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Decision: MCP Rust SDK

Chose the official modelcontextprotocol/rust-sdk crate rmcp pinned to 2.2.0 for the local history sidecar.

Evaluated 2026-07-13 for the local CodeVetter history sidecar.

Decision

Use the official modelcontextprotocol/rust-sdk crate rmcp pinned to 2.2.0. The production dependency disables default features and enables only server, transport-io, and macros. HTTP/SSE, OAuth, client, child-process, reqwest, and network-server features are absent. The test-only dependency additionally enables client for real lifecycle/framing tests.

The current stable protocol remains 2025-11-25. The SDK also contains later revision support, but CodeVetter declares the stable revision and lets the SDK’s negotiation layer handle compatible clients. The 2026-07-28 protocol was still a release candidate on the evaluation date and is not the advertised baseline.

Why this dependency

The official SDK owns JSON-RPC framing, initialization/version negotiation, capability routing, cancellation plumbing, MCP error types, schema models, stdio concurrency, and backward-compatible resource-not-found behavior. Reimplementing those protocol mechanics would add more security and interoperability risk than the dependency saves. CodeVetter still owns authorization, canonical queries, redaction, limits, cursor validation, and product semantics.

License, security, and dependency surface

  • License: Apache-2.0.
  • Upstream: https://github.com/modelcontextprotocol/rust-sdk
  • Production feature closure: server + async read/write codec + stdio + schema support and macros. Direct runtime families are Tokio/Tokio-util, Serde, Schemars, Futures, Tracing, Chrono, Thiserror, and the SDK macros. Most were already present in the desktop dependency graph.
  • Explicitly absent from the selected production features: reqwest, HTTP server, SSE, OAuth, JWT, URL-based elicitation, child-process client, and network transports.
  • The upstream GitHub security/advisory review and GitHub Advisory Database search on 2026-07-13 found no published advisory specifically for rmcp 2.2.0. The local environment did not have cargo-audit, so this is a dated review, not a claim that future advisories cannot exist. CI should add an ecosystem advisory scanner when the fleet standard provides one.

Measured distribution cost

The Apple Silicon release sidecar is 7.04 MiB and idles at 12.31 MiB RSS. That binary size includes CodeVetter’s shared graph/history/SQLite code and linked desktop crate surface, so it is an upper bound—not an attribution of 6.80 MiB to rmcp. Tauri packages the target-suffixed executable beside the app and applies the same app signing/notarization pipeline. A local build is linker ad-hoc signed; the signed release artifact remains the distribution proof.

The final release-binary benchmark on 2026-07-14 used a 10,000-event fixture and measured cold initialize at 5.28 ms p50 / 7.90 ms p95. Steady compact queries were 2.16–2.34 ms p50 and 2.43–2.56 ms p95, with 1.4–2.0 KiB responses; resource listing was 2.15 ms. The 25-launch sample contained one 442.81 ms cold outlier. An earlier small fixture measured 5.30 ms / 6.18 ms cold p50/p95 and 1.37–1.40 ms warm p50. Both runs verified zero TCP listeners and no target-repository mutation. The benchmark should be rerun after any SDK, linking, schema, audit, or packaging change.

Rust versus Go

Keep the sidecar in Rust. Its canonical graph/history services and SQLite types already live in Rust, so a Go process would either duplicate product semantics or add another IPC boundary back into Rust. With warm queries around 2.2 ms, 12 MiB RSS, a single 7.0 MiB packaged binary, and no runtime download, there is no measured latency or distribution gap for Go to recover. A Go prototype is justified only if a future isolated workload has an end-to-end benchmark—including process startup, serialization, memory, signing, artifact size, and maintenance—that beats this baseline materially.

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