feat(#61): named leaders — assassination / death / appointment with succession (v0.38.0)

Per-nation named leaders (Nation.leader) and a required TurnResult.leaders
lever ({ changes: [{ target, name, cause }] }). Each change sets the target
nation's leader and applies a deterministic stability dip by cause
(assassination -15, death -3, appointed 0) mirrored to its regions and
re-derived into its stats, plus a narration event (military for an
assassination, political for a death/appointment). An assassination/death
requires the target to already have a leader (a leaderless target is
dropped); an appointment always creates/sets one. Unknown/ambiguous targets
are dropped, never thrown.

- shared/types.ts: optional Nation.leader
- shared/protocol.ts: LeaderCause/LeaderChange/LeaderOps, LEADER_STABILITY_EFFECT,
  TurnResult.leaders (required, between nuclear and markers), leader in nationForPrompt
- server/engine.ts: validateLeaderOps, applyLeaderChange, the applyTurnResult
  leader block (after nuclear, before markers), isMeaningful, system-prompt
  contract + constraint, validateTurnResult + runTurn fallback
- server/stub.ts: leaders always { changes: [] } (e2e unaffected)
- tests: 15 engine.test.ts leader tests + 2 db.test.ts round-trips
- version 0.37.0 -> 0.38.0, CHANGELOG entry

shared/protocol.ts

@@ -468,6 +468,48 @@ export interface NuclearOps {
   strikes: NuclearStrike[];
 }
 
+// --- Named leaders (v0.38, #61) -----------------------------------------------
+//
+// Each nation may have a single named leader (`Nation.leader`). The LLM changes
+// it each turn via `TurnResult.leaders`. A change names a target nation (id or
+// name) and the outcome: an `assassination` (a leader killed — a dramatic,
+// destabilizing blow), a `death` (a leader dies of natural causes — a quieter
+// succession), or an `appointed` leader (a neutral succession / new head of
+// state). The engine sets the nation's leader to the new name and applies a
+// DETERMINISTIC stability dip (see `LEADER_STABILITY_EFFECT` below) — no hidden
+// randomness. A change whose target has no current leader may only *appoint*
+// one (an assassination/death of a leaderless nation is dropped, not thrown).
+
+/** How a nation's leader changed this turn (v0.38, #61). */
+export type LeaderCause = 'assassination' | 'death' | 'appointed';
+
+/** A single leader change: the target nation, the new leader's name, the cause. */
+export interface LeaderChange {
+  /** The target nation, by id or name (resolved by the shared resolver). */
+  target: string;
+  /** The new leader's name (the incoming / successor head of state). */
+  name: string;
+  /** What happened to the leader this turn. */
+  cause: LeaderCause;
+}
+
+/** The leader-ops block of a `TurnResult`. Required; default `{ changes: [] }`. */
+export interface LeaderOps {
+  changes: LeaderChange[];
+}
+
+/**
+ * The deterministic stability effect of each leader-cause (v0.38, #61).
+ * Assassination is the most destabilizing, a natural death a minor wobble, an
+ * appointment is neutral. Applied to the target's `stability` (clamped 0–100),
+ * mirrored to its `regionStats`, and its derived stats re-derived afterwards.
+ */
+export const LEADER_STABILITY_EFFECT: Record<LeaderCause, number> = {
+  assassination: -15,
+  death: -3,
+  appointed: 0,
+};
+
 // --- Nuclear / WMD effect math (v0.37, #60) ----------------------------------
 //
 // A nuclear strike is a DETERMINISTIC, devastating stat collapse — there is no
@@ -637,6 +679,21 @@ export interface TurnResult {
    * never queued. Required; default `{ arm: [], strikes: [] }`.
    */
   nuclear: NuclearOps;
+  /**
+   * (v0.38, #61) Leader changes this turn. Each change names a target nation
+   * (id or name) and sets its leader to the new name, applying a deterministic
+   * stability effect by cause: `assassination` (leader killed — a dramatic
+   * −15 to the target's stability, a `military` event), `death` (natural
+   * causes — a quieter −3 succession, a `political` event), or `appointed`
+   * (a neutral 0 succession, a `political` event). An assassination/death
+   * requires the target to already have a leader (a leaderless target is
+   * dropped, never thrown); an appointment is always valid (it creates the
+   * first leader). At most 1–2 per turn, each narrated in `events`. This is
+   * the *leader* lever — heavier and more destabilizing than the lighter
+   * `hybrid.assassinate` op (a −5 stability dip on a nation or region, with
+   * no leader replacement). Required; default `{ changes: [] }`.
+   */
+  leaders: LeaderOps;
   /**
    * (v0.27, #44) Map-marker ops this turn. `add` places new named markers
    * (the engine positions each at its region's centroid + a small
@@ -949,6 +1006,7 @@ export function nationForPrompt(n: Nation) {
     stats: n.stats,
     territory: n.territory,
     relations: n.relations,
+    leader: n.leader,
   };
 }
 

shared/types.ts

@@ -80,6 +80,14 @@ export interface Nation {
    * `isNuclearCapable` in `protocol.ts`).
    */
   nuclear?: boolean;
+  /**
+   * The nation's current named leader (v0.38, #61). Optional — a legacy game
+   * (or a nation the LLM has never given a leader to) has none, which is the
+   * "no leader" baseline. The LLM changes it via `TurnResult.leaders`
+   * (assassination / death / appointment, see `LeaderChange` in `protocol.ts`);
+   * each change carries a deterministic stability effect + a narration event.
+   */
+  leader?: { name: string };
 }
 
 /** Categories a narrative event can take. */