survivor is us — deliberately listed
+   * second in nationRefs, so the "survivor's view wins" rule can be observed
+   * overwriting the first input's views). uk, fr and ja survive as third
+   * parties; the survivor has no view on ja, so ja must come from the first
+   * input's map.
+   */
+  function mergeState(): GameState {
+    const s = baseState();
+    s.nations.de.relations = { us: 'rival', uk: 'hostile', fr: 'rival', ja: 'rival' };
+    s.nations.us.relations = { de: 'ally', uk: 'ally', fr: 'neutral' }; // no view on ja
+    s.nations.uk.relations = { us: 'ally', de: 'hostile', fr: 'neutral', ja: 'neutral' };
+    s.nations.fr = {
+      id: 'fr',
+      type: 'major',
+      name: 'FR',
+      stats: { military: 40, economy: 60, stability: 70, population: 60 },
+      territory: ['FRA'],
+      relations: { us: 'neutral', de: 'rival', uk: 'neutral', ja: 'neutral' },
+    };
+    s.nations.ja = {
+      id: 'ja',
+      type: 'major',
+      name: 'JA',
+      stats: { military: 30, economy: 80, stability: 50, population: 90 },
+      territory: ['JPN'],
+      relations: { us: 'neutral', de: 'rival', uk: 'neutral', fr: 'neutral' },
+    };
+    return s;
+  }
+
+  it('folds the inputs into the survivor: union territory (survivor first), survivor stats, survivor view wins per third party (else first input), non-input third parties kept, removed ids dropped from everyone else, into-name', () => {
+    const state = mergeState();
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' });
+    // the removed input is gone; the survivor and all non-inputs survive
+    expect(state.nations.de).toBeUndefined();
+    expect(Object.keys(state.nations).sort()).toEqual(['fr', 'ja', 'uk', 'us']);
+    // the survivor keeps its id, its own stats, and the merged name
+    expect(state.nations.us.id).toBe('us');
+    expect(state.nations.us.stats).toEqual({ military: 60, economy: 90, stability: 80, population: 80 });
+    expect(state.nations.us.name).toBe('Union');
+    // territory: the union — the survivor's keys first, then the other input's
+    expect(state.nations.us.territory).toEqual(['USA', 'DEU']);
+    // relations: on uk and fr the survivor's own views (ally/neutral) beat the
+    // first input's (hostile/rival); ja has no survivor view, so the first
+    // input's (rival) stands; the removed input's id is gone from the map.
+    expect(state.nations.us.relations).toEqual({ uk: 'ally', fr: 'neutral', ja: 'rival' });
+    // the removed id is dropped from every remaining nation's relations map
+    expect(state.nations.uk.relations).toEqual({ us: 'ally', fr: 'neutral', ja: 'neutral' });
+    expect(state.nations.fr.relations).toEqual({ us: 'neutral', uk: 'neutral', ja: 'neutral' });
+    expect(state.nations.ja.relations).toEqual({ us: 'neutral', uk: 'neutral', fr: 'neutral' });
+    // the player (uk) is not part of the merge — the pointer stays valid
+    expect(state.playerNationId).toBe('uk');
+  });
+
+  it('the player pointer moves to the survivor when the player led a removed input', () => {
+    const state = mergeState();
+    state.playerNationId = 'de'; // the player's nation is absorbed
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' });
+    expect(state.playerNationId).toBe('us');
+    expect(state.nations[state.playerNationId].name).toBe('Union');
+  });
+
+  it('edits.name overrides the merged name; an empty edit falls back to "into", then to the survivor name', () => {
+    const state = mergeState();
+    applyNationOp(state, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' }, { name: 'United World' });
+    expect(state.nations.us.name).toBe('United World');
+
+    const state2 = mergeState();
+    applyNationOp(state2, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: 'Union' }, { name: '   ' });
+    expect(state2.nations.us.name).toBe('Union');
+
+    const state3 = mergeState();
+    applyNationOp(state3, { kind: 'merge', nationRefs: ['de', 'us'], survivingRef: 'us', into: '' }); // empty into: keep the survivor's name
+    expect(state3.nations.us.name).toBe('US');
+  });
+
+  it('an unresolvable input ref is a no-op (never throws, world untouched)', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'zzz-not-a-nation'],
+      survivingRef: 'uk',
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('a survivor that is not one of the inputs is a no-op', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'de'],
+      survivingRef: 'uk', // uk is not an input
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+
+  it('fewer than two DISTINCT inputs is a no-op (the same nation named twice)', () => {
+    const state = mergeState();
+    const before = JSON.parse(JSON.stringify(state));
+    applyNationOp(state, {
+      kind: 'merge',
+      nationRefs: ['us', 'US'], // both resolve to 'us'
+      survivingRef: 'us',
+      into: 'X',
+    });
+    expect(state).toEqual(before);
+  });
+});
+
 describe('parseTurnResult', () => {
   it('parses a fenced JSON block', () => {
     const r = parseTurnResult('```json\n{"date":"1939-09-03","events":[{"nation":"uk","type":"military","title":"t","text":"b","outcome":"success"}]}\n```');

server/engine.ts

@@ -7,6 +7,8 @@ import type {
   EventOutcome,
   EventType,
   GameState,
+  Nation,
+  NationStats,
   Preset,
   RelationStatus,
   RoundItem,
@@ -134,7 +136,9 @@ export function playerFrontier(
  * When `withNeighboursTool` is set (the turn runs with the getNeighbours tool
  * available) the contract gains the contiguity rules for territory transfers
  * (v0.21, #16 P2): the model may only move regions across a shared border, and
- * may verify borders with the tool before answering.
+ * may verify borders with the tool before answering. The contract also
+ * documents the `nationOps` proposal queue (v0.23, #16 P4a) — rename plus the
+ * split/merge shapes applied on player confirm (v0.24, #16 P4b).
  */
 export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): string {
   const rules = preset.simulationRules
@@ -178,14 +182,21 @@ export function buildSystemPrompt(preset: Preset, withNeighboursTool = false): s
     '  "relations": [{"a":"<nationId>","b":"<nationId>","set":"<ally|neutral|rival|hostile|war>"}],',
     '  "territoryChanges": [{"nation":"<nationId>","gain":["<region key>"],"lose":["<region key>"]}],',
     '  "unowned": ["<region key>"],',
-    '  "nationOps": [{"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"}]',
+    '  "nationOps": [',
+    '    {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"},',
+    '    {"kind":"split","nationRef":"<nation id or name>","parts":[{"name":"<new name>","territory":["<region key>"]}]}',
+    '    {"kind":"merge","nationRefs":["<id>","<id>"],"survivingRef":"<id of the surviving nation>","into":"<new name>"}',
+    '  ],',
     '}',
     '',
     'HARD CONSTRAINTS',
     '- Use only nation ids and region keys that exist in the provided state.',
     '- A region key identifies one sub-region; the "regions" table in the user message maps each key to "<region name> (<parent country ISO_A3>)". Use those keys in territoryChanges and unowned.',
     '- List in "unowned" only region keys that a nation currently owns, and narrate each release in "events".',
-    '- To rename a nation, add {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"} to "nationOps". This is a PROPOSAL: it only takes effect if the player confirms it, so use it only when the narrative justifies it (a revolution, reunification, regime change) — at most 1-2 per turn — and narrate it in "events".',
+    '- Nation-management ops ("nationOps") are PROPOSALS: they only take effect if the player confirms them afterwards. Propose at most 1-2 per turn, only when the narrative justifies it, and narrate each one in "events".',
+    '- Rename: add {"kind":"rename","nationRef":"<nation id or name>","to":"<new name>"} for a revolution, regime change or reunification that changes a nation\'s name.',
+    '- Split: add {"kind":"split","nationRef":"<nation id or name>","parts":[{"name":"<new name>","territory":["<region key>"]}, ...]} when a state breaks up (dissolution, secession). Use at least 2 parts and assign each of the nation\'s region keys to at most one part — any key you leave unassigned goes to the first part.',
+    '- Merge: add {"kind":"merge","nationRefs":["<id or name>","<id or name>"],"survivingRef":"<id or name of the surviving nation>","into":"<new name>"} when states reunify or one is absorbed. Use at least 2 input nations and "survivingRef" must name one of them — the survivor keeps its id and its stats.',
     '- 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.',
@@ -700,39 +711,208 @@ export function resolveNationRef(state: GameState, ref: string): string | null {
   return matches.length === 1 ? matches[0].id : null;
 }
 
+/**
+ * Generate a fresh, unused nation id for a newly created nation (split
+ * parts, v0.24 #16 P4b): the first free of `n1`, `n2`, ... The caller adds
+ * each id it creates to `taken` as it goes, so ids stay unique within an
+ * op and are never reused from a removed nation.
+ */
+export function freshNationId(taken: ReadonlySet<string>): string {
+  for (let i = 1; ; i++) {
+    const id = `n${i}`;
+    if (!taken.has(id)) return id;
+  }
+}
+
+/**
+ * The baseline stats a freshly created nation starts with (split parts,
+ * v0.24 #16 P4b) — a neutral middle-of-the-scale profile, deliberately NOT
+ * a copy of the parent's stats (a small rump state is not the parent's
+ * military power).
+ */
+export const NEW_NATION_STATS: NationStats = {
+  military: 50,
+  economy: 50,
+  stability: 50,
+  population: 50,
+};
+
+/**
+ * Defensive cleanup after nations are removed (merge, v0.24 #16 P4b): drop
+ * the removed nations' ids from every remaining nation's `relations` map so
+ * no key dangles. (The client already degrades gracefully on a missing
+ * target, but consistent data is cleaner.)
+ */
+function dropRelationsTo(state: GameState, removedIds: ReadonlySet<string>): void {
+  for (const n of Object.values(state.nations)) {
+    for (const id of removedIds) {
+      if (id in n.relations) delete n.relations[id];
+    }
+  }
+}
+
 /**
  * Apply one NationOp to a state, MUTATING the passed object in place (the
  * caller passes a clone — confirmNationOp does) and NOT bumping `version`
- * (the route-level functions do that once per decision). Rename changes only
- * `Nation.name` — the id, its territory, its relations (keyed by id), and the
- * player pointer all stay valid, so nothing downstream breaks; a
- * player-supplied `edits.name` overrides the proposed `to` (an empty edit
- * falls back to the proposal's own name). An unresolvable or ambiguous
- * `nationRef` is a silent no-op. Split and merge are declared for P4b and are
- * a no-op until then — the op stays pending-free once the player resolves it,
- * but the world does not change yet.
+ * (the route-level functions do that once per decision). It never throws:
+ * any unresolvable reference or malformed op is a silent no-op (the op is
+ * still removed by confirmNationOp — the world simply doesn't change).
+ *
+ *  - **rename** (v0.23, #16 P4a): changes only `Nation.name` — the id, its
+ *    territory, its relations (keyed by id), and the player pointer all stay
+ *    valid, so nothing downstream breaks; a player-supplied `edits.name`
+ *    overrides the proposed `to` (an empty edit falls back to the proposal's
+ *    own name).
+ *
+ *  - **split** (v0.24, #16 P4b): the `nationRef` must resolve and there must
+ *    be at least two named parts, else no-op. Parts are processed in order;
+ *    each receives the region keys of its `territory` that (a) the parent
+ *    owns and (b) no earlier part claimed — the first part to name a key
+ *    wins. Keys of the parent's territory that no part claimed go to part 0
+ *    (in the parent's `territory` order), so the parent's territory is fully
+ *    partitioned — no key is lost or ever held twice. Each part gets a
+ *    FRESH id (`freshNationId`) and the baseline `NEW_NATION_STATS` (not a
+ *    copy of the parent's), plus a copy of the parent's relations; the
+ *    parent is then removed. If the parent was the player's nation,
+ *    `playerNationId` moves to the chosen part (`edits.playerPart`, clamped
+ *    into range, default 0); `edits.name` renames that same chosen part.
+ *
+ *  - **merge** (v0.24, #16 P4b): every input ref plus the survivor ref must
+ *    resolve, at least two inputs must resolve to DISTINCT nations, and the
+ *    survivor must be one of them — else no-op. The survivor keeps its id,
+ *    keeps its own stats, gains the union of all inputs' territories
+ *    (survivor's keys first, then each other input's unclaimed keys in its
+ *    own order), and gains a union of the inputs' relations (on a third
+ *    party the survivor's own view wins, else the first input's). The other
+ *    inputs are removed (their ids dropped from everyone else's relations
+ *    maps), and if the player led a removed input, `playerNationId` moves to
+ *    the survivor. The merged name is `edits.name` (if non-empty), else
+ *    `op.into`, else the survivor's current name.
  */
-export function applyNationOp(state: GameState, op: NationOp, edits?: { name?: string }): void {
-  if (op.kind !== 'rename') return; // split/merge: declared for P4b, not applied yet
-  const id = resolveNationRef(state, op.nationRef);
-  if (id === null) return; // invalid/ambiguous ref: no-op
-  const n = state.nations[id];
-  if (!n) return;
-  const name = (edits?.name ?? '').trim() || op.to.trim();
-  if (name) n.name = name;
+export function applyNationOp(
+  state: GameState,
+  op: NationOp,
+  edits?: { name?: string; playerPart?: number },
+): void {
+  if (op.kind === 'rename') {
+    const id = resolveNationRef(state, op.nationRef);
+    if (id === null) return; // invalid/ambiguous ref: no-op
+    const n = state.nations[id];
+    if (!n) return;
+    const name = (edits?.name ?? '').trim() || op.to.trim();
+    if (name) n.name = name;
+    return;
+  }
+
+  if (op.kind === 'split') {
+    const id = resolveNationRef(state, op.nationRef);
+    if (id === null || op.parts.length < 2) return; // invalid ref / not enough parts: no-op
+    const parent = state.nations[id];
+    if (!parent) return;
+    const taken = new Set(Object.keys(state.nations));
+    const created: string[] = [];
+    const claimed = new Set<string>();
+    for (const part of op.parts) {
+      const newId = freshNationId(taken);
+      taken.add(newId);
+      const keys = (part.territory ?? [])
+        .filter((k) => parent.territory.includes(k) && !claimed.has(k));
+      for (const k of keys) claimed.add(k);
+      const partNation: Nation = {
+        id: newId,
+        type: parent.type, // a part keeps the parent's form of state
+        name: part.name,
+        stats: { ...NEW_NATION_STATS },
+        territory: keys,
+        relations: { ...parent.relations },
+      };
+      state.nations[newId] = partNation;
+      created.push(newId);
+    }
+    // Keys the parent owned but no part claimed go to part 0 (in the
+    // parent's territory order) — nothing is lost or duplicated.
+    for (const k of parent.territory) {
+      if (!claimed.has(k)) state.nations[created[0]].territory.push(k);
+    }
+    // The player chooses which part is its successor (edits.playerPart,
+    // clamped into range; default 0) — only relevant when the parent was
+    // the player's nation; the same part also gets a player-edited name.
+    const partIdx =
+      Math.min(Math.max(edits?.playerPart ?? 0, 0), created.length - 1);
+    if (state.playerNationId === id) state.playerNationId = created[partIdx];
+    const editedName = (edits?.name ?? '').trim();
+    if (editedName) state.nations[created[partIdx]].name = editedName;
+    delete state.nations[id];
+    dropRelationsTo(state, new Set([id]));
+    return;
+  }
+
+  // merge
+  const resolved: string[] = [];
+  for (const ref of op.nationRefs) {
+    const rid = resolveNationRef(state, ref);
+    if (rid === null) return; // any unresolvable input: no-op
+    resolved.push(rid);
+  }
+  const inputIds = new Set(resolved);
+  const survivorId = resolveNationRef(state, op.survivingRef);
+  if (survivorId === null || !inputIds.has(survivorId) || inputIds.size < 2) return;
+  const survivor = state.nations[survivorId];
+  if (!survivor) return;
+  // Territory: the union of all inputs — the survivor's keys first (stable
+  // order), then each other input's unclaimed keys in its own order.
+  const territory = [...survivor.territory];
+  const seen = new Set(territory);
+  for (const rid of resolved) {
+    for (const k of state.nations[rid].territory) {
+      if (!seen.has(k)) {
+        seen.add(k);
+        territory.push(k);
+      }
+    }
+  }
+  // Relations: the union of all inputs' relations; the first input to name a
+  // third party sets it, then the survivor's own view overwrites per key.
+  const relations: Record<string, RelationStatus> = {};
+  for (const rid of resolved) {
+    for (const [other, status] of Object.entries(state.nations[rid].relations)) {
+      if (other === survivorId) continue; // never relate to oneself
+      if (!(other in relations)) relations[other] = status;
+    }
+  }
+  for (const [other, status] of Object.entries(survivor.relations)) {
+    if (other !== survivorId) relations[other] = status;
+  }
+  const removed = new Set<string>();
+  for (const rid of inputIds) {
+    if (rid === survivorId) continue;
+    delete state.nations[rid];
+    removed.add(rid);
+  }
+  if (state.playerNationId !== survivorId && removed.has(state.playerNationId)) {
+    state.playerNationId = survivorId;
+  }
+  const name = (edits?.name ?? '').trim() || op.into.trim() || survivor.name;
+  if (name) survivor.name = name;
+  survivor.territory = territory;
+  survivor.relations = relations;
+  dropRelationsTo(state, removed);
 }
 
 /**
  * Confirm a pending nation-op proposal by index: apply it (a rename takes
- * effect, optionally with a player-edited name; split/merge are a no-op until
- * P4b) and remove it from `pendingNationOps`, bumping `version`. Returns
- * `null` for an invalid index, so the route answers 400 without mutating.
- * Reused by the /nation-op/confirm route.
+ * effect, optionally with a player-edited name; a split partitions the
+ * nation's territory into the new parts, the player picking which part is
+ * its successor via `edits.playerPart`; a merge folds the inputs into the
+ * survivor, optionally renamed via `edits.name`) and remove it from
+ * `pendingNationOps`, bumping `version`. Returns `null` for an invalid
+ * index, so the route answers 400 without mutating. Reused by the
+ * /nation-op/confirm route.
  */
 export function confirmNationOp(
   state: GameState,
   index: number,
-  edits?: { name?: string },
+  edits?: { name?: string; playerPart?: number },
 ): GameState | null {
   if (!validPendingOpIndex(state, index)) return null;
   const next: GameState = JSON.parse(JSON.stringify(state));

server/index.ts

@@ -230,10 +230,14 @@ app.post('/api/games/:id/queue/remove', (req, res) => {
   res.json({ game: next });
 });
 
-// (v0.23, #16 P4a) Resolve a pending nation-op proposal (a rename the LLM
-// proposed in an earlier turn, waiting in game.pendingNationOps). No LLM call,
-// no turn advance — same fast save → broadcast → respond order as
-// /queue/remove. The version bump lets "never go backwards" clients reconcile.
+// (v0.23, #16 P4a; v0.24, #16 P4b) Resolve a pending nation-op proposal
+// waiting in game.pendingNationOps: a rename takes effect (body.edits.name
+// may override the proposed name), a split partitions the nation's territory
+// into the proposed parts (body.edits.playerPart picks which part the player
+// leads, default 0), and a merge folds its inputs into the survivor
+// (body.edits.name may override the merged name). No LLM call, no turn
+// advance — same fast save → broadcast → respond order as /queue/remove.
+// The version bump lets "never go backwards" clients reconcile.
 app.post('/api/games/:id/nation-op/confirm', (req, res) => {
   const id = req.params.id;
   const game = db.load(id);

shared/protocol.ts

@@ -30,15 +30,14 @@ export interface TerritoryChange {
   lose: string[];
 }
 
-// --- Nation-management ops (v0.23, #16 P4a: the hybrid "LLM proposes, player
-// confirms" model) -----------------------------------------------------------
+// --- Nation-management ops (v0.23 P4a / v0.24 P4b, #16: the hybrid "LLM
+// proposes, player confirms" model) ------------------------------------------
 //
 // Unlike stat / relation / territory deltas, a NationOp proposed in a turn is
 // NOT applied by that turn. It is stored as a *pending proposal* in
 // `GameState.pendingNationOps` and only takes effect when the player confirms
-// it (optionally editing it) or is dropped when the player rejects it. Rename
-// is implemented in v0.23 (P4a); split and merge are declared here so the union
-// is stable for P4b, and are defensively accepted-but-not-applied until then.
+// it (optionally editing it) or is dropped when the player rejects it. All
+// three kinds are implemented: rename (v0.23 P4a), split and merge (v0.24 P4b).
 
 /**
  * The identity reference a nation is addressed by inside a {@link NationOp}.
@@ -63,9 +62,13 @@ export interface RenameOp {
 }
 
 /**
- * A **split** proposal (declared for #16 P4b; **not** applied by the engine yet
- * — it is accepted into the pending list, but confirming it is a no-op until
- * P4b lands). Describes the new nations a source nation is divided into.
+ * A **split** proposal (v0.24, #16 P4b). Describes the new nations a source
+ * nation is divided into. On confirm the source is dissolved: each part gets a
+ * fresh id, the region keys it was given (restricted to keys the source
+ * actually owns — first claim wins), fresh baseline stats, and a copy of the
+ * source's relations; any of the source's unclaimed keys go to `parts[0]`.
+ * When the source is the player's own nation the player chooses which part
+ * they lead (the confirm request's `edits.playerPart`, default `parts[0]`).
  */
 export interface SplitOp {
   kind: 'split';
@@ -76,9 +79,13 @@ export interface SplitOp {
 }
 
 /**
- * A **merge** proposal (declared for #16 P4b; **not** applied by the engine yet
- * — accepted into the pending list, no-op on confirm until P4b). Folds several
- * nations into a single surviving nation.
+ * A **merge** proposal (v0.24, #16 P4b). Folds several nations into a single
+ * surviving nation. On confirm the survivor keeps its id (renamed to `into`,
+ * or to the confirm request's `edits.name`), its territory becomes the union
+ * of all inputs' territories, it keeps its own stats, and it inherits the
+ * union of all inputs' relations (its own winning per third party, else the
+ * first input's); every non-survivor input is removed. If the player's nation
+ * was a non-survivor input the player pointer is re-pointed to the survivor.
  */
 export interface MergeOp {
   kind: 'merge';
@@ -93,8 +100,8 @@ export interface MergeOp {
 /**
  * A structural operation on the set of nations that the LLM may propose in a
  * turn (`TurnResult.nationOps`). See the section comment above for the hybrid
- * propose→confirm semantics. Rename is implemented (P4a); split/merge are
- * declared for P4b and are a safe no-op until then.
+ * propose→confirm semantics. All three kinds are implemented: rename (P4a),
+ * and split / merge (P4b, v0.24).
  */
 export type NationOp = RenameOp | SplitOp | MergeOp;
 
@@ -125,12 +132,13 @@ export interface TurnResult {
    */
   unowned: string[];
   /**
-   * (v0.23, #16 P4a) Nation-management ops the LLM proposes this turn. These
-   * are NOT applied by the turn: each is appended to
+   * (v0.23 P4a / v0.24 P4b, #16) Nation-management ops the LLM proposes this
+   * turn. These are NOT applied by the turn: each is appended to
    * `GameState.pendingNationOps` as a proposal awaiting the player's
-   * confirm/reject. Rename is the only kind the engine currently applies;
-   * split/merge are declared for P4b and are accepted-but-dropped. Empty on
-   * turns where the model proposes none.
+   * confirm/reject. All three kinds (rename, split, merge) are implemented —
+   * a confirmed rename changes `Nation.name`; a confirmed split dissolves the
+   * source into its parts; a confirmed merge folds its inputs into the
+   * survivor. Empty on turns where the model proposes none.
    */
   nationOps: NationOp[];
 }
@@ -240,15 +248,22 @@ export interface RemoveQueueItemResponse {
 }
 
 /**
- * (v0.23, #16 P4a) Confirm a pending nation-op proposal by its index in
- * `game.pendingNationOps`. A rename takes effect (the player may override the
- * proposed name via `edits.name`); split/merge proposals are a no-op on
- * confirm until P4b. No LLM call, no turn advance.
+ * (v0.23 P4a / v0.24 P4b, #16) Confirm a pending nation-op proposal by its
+ * index in `game.pendingNationOps`. A rename takes effect (the player may
+ * override the proposed name via `edits.name`); a split and a merge are fully
+ * applied (v0.24 P4b). No LLM call, no turn advance.
  */
 export interface ConfirmNationOpRequest {
   index: number;
-  /** Optional player edits applied on confirm (rename: the final display name). */
-  edits?: { name?: string };
+  /**
+   * Optional player edits applied on confirm.
+   * - `name`: the final display name — overrides a rename's `to`, a merge's
+   *   `into`, or (for a split) the name of the part the player leads.
+   * - `playerPart`: for a split of the player's own nation, which part (index
+   *   into the op's `parts`) the player will lead (default `0` when missing or
+   *   out of range, so the player is never orphaned).
+   */
+  edits?: { name?: string; playerPart?: number };
 }
 export interface ConfirmNationOpResponse {
   game: GameState;

shared/types.ts

@@ -138,18 +138,19 @@ export interface GameState {
    */
   unowned: string[];
   /**
-   * (v0.23, #16 P4a) Nation-management ops the LLM has proposed but the player
-   * has not yet resolved: a *pending proposal* list, as opposed to `pending`
-   * (the current round's queued player actions). A turn NEVER applies one —
-   * `applyTurnResult` appends the turn's `nationOps` to this list, and each
-   * proposal survives across turns until the player resolves it: confirming
-   * applies it (a rename changes `Nation.name` only — the id, its territory,
-   * its relations, and the player pointer all stay valid) and removes it;
-   * rejecting removes it without applying. Split/merge are declared for P4b
-   * and are a safe no-op on confirm until then. Always `[]` on a fresh game;
-   * rows saved before v0.23 load with this defaulted to `[]` (see server/db.ts).
-   * (The `NationOp` type lives in protocol.ts; the import there is type-only,
-   * so this file still has no runtime dependencies.)
+   * (v0.23, #16 P4a; v0.24, #16 P4b) Nation-management ops the LLM has
+   * proposed but the player has not yet resolved: a *pending proposal* list,
+   * as opposed to `pending` (the current round's queued player actions). A
+   * turn NEVER applies one — `applyTurnResult` appends the turn's
+   * `nationOps` to this list, and each proposal survives across turns until
+   * the player resolves it: confirming applies it (a rename changes
+   * `Nation.name` only; a split partitions the nation's region-key territory
+   * into the new nations' territories; a merge folds the inputs' territory
+   * into the survivor) and removes it; rejecting removes it without
+   * applying. Always `[]` on a fresh game; rows saved before v0.23 load with
+   * this defaulted to `[]` (see server/db.ts). (The `NationOp` type lives in
+   * protocol.ts; the import there is type-only, so this file still has no
+   * runtime dependencies.)
    */
   pendingNationOps: NationOp[];
 }