feat(telemetry): Add telemetry and metrics for model routing (#8518)

packages/core/src/routing/modelRouterService.ts

@@ -16,6 +16,9 @@ import { CompositeStrategy } from './strategies/compositeStrategy.js';
 import { FallbackStrategy } from './strategies/fallbackStrategy.js';
 import { OverrideStrategy } from './strategies/overrideStrategy.js';
 
+import { logModelRouting } from '../telemetry/loggers.js';
+import { ModelRoutingEvent } from '../telemetry/types.js';
+
 /**
  * A centralized service for making model routing decisions.
  */
@@ -49,12 +52,55 @@ export class ModelRouterService {
    * @returns A promise that resolves to a RoutingDecision.
    */
   async route(context: RoutingContext): Promise<RoutingDecision> {
-    const decision = await this.strategy.route(
-      context,
-      this.config,
-      this.config.getBaseLlmClient(),
-    );
+    const startTime = Date.now();
+    let decision: RoutingDecision;
 
-    return decision;
+    try {
+      decision = await this.strategy.route(
+        context,
+        this.config,
+        this.config.getBaseLlmClient(),
+      );
+
+      const event = new ModelRoutingEvent(
+        decision.model,
+        decision.metadata.source,
+        decision.metadata.latencyMs,
+        decision.metadata.reasoning,
+        false, // failed
+        undefined, // error_message
+      );
+      logModelRouting(this.config, event);
+
+      return decision;
+    } catch (e) {
+      const failed = true;
+      const error_message = e instanceof Error ? e.message : String(e);
+      // Create a fallback decision for logging purposes
+      // We do not actually route here. This should never happen so we should
+      // fail loudly to catch any issues where this happens.
+      decision = {
+        model: this.config.getModel(),
+        metadata: {
+          source: 'router-exception',
+          latencyMs: Date.now() - startTime,
+          reasoning: 'An exception occurred during routing.',
+          error: error_message,
+        },
+      };
+
+      const event = new ModelRoutingEvent(
+        decision.model,
+        decision.metadata.source,
+        decision.metadata.latencyMs,
+        decision.metadata.reasoning,
+        failed,
+        error_message,
+      );
+
+      logModelRouting(this.config, event);
+
+      throw e;
+    }
   }
 }