Fix/signal group sender message keys init (#1731)

* fix(signal-group): initialize senderMessageKeys when deserializing SenderKeyState

* test(signal-group): add regression test for missing senderMessageKeys initialization

src/__tests__/Signal/Group/sender-key-state-regression.test.ts

@@ -0,0 +1,22 @@
+import { SenderKeyState } from '../../../Signal/Group/sender-key-state'
+import { SenderMessageKey } from '../../../Signal/Group/sender-message-key'
+
+describe('SenderKeyState regression: missing senderMessageKeys array', () => {
+	it('should initialize senderMessageKeys when absent in provided structure', () => {
+		const legacyStructure = {
+			senderKeyId: 42,
+			senderChainKey: { iteration: 0, seed: Buffer.from([1, 2, 3]) },
+			senderSigningKey: { public: Buffer.from([4, 5, 6]) }
+		}
+
+		const state = new SenderKeyState(null, null, null, null, null, null, legacyStructure as any)
+		const msgKey = new SenderMessageKey(0, Buffer.from([7, 8, 9]))
+		state.addSenderMessageKey(msgKey)
+
+		const structure = state.getStructure()
+		expect(structure.senderMessageKeys).toBeDefined()
+		expect(Array.isArray(structure.senderMessageKeys)).toBe(true)
+		expect(structure.senderMessageKeys.length).toBe(1)
+		expect(structure.senderMessageKeys[0]?.iteration).toBe(0)
+	})
+})