fix: stdio tests failing due to Zod v4 key reordering

The stdio tests were timing out because Zod v4 reconstructs objects
with keys in schema definition order, causing JSON.stringify-based
message comparisons to fail.

Root cause:
- Tests sent messages with keys: {jsonrpc, method, ...}
- Zod parsed and returned: {method, jsonrpc, ...}
- String comparison failed: JSON.stringify(received) !== JSON.stringify(expected)
- Promise never resolved, tests timed out

Fix:
- Replace fragile JSON.stringify comparisons with property-based comparison
- Compare actual message content (method, jsonrpc) instead of serialized strings
- Key order doesn't matter for semantic equality

This is not a breaking change - JSON-RPC doesn't mandate key order,
and the SDK handles messages correctly. Only test assertions needed updating.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ochafik

test/client/stdio.test.ts

@@ -52,7 +52,9 @@ test('should read messages', async () => {
         client.onmessage = message => {
             readMessages.push(message);
 
-            if (JSON.stringify(message) === JSON.stringify(messages[1])) {
+            // Compare message content instead of JSON.stringify (Zod reorders keys)
+            const msg1 = messages[1];
+            if (message.method === msg1.method && message.jsonrpc === msg1.jsonrpc) {
                 resolve();
             }
         };

test/server/stdio.test.ts

@@ -87,7 +87,9 @@ test('should read multiple messages', async () => {
     const finished = new Promise<void>(resolve => {
         server.onmessage = message => {
             readMessages.push(message);
-            if (JSON.stringify(message) === JSON.stringify(messages[1])) {
+            // Compare message content instead of JSON.stringify (Zod reorders keys)
+            const msg1 = messages[1];
+            if (message.method === msg1.method && message.jsonrpc === msg1.jsonrpc) {
                 resolve();
             }
         };