feat(abilities): add migration & refugees lever (v0.42.0, #64)

Add the 10th modular LLM ability: a turn-transient TurnResult.migration
lever declaring population flows between nations (migration / refugees /
diaspora / exodus). The source loses a little population + economy, the
destination gains a little (a large influx also strains its stability),
and the from<->to relation is nudged one step toward the positive end of
the ally/neutral/rival/hostile ladder (capped by kind; a war is never
touched). Deterministic per-scale tables, no hidden randomness, clamped
0-100, mirrored to owned regions, re-derived aggregates; never moves
territory. Registered last in ABILITIES; user prompt unchanged
(user.txt golden byte-identical), system goldens re-baselined. Fixes #64.

server/abilities/registry.test.ts

@@ -12,7 +12,7 @@
 //      by the disasters feature (its payload is always empty).
 //
 //   2. REGISTRY CONTRACT — the ABILITIES registry is the canonical ordered
-//      list of the 9 abilities; each ability's default() equals the canonical
+//      list of the 10 abilities; each ability's default() equals the canonical
 //      TurnResult default for its field, is a FRESH value (never a shared
 //      reference), its default is not "meaningful" while a populated value is,
 //      and the registry composes (a hypothetical extra ability can be appended
@@ -31,6 +31,7 @@ import {
   activeWarPairs,
   applyDisasterEvent,
   applyIndustryEffects,
+  applyMigrationOp,
   atWar,
   buildSystemPrompt,
   buildUserPrompt,
@@ -44,10 +45,18 @@ import {
   isDisasterType,
   isHybridOpType,
   isIndustryType,
+  isMigrationKind,
+  isMigrationScale,
+  LARGE_INFLUX_STABILITY_DIP,
+  MIGRATION_DESTINATION_EFFECTS,
+  MIGRATION_KINDS,
+  MIGRATION_SCALES,
+  MIGRATION_SOURCE_EFFECTS,
   NEW_NATION_STATS,
   resolveNationRef,
   resolveRegionKey,
   shiftRelationTowardHostile,
+  shiftRelationTowardPositive,
   syncWarRelations,
   validateDisasterEvents,
   validateEconomyOps,
@@ -55,6 +64,7 @@ import {
   validateIdeologyOps,
   validateIndustryOps,
   validateLeaderOps,
+  validateMigrationOps,
   validateNuclearOps,
   validateTakeovers,
   validateWarOps,
@@ -217,6 +227,7 @@ function fullDefaultTurn(): TurnResult {
     leaders: { changes: [] },
     ideology: { changes: [] },
     disasters: { events: [] },
+    migration: { ops: [] },
     markers: { add: [], remove: [] },
   };
 }
@@ -242,11 +253,13 @@ function meaningfulFor(field: AbilityField): TurnResult[AbilityField] {
       return { changes: [{ target: 'a1', to: 'democracy' }] };
     case 'disasters':
       return { events: [{ type: 'earthquake', target: 'a1', severity: 'minor' }] };
+    case 'migration':
+      return { ops: [{ kind: 'migration', from: 'a1', to: 'b2', scale: 'small' }] };
   }
 }
 
 describe('ABILITIES registry (v0.40.0, #67)', () => {
-  it('is the canonical 9-ability order (takeovers → disasters)', () => {
+  it('is the canonical 10-ability order (takeovers → migration)', () => {
     expect(ABILITIES.map((a) => a.field)).toEqual([
       'takeovers',
       'wars',
@@ -257,13 +270,14 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       'leaders',
       'ideology',
       'disasters',
+      'migration',
     ]);
   });
 
-  it('lists 9 distinct fields, each a key of TurnResult', () => {
+  it('lists 10 distinct fields, each a key of TurnResult', () => {
     const fields = ABILITIES.map((a) => a.field);
-    expect(fields).toHaveLength(9);
-    expect(new Set(fields).size).toBe(9);
+    expect(fields).toHaveLength(10);
+    expect(new Set(fields).size).toBe(10);
     const all = fullDefaultTurn();
     for (const f of fields) expect(f in all).toBe(true);
   });
@@ -328,7 +342,7 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
   it('composes: a hypothetical extra ability can be appended and every uniform loop still runs', () => {
     // The registry is a plain ordered array the engine iterates uniformly. A
     // structural (field-name-agnostic) loop over the abilities — schema line,
-    // constraint bullet — must keep working when a 10th ability is appended.
+    // constraint bullet — must keep working when an 11th ability is appended.
     // This documents the extension point without widening the closed
     // AbilityField union.
     interface Loopable {
@@ -347,9 +361,9 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       'custom',
     ]);
     // every uniform loop runs over all N abilities, the appended one included:
-    expect(extended.map((a) => a.schemaLine())).toHaveLength(10);
-    expect(extended.map((a) => a.constraint())).toHaveLength(10);
-    expect(extended[9].schemaLine()).toBe('  "custom": [],');
+    expect(extended.map((a) => a.schemaLine())).toHaveLength(11);
+    expect(extended.map((a) => a.constraint())).toHaveLength(11);
+    expect(extended[10].schemaLine()).toBe('  "custom": [],');
   });
 
   it('the engine still re-exports every name its callers import from it', () => {
@@ -388,6 +402,17 @@ describe('ABILITIES registry (v0.40.0, #67)', () => {
       DISASTER_TYPES,
       DISASTER_SEVERITIES,
       DISASTER_EFFECTS,
+      // migration (v0.42.0, #64)
+      validateMigrationOps,
+      applyMigrationOp,
+      shiftRelationTowardPositive,
+      isMigrationKind,
+      isMigrationScale,
+      MIGRATION_KINDS,
+      MIGRATION_SCALES,
+      MIGRATION_SOURCE_EFFECTS,
+      MIGRATION_DESTINATION_EFFECTS,
+      LARGE_INFLUX_STABILITY_DIP,
     };
     for (const [name, value] of Object.entries(reexported)) {
       expect(value, `engine should re-export ${name}`).toBeDefined();