The dirty stdio slice had two real regressions in its new JSON-RPC test coverage: the embedded Python helper was written with broken string literals, and direct execution of the freshly written helper could fail with ETXTBSY on Linux. The repair keeps scope inside mcp_stdio.rs by fixing the helper strings and invoking the JSON-RPC helper through python3 while leaving the existing stdio process behavior unchanged.
Constraint: Keep the repair limited to rust/crates/runtime/src/mcp_stdio.rs
Constraint: Must satisfy fmt, clippy -D warnings, and runtime tests before shipping
Rejected: Revert the entire JSON-RPC stdio coverage addition | unnecessary once the helper/test defects were isolated
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep ephemeral stdio test helpers portable and avoid directly execing freshly written scripts when an interpreter invocation is sufficient
Tested: cargo fmt --all; cargo clippy -p runtime --all-targets -- -D warnings; cargo test -p runtime
Not-tested: Cross-platform behavior outside the current Linux runtime
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