Implement WASI-MCP component model interfaces and reference implementation

[avrabe]

Summary

Implement the WASI-MCP proposal as a reference implementation, providing WebAssembly Component Model interfaces for the Model Context Protocol with async support and host integration.

Background

The WASI-MCP proposal defines a standardized WebAssembly interface for MCP that enables:

• Async-first architecture with future<T> and stream<T> types
• Multi-interface design separating types, server, client, and streaming
• Resource-based security model using WebAssembly's capability system
• Integration with WASI Preview3 async patterns

This implementation will serve as the reference for the proposal and enable MCP servers to run as secure, sandboxed WebAssembly components.

Implementation Tasks

WIT Interface Definitions

• Create wit/ directory with interface definitions
• Implement types.wit - Core types and error handling
• Implement server.wit - Async server operations interface
• Implement client.wit - Service consumption interface
• Implement streaming.wit - Large data and long-running tool support

Core Component Implementation

• Create pulseengine-mcp-wasi crate for component implementation
• Generate Rust bindings using wit-bindgen
• Implement async server component wrapper
• Create client component implementation
• Add streaming operations support

Resource Management

• Implement WebAssembly resource handles for MCP entities
• Create capability-based security model
• Add resource lifecycle management
• Implement sandboxed execution context

Async Support (WASI Preview3)

• Integrate with Preview3 async patterns
• Implement future<T> operations for non-blocking calls
• Add stream<T> support for large data transfers
• Create cancellation and progress monitoring

Host Integration Layer

• Design host-side component instantiation
• Implement component composition and linking
• Add inter-component communication
• Create host resource provision

Error Handling & Diagnostics

• Implement comprehensive error types
• Add structured error reporting
• Create debugging and profiling hooks
• Add component health monitoring

Integration with Existing Framework

Protocol Mapping

• Map existing MCP protocol types to WASI-MCP interfaces
• Create bidirectional conversion utilities
• Ensure feature parity with stdio/HTTP transports
• Add protocol version negotiation

Framework Integration

• Integrate with pulseengine-mcp-server framework
• Add component-based server deployment
• Create development and testing tools
• Add documentation and examples

WRT Integration (Separate Issue)

• Interface with WRT WebAssembly interpreter
• Provide host implementation reference
• Create secure component execution environment

Example Usage

// Component interface definition
use pulseengine_mcp_wasi::*;

#[async_trait]
impl McpServer for MyServer {
    async fn list_resources(&self) -> Result<Vec<Resource>, McpError> {
        // Implementation
    }
    
    async fn call_tool(&self, name: String, args: Value) -> Result<ToolResult, McpError> {
        // Implementation  
    }
}

// Host-side instantiation
let component = Component::from_file("my_server.wasm")?;
let server = McpServerComponent::new(component)?;
let result = server.list_resources().await?;

Acceptance Criteria

• Complete WIT interface definitions matching proposal
• Reference implementation compiles for wasm32-wasip2
• Async operations work correctly in component context
• Resource management prevents capability leaks
• Host integration provides secure sandboxing
• Performance comparable to native MCP implementations
• Comprehensive test suite and examples

Related Issues

• WASM32-WASIP2 Target Support (Add WASM32-WASIP2 target support for WebAssembly deployment #26)
• WRT Integration Layer (#TBD)
• Component Model Examples (#TBD)

References

• WASI-MCP Proposal
• WebAssembly Component Model
• WASI Preview3 Async Specification
• WIT Interface Definition Language