The runtime already framed JSON-RPC initialize traffic over stdio, so this extends the same transport with typed helpers for tools/list, tools/call, resources/list, and resources/read plus fake-server tests that exercise real request/response roundtrips.
Constraint: Must build on the existing stdio JSON-RPC framing rather than introducing a separate MCP client layer
Rejected: Leave method payloads as untyped serde_json::Value blobs | weakens call sites and test assertions
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep new MCP stdio methods aligned with upstream MCP camelCase field names when adding more request/response types
Tested: cargo fmt --manifest-path rust/Cargo.toml --all; cargo clippy --manifest-path rust/Cargo.toml -p runtime --all-targets -- -D warnings; cargo test --manifest-path rust/Cargo.toml -p runtime
Not-tested: Live integration against external MCP servers
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