fix: add null check for WebSocket subscription params

[AlexeySamosadov]

Summary

• Add defensive null check in handleMessage for malformed subscription events
• Prevents TypeError: Cannot read properties of undefined (reading 'subscription') during WebSocket reconnection

Motivation

Fixes #547 - During WebSocket reconnections, message.params can be undefined causing a crash. The isSubscriptionEvent() type guard only checks that the message is NOT a response, but doesn't validate that params exists.

Changes

File: src/api/alchemy-websocket-provider.ts

Added guard at line 500:

// Guard against malformed subscription events that pass the type guard
// but have missing params during WebSocket reconnection (Issue #547)
if (!message.params || !message.params.subscription) {
  return;
}

Test Plan

• TypeScript compilation passes
• All 406 unit tests pass
• ESLint passes
• Prettier formatting passes
• Pre-commit hooks pass

---

🤖 Generated with Claude Code