structured-runtime-logging

# Structured Runtime Logging When logging runtime service identity, emit stable tracing fields instead of recording `RuntimeServiceMetadata`, `ConfigurationInstanceId`, or related structs through `Debug` formatting. Use the canonical fields: - `service_role` — the canonical role identifier, such as `http_tracker`. - `instance_index` — the canonical zero-based configuration instance index. - `service_binding` — the final protocol and bound socket address, after the listener has successfully bound. ## Correct Form Exclude metadata from automatic `#[instrument]` capture and add canonical fields explicitly: ```rust #[instrument( skip(metadata), fields( service_role = metadata.service_role().as_str(), instance_index = metadata.configuration_instance_id().instance_index(), ) )] ``` When a listener binds, log its final `service_binding` as an explicit field. ```rust tracing::info!( service_binding = %service_binding.url(), "Started HTTP tracker" ); ``` The resulting event has stable, queryable fields: ```text INFO start_job{service_role="http_tracker" instance_index=1}: Started HTTP tracker service_binding=http://0.0.0.0:7171 ``` ## Incorrect Form Do not let `#[instrument]` capture the metadata parameter automatically, and do not log the metadata with `?` or `%` formatting: ```rust #[instrument] async fn start(metadata: RuntimeServiceMetadata) { tracing::info!(?metadata, "Started HTTP tracker"); } ``` This creates log output coupled to the Rust struct's `Debug` representation, such as `metadata=RuntimeServiceMetadata { configuration_instance_id: ... }`. It is not a stable, queryable log contract. For example, automatic span capture and `?metadata` produce implementation detail in the log instead of canonical fields: ```text INFO start_job{idx=1 metadata=RuntimeServiceMetadata { configuration_instance_id: ConfigurationInstanceId { service_role: HttpTracker, instance_index: 1 } }}: Started HTTP tracker metadata=RuntimeServiceMetadata { configuration_instance_id: ConfigurationInstanceId { service_role: HttpTracker, instance_index: 1 } } ``` Do not make Rust field names, struct nesting, or a `Debug` implementation an observability contract.