feat(gateway): add node capability negotiation foundation

src/gateway/protocol.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import {
   isValidRequest,
   parseMessage,
+  parseNodeRegisterParams,
   makeResponse,
   makeError,
   makeEvent,
@@ -60,6 +61,49 @@ describe('protocol', () => {
     });
   });
 
+  describe('parseNodeRegisterParams', () => {
+    it('parses valid node registration params', () => {
+      const parsed = parseNodeRegisterParams({
+        connectionId: 'conn-1',
+        nodeId: 'node-a',
+        role: 'companion',
+        protocolVersion: 1,
+        capabilities: ['ui.canvas', 'notifications'],
+      });
+      expect(parsed).toEqual({
+        connectionId: 'conn-1',
+        nodeId: 'node-a',
+        role: 'companion',
+        protocolVersion: 1,
+        capabilities: ['ui.canvas', 'notifications'],
+      });
+    });
+
+    it('rejects invalid node registration params', () => {
+      expect(parseNodeRegisterParams({
+        connectionId: 'conn-1',
+        nodeId: '',
+        role: 'companion',
+        protocolVersion: 1,
+        capabilities: [],
+      })).toBeNull();
+      expect(parseNodeRegisterParams({
+        connectionId: 'conn-1',
+        nodeId: 'node',
+        role: 'companion',
+        protocolVersion: 0,
+        capabilities: [],
+      })).toBeNull();
+      expect(parseNodeRegisterParams({
+        connectionId: 'conn-1',
+        nodeId: 'node',
+        role: 'companion',
+        protocolVersion: 1,
+        capabilities: [1],
+      })).toBeNull();
+    });
+  });
+
   describe('makeResponse', () => {
     it('creates a response message', () => {
       expect(makeResponse(1, { status: 'ok' })).toEqual({