maintain-observability

# Maintain Observability Surfaces Use this skill when changing event fields, exporter behavior, subscriber config, or binding parity for ATIF or the `full`, `gen_ai`, and `openinference` OpenTelemetry projections. ## Surfaces To Keep In Sync - Core event model and emitted fields - `crates/core/src/observability/atif.rs` - `crates/core/src/observability/otel.rs` - `crates/core/src/observability/openinference.rs` - FFI and binding-native wrappers where the config or lifecycle is exposed - Python, Go, and Node.js config objects and subscriber/exporter methods - Observability config version 3, where one `opentelemetry` section contains typed endpoints and OpenInference has no standalone public surface - Docs under `docs/about-nemo-relay/concepts/subscribers.mdx` and `docs/configure-plugins/observability/` ## Design Checklist - [ ] Is this an event-model change, exporter-config change, or lifecycle change? - [ ] Do all bindings expose the same logical knobs and semantics? - [ ] Does every OpenTelemetry endpoint require a type and nonblank destination? - [ ] Does each endpoint resolve `header_env` values at activation and reject missing, blank, or duplicate headers? - [ ] Do layered ATOF sink, ATIF storage, and OpenTelemetry endpoint lists concatenate with higher-precedence entries first? - [ ] Are OpenTelemetry and OpenInference dependencies unconditional rather than Cargo feature-gated? - [ ] Does `gen_ai` avoid `nemo_relay.*`, project sanitized LLM instructions ...