perf: integrate go-sdk schema caching optimization (Phase 1)

[Copilot]

Closes: #767

Integrates schema caching optimization from go-sdk fork to eliminate expensive reflection-based schema generation on every AddTool call. Critical for stateless server patterns where a new server is created per HTTP request.

Benchmark improvements:

• 132x faster tool registration
• 51x fewer allocations
• 19% faster per-tool-call validation

Changes

• Added replace directive in go.mod pointing to github.com/SamMorrowDrums/go-sdk fork with schema caching
• Updated go.sum with fork dependencies
• Updated third-party license files via script/licenses

No code changes required—optimization is transparent to integrators.

Tradeoffs

Using a fork temporarily until the optimization is merged upstream. The fork tracks the perf/phase1-schema-cache branch from SamMorrowDrums/go-sdk#1.

Alternatives

Could wait for upstream merge, but the performance impact on stateless server patterns is significant enough to warrant immediate integration.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>perf: integrate go-sdk schema caching optimization (Phase 1)</issue_title>
<issue_description>## Summary

Integrate the schema caching optimization from the go-sdk fork to dramatically improve tool registration performance.

Background

The go-sdk currently performs expensive reflection-based schema generation on every AddTool call. In stateless server patterns (like github-mcp-server where a new server is created per HTTP request), this causes significant overhead.

The optimization adds automatic schema caching that provides:

• 132x faster tool registration
• 51x fewer allocations
• 19% faster per-tool-call validation

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 v0.0.0-20251204132239-46310a70a79a

Or use the branch reference:

replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk perf/phase1-schema-cache

2. Run go mod tidy

go mod tidy

3. Verify all tests pass

go test ./...

Expected Impact

No code changes should be required in github-mcp-server. The optimization is automatic and transparent to integrators.

Fork Branch

• Repository: https://github.com/SamMorrowDrums/go-sdk
• Branch: perf/phase1-schema-cache
• PR: perf: add schema caching to avoid repeated reflection SamMorrowDrums/go-sdk#1

Benchmark Results

BenchmarkAddTool_TypedHandler-22          977080    1223 ns/op     1208 B/op    21 allocs/op
BenchmarkAddTool_TypedHandler_NoCache-22    6764  161463 ns/op    39262 B/op  1072 allocs/op
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes perf: integrate go-sdk schema caching optimization (Phase 1) #1530

---

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[SamMorrowDrums]

@copilot Run licenses check

[Copilot]

@copilot Run licenses check

Ran script/licenses and the license check now passes. Updated third-party license files committed in bc465b4.

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• go.yaml.in
  • Triggering command: /home/REDACTED/go/bin/go-licenses go-licenses report ./... --template .github/licenses.tmpl -c=4 -nolocalimports -importcfg /tmp/go-build2213730874/b348/importcfg -pack /home/REDACTED/go/pkg/mod/k8s.io/klog/[email protected]/internal/buffer/buffer.go x64/pkg/tool/lin-I (dns block)
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• gopkg.in
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  • Triggering command: /home/REDACTED/go/bin/go-licenses go-licenses report ./... --template .github/licenses.tmpl -D GOAMD64_v1 -o /tmp/go-build2213730874/b356/debug.o /opt/hostedtoolcache/go/1.24.10/x64/src/runtime/debug/debug.s (dns block)
  • Triggering command: /home/REDACTED/go/bin/go-licenses go-licenses report ./... --template .github/licenses.tmpl -c=4 -nolocalimports -importcfg /tmp/go-build2213730874/b365/importcfg -pack /home/REDACTED/go/pkg/mod/golang.org/x/[email protected]/internal/tag/tag.go x64/pkg/tool/lin-I (dns block)

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[SamMorrowDrums]

Update Required

The upstream go-sdk PR has been cleaned up based on reviewer feedback. The input validation optimization (ApplyDefaults on structs) was removed because it's fundamentally broken per the jsonschema-go maintainer.

What changed in go-sdk PR #685:

• ❌ Removed: Input validation optimization commit (ApplyDefaults is broken for structs)
• ✅ Kept: Schema caching (the main performance win)
• ✅ Fixed: Use sync.Map.Clear() instead of reassignment
• ✅ Fixed: Removed underscores from benchmark names

New commit to reference:

replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk v0.0.0-20251205102140-988974db6bfb

The old commit 46310a70a79a includes the broken input validation optimization. This PR needs to be updated to use the new commit 988974db6bfb.

Performance impact: Still get the 132x faster tool registration from schema caching, just without the per-call validation optimization (which was wrong anyway).