feat(engine): range-bonus modifier descriptor

Add RANGE_BONUS_DESCRIPTOR that seeds RangeBonus fact on piece entities,
and update getSlidingMoves to respect it via a per-ray maxSteps cap.
Clamped to [0,7] in apply(); standard boards are unaffected (RangeBonus=0
→ maxSteps=7, identical to prior behaviour). Foundation for range-limit presets.

packages/chess/src/modifiers/descriptors/range-bonus.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect } from "vitest";
+import { Session, type EntityId } from "@paratype/rete";
+import { RANGE_BONUS_DESCRIPTOR } from "./range-bonus.js";
+import { MODIFIER_REGISTRY } from "../registry.js";
+
+function setupSession(): Session {
+  return new Session({ autoFire: false });
+}
+
+describe("RANGE_BONUS_DESCRIPTOR", () => {
+  it("registers in MODIFIER_REGISTRY with id 'range-bonus'", () => {
+    expect(MODIFIER_REGISTRY.has("range-bonus")).toBe(true);
+    expect(MODIFIER_REGISTRY.get("range-bonus")).toBe(RANGE_BONUS_DESCRIPTOR);
+  });
+
+  it("has correct metadata", () => {
+    expect(RANGE_BONUS_DESCRIPTOR.id).toBe("range-bonus");
+    expect(RANGE_BONUS_DESCRIPTOR.attrName).toBe("RangeBonus");
+    expect(RANGE_BONUS_DESCRIPTOR.stackingRule).toBe("additive");
+    expect(RANGE_BONUS_DESCRIPTOR.uiForm).toBe("number");
+  });
+
+  describe("describe()", () => {
+    it("returns 'Range +N' for non-negative values", () => {
+      expect(RANGE_BONUS_DESCRIPTOR.describe(2)).toBe("Range +2");
+      expect(RANGE_BONUS_DESCRIPTOR.describe(0)).toBe("Range +0");
+      expect(RANGE_BONUS_DESCRIPTOR.describe(7)).toBe("Range +7");
+    });
+
+    it("returns 'Range -N' for negative values", () => {
+      expect(RANGE_BONUS_DESCRIPTOR.describe(-1)).toBe("Range -1");
+      expect(RANGE_BONUS_DESCRIPTOR.describe(-7)).toBe("Range -7");
+    });
+  });
+
+  describe("apply()", () => {
+    it("inserts RangeBonus fact on the piece entity", () => {
+      const session = setupSession();
+      RANGE_BONUS_DESCRIPTOR.apply(session, 1 as EntityId, 3);
+      expect(session.get(1 as EntityId, "RangeBonus")).toBe(3);
+    });
+
+    it("clamps effectiveValue above RANGE_MAX (7) down to 7", () => {
+      const session = setupSession();
+      RANGE_BONUS_DESCRIPTOR.apply(session, 1 as EntityId, 10 as number);
+      expect(session.get(1 as EntityId, "RangeBonus")).toBe(7);
+    });
+
+    it("clamps negative effectiveValue to 0", () => {
+      const session = setupSession();
+      RANGE_BONUS_DESCRIPTOR.apply(session, 1 as EntityId, -5 as number);
+      expect(session.get(1 as EntityId, "RangeBonus")).toBe(0);
+    });
+
+    it("applies exactly RANGE_MAX (7) without clamping", () => {
+      const session = setupSession();
+      RANGE_BONUS_DESCRIPTOR.apply(session, 2 as EntityId, 7);
+      expect(session.get(2 as EntityId, "RangeBonus")).toBe(7);
+    });
+
+    it("applies zero without clamping", () => {
+      const session = setupSession();
+      RANGE_BONUS_DESCRIPTOR.apply(session, 3 as EntityId, 0);
+      expect(session.get(3 as EntityId, "RangeBonus")).toBe(0);
+    });
+  });
+});

packages/chess/src/modifiers/descriptors/range-bonus.ts

@@ -0,0 +1,25 @@
+import { z } from "zod";
+import { MODIFIER_REGISTRY } from "../registry.js";
+import type { ModifierDescriptor } from "../types.js";
+
+const RANGE_MAX = 7;
+const schema = z.number().int().min(-7).max(7);
+type Value = z.infer<typeof schema>;
+
+export const RANGE_BONUS_DESCRIPTOR: ModifierDescriptor<Value> = {
+  id: "range-bonus",
+  attrName: "RangeBonus",
+  label: "Range Bonus",
+  valueSchema: schema,
+  stackingRule: "additive",
+  uiForm: "number",
+  apply(session, pieceId, effectiveValue) {
+    const clamped = Math.max(0, Math.min(RANGE_MAX, effectiveValue));
+    session.insert(pieceId, "RangeBonus", clamped);
+  },
+  describe(value) {
+    return `Range ${value >= 0 ? "+" : ""}${value}`;
+  },
+};
+
+MODIFIER_REGISTRY.register(RANGE_BONUS_DESCRIPTOR);