feat: add core contracts

packages/core/src/hash.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+
+import { canonicalize, hash } from "./hash.js";
+
+describe("content hashing", () => {
+  it("canonicalizes object keys lexicographically while preserving array order", () => {
+    expect(canonicalize({ z: 1, a: [{ b: true, a: null }] })).toBe(
+      '{"a":[{"a":null,"b":true}],"z":1}',
+    );
+  });
+
+  it("hashes equivalent object key orders to the same sha256 hex", () => {
+    const left = hash({ z: 1, a: 2 });
+    const right = hash({ a: 2, z: 1 });
+
+    expect(left).toBe(right);
+    expect(left).toMatch(/^[a-f0-9]{64}$/);
+  });
+
+  it("rejects values that are not JSON-safe", () => {
+    expect(() => canonicalize({ date: new Date("2026-05-09T00:00:00Z") })).toThrow(
+      /non-plain object/,
+    );
+    expect(() => canonicalize({ missing: undefined })).toThrow(/undefined/);
+  });
+});