Add opt-in observations for distributed action costs

crates/sail-common/src/config/application.rs

@@ -943,6 +943,7 @@ pub struct FlightConfig {
 #[serde(deny_unknown_fields)]
 pub struct TelemetryConfig {
     pub export_traces: bool,
+    pub c2_observer: bool,
     pub export_metrics: bool,
     pub export_logs: bool,
     pub exporter: TelemetryExporterConfig,

crates/sail-common/src/config/application.yaml

@@ -975,6 +975,15 @@
   description: Whether to export traces to an OpenTelemetry collector.
   experimental: true
 
+- key: telemetry.c2_observer
+  type: boolean
+  default: "false"
+  description: >-
+    Observe existing planning and execution calls for C2 through the configured
+    trace exporter. Requires telemetry.export_traces and an OTLP endpoint.
+    Durations overlap and do not form an additive execution breakdown.
+  experimental: true
+
 - key: telemetry.export_metrics
   type: boolean
   default: "false"