feat(core): expose droppedEvents() on SegmentClient

Replace fragile log-interception pattern in e2e-cli with a proper
counter on SegmentDestination. The CLI now calls client.droppedEvents()
instead of monkey-patching logger.error and regex-matching drop messages.

- Add droppedEventCount property to SegmentDestination
- Add droppedEvents() accessor on SegmentClient (mirrors pendingEvents)
- Remove interceptDropCount helper from e2e-cli

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abueide

e2e-cli/src/cli.ts

@@ -168,26 +168,6 @@ async function waitForQueueDrain(
   return false;
 }
 
-/**
- * Intercepts logger.error() to count permanently dropped events.
- * Coupled to the log format in SegmentDestination.ts — matches:
- *   "Dropped N events due to permanent errors"
- *   "Dropped N events due to retry limit exceeded"
- */
-function interceptDropCount(logger: Logger): () => number {
-  let count = 0;
-  const origError = logger.error;
-  logger.error = (message?: unknown, ...rest: unknown[]) => {
-    const match = String(message ?? '').match(/Dropped (\d+) events/);
-    if (match) count += parseInt(match[1], 10);
-    origError.call(logger, message, ...rest);
-  };
-  return () => {
-    logger.error = origError;
-    return count;
-  };
-}
-
 // ============================================================================
 // Main
 // ============================================================================
@@ -233,10 +213,9 @@ async function main() {
       }
     }
 
-    const getDropCount = interceptDropCount(logger);
     await client.flush();
     const drained = await waitForQueueDrain(client);
-    const permanentDropCount = getDropCount();
+    const permanentDropCount = client.droppedEvents();
 
     const finalPending = drained ? 0 : await client.pendingEvents();
     const totalEvents = input.sequences.reduce(

packages/core/src/analytics.ts

@@ -1048,6 +1048,20 @@ export class SegmentClient {
 
     return totalEventsCount;
   }
+
+  /**
+   * Method to get count of events permanently dropped by SegmentDestination.
+   */
+  droppedEvents(): number {
+    let count = 0;
+    for (const plugin of this.getPlugins()) {
+      if (plugin instanceof SegmentDestination) {
+        count += plugin.droppedEventCount;
+      }
+    }
+    return count;
+  }
+
   private resumeTimeoutId?: ReturnType<typeof setTimeout>;
   private waitingPlugins = new Set<WaitingPlugin>();
 

packages/core/src/plugins/SegmentDestination.ts

@@ -22,6 +22,7 @@ export const SEGMENT_DESTINATION_KEY = 'Segment.io';
 export class SegmentDestination extends DestinationPlugin {
   type = PluginType.destination;
   key = SEGMENT_DESTINATION_KEY;
+  droppedEventCount = 0;
   private apiHost?: string;
   private settingsResolve: () => void;
   private settingsPromise: Promise<void>;