Interceptor interfaces and types for MCP client tool call lifecycle management.
This module provides an interceptor interface for wrapping and controlling MCP tool call execution with a handler callback pattern.
In the future, we might add more interceptors for other parts of the request / result lifecycle, for example to support elicitation.
Tool execution request passed to MCP tool call interceptors.
This tool call request follows a similar pattern to LangChain's ToolCallRequest (flat namespace) rather than separating the call data and context into nested objects.
Modifiable fields (override these to change behavior): name: Tool name to invoke. args: Tool arguments as key-value pairs. headers: HTTP headers for applicable transports (SSE, HTTP).
Context fields (read-only, use for routing/logging): server_name: Name of the MCP server handling the tool. runtime: LangGraph runtime context (optional, None if outside graph).
Protocol for tool call interceptors using handler callback pattern.
Interceptors wrap tool execution to enable request/response modification, retry logic, caching, rate limiting, and other cross-cutting concerns. Multiple interceptors compose in "onion" pattern (first is outermost).
The handler can be called multiple times (retry), skipped (caching/short-circuit), or wrapped with error handling. Each handler call is independent.
Similar to LangChain's middleware pattern but adapted for MCP remote tools.
