MAJOR from the 2026-04-22 review (crates/mcp/src/main.rs:26-30): the
stdio transport logged malformed JSON lines to stderr and continued
without sending any JSON-RPC response. Clients saw silence instead of
the -32700 Parse Error they could key off. handle_message has a
parse-error branch for shape mismatch, but it never ran for bytes
that failed to parse as JSON at all.
Exposes a new public helper kon_mcp::parse_error_response(detail)
that mirrors the existing internal error_response pattern, filling
id with null per JSON-RPC 2.0 §5.1 (parse error, no id recoverable).
main.rs now writes that response out before continuing the read
loop.
Regression test on the helper asserts: jsonrpc "2.0", id null,
code -32700, message starts with "Parse error" and includes the
underlying serde detail.
Jake
d25b095788