Type-Safe and Unified RPC Communication

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This PR improves RPC communication across the entire project by enhancing type safety and unifying implementations across all platform packages.

🎯 Motivation

The previous RPC communication had several issues:

• Inconsistent type definitions across different packages
• Lack of type safety in message handling
• Redundant implementations
• Weak error handling
• Unclear interfaces between core and platform-specific implementations

🔧 Key Changes

Core Package Improvements (message-channel-core)

New Type Definitions:

• RpcEngineType enum for unified message types
• RpcEngineParamMap for type-safe parameter mapping
• EngineRpcRegistry interface for registry typing

New Utility Functions:

• Type guards for runtime type checking (isRpcRequest, isRpcResponse)
• Serialization/deserialization for secure message transmission
• Standardized error handling with createRpcError

Platform-Specific Updates

GJS Package (message-channel-gjs):

• RpcEndpoint as generic class with RpcMethodRegistry
• WebKit integration for GTK WebViews
• Type-safe handler registration

Web Package (message-channel-web):

• Iframe context handling
• PostMessage API with type safety
• Bidirectional communication

WebView Package (message-channel-webview):

• WebKit message handler integration
• Native bridge for Electron/WebView

Engine Integration

Excalibur Engine:

• RpcEngineType integration instead of old EngineMessageType
• Type-safe event dispatcher
• Improved error handling

GJS Engine:

• Unified RPC handlers
• Type-safe parameter validation

📁 Affected Files

Core Packages

• packages/message-channel-core/src/types/rpc.ts - New RPC types
• packages/message-channel-core/src/utils/serialization.ts - Serialization
• packages/message-channel-core/src/utils/validation.ts - Type guards

Platform Packages

• packages/message-channel-gjs/src/rpc-endpoint.ts - GJS RPC endpoint
• packages/message-channel-web/src/iframe-context.ts - Web iframe context
• packages/message-channel-webview/src/webkit-message-handler.ts - WebView handler

Engine Packages

• packages/engine-excalibur/src/systems/editor-input.system.ts - Input system
• packages/engine-gjs/src/widgets/webview.ts - GJS WebView widget

⚠️ Breaking Changes

API Changes

• EngineMessageType → RpcEngineType (enum values remain the same)
• RpcEndpoint is now generic with RpcMethodRegistry<T>
• Message handler signatures have changed

Migration Guide

// Before
const endpoint = new RpcEndpoint();
endpoint.registerHandler('loadProject', (params: any) => { ... });

// After
const endpoint = new RpcEndpoint<EngineRpcRegistry>();
endpoint.registerHandler(RpcEngineType.LOAD_PROJECT, (params: LoadProjectParams) => { ... });