Implement remaining TODOs: exponential backoff, notifications, cleanup, and HTTP transport

[Copilot]

This PR implements all 7 remaining TODO items in the GABS codebase, providing production-ready implementations with comprehensive testing.

Key Changes

1. Exponential Backoff with Jitter (internal/gabp/client.go)

Replaced the fixed delay retry mechanism with proper exponential backoff:

• Mathematical exponential growth: backoffMin * 2^attempts
• ±25% randomized jitter to prevent thundering herd problems
• Respects backoffMin and backoffMax parameters
• Prevents simultaneous game connection issues

// Before: time.Sleep(backoffMin)
// After: Exponential backoff with jitter
multiplier := math.Pow(2, float64(attempts))
backoffDelay := time.Duration(float64(backoffMin) * multiplier)
if backoffDelay > backoffMax {
    backoffDelay = backoffMax
}
// Add ±25% jitter

2. Real-time Notification System (internal/mirror/mirror.go, internal/mcp/stdio_server.go)

Implemented MCP-compliant notification system:

• Automatic tools/list_changed notifications when new tools are registered
• resources/list_changed notifications for dynamic resource updates
• Client connection tracking for notification broadcasting
• Both stdio and HTTP transport support

3. Comprehensive Resource Mirroring (internal/mirror/mirror.go)

Enhanced GABP resource mirroring with three resource types:

• Event Logs: Real-time GABP events with structured JSON data
• Game State: Current game capabilities and tool availability
• Event Stream: Real-time event streaming support (extensible for full GABP event subscription)

4. Automatic Resource Cleanup (internal/mcp/stdio_server.go)

Implemented comprehensive cleanup when games terminate:

• Tracks game-specific tools and resources via gameTools and gameResources maps
• Automatically unregisters all game-specific tools (e.g., minecraft.*)
• Cleans up bridge configuration files using new GetBridgeConfigPath()
• Sends notifications to alert AI agents when tools/resources are removed

5. Full HTTP Transport (internal/mcp/http_server.go)

Complete MCP over HTTP implementation:

• JSON-RPC over HTTP: POST /mcp endpoint handling all MCP methods
• Server-Sent Events: GET /mcp/events for real-time notifications
• Proper HTTP method validation and error handling
• Connection management with graceful shutdown
• Health check endpoint at /health

POST /mcp
Content-Type: application/json

{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}

Testing Coverage

Added comprehensive test suites:

• Exponential backoff: 3 test cases validating timing, jitter, and maximum capping
• Notification system: Mock server testing for proper notification delivery
• Resource cleanup: Tests for tool/resource tracking and cleanup operations
• HTTP transport: 5 test cases covering JSON-RPC, SSE, method validation, and error handling

Technical Details

Architecture Improvements

• Interface-based design: Created MCPServer and GABPClient interfaces for better testability
• Resource tracking: Added gameTools and gameResources maps for ownership tracking
• Connection management: Proper client connection tracking for notification broadcasting

Error Handling

• Robust HTTP error responses with proper status codes
• Graceful handling of disconnected notification clients
• Safe cleanup operations that won't panic on missing resources

Performance Considerations

• Efficient notification broadcasting to multiple clients
• Non-blocking notification delivery with timeouts
• Minimal memory overhead for resource tracking

Backward Compatibility

All changes are fully backward compatible:

• Existing APIs and method signatures unchanged
• Previous behavior preserved for all existing functionality
• New features are additive and don't affect existing workflows

Usage Examples

HTTP Transport

# Start GABS with HTTP transport
gabs serve --http :8080

# Make MCP requests
curl -X POST http://localhost:8080/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}'

# Subscribe to notifications via SSE
curl -N http://localhost:8080/mcp/events

Automatic Notifications

When games start/stop or tools change, AI agents automatically receive:

{
  "jsonrpc": "2.0",
  "method": "notifications/tools/list_changed", 
  "params": {}
}

This completes the TODO implementation roadmap, providing GABS with production-ready reliability improvements, real-time capabilities, and comprehensive HTTP transport support.

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