[codex] Guard subprocess MCP client initialize protocol

[Atomics-hub]

Summary

• Extend the subprocess MCP initialize release-audit smoke to cover invalid client initialize.protocolVersion.
• Prove bad client initialize params fail closed before downstream forwarding, keep the session unready, and do not return or log the raw client protocol marker.
• Keep the existing downstream unsupported-protocol redaction coverage in the same release-audit row.

Why

The local subprocess stdio proxy is the v0.1 operator path. Client-side initialization variants should fail before they cross the boundary, while downstream initialization failures should remain sanitized.

Verification

• cargo fmt --check
• cargo test release_audit_subprocess_mcp_proxy_initialize_guard_smoke_rejects_bad_protocols -- --nocapture
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo run --locked -- release-audit