perf: integrate go-sdk mcpgen code generator (Phase 3)

[SamMorrowDrums]

Summary

Integrate the mcpgen code generator from the go-sdk fork to generate zero-reflection schema implementations for all tool input types.

Background

Building on Phase 1 (schema caching) and Phase 2 (SchemaProvider interface), this phase uses the mcpgen code generator to automatically generate SchemaProvider implementations, achieving zero runtime reflection.

Implementation

1. Update go.mod to use the fork

Add a replace directive to use the optimized fork:

replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk v0.0.0-20251204142831-b450c9exxxxx

Or use the branch reference:

replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk perf/phase3-mcpgen

2. Install mcpgen

go install github.com/SamMorrowDrums/go-sdk/cmd/mcpgen@perf/phase3-mcpgen

3. Add go:generate directives to tool input types

For each package with tool input structs, add generate directives:

// pkg/github/search.go
//go:generate mcpgen -type=SearchRepositoriesInput,SearchCodeInput,SearchUsersInput

4. Run go generate

go generate ./...

This creates *_mcp_gen.go files with SchemaProvider implementations.

5. Verify all tests pass

go test ./...

Example Generated Code

For a type like:

type CreateIssueInput struct {
    Title string `json:"title" jsonschema:"required,description=Issue title"`
    Body  string `json:"body"`
}

mcpgen generates:

// Code generated by mcpgen. DO NOT EDIT.

var _createissueinputSchema = &jsonschema.Schema{
    Type: "object",
    Properties: map[string]*jsonschema.Schema{
        "title": {Type: "string", Description: "Issue title"},
        "body":  {Type: "string"},
    },
    Required: []string{"title"},
}
var _createissueinputResolved, _ = _createissueinputSchema.Resolve(nil)

func (CreateIssueInput) MCPSchema() *jsonschema.Schema {
    return _createissueinputSchema
}

func (CreateIssueInput) MCPResolvedSchema() *jsonschema.Resolved {
    return _createissueinputResolved
}

Expected Impact

• Zero runtime reflection for schema generation
• Pre-resolved schemas skip resolution step
• Compile-time validation of schema correctness

Fork Branch

• Repository: https://github.com/SamMorrowDrums/go-sdk
• Branch: perf/phase3-mcpgen
• PR: feat: add mcpgen code generator for zero-reflection schemas SamMorrowDrums/go-sdk#3

Dependencies

This builds on:

• Phase 1: perf: integrate go-sdk schema caching optimization (Phase 1) #1530
• Phase 2: perf: integrate go-sdk SchemaProvider interface (Phase 2) #1531