feat(backend): implement MCP client infrastructure (#55)

Core MCP client implementation with comprehensive tooling:

**Services:**
- MCPClientManager: Main facade for all MCP operations
- MCPServerRegistry: Thread-safe singleton for server configs
- ConnectionPool: Connection pooling with auto-reconnection
- ToolRouter: Automatic tool routing with circuit breaker
- AsyncCircuitBreaker: Custom async-compatible circuit breaker

**Configuration:**
- YAML-based config with Pydantic models
- Environment variable expansion support
- Transport types: HTTP, SSE, STDIO

**API Endpoints:**
- GET /mcp/servers - List all MCP servers
- GET /mcp/servers/{name}/tools - List server tools
- GET /mcp/tools - List all tools from all servers
- GET /mcp/health - Health check all servers
- POST /mcp/call - Execute tool (admin only)
- GET /mcp/circuit-breakers - Circuit breaker status
- POST /mcp/circuit-breakers/{name}/reset - Reset circuit breaker
- POST /mcp/servers/{name}/reconnect - Force reconnection

**Testing:**
- 156 unit tests with comprehensive coverage
- Tests for all services, routes, and error handling
- Proper mocking and async test support

**Documentation:**
- MCP_CLIENT.md with usage examples
- Phase 2+ workflow documentation

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/mcp/__init__.py

@@ -0,0 +1,85 @@
+"""
+MCP Client Service Package
+
+Provides infrastructure for communicating with MCP (Model Context Protocol)
+servers. This is the foundation for AI agent tool integration.
+
+Usage:
+    from app.services.mcp import get_mcp_client, MCPClientManager
+
+    # In FastAPI route
+    async def my_route(mcp: MCPClientManager = Depends(get_mcp_client)):
+        result = await mcp.call_tool("llm-gateway", "chat", {"prompt": "Hello"})
+
+    # Direct usage
+    manager = MCPClientManager()
+    await manager.initialize()
+    result = await manager.call_tool("issues", "create_issue", {...})
+    await manager.shutdown()
+"""
+
+from .client_manager import (
+    MCPClientManager,
+    ServerHealth,
+    get_mcp_client,
+    reset_mcp_client,
+    shutdown_mcp_client,
+)
+from .config import (
+    MCPConfig,
+    MCPServerConfig,
+    TransportType,
+    create_default_config,
+    load_mcp_config,
+)
+from .connection import ConnectionPool, ConnectionState, MCPConnection
+from .exceptions import (
+    MCPCircuitOpenError,
+    MCPConnectionError,
+    MCPError,
+    MCPServerNotFoundError,
+    MCPTimeoutError,
+    MCPToolError,
+    MCPToolNotFoundError,
+    MCPValidationError,
+)
+from .registry import MCPServerRegistry, ServerCapabilities, get_registry
+from .routing import AsyncCircuitBreaker, CircuitState, ToolInfo, ToolResult, ToolRouter
+
+__all__ = [
+    # Main facade
+    "MCPClientManager",
+    "get_mcp_client",
+    "shutdown_mcp_client",
+    "reset_mcp_client",
+    "ServerHealth",
+    # Configuration
+    "MCPConfig",
+    "MCPServerConfig",
+    "TransportType",
+    "load_mcp_config",
+    "create_default_config",
+    # Registry
+    "MCPServerRegistry",
+    "ServerCapabilities",
+    "get_registry",
+    # Connection
+    "ConnectionPool",
+    "ConnectionState",
+    "MCPConnection",
+    # Routing
+    "ToolRouter",
+    "ToolInfo",
+    "ToolResult",
+    "AsyncCircuitBreaker",
+    "CircuitState",
+    # Exceptions
+    "MCPError",
+    "MCPConnectionError",
+    "MCPTimeoutError",
+    "MCPToolError",
+    "MCPServerNotFoundError",
+    "MCPToolNotFoundError",
+    "MCPCircuitOpenError",
+    "MCPValidationError",
+]

backend/app/services/mcp/client_manager.py

@@ -0,0 +1,417 @@
+"""
+MCP Client Manager
+
+Main facade for all MCP operations. Manages server connections,
+tool discovery, and provides a unified interface for tool calls.
+"""
+
+import asyncio
+import logging
+from dataclasses import dataclass
+from typing import Any
+
+from .config import MCPConfig, MCPServerConfig, load_mcp_config
+from .connection import ConnectionPool, ConnectionState
+from .exceptions import MCPServerNotFoundError
+from .registry import MCPServerRegistry, get_registry
+from .routing import ToolInfo, ToolResult, ToolRouter
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class ServerHealth:
+    """Health status for an MCP server."""
+
+    name: str
+    healthy: bool
+    state: str
+    url: str
+    error: str | None = None
+    tools_count: int = 0
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert to dictionary."""
+        return {
+            "name": self.name,
+            "healthy": self.healthy,
+            "state": self.state,
+            "url": self.url,
+            "error": self.error,
+            "tools_count": self.tools_count,
+        }
+
+
+class MCPClientManager:
+    """
+    Central manager for all MCP client operations.
+
+    Provides a unified interface for:
+    - Connecting to MCP servers
+    - Discovering and calling tools
+    - Health monitoring
+    - Connection lifecycle management
+
+    This is the main entry point for MCP operations in the application.
+    """
+
+    def __init__(
+        self,
+        config: MCPConfig | None = None,
+        registry: MCPServerRegistry | None = None,
+    ) -> None:
+        """
+        Initialize the MCP client manager.
+
+        Args:
+            config: Optional MCP configuration. If None, loads from default.
+            registry: Optional registry instance. If None, uses singleton.
+        """
+        self._registry = registry or get_registry()
+        self._pool = ConnectionPool()
+        self._router: ToolRouter | None = None
+        self._initialized = False
+        self._lock = asyncio.Lock()
+
+        # Load configuration if provided
+        if config is not None:
+            self._registry.load_config(config)
+
+    @property
+    def is_initialized(self) -> bool:
+        """Check if the manager is initialized."""
+        return self._initialized
+
+    async def initialize(self, config: MCPConfig | None = None) -> None:
+        """
+        Initialize the MCP client manager.
+
+        Loads configuration, creates connections, and discovers tools.
+
+        Args:
+            config: Optional configuration to load
+        """
+        async with self._lock:
+            if self._initialized:
+                logger.warning("MCPClientManager already initialized")
+                return
+
+            logger.info("Initializing MCP Client Manager")
+
+            # Load configuration
+            if config is not None:
+                self._registry.load_config(config)
+            elif len(self._registry.list_servers()) == 0:
+                # Try to load from default location
+                self._registry.load_config(load_mcp_config())
+
+            # Create router
+            self._router = ToolRouter(self._registry, self._pool)
+
+            # Connect to all enabled servers
+            await self._connect_all_servers()
+
+            # Discover tools from all servers
+            if self._router:
+                await self._router.discover_tools()
+
+            self._initialized = True
+            logger.info(
+                "MCP Client Manager initialized with %d servers",
+                len(self._registry.list_enabled_servers()),
+            )
+
+    async def _connect_all_servers(self) -> None:
+        """Connect to all enabled MCP servers."""
+        enabled_servers = self._registry.get_enabled_configs()
+
+        for name, config in enabled_servers.items():
+            try:
+                await self._pool.get_connection(name, config)
+                logger.info("Connected to MCP server: %s", name)
+            except Exception as e:
+                logger.error("Failed to connect to MCP server %s: %s", name, e)
+
+    async def shutdown(self) -> None:
+        """
+        Shutdown the MCP client manager.
+
+        Closes all connections and cleans up resources.
+        """
+        async with self._lock:
+            if not self._initialized:
+                return
+
+            logger.info("Shutting down MCP Client Manager")
+
+            await self._pool.close_all()
+            self._initialized = False
+
+            logger.info("MCP Client Manager shutdown complete")
+
+    async def connect(self, server_name: str) -> None:
+        """
+        Connect to a specific MCP server.
+
+        Args:
+            server_name: Name of the server to connect to
+
+        Raises:
+            MCPServerNotFoundError: If server is not registered
+        """
+        config = self._registry.get(server_name)
+        await self._pool.get_connection(server_name, config)
+        logger.info("Connected to MCP server: %s", server_name)
+
+    async def disconnect(self, server_name: str) -> None:
+        """
+        Disconnect from a specific MCP server.
+
+        Args:
+            server_name: Name of the server to disconnect from
+        """
+        await self._pool.close_connection(server_name)
+        logger.info("Disconnected from MCP server: %s", server_name)
+
+    async def disconnect_all(self) -> None:
+        """Disconnect from all MCP servers."""
+        await self._pool.close_all()
+
+    async def call_tool(
+        self,
+        server: str,
+        tool: str,
+        args: dict[str, Any] | None = None,
+        timeout: float | None = None,
+    ) -> ToolResult:
+        """
+        Call a tool on a specific MCP server.
+
+        Args:
+            server: Name of the MCP server
+            tool: Name of the tool to call
+            args: Tool arguments
+            timeout: Optional timeout override
+
+        Returns:
+            Tool execution result
+        """
+        if not self._initialized or self._router is None:
+            await self.initialize()
+
+        assert self._router is not None  # Guaranteed after initialize()
+        return await self._router.call_tool(
+            server_name=server,
+            tool_name=tool,
+            arguments=args,
+            timeout=timeout,
+        )
+
+    async def route_tool(
+        self,
+        tool: str,
+        args: dict[str, Any] | None = None,
+        timeout: float | None = None,
+    ) -> ToolResult:
+        """
+        Route a tool call to the appropriate server automatically.
+
+        Args:
+            tool: Name of the tool to call
+            args: Tool arguments
+            timeout: Optional timeout override
+
+        Returns:
+            Tool execution result
+        """
+        if not self._initialized or self._router is None:
+            await self.initialize()
+
+        assert self._router is not None  # Guaranteed after initialize()
+        return await self._router.route_tool(
+            tool_name=tool,
+            arguments=args,
+            timeout=timeout,
+        )
+
+    async def list_tools(self, server: str) -> list[ToolInfo]:
+        """
+        List all tools available on a specific server.
+
+        Args:
+            server: Name of the MCP server
+
+        Returns:
+            List of tool information
+        """
+        capabilities = await self._registry.get_capabilities(server)
+        return [
+            ToolInfo(
+                name=t.get("name", ""),
+                description=t.get("description"),
+                server_name=server,
+                input_schema=t.get("input_schema"),
+            )
+            for t in capabilities.tools
+        ]
+
+    async def list_all_tools(self) -> list[ToolInfo]:
+        """
+        List all tools from all servers.
+
+        Returns:
+            List of tool information
+        """
+        if not self._initialized or self._router is None:
+            await self.initialize()
+
+        assert self._router is not None  # Guaranteed after initialize()
+        return await self._router.list_all_tools()
+
+    async def health_check(self) -> dict[str, ServerHealth]:
+        """
+        Perform health check on all MCP servers.
+
+        Returns:
+            Dict mapping server names to health status
+        """
+        results: dict[str, ServerHealth] = {}
+        pool_status = self._pool.get_status()
+        pool_health = await self._pool.health_check_all()
+
+        for server_name in self._registry.list_servers():
+            try:
+                config = self._registry.get(server_name)
+                status = pool_status.get(server_name, {})
+                healthy = pool_health.get(server_name, False)
+
+                capabilities = self._registry.get_cached_capabilities(server_name)
+
+                results[server_name] = ServerHealth(
+                    name=server_name,
+                    healthy=healthy,
+                    state=status.get("state", ConnectionState.DISCONNECTED.value),
+                    url=config.url,
+                    tools_count=len(capabilities.tools),
+                )
+            except MCPServerNotFoundError:
+                pass
+            except Exception as e:
+                results[server_name] = ServerHealth(
+                    name=server_name,
+                    healthy=False,
+                    state=ConnectionState.ERROR.value,
+                    url="unknown",
+                    error=str(e),
+                )
+
+        return results
+
+    def list_servers(self) -> list[str]:
+        """Get list of all registered server names."""
+        return self._registry.list_servers()
+
+    def list_enabled_servers(self) -> list[str]:
+        """Get list of enabled server names."""
+        return self._registry.list_enabled_servers()
+
+    def get_server_config(self, server_name: str) -> MCPServerConfig:
+        """
+        Get configuration for a specific server.
+
+        Args:
+            server_name: Name of the server
+
+        Returns:
+            Server configuration
+
+        Raises:
+            MCPServerNotFoundError: If server is not registered
+        """
+        return self._registry.get(server_name)
+
+    def register_server(
+        self,
+        name: str,
+        config: MCPServerConfig,
+    ) -> None:
+        """
+        Register a new MCP server at runtime.
+
+        Args:
+            name: Unique server name
+            config: Server configuration
+        """
+        self._registry.register(name, config)
+
+    def unregister_server(self, name: str) -> bool:
+        """
+        Unregister an MCP server.
+
+        Args:
+            name: Server name to unregister
+
+        Returns:
+            True if server was found and removed
+        """
+        return self._registry.unregister(name)
+
+    def get_circuit_breaker_status(self) -> dict[str, dict[str, Any]]:
+        """Get status of all circuit breakers."""
+        if self._router is None:
+            return {}
+        return self._router.get_circuit_breaker_status()
+
+    async def reset_circuit_breaker(self, server_name: str) -> bool:
+        """
+        Reset a circuit breaker for a server.
+
+        Args:
+            server_name: Name of the server
+
+        Returns:
+            True if circuit breaker was reset
+        """
+        if self._router is None:
+            return False
+        return await self._router.reset_circuit_breaker(server_name)
+
+
+# Singleton instance
+_manager_instance: MCPClientManager | None = None
+_manager_lock = asyncio.Lock()
+
+
+async def get_mcp_client() -> MCPClientManager:
+    """
+    Get the global MCP client manager instance.
+
+    This is the main dependency injection point for FastAPI.
+    Uses proper locking to avoid race conditions in async contexts.
+    """
+    global _manager_instance
+
+    # Use lock for the entire check-and-create operation to avoid race conditions
+    async with _manager_lock:
+        if _manager_instance is None:
+            _manager_instance = MCPClientManager()
+            await _manager_instance.initialize()
+
+    return _manager_instance
+
+
+async def shutdown_mcp_client() -> None:
+    """Shutdown the global MCP client manager."""
+    global _manager_instance
+
+    # Use lock to prevent race with get_mcp_client()
+    async with _manager_lock:
+        if _manager_instance is not None:
+            await _manager_instance.shutdown()
+            _manager_instance = None
+
+
+def reset_mcp_client() -> None:
+    """Reset the global MCP client manager (for testing)."""
+    global _manager_instance
+    _manager_instance = None

backend/app/services/mcp/config.py

@@ -0,0 +1,234 @@
+"""
+MCP Configuration System
+
+Pydantic models for MCP server configuration with YAML file loading
+and environment variable overrides.
+"""
+
+import os
+from enum import Enum
+from pathlib import Path
+from typing import Any
+
+import yaml
+from pydantic import BaseModel, Field, field_validator
+
+
+class TransportType(str, Enum):
+    """Supported MCP transport types."""
+
+    HTTP = "http"
+    STDIO = "stdio"
+    SSE = "sse"
+
+
+class MCPServerConfig(BaseModel):
+    """Configuration for a single MCP server."""
+
+    url: str = Field(..., description="Server URL (supports ${ENV_VAR} syntax)")
+    transport: TransportType = Field(
+        default=TransportType.HTTP,
+        description="Transport protocol to use",
+    )
+    timeout: int = Field(
+        default=30,
+        ge=1,
+        le=600,
+        description="Request timeout in seconds",
+    )
+    retry_attempts: int = Field(
+        default=3,
+        ge=0,
+        le=10,
+        description="Number of retry attempts on failure",
+    )
+    retry_delay: float = Field(
+        default=1.0,
+        ge=0.1,
+        le=60.0,
+        description="Initial delay between retries in seconds",
+    )
+    retry_max_delay: float = Field(
+        default=30.0,
+        ge=1.0,
+        le=300.0,
+        description="Maximum delay between retries in seconds",
+    )
+    circuit_breaker_threshold: int = Field(
+        default=5,
+        ge=1,
+        le=50,
+        description="Number of failures before opening circuit",
+    )
+    circuit_breaker_timeout: float = Field(
+        default=30.0,
+        ge=5.0,
+        le=300.0,
+        description="Seconds to wait before attempting to close circuit",
+    )
+    enabled: bool = Field(
+        default=True,
+        description="Whether this server is enabled",
+    )
+    description: str | None = Field(
+        default=None,
+        description="Human-readable description of the server",
+    )
+
+    @field_validator("url", mode="before")
+    @classmethod
+    def expand_env_vars(cls, v: str) -> str:
+        """Expand environment variables in URL using ${VAR:-default} syntax."""
+        if not isinstance(v, str):
+            return v
+
+        result = v
+        # Find all ${VAR} or ${VAR:-default} patterns
+        import re
+
+        pattern = r"\$\{([^}]+)\}"
+        matches = re.findall(pattern, v)
+
+        for match in matches:
+            if ":-" in match:
+                var_name, default = match.split(":-", 1)
+            else:
+                var_name, default = match, ""
+
+            env_value = os.environ.get(var_name.strip(), default)
+            result = result.replace(f"${{{match}}}", env_value)
+
+        return result
+
+
+class MCPConfig(BaseModel):
+    """Root configuration for all MCP servers."""
+
+    mcp_servers: dict[str, MCPServerConfig] = Field(
+        default_factory=dict,
+        description="Map of server names to their configurations",
+    )
+
+    # Global defaults
+    default_timeout: int = Field(
+        default=30,
+        description="Default timeout for all servers",
+    )
+    default_retry_attempts: int = Field(
+        default=3,
+        description="Default retry attempts for all servers",
+    )
+    connection_pool_size: int = Field(
+        default=10,
+        ge=1,
+        le=100,
+        description="Maximum connections per server",
+    )
+    health_check_interval: int = Field(
+        default=30,
+        ge=5,
+        le=300,
+        description="Seconds between health checks",
+    )
+
+    @classmethod
+    def from_yaml(cls, path: str | Path) -> "MCPConfig":
+        """Load configuration from a YAML file."""
+        path = Path(path)
+        if not path.exists():
+            raise FileNotFoundError(f"MCP config file not found: {path}")
+
+        with path.open("r") as f:
+            data = yaml.safe_load(f)
+
+        if data is None:
+            data = {}
+
+        return cls.model_validate(data)
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> "MCPConfig":
+        """Load configuration from a dictionary."""
+        return cls.model_validate(data)
+
+    def get_server(self, name: str) -> MCPServerConfig | None:
+        """Get a server configuration by name."""
+        return self.mcp_servers.get(name)
+
+    def get_enabled_servers(self) -> dict[str, MCPServerConfig]:
+        """Get all enabled server configurations."""
+        return {
+            name: config
+            for name, config in self.mcp_servers.items()
+            if config.enabled
+        }
+
+    def list_server_names(self) -> list[str]:
+        """Get list of all configured server names."""
+        return list(self.mcp_servers.keys())
+
+
+# Default configuration path
+DEFAULT_CONFIG_PATH = Path(__file__).parent.parent.parent.parent / "mcp_servers.yaml"
+
+
+def load_mcp_config(path: str | Path | None = None) -> MCPConfig:
+    """
+    Load MCP configuration from file or environment.
+
+    Priority:
+    1. Explicit path parameter
+    2. MCP_CONFIG_PATH environment variable
+    3. Default path (backend/mcp_servers.yaml)
+    4. Empty config if no file exists
+    """
+    if path is None:
+        path = os.environ.get("MCP_CONFIG_PATH", str(DEFAULT_CONFIG_PATH))
+
+    path = Path(path)
+
+    if not path.exists():
+        # Return empty config if no file exists (allows runtime registration)
+        return MCPConfig()
+
+    return MCPConfig.from_yaml(path)
+
+
+def create_default_config() -> MCPConfig:
+    """
+    Create a default MCP configuration with standard servers.
+
+    This is useful for development and as a template.
+    """
+    return MCPConfig(
+        mcp_servers={
+            "llm-gateway": MCPServerConfig(
+                url="${LLM_GATEWAY_URL:-http://localhost:8001}",
+                transport=TransportType.HTTP,
+                timeout=60,
+                description="LLM Gateway for multi-provider AI interactions",
+            ),
+            "knowledge-base": MCPServerConfig(
+                url="${KNOWLEDGE_BASE_URL:-http://localhost:8002}",
+                transport=TransportType.HTTP,
+                timeout=30,
+                description="Knowledge Base for RAG and document retrieval",
+            ),
+            "git-ops": MCPServerConfig(
+                url="${GIT_OPS_URL:-http://localhost:8003}",
+                transport=TransportType.HTTP,
+                timeout=120,
+                description="Git Operations for repository management",
+            ),
+            "issues": MCPServerConfig(
+                url="${ISSUES_URL:-http://localhost:8004}",
+                transport=TransportType.HTTP,
+                timeout=30,
+                description="Issue Tracker for Gitea/GitHub/GitLab",
+            ),
+        },
+        default_timeout=30,
+        default_retry_attempts=3,
+        connection_pool_size=10,
+        health_check_interval=30,
+    )

backend/app/services/mcp/connection.py

@@ -0,0 +1,435 @@
+"""
+MCP Connection Management
+
+Handles connection lifecycle, pooling, and automatic reconnection
+for MCP servers.
+"""
+
+import asyncio
+import logging
+import time
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
+from enum import Enum
+from typing import Any
+
+import httpx
+
+from .config import MCPServerConfig, TransportType
+from .exceptions import MCPConnectionError, MCPTimeoutError
+
+logger = logging.getLogger(__name__)
+
+
+class ConnectionState(str, Enum):
+    """Connection state enumeration."""
+
+    DISCONNECTED = "disconnected"
+    CONNECTING = "connecting"
+    CONNECTED = "connected"
+    RECONNECTING = "reconnecting"
+    ERROR = "error"
+
+
+class MCPConnection:
+    """
+    Manages a single connection to an MCP server.
+
+    Handles connection lifecycle, health checking, and automatic reconnection.
+    """
+
+    def __init__(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+    ) -> None:
+        """
+        Initialize connection.
+
+        Args:
+            server_name: Name of the MCP server
+            config: Server configuration
+        """
+        self.server_name = server_name
+        self.config = config
+        self._state = ConnectionState.DISCONNECTED
+        self._client: httpx.AsyncClient | None = None
+        self._lock = asyncio.Lock()
+        self._last_activity: float | None = None
+        self._connection_attempts = 0
+        self._last_error: Exception | None = None
+
+        # Reconnection settings
+        self._base_delay = config.retry_delay
+        self._max_delay = config.retry_max_delay
+        self._max_attempts = config.retry_attempts
+
+    @property
+    def state(self) -> ConnectionState:
+        """Get current connection state."""
+        return self._state
+
+    @property
+    def is_connected(self) -> bool:
+        """Check if connection is established."""
+        return self._state == ConnectionState.CONNECTED
+
+    @property
+    def last_error(self) -> Exception | None:
+        """Get the last error that occurred."""
+        return self._last_error
+
+    async def connect(self) -> None:
+        """
+        Establish connection to the MCP server.
+
+        Raises:
+            MCPConnectionError: If connection fails after all retries
+        """
+        async with self._lock:
+            if self._state == ConnectionState.CONNECTED:
+                return
+
+            self._state = ConnectionState.CONNECTING
+            self._connection_attempts = 0
+            self._last_error = None
+
+            while self._connection_attempts < self._max_attempts:
+                try:
+                    await self._do_connect()
+                    self._state = ConnectionState.CONNECTED
+                    self._last_activity = time.time()
+                    logger.info(
+                        "Connected to MCP server: %s at %s",
+                        self.server_name,
+                        self.config.url,
+                    )
+                    return
+                except Exception as e:
+                    self._connection_attempts += 1
+                    self._last_error = e
+                    logger.warning(
+                        "Connection attempt %d/%d failed for %s: %s",
+                        self._connection_attempts,
+                        self._max_attempts,
+                        self.server_name,
+                        e,
+                    )
+
+                    if self._connection_attempts < self._max_attempts:
+                        delay = self._calculate_backoff_delay()
+                        logger.debug(
+                            "Retrying connection to %s in %.1fs",
+                            self.server_name,
+                            delay,
+                        )
+                        await asyncio.sleep(delay)
+
+            # All attempts failed
+            self._state = ConnectionState.ERROR
+            raise MCPConnectionError(
+                f"Failed to connect after {self._max_attempts} attempts",
+                server_name=self.server_name,
+                url=self.config.url,
+                cause=self._last_error,
+            )
+
+    async def _do_connect(self) -> None:
+        """Perform the actual connection (transport-specific)."""
+        if self.config.transport == TransportType.HTTP:
+            self._client = httpx.AsyncClient(
+                base_url=self.config.url,
+                timeout=httpx.Timeout(self.config.timeout),
+                headers={
+                    "User-Agent": "Syndarix-MCP-Client/1.0",
+                    "Accept": "application/json",
+                },
+            )
+            # Verify connectivity with a simple request
+            try:
+                # Try to hit the MCP capabilities endpoint
+                response = await self._client.get("/mcp/capabilities")
+                if response.status_code not in (200, 404):
+                    # 404 is acceptable - server might not have capabilities endpoint
+                    response.raise_for_status()
+            except httpx.HTTPStatusError as e:
+                if e.response.status_code != 404:
+                    raise
+            except httpx.ConnectError as e:
+                raise MCPConnectionError(
+                    "Failed to connect to server",
+                    server_name=self.server_name,
+                    url=self.config.url,
+                    cause=e,
+                )
+        else:
+            # For STDIO and SSE transports, we'll implement later
+            raise NotImplementedError(
+                f"Transport {self.config.transport} not yet implemented"
+            )
+
+    def _calculate_backoff_delay(self) -> float:
+        """Calculate exponential backoff delay with jitter."""
+        import random
+
+        delay = self._base_delay * (2 ** (self._connection_attempts - 1))
+        delay = min(delay, self._max_delay)
+        # Add jitter (±25%)
+        jitter = delay * 0.25 * (random.random() * 2 - 1)
+        return delay + jitter
+
+    async def disconnect(self) -> None:
+        """Disconnect from the MCP server."""
+        async with self._lock:
+            if self._client is not None:
+                try:
+                    await self._client.aclose()
+                except Exception as e:
+                    logger.warning(
+                        "Error closing connection to %s: %s",
+                        self.server_name,
+                        e,
+                    )
+                finally:
+                    self._client = None
+
+            self._state = ConnectionState.DISCONNECTED
+            logger.info("Disconnected from MCP server: %s", self.server_name)
+
+    async def reconnect(self) -> None:
+        """Reconnect to the MCP server."""
+        async with self._lock:
+            self._state = ConnectionState.RECONNECTING
+        await self.disconnect()
+        await self.connect()
+
+    async def health_check(self) -> bool:
+        """
+        Perform a health check on the connection.
+
+        Returns:
+            True if connection is healthy
+        """
+        if not self.is_connected or self._client is None:
+            return False
+
+        try:
+            if self.config.transport == TransportType.HTTP:
+                response = await self._client.get(
+                    "/health",
+                    timeout=5.0,
+                )
+                return response.status_code == 200
+            return True
+        except Exception as e:
+            logger.warning(
+                "Health check failed for %s: %s",
+                self.server_name,
+                e,
+            )
+            return False
+
+    async def execute_request(
+        self,
+        method: str,
+        path: str,
+        data: dict[str, Any] | None = None,
+        timeout: float | None = None,
+    ) -> dict[str, Any]:
+        """
+        Execute an HTTP request to the MCP server.
+
+        Args:
+            method: HTTP method (GET, POST, etc.)
+            path: Request path
+            data: Optional request body
+            timeout: Optional timeout override
+
+        Returns:
+            Response data
+
+        Raises:
+            MCPConnectionError: If not connected
+            MCPTimeoutError: If request times out
+        """
+        if not self.is_connected or self._client is None:
+            raise MCPConnectionError(
+                "Not connected to server",
+                server_name=self.server_name,
+            )
+
+        effective_timeout = timeout or self.config.timeout
+
+        try:
+            if method.upper() == "GET":
+                response = await self._client.get(
+                    path,
+                    timeout=effective_timeout,
+                )
+            elif method.upper() == "POST":
+                response = await self._client.post(
+                    path,
+                    json=data,
+                    timeout=effective_timeout,
+                )
+            else:
+                response = await self._client.request(
+                    method.upper(),
+                    path,
+                    json=data,
+                    timeout=effective_timeout,
+                )
+
+            self._last_activity = time.time()
+            response.raise_for_status()
+            return response.json()
+
+        except httpx.TimeoutException as e:
+            raise MCPTimeoutError(
+                "Request timed out",
+                server_name=self.server_name,
+                timeout_seconds=effective_timeout,
+                operation=f"{method} {path}",
+            ) from e
+        except httpx.HTTPStatusError as e:
+            raise MCPConnectionError(
+                f"HTTP error: {e.response.status_code}",
+                server_name=self.server_name,
+                url=f"{self.config.url}{path}",
+                cause=e,
+            )
+        except Exception as e:
+            raise MCPConnectionError(
+                f"Request failed: {e}",
+                server_name=self.server_name,
+                cause=e,
+            )
+
+
+class ConnectionPool:
+    """
+    Pool of connections to MCP servers.
+
+    Manages connection lifecycle and provides connection reuse.
+    """
+
+    def __init__(self, max_connections_per_server: int = 10) -> None:
+        """
+        Initialize connection pool.
+
+        Args:
+            max_connections_per_server: Maximum connections per server
+        """
+        self._connections: dict[str, MCPConnection] = {}
+        self._lock = asyncio.Lock()
+        self._max_per_server = max_connections_per_server
+
+    async def get_connection(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+    ) -> MCPConnection:
+        """
+        Get or create a connection to a server.
+
+        Args:
+            server_name: Name of the server
+            config: Server configuration
+
+        Returns:
+            Active connection
+        """
+        async with self._lock:
+            if server_name not in self._connections:
+                connection = MCPConnection(server_name, config)
+                await connection.connect()
+                self._connections[server_name] = connection
+
+            connection = self._connections[server_name]
+
+            # Reconnect if not connected
+            if not connection.is_connected:
+                await connection.connect()
+
+            return connection
+
+    async def release_connection(self, server_name: str) -> None:
+        """
+        Release a connection (currently just tracks usage).
+
+        Args:
+            server_name: Name of the server
+        """
+        # For now, we keep connections alive
+        # Future: implement connection reaping for idle connections
+
+    async def close_connection(self, server_name: str) -> None:
+        """
+        Close and remove a connection.
+
+        Args:
+            server_name: Name of the server
+        """
+        async with self._lock:
+            if server_name in self._connections:
+                await self._connections[server_name].disconnect()
+                del self._connections[server_name]
+
+    async def close_all(self) -> None:
+        """Close all connections in the pool."""
+        async with self._lock:
+            for connection in self._connections.values():
+                try:
+                    await connection.disconnect()
+                except Exception as e:
+                    logger.warning("Error closing connection: %s", e)
+
+            self._connections.clear()
+            logger.info("Closed all MCP connections")
+
+    async def health_check_all(self) -> dict[str, bool]:
+        """
+        Perform health check on all connections.
+
+        Returns:
+            Dict mapping server names to health status
+        """
+        results = {}
+        for name, connection in self._connections.items():
+            results[name] = await connection.health_check()
+        return results
+
+    def get_status(self) -> dict[str, dict[str, Any]]:
+        """
+        Get status of all connections.
+
+        Returns:
+            Dict mapping server names to status info
+        """
+        return {
+            name: {
+                "state": conn.state.value,
+                "is_connected": conn.is_connected,
+                "url": conn.config.url,
+            }
+            for name, conn in self._connections.items()
+        }
+
+    @asynccontextmanager
+    async def connection(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+    ) -> AsyncGenerator[MCPConnection, None]:
+        """
+        Context manager for getting a connection.
+
+        Usage:
+            async with pool.connection("server", config) as conn:
+                result = await conn.execute_request("POST", "/tool", data)
+        """
+        conn = await self.get_connection(server_name, config)
+        try:
+            yield conn
+        finally:
+            await self.release_connection(server_name)

backend/app/services/mcp/exceptions.py

@@ -0,0 +1,201 @@
+"""
+MCP Exception Classes
+
+Custom exceptions for MCP client operations with detailed error context.
+"""
+
+from typing import Any
+
+
+class MCPError(Exception):
+    """Base exception for all MCP-related errors."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        server_name: str | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message)
+        self.message = message
+        self.server_name = server_name
+        self.details = details or {}
+
+    def __str__(self) -> str:
+        parts = [self.message]
+        if self.server_name:
+            parts.append(f"server={self.server_name}")
+        if self.details:
+            parts.append(f"details={self.details}")
+        return " | ".join(parts)
+
+
+class MCPConnectionError(MCPError):
+    """Raised when connection to an MCP server fails."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        server_name: str | None = None,
+        url: str | None = None,
+        cause: Exception | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, server_name=server_name, details=details)
+        self.url = url
+        self.cause = cause
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.url:
+            base = f"{base} | url={self.url}"
+        if self.cause:
+            base = f"{base} | cause={type(self.cause).__name__}: {self.cause}"
+        return base
+
+
+class MCPTimeoutError(MCPError):
+    """Raised when an MCP operation times out."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        server_name: str | None = None,
+        timeout_seconds: float | None = None,
+        operation: str | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, server_name=server_name, details=details)
+        self.timeout_seconds = timeout_seconds
+        self.operation = operation
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.timeout_seconds is not None:
+            base = f"{base} | timeout={self.timeout_seconds}s"
+        if self.operation:
+            base = f"{base} | operation={self.operation}"
+        return base
+
+
+class MCPToolError(MCPError):
+    """Raised when a tool execution fails."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        server_name: str | None = None,
+        tool_name: str | None = None,
+        tool_args: dict[str, Any] | None = None,
+        error_code: str | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, server_name=server_name, details=details)
+        self.tool_name = tool_name
+        self.tool_args = tool_args
+        self.error_code = error_code
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.tool_name:
+            base = f"{base} | tool={self.tool_name}"
+        if self.error_code:
+            base = f"{base} | error_code={self.error_code}"
+        return base
+
+
+class MCPServerNotFoundError(MCPError):
+    """Raised when a requested MCP server is not registered."""
+
+    def __init__(
+        self,
+        server_name: str,
+        *,
+        available_servers: list[str] | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        message = f"MCP server not found: {server_name}"
+        super().__init__(message, server_name=server_name, details=details)
+        self.available_servers = available_servers or []
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.available_servers:
+            base = f"{base} | available={self.available_servers}"
+        return base
+
+
+class MCPToolNotFoundError(MCPError):
+    """Raised when a requested tool is not found on any server."""
+
+    def __init__(
+        self,
+        tool_name: str,
+        *,
+        server_name: str | None = None,
+        available_tools: list[str] | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        message = f"Tool not found: {tool_name}"
+        super().__init__(message, server_name=server_name, details=details)
+        self.tool_name = tool_name
+        self.available_tools = available_tools or []
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.available_tools:
+            base = f"{base} | available_tools={self.available_tools[:5]}..."
+        return base
+
+
+class MCPCircuitOpenError(MCPError):
+    """Raised when a circuit breaker is open (server temporarily unavailable)."""
+
+    def __init__(
+        self,
+        server_name: str,
+        *,
+        failure_count: int | None = None,
+        reset_timeout: float | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        message = f"Circuit breaker open for server: {server_name}"
+        super().__init__(message, server_name=server_name, details=details)
+        self.failure_count = failure_count
+        self.reset_timeout = reset_timeout
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.failure_count is not None:
+            base = f"{base} | failures={self.failure_count}"
+        if self.reset_timeout is not None:
+            base = f"{base} | reset_in={self.reset_timeout}s"
+        return base
+
+
+class MCPValidationError(MCPError):
+    """Raised when tool arguments fail validation."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        tool_name: str | None = None,
+        field_errors: dict[str, str] | None = None,
+        details: dict[str, Any] | None = None,
+    ) -> None:
+        super().__init__(message, details=details)
+        self.tool_name = tool_name
+        self.field_errors = field_errors or {}
+
+    def __str__(self) -> str:
+        base = super().__str__()
+        if self.tool_name:
+            base = f"{base} | tool={self.tool_name}"
+        if self.field_errors:
+            base = f"{base} | fields={list(self.field_errors.keys())}"
+        return base

backend/app/services/mcp/registry.py

@@ -0,0 +1,305 @@
+"""
+MCP Server Registry
+
+Thread-safe singleton registry for managing MCP server configurations
+and their capabilities.
+"""
+
+import asyncio
+import logging
+from threading import Lock
+from typing import Any
+
+from .config import MCPConfig, MCPServerConfig, load_mcp_config
+from .exceptions import MCPServerNotFoundError
+
+logger = logging.getLogger(__name__)
+
+
+class ServerCapabilities:
+    """Cached capabilities for an MCP server."""
+
+    def __init__(
+        self,
+        tools: list[dict[str, Any]] | None = None,
+        resources: list[dict[str, Any]] | None = None,
+        prompts: list[dict[str, Any]] | None = None,
+    ) -> None:
+        self.tools = tools or []
+        self.resources = resources or []
+        self.prompts = prompts or []
+        self._loaded = False
+        self._load_time: float | None = None
+
+    @property
+    def is_loaded(self) -> bool:
+        """Check if capabilities have been loaded."""
+        return self._loaded
+
+    @property
+    def tool_names(self) -> list[str]:
+        """Get list of tool names."""
+        return [t.get("name", "") for t in self.tools if t.get("name")]
+
+    def mark_loaded(self) -> None:
+        """Mark capabilities as loaded."""
+        import time
+
+        self._loaded = True
+        self._load_time = time.time()
+
+
+class MCPServerRegistry:
+    """
+    Thread-safe singleton registry for MCP servers.
+
+    Manages server configurations and caches their capabilities.
+    """
+
+    _instance: "MCPServerRegistry | None" = None
+    _lock = Lock()
+
+    def __new__(cls) -> "MCPServerRegistry":
+        """Ensure singleton pattern."""
+        with cls._lock:
+            if cls._instance is None:
+                cls._instance = super().__new__(cls)
+                cls._instance._initialized = False
+            return cls._instance
+
+    def __init__(self) -> None:
+        """Initialize registry (only runs once due to singleton)."""
+        if getattr(self, "_initialized", False):
+            return
+
+        self._config: MCPConfig = MCPConfig()
+        self._capabilities: dict[str, ServerCapabilities] = {}
+        self._capabilities_lock = asyncio.Lock()
+        self._initialized = True
+
+        logger.info("MCP Server Registry initialized")
+
+    @classmethod
+    def get_instance(cls) -> "MCPServerRegistry":
+        """Get the singleton registry instance."""
+        return cls()
+
+    @classmethod
+    def reset_instance(cls) -> None:
+        """Reset the singleton (for testing)."""
+        with cls._lock:
+            cls._instance = None
+
+    def load_config(self, config: MCPConfig | None = None) -> None:
+        """
+        Load configuration into the registry.
+
+        Args:
+            config: Optional config to load. If None, loads from default path.
+        """
+        if config is None:
+            config = load_mcp_config()
+
+        self._config = config
+        self._capabilities.clear()
+
+        logger.info(
+            "Loaded MCP configuration with %d servers",
+            len(config.mcp_servers),
+        )
+        for name in config.list_server_names():
+            logger.debug("Registered MCP server: %s", name)
+
+    def register(self, name: str, config: MCPServerConfig) -> None:
+        """
+        Register a new MCP server.
+
+        Args:
+            name: Unique server name
+            config: Server configuration
+        """
+        self._config.mcp_servers[name] = config
+        self._capabilities.pop(name, None)  # Clear any cached capabilities
+
+        logger.info("Registered MCP server: %s at %s", name, config.url)
+
+    def unregister(self, name: str) -> bool:
+        """
+        Unregister an MCP server.
+
+        Args:
+            name: Server name to unregister
+
+        Returns:
+            True if server was found and removed
+        """
+        if name in self._config.mcp_servers:
+            del self._config.mcp_servers[name]
+            self._capabilities.pop(name, None)
+            logger.info("Unregistered MCP server: %s", name)
+            return True
+
+        return False
+
+    def get(self, name: str) -> MCPServerConfig:
+        """
+        Get a server configuration by name.
+
+        Args:
+            name: Server name
+
+        Returns:
+            Server configuration
+
+        Raises:
+            MCPServerNotFoundError: If server is not registered
+        """
+        config = self._config.get_server(name)
+        if config is None:
+            raise MCPServerNotFoundError(
+                server_name=name,
+                available_servers=self.list_servers(),
+            )
+        return config
+
+    def get_or_none(self, name: str) -> MCPServerConfig | None:
+        """
+        Get a server configuration by name, or None if not found.
+
+        Args:
+            name: Server name
+
+        Returns:
+            Server configuration or None
+        """
+        return self._config.get_server(name)
+
+    def list_servers(self) -> list[str]:
+        """Get list of all registered server names."""
+        return self._config.list_server_names()
+
+    def list_enabled_servers(self) -> list[str]:
+        """Get list of enabled server names."""
+        return list(self._config.get_enabled_servers().keys())
+
+    def get_all_configs(self) -> dict[str, MCPServerConfig]:
+        """Get all server configurations."""
+        return dict(self._config.mcp_servers)
+
+    def get_enabled_configs(self) -> dict[str, MCPServerConfig]:
+        """Get all enabled server configurations."""
+        return self._config.get_enabled_servers()
+
+    async def get_capabilities(
+        self,
+        name: str,
+        force_refresh: bool = False,
+    ) -> ServerCapabilities:
+        """
+        Get capabilities for a server (lazy-loaded and cached).
+
+        Args:
+            name: Server name
+            force_refresh: If True, refresh cached capabilities
+
+        Returns:
+            Server capabilities
+
+        Raises:
+            MCPServerNotFoundError: If server is not registered
+        """
+        # Verify server exists
+        self.get(name)
+
+        async with self._capabilities_lock:
+            if name not in self._capabilities or force_refresh:
+                # Will be populated by connection manager when connecting
+                self._capabilities[name] = ServerCapabilities()
+
+            return self._capabilities[name]
+
+    def set_capabilities(
+        self,
+        name: str,
+        tools: list[dict[str, Any]] | None = None,
+        resources: list[dict[str, Any]] | None = None,
+        prompts: list[dict[str, Any]] | None = None,
+    ) -> None:
+        """
+        Set capabilities for a server (called by connection manager).
+
+        Args:
+            name: Server name
+            tools: List of tool definitions
+            resources: List of resource definitions
+            prompts: List of prompt definitions
+        """
+        capabilities = ServerCapabilities(
+            tools=tools,
+            resources=resources,
+            prompts=prompts,
+        )
+        capabilities.mark_loaded()
+        self._capabilities[name] = capabilities
+
+        logger.debug(
+            "Updated capabilities for %s: %d tools, %d resources, %d prompts",
+            name,
+            len(capabilities.tools),
+            len(capabilities.resources),
+            len(capabilities.prompts),
+        )
+
+    def get_cached_capabilities(self, name: str) -> ServerCapabilities:
+        """
+        Get cached capabilities without async loading.
+
+        Use this for synchronous access when you only need
+        cached values (e.g., for health check responses).
+
+        Args:
+            name: Server name
+
+        Returns:
+            Cached capabilities or empty ServerCapabilities
+        """
+        return self._capabilities.get(name, ServerCapabilities())
+
+    def find_server_for_tool(self, tool_name: str) -> str | None:
+        """
+        Find which server provides a specific tool.
+
+        Args:
+            tool_name: Name of the tool to find
+
+        Returns:
+            Server name or None if not found
+        """
+        for name, caps in self._capabilities.items():
+            if tool_name in caps.tool_names:
+                return name
+        return None
+
+    def get_all_tools(self) -> dict[str, list[dict[str, Any]]]:
+        """
+        Get all tools from all servers.
+
+        Returns:
+            Dict mapping server name to list of tool definitions
+        """
+        return {
+            name: caps.tools
+            for name, caps in self._capabilities.items()
+            if caps.is_loaded
+        }
+
+    @property
+    def global_config(self) -> MCPConfig:
+        """Get the global MCP configuration."""
+        return self._config
+
+
+# Module-level convenience function
+def get_registry() -> MCPServerRegistry:
+    """Get the global MCP server registry instance."""
+    return MCPServerRegistry.get_instance()

backend/app/services/mcp/routing.py

@@ -0,0 +1,619 @@
+"""
+MCP Tool Call Routing
+
+Routes tool calls to appropriate servers with retry logic,
+circuit breakers, and request/response serialization.
+"""
+
+import asyncio
+import logging
+import time
+import uuid
+from dataclasses import dataclass, field
+from enum import Enum
+from typing import Any
+
+from .config import MCPServerConfig
+from .connection import ConnectionPool, MCPConnection
+from .exceptions import (
+    MCPCircuitOpenError,
+    MCPError,
+    MCPTimeoutError,
+    MCPToolError,
+    MCPToolNotFoundError,
+)
+from .registry import MCPServerRegistry
+
+logger = logging.getLogger(__name__)
+
+
+class CircuitState(Enum):
+    """Circuit breaker states."""
+
+    CLOSED = "closed"
+    OPEN = "open"
+    HALF_OPEN = "half-open"
+
+
+class AsyncCircuitBreaker:
+    """
+    Async-compatible circuit breaker implementation.
+
+    Unlike pybreaker which wraps sync functions, this implementation
+    provides explicit success/failure tracking for async code.
+    """
+
+    def __init__(
+        self,
+        fail_max: int = 5,
+        reset_timeout: float = 30.0,
+        name: str = "",
+    ) -> None:
+        """
+        Initialize circuit breaker.
+
+        Args:
+            fail_max: Maximum failures before opening circuit
+            reset_timeout: Seconds to wait before trying again
+            name: Name for logging
+        """
+        self.fail_max = fail_max
+        self.reset_timeout = reset_timeout
+        self.name = name
+        self._state = CircuitState.CLOSED
+        self._fail_counter = 0
+        self._last_failure_time: float | None = None
+        self._lock = asyncio.Lock()
+
+    @property
+    def current_state(self) -> str:
+        """Get current state as string."""
+        # Check if we should transition from OPEN to HALF_OPEN
+        if self._state == CircuitState.OPEN:
+            if self._should_try_reset():
+                return CircuitState.HALF_OPEN.value
+        return self._state.value
+
+    @property
+    def fail_counter(self) -> int:
+        """Get current failure count."""
+        return self._fail_counter
+
+    def _should_try_reset(self) -> bool:
+        """Check if enough time has passed to try resetting."""
+        if self._last_failure_time is None:
+            return True
+        return (time.time() - self._last_failure_time) >= self.reset_timeout
+
+    async def success(self) -> None:
+        """Record a successful call."""
+        async with self._lock:
+            self._fail_counter = 0
+            self._state = CircuitState.CLOSED
+            self._last_failure_time = None
+
+    async def failure(self) -> None:
+        """Record a failed call."""
+        async with self._lock:
+            self._fail_counter += 1
+            self._last_failure_time = time.time()
+
+            if self._fail_counter >= self.fail_max:
+                self._state = CircuitState.OPEN
+                logger.warning(
+                    "Circuit breaker %s opened after %d failures",
+                    self.name,
+                    self._fail_counter,
+                )
+
+    def is_open(self) -> bool:
+        """Check if circuit is open (not allowing calls)."""
+        if self._state == CircuitState.OPEN:
+            return not self._should_try_reset()
+        return False
+
+    async def reset(self) -> None:
+        """Manually reset the circuit breaker."""
+        async with self._lock:
+            self._state = CircuitState.CLOSED
+            self._fail_counter = 0
+            self._last_failure_time = None
+
+
+@dataclass
+class ToolInfo:
+    """Information about an available tool."""
+
+    name: str
+    description: str | None = None
+    server_name: str | None = None
+    input_schema: dict[str, Any] | None = None
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert to dictionary."""
+        return {
+            "name": self.name,
+            "description": self.description,
+            "server_name": self.server_name,
+            "input_schema": self.input_schema,
+        }
+
+
+@dataclass
+class ToolResult:
+    """Result of a tool execution."""
+
+    success: bool
+    data: Any = None
+    error: str | None = None
+    error_code: str | None = None
+    tool_name: str | None = None
+    server_name: str | None = None
+    execution_time_ms: float = 0.0
+    request_id: str = field(default_factory=lambda: str(uuid.uuid4()))
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert to dictionary."""
+        return {
+            "success": self.success,
+            "data": self.data,
+            "error": self.error,
+            "error_code": self.error_code,
+            "tool_name": self.tool_name,
+            "server_name": self.server_name,
+            "execution_time_ms": self.execution_time_ms,
+            "request_id": self.request_id,
+        }
+
+
+class ToolRouter:
+    """
+    Routes tool calls to the appropriate MCP server.
+
+    Features:
+    - Tool name to server mapping
+    - Retry logic with exponential backoff
+    - Circuit breaker pattern for fault tolerance
+    - Request/response serialization
+    - Execution timing and metrics
+    """
+
+    def __init__(
+        self,
+        registry: MCPServerRegistry,
+        connection_pool: ConnectionPool,
+    ) -> None:
+        """
+        Initialize the tool router.
+
+        Args:
+            registry: MCP server registry
+            connection_pool: Connection pool for servers
+        """
+        self._registry = registry
+        self._pool = connection_pool
+        self._circuit_breakers: dict[str, AsyncCircuitBreaker] = {}
+        self._tool_to_server: dict[str, str] = {}
+        self._lock = asyncio.Lock()
+
+    def _get_circuit_breaker(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+    ) -> AsyncCircuitBreaker:
+        """Get or create a circuit breaker for a server."""
+        if server_name not in self._circuit_breakers:
+            self._circuit_breakers[server_name] = AsyncCircuitBreaker(
+                fail_max=config.circuit_breaker_threshold,
+                reset_timeout=config.circuit_breaker_timeout,
+                name=f"mcp-{server_name}",
+            )
+        return self._circuit_breakers[server_name]
+
+    async def register_tool_mapping(
+        self,
+        tool_name: str,
+        server_name: str,
+    ) -> None:
+        """
+        Register a mapping from tool name to server.
+
+        Args:
+            tool_name: Name of the tool
+            server_name: Name of the server providing the tool
+        """
+        async with self._lock:
+            self._tool_to_server[tool_name] = server_name
+            logger.debug("Registered tool %s -> server %s", tool_name, server_name)
+
+    async def discover_tools(self) -> None:
+        """
+        Discover all tools from registered servers and build mappings.
+        """
+        for server_name in self._registry.list_enabled_servers():
+            try:
+                config = self._registry.get(server_name)
+                connection = await self._pool.get_connection(server_name, config)
+
+                # Fetch tools from server
+                tools = await self._fetch_tools_from_server(connection)
+
+                # Update registry with capabilities
+                self._registry.set_capabilities(
+                    server_name,
+                    tools=[t.to_dict() for t in tools],
+                )
+
+                # Update tool mappings
+                for tool in tools:
+                    await self.register_tool_mapping(tool.name, server_name)
+
+                logger.info(
+                    "Discovered %d tools from server %s",
+                    len(tools),
+                    server_name,
+                )
+            except Exception as e:
+                logger.warning(
+                    "Failed to discover tools from %s: %s",
+                    server_name,
+                    e,
+                )
+
+    async def _fetch_tools_from_server(
+        self,
+        connection: MCPConnection,
+    ) -> list[ToolInfo]:
+        """Fetch available tools from an MCP server."""
+        try:
+            response = await connection.execute_request(
+                "GET",
+                "/mcp/tools",
+            )
+
+            tools = []
+            for tool_data in response.get("tools", []):
+                tools.append(
+                    ToolInfo(
+                        name=tool_data.get("name", ""),
+                        description=tool_data.get("description"),
+                        server_name=connection.server_name,
+                        input_schema=tool_data.get("inputSchema"),
+                    )
+                )
+            return tools
+        except Exception as e:
+            logger.warning(
+                "Error fetching tools from %s: %s",
+                connection.server_name,
+                e,
+            )
+            return []
+
+    def find_server_for_tool(self, tool_name: str) -> str | None:
+        """
+        Find which server provides a specific tool.
+
+        Args:
+            tool_name: Name of the tool
+
+        Returns:
+            Server name or None if not found
+        """
+        return self._tool_to_server.get(tool_name)
+
+    async def call_tool(
+        self,
+        server_name: str,
+        tool_name: str,
+        arguments: dict[str, Any] | None = None,
+        timeout: float | None = None,
+    ) -> ToolResult:
+        """
+        Call a tool on a specific server.
+
+        Args:
+            server_name: Name of the MCP server
+            tool_name: Name of the tool to call
+            arguments: Tool arguments
+            timeout: Optional timeout override
+
+        Returns:
+            Tool execution result
+        """
+        start_time = time.time()
+        request_id = str(uuid.uuid4())
+
+        logger.debug(
+            "Tool call [%s]: %s.%s with args %s",
+            request_id,
+            server_name,
+            tool_name,
+            arguments,
+        )
+
+        try:
+            config = self._registry.get(server_name)
+            circuit_breaker = self._get_circuit_breaker(server_name, config)
+
+            # Check circuit breaker state
+            if circuit_breaker.is_open():
+                raise MCPCircuitOpenError(
+                    server_name=server_name,
+                    failure_count=circuit_breaker.fail_counter,
+                    reset_timeout=config.circuit_breaker_timeout,
+                )
+
+            # Execute with retry logic
+            result = await self._execute_with_retry(
+                server_name=server_name,
+                config=config,
+                tool_name=tool_name,
+                arguments=arguments or {},
+                timeout=timeout,
+                circuit_breaker=circuit_breaker,
+            )
+
+            execution_time = (time.time() - start_time) * 1000
+
+            return ToolResult(
+                success=True,
+                data=result,
+                tool_name=tool_name,
+                server_name=server_name,
+                execution_time_ms=execution_time,
+                request_id=request_id,
+            )
+
+        except MCPCircuitOpenError:
+            raise
+        except MCPError as e:
+            execution_time = (time.time() - start_time) * 1000
+            logger.error(
+                "Tool call failed [%s]: %s.%s - %s",
+                request_id,
+                server_name,
+                tool_name,
+                e,
+            )
+            return ToolResult(
+                success=False,
+                error=str(e),
+                error_code=type(e).__name__,
+                tool_name=tool_name,
+                server_name=server_name,
+                execution_time_ms=execution_time,
+                request_id=request_id,
+            )
+        except Exception as e:
+            execution_time = (time.time() - start_time) * 1000
+            logger.exception(
+                "Unexpected error in tool call [%s]: %s.%s",
+                request_id,
+                server_name,
+                tool_name,
+            )
+            return ToolResult(
+                success=False,
+                error=str(e),
+                error_code="UnexpectedError",
+                tool_name=tool_name,
+                server_name=server_name,
+                execution_time_ms=execution_time,
+                request_id=request_id,
+            )
+
+    async def _execute_with_retry(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+        tool_name: str,
+        arguments: dict[str, Any],
+        timeout: float | None,
+        circuit_breaker: AsyncCircuitBreaker,
+    ) -> Any:
+        """Execute tool call with retry logic."""
+        last_error: Exception | None = None
+        attempts = 0
+        max_attempts = config.retry_attempts + 1  # +1 for initial attempt
+
+        while attempts < max_attempts:
+            attempts += 1
+
+            try:
+                # Use circuit breaker to track failures
+                result = await self._execute_tool_call(
+                    server_name=server_name,
+                    config=config,
+                    tool_name=tool_name,
+                    arguments=arguments,
+                    timeout=timeout,
+                )
+
+                # Success - record it
+                await circuit_breaker.success()
+                return result
+
+            except MCPCircuitOpenError:
+                raise
+            except MCPTimeoutError:
+                # Timeout - don't retry
+                await circuit_breaker.failure()
+                raise
+            except MCPToolError:
+                # Tool-level error - don't retry (user error)
+                raise
+            except Exception as e:
+                last_error = e
+                await circuit_breaker.failure()
+
+                if attempts < max_attempts:
+                    delay = self._calculate_retry_delay(attempts, config)
+                    logger.warning(
+                        "Tool call attempt %d/%d failed for %s.%s: %s. "
+                        "Retrying in %.1fs",
+                        attempts,
+                        max_attempts,
+                        server_name,
+                        tool_name,
+                        e,
+                        delay,
+                    )
+                    await asyncio.sleep(delay)
+
+        # All attempts failed
+        raise MCPToolError(
+            f"Tool call failed after {max_attempts} attempts",
+            server_name=server_name,
+            tool_name=tool_name,
+            tool_args=arguments,
+            details={"last_error": str(last_error)},
+        )
+
+    def _calculate_retry_delay(
+        self,
+        attempt: int,
+        config: MCPServerConfig,
+    ) -> float:
+        """Calculate exponential backoff delay with jitter."""
+        import random
+
+        delay = config.retry_delay * (2 ** (attempt - 1))
+        delay = min(delay, config.retry_max_delay)
+        # Add jitter (±25%)
+        jitter = delay * 0.25 * (random.random() * 2 - 1)
+        return max(0.1, delay + jitter)
+
+    async def _execute_tool_call(
+        self,
+        server_name: str,
+        config: MCPServerConfig,
+        tool_name: str,
+        arguments: dict[str, Any],
+        timeout: float | None,
+    ) -> Any:
+        """Execute a single tool call."""
+        connection = await self._pool.get_connection(server_name, config)
+
+        # Build MCP tool call request
+        request_body = {
+            "jsonrpc": "2.0",
+            "method": "tools/call",
+            "params": {
+                "name": tool_name,
+                "arguments": arguments,
+            },
+            "id": str(uuid.uuid4()),
+        }
+
+        response = await connection.execute_request(
+            method="POST",
+            path="/mcp",
+            data=request_body,
+            timeout=timeout,
+        )
+
+        # Handle JSON-RPC response
+        if "error" in response:
+            error = response["error"]
+            raise MCPToolError(
+                error.get("message", "Tool execution failed"),
+                server_name=server_name,
+                tool_name=tool_name,
+                tool_args=arguments,
+                error_code=str(error.get("code", "UNKNOWN")),
+            )
+
+        return response.get("result")
+
+    async def route_tool(
+        self,
+        tool_name: str,
+        arguments: dict[str, Any] | None = None,
+        timeout: float | None = None,
+    ) -> ToolResult:
+        """
+        Route a tool call to the appropriate server.
+
+        Automatically discovers which server provides the tool.
+
+        Args:
+            tool_name: Name of the tool to call
+            arguments: Tool arguments
+            timeout: Optional timeout override
+
+        Returns:
+            Tool execution result
+
+        Raises:
+            MCPToolNotFoundError: If no server provides the tool
+        """
+        server_name = self.find_server_for_tool(tool_name)
+
+        if server_name is None:
+            # Try to find from registry
+            server_name = self._registry.find_server_for_tool(tool_name)
+
+        if server_name is None:
+            raise MCPToolNotFoundError(
+                tool_name=tool_name,
+                available_tools=list(self._tool_to_server.keys()),
+            )
+
+        return await self.call_tool(
+            server_name=server_name,
+            tool_name=tool_name,
+            arguments=arguments,
+            timeout=timeout,
+        )
+
+    async def list_all_tools(self) -> list[ToolInfo]:
+        """
+        Get all available tools from all servers.
+
+        Returns:
+            List of tool information
+        """
+        tools = []
+        all_server_tools = self._registry.get_all_tools()
+
+        for server_name, server_tools in all_server_tools.items():
+            for tool_data in server_tools:
+                tools.append(
+                    ToolInfo(
+                        name=tool_data.get("name", ""),
+                        description=tool_data.get("description"),
+                        server_name=server_name,
+                        input_schema=tool_data.get("input_schema"),
+                    )
+                )
+
+        return tools
+
+    def get_circuit_breaker_status(self) -> dict[str, dict[str, Any]]:
+        """Get status of all circuit breakers."""
+        return {
+            name: {
+                "state": cb.current_state,
+                "failure_count": cb.fail_counter,
+            }
+            for name, cb in self._circuit_breakers.items()
+        }
+
+    async def reset_circuit_breaker(self, server_name: str) -> bool:
+        """
+        Manually reset a circuit breaker.
+
+        Args:
+            server_name: Name of the server
+
+        Returns:
+            True if circuit breaker was reset
+        """
+        async with self._lock:
+            if server_name in self._circuit_breakers:
+                # Reset by removing (will be recreated on next call)
+                del self._circuit_breakers[server_name]
+                logger.info("Reset circuit breaker for %s", server_name)
+                return True
+            return False