Verify and document MCP server handler context concurrency safety

[Copilot]

Addresses question: Is the request context in the server handler concurrency-safe?

Answer: Yes. Each request receives an isolated context.Context from the MCP framework. No context mutation occurs (WithValue() not used). Shared state uses sync.Map.

Changes

• Test: TestConcurrentHandlerInvocations - 20 concurrent handler invocations, passes with race detector
• Documentation: CONCURRENCY.md - Details isolation guarantees and thread-safety mechanisms
• Code comments: Document safety guarantees in NewTool()

Safety Mechanisms

Handler: func(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
    // ctx is unique per request - no sharing between concurrent invocations
    var req R
    request.BindArguments(&req)
    resp, err := handler(ctx, req)  // isolated execution
    // ...
}

type ASTReadTools struct {
    repos sync.Map  // thread-safe for concurrent reads
    // ...
}

Original prompt

server handler 中的 request context 是并发安全的么？

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