fix(node): use process.on instead of process.once for beforeExit listener

Fixes the beforeExit listener to fire on every invocation in serverless
warm starts (e.g. AWS Lambda). Also properly removes the old listener on
re-init to avoid accumulation.

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

Author: chargome

packages/node-core/src/integrations/nodeRuntimeMetrics.ts

@@ -94,6 +94,7 @@ export const nodeRuntimeMetricsIntegration = defineIntegration((options: NodeRun
   const needsCpu = collect.cpuUtilization || collect.cpuTime;
 
   let intervalId: ReturnType<typeof setInterval> | undefined;
+  let beforeExitListener: (() => void) | undefined;
   let prevCpuUsage: NodeJS.CpuUsage | undefined;
   let prevElu: ReturnType<typeof performance.eventLoopUtilization> | undefined;
   let prevFlushTime: number = 0;
@@ -192,20 +193,26 @@ export const nodeRuntimeMetricsIntegration = defineIntegration((options: NodeRun
       }
       prevFlushTime = _INTERNAL_safeDateNow();
 
-      // Guard against double setup (e.g. re-init).
+      // Guard against double setup (e.g. re-init): clean up previous resources.
       if (intervalId) {
         clearInterval(intervalId);
       }
+      if (beforeExitListener) {
+        process.off('beforeExit', beforeExitListener);
+      }
+
       intervalId = setInterval(collectMetrics, collectionIntervalMs);
       // Do not keep the process alive solely for metric collection.
       intervalId.unref();
 
-      // Collect and flush at the end of every invocation. In non-serverless environments
-      // flushIfServerless is a no-op, so this is safe to call unconditionally.
-      process.once('beforeExit', () => {
+      // Collect and flush at the end of every invocation. Uses process.on (not once) so
+      // that serverless warm starts (e.g. Lambda) trigger a flush on every invocation.
+      // In non-serverless environments flushIfServerless is a no-op.
+      beforeExitListener = () => {
         collectMetrics();
         void flushIfServerless();
-      });
+      };
+      process.on('beforeExit', beforeExitListener);
     },
   };
 });