add-binding-feature

# Add a Binding Feature ## Companion Guidance Use `karpathy-guidelines` alongside this skill for implementation or review work. Keep changes scoped, surface assumptions, and define focused validation before editing. Use this skill when a change affects the public runtime surface and must stay in parity across the Rust core, FFI, and one or more bindings. Do not use this skill for: - Internal-only core refactors with no public API change - Binding-local bug fixes that do not change shared behavior - Docs-only or example-only updates ## Implementation Order 1. **Core Rust** Implement the behavior first in `crates/core/src/api/` and related core modules such as `crates/core/src/api/runtime/`, `crates/core/src/codec/`, or `crates/core/src/json.rs`. 2. **FFI / shared C surface** Add or update FFI wrappers in the relevant `crates/ffi/src/api/*.rs` module, re-export them through `crates/ffi/src/api/mod.rs`, and ensure the generated `crates/ffi/nemo_relay.h` stays correct. 3. **Language-native bindings** Update Python, Go, and Node.js for every surface that should expose the capability. 4. **Language wrapper helpers** Update Python wrapper modules, Go shorthand packages, typed helpers, or adaptive/plugin helpers if the new behavior belongs there. 5. **Docs and examples** Update reference docs, language-binding docs, and examples when the public surface or expected usage changed. 6. **Validation** Run the validation matrix from the `valida...