New cmd/mcpd binary using github.com/modelcontextprotocol/go-sdk
v1.5.0 over stdio transport. Exposes Lakehouse capabilities as MCP
tools: list_datasets, get_manifest, query_sql, embed_text,
search_vectors. Each tool proxies to the gateway via HTTP.
Replaces the MCP-tool subset of the Rust system's Bun mcp-server.ts
(the audit's "split this 2520-line empire" finding from R-005). HTTP
demo routes (the staffing co-pilot UI at /api/intelligence/*,
/headshots/*, etc.) stay Bun until G5 cutover — those are demo-
specific and depend on matrix-indexer signals not yet ported.
Architecture:
cmd/mcpd/main.go (235 LoC)
main() reads --gateway flag, builds server via buildServer(),
runs on StdioTransport. Each tool's args is a typed struct with
jsonschema tags (the SDK's canonical pattern); reflection
generates the JSON Schema automatically.
gatewayClient: thin HTTP wrapper over the configured gateway URL.
30s per-request timeout. 16 MiB tool-response cap. Non-2xx
surfaces as IsError CallToolResult (NOT as transport error) so
the LLM caller sees the error text and can decide how to react.
proxy() handles GET + POST + JSON body uniformly. errorResult()
+ jsonResult() helpers normalize CallToolResult shape.
cmd/mcpd/main_test.go (13 test funcs)
Tests the full MCP wire end-to-end without a subprocess: spin
up a fake gateway via httptest, build the MCP server pointed at
it, connect a client via in-memory transports (NewInMemoryTransports),
call each tool. Each tool gets:
- happy path (gateway returns 200 → tool returns content)
- input validation (missing required fields → IsError)
- upstream error (gateway 4xx → tool returns IsError)
Plus TestListTools verifies all 5 tools register; TestGatewayUnreachable
verifies network-level failures surface as IsError, not panics.
Setup for Claude Desktop / Code documented in README:
{
"mcpServers": {
"lakehouse": {
"command": "/path/to/bin/mcpd",
"args": ["--gateway", "http://127.0.0.1:3110"]
}
}
}
Verified:
go test -count=1 ./cmd/mcpd/ — 13/13 green
just verify — vet + test + 9 smokes 35s
Out of scope for this commit:
- Resources (mcp.AddResource): not needed yet; tools cover the
interactive surface. Add when an LLM-side use case shows up.
- Prompts (mcp.AddPrompt): same.
- Streamable transports (HTTP, SSE): stdio is the universal one;
streamable can be added with srv.Run(ctx, &mcp.StreamableHTTPHandler{})
swap if a daemon-mode deploy makes sense.
- mcpd inside the daemon-supervised stack: it's stdio-only and
spawned by the MCP client, not run as a service. Adding a
daemon-mode (HTTP transport on a port) is a follow-up if MCP
consumers want long-lived sessions.
This is a tool-surface only port. The Bun mcp-server.ts also serves
HTTP demo routes (/api/catalog/datasets, /intelligence/*, /headshots/*)
that depend on the matrix-indexer signals from the Rust system; those
stay Bun until G5 cutover when the staffing co-pilot service ports
to Go.
Direct deps added:
github.com/modelcontextprotocol/go-sdk v1.5.0
Transitive (resolved by go mod tidy):
github.com/google/jsonschema-go v0.4.2
github.com/yosida95/uritemplate/v3 v3.0.2
golang.org/x/oauth2 v0.35.0
github.com/segmentio/encoding v0.5.4
github.com/golang-jwt/jwt/v5 v5.3.1
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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