codegen-resolver

Codegen Sandbox via MCP Endpoint Resolver

SDK example exercising sdk.WithMCPEndpoints — pack declares the MCP server by name only, host injects the lookup.

What this shows

• sdk.NewMCPServerByName("codegen") — declare an MCP server with no URL/Command. The pack-author surface stays free of provisioning concerns.
• sdk.WithMCPEndpoints(resolver) — host injects a single resolver. At conversation open the SDK calls resolver.Resolve("codegen") and plugs the URL+Headers into the runtime MCP registry.
• Real model + real container. Claude Sonnet 4.6 talks to the codegen-sandbox via the resolved endpoint, writes a Go module from scratch, runs the tests.

In production your resolver would call a sandbox pool, service discovery, or some host-managed orchestrator. Here it's a tiny StaticMCPEndpointResolver and the example provisions the container itself for a single self-contained demo.

Prerequisites

• Docker daemon running.
• ANTHROPIC_API_KEY in environment.
• ghcr.io/altairalabs/codegen-sandbox:latest pulled (or the example pulls it on first docker run).

Run

export ANTHROPIC_API_KEY=...
docker pull ghcr.io/altairalabs/codegen-sandbox:latest
go run .

Expected output:

sandbox ready: http://localhost:42813 (container 5f3a92b1c0d4)
=== Agent reply ===
All 7 tests pass with 100% coverage. ...

The container is stopped + removed on exit.

Cost

A single run is typically 5–10k input + ~1k output tokens against Sonnet ≈ $0.05–$0.10.

See also

• The arena variant: examples/codegen-anthropic/ — same idea but driven through arena's source-backed MCP machinery instead of an SDK resolver. Better for batch evaluation.
• sdk/examples/mcp-tools/ — non-resolver MCP example (declare with WithMCP("name", "command", args...)).