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/index.ts

@@ -1,8 +1,8 @@
 // The ordered LLM-ability registry.
 //
-// `ABILITIES` is the single source of truth for the 9 per-feature LLM abilities.
+// `ABILITIES` is the single source of truth for the 10 per-feature LLM abilities.
 // The engine iterates it in this order:
-//   takeovers → wars → hybrid → economy → industry → nuclear → leaders → ideology → disasters
+//   takeovers → wars → hybrid → economy → industry → nuclear → leaders → ideology → disasters → migration
 // for (a) the system-prompt schema lines + constraint bullets, (b) the per-ability
 // validate calls inside validateTurnResult, (c) the payload fields in buildUserPrompt,
 // (d) the ordered apply block inside applyTurnResult, (e) the isMeaningful check,
@@ -23,13 +23,16 @@ import { nuclear } from './nuclear';
 import { leaders } from './leaders';
 import { ideology } from './ideology';
 import { disasters } from './disasters';
+import { migration } from './migration';
 import type { Ability, AbilityField } from './types';
 
 /**
- * The 9 per-feature LLM abilities in their canonical apply order.
+ * The 10 per-feature LLM abilities in their canonical apply order.
  * The order matters: it determines the order of the schema lines in the
  * system prompt, the order of the validate calls, the order of the apply
- * steps, and the order of the payload fields in the user prompt.
+ * steps, and the order of the payload fields in the user prompt. New
+ * abilities are APPENDED last — never reorder existing entries (their order
+ * is pinned by the goldens and the stub's byte-identical output).
  */
 export const ABILITIES: readonly Ability<AbilityField>[] = [
   takeovers,
@@ -41,6 +44,7 @@ export const ABILITIES: readonly Ability<AbilityField>[] = [
   leaders,
   ideology,
   disasters,
+  migration,
 ];
 
 // ── type re-exports ────────────────────────────────────────────────────────────
@@ -139,3 +143,18 @@ export {
   DISASTER_SEVERITIES,
   DISASTER_EFFECTS,
 } from './disasters';
+
+// ── migration ────────────────────────────────────────────────────────────────
+
+export {
+  validateMigrationOps,
+  applyMigrationOp,
+  shiftRelationTowardPositive,
+  isMigrationKind,
+  isMigrationScale,
+  MIGRATION_KINDS,
+  MIGRATION_SCALES,
+  MIGRATION_SOURCE_EFFECTS,
+  MIGRATION_DESTINATION_EFFECTS,
+  LARGE_INFLUX_STABILITY_DIP,
+} from './migration';