From 143bb63483ad432cb3184a693e95f7a7179cb563 Mon Sep 17 00:00:00 2001
From: Gaurav <39389231+gsquared94@users.noreply.github.com>
Date: Wed, 7 Jan 2026 11:26:25 -0800
Subject: [PATCH] Add exp.gws_experiment field to LogEventEntry (#16062)

---
 .../clearcut-logger/clearcut-logger.test.ts   | 58 +++++++++++++++++--
 .../clearcut-logger/clearcut-logger.ts        | 25 +++++---
 2 files changed, 71 insertions(+), 12 deletions(-)

diff --git a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.test.ts b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.test.ts
index c7cc10cdaa..349fa182eb 100644
--- a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.test.ts
+++ b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.test.ts
@@ -93,6 +93,22 @@ expect.extend({
         `event ${received} ${isNot ? 'has' : 'does not have'} the metadata key ${key}`,
     };
   },
+
+  toHaveGwsExperiments(received: LogEventEntry[], exps: number[]) {
+    const { isNot } = this;
+    const gwsExperiment = received[0].exp?.gws_experiment;
+
+    const pass =
+      gwsExperiment !== undefined &&
+      gwsExperiment.length === exps.length &&
+      gwsExperiment.every((val, idx) => val === exps[idx]);
+
+    return {
+      pass,
+      message: () =>
+        `exp.gws_experiment ${JSON.stringify(gwsExperiment)} does${isNot ? '' : ' not'} match ${JSON.stringify(exps)}`,
+    };
+  },
 });
 
 vi.mock('../../utils/userAccountManager.js');
@@ -850,19 +866,53 @@ describe('ClearcutLogger', () => {
   });
 
   describe('logExperiments', () => {
-    it('logs an event with gws_experiment field containing exp ids', () => {
+    it('async path includes exp.gws_experiment field with experiment IDs', async () => {
       const { logger } = setup();
-      const event = new AgentStartEvent('agent-123', 'TestAgent');
+      const event = logger!.createLogEvent(EventNames.START_SESSION, []);
 
-      logger?.logAgentStartEvent(event);
+      await logger?.enqueueLogEventAfterExperimentsLoadAsync(event);
+      await vi.runAllTimersAsync();
 
       const events = getEvents(logger!);
       expect(events.length).toBe(1);
-      expect(events[0]).toHaveEventName(EventNames.AGENT_START);
+      expect(events[0]).toHaveEventName(EventNames.START_SESSION);
+      // Both metadata and exp.gws_experiment should be populated
       expect(events[0]).toHaveMetadataValue([
         EventMetadataKey.GEMINI_CLI_EXPERIMENT_IDS,
         '123,456,789',
       ]);
+      expect(events[0]).toHaveGwsExperiments([123, 456, 789]);
+    });
+
+    it('async path includes empty gws_experiment array when no experiments', async () => {
+      const { logger } = setup({
+        config: {
+          experiments: {
+            experimentIds: [],
+          },
+        } as unknown as Partial<ConfigParameters>,
+      });
+      const event = logger!.createLogEvent(EventNames.START_SESSION, []);
+
+      await logger?.enqueueLogEventAfterExperimentsLoadAsync(event);
+      await vi.runAllTimersAsync();
+
+      const events = getEvents(logger!);
+      expect(events.length).toBe(1);
+      expect(events[0]).toHaveGwsExperiments([]);
+    });
+
+    it('non-async path does not include exp.gws_experiment field', () => {
+      const { logger } = setup();
+      const event = new AgentStartEvent('agent-123', 'TestAgent');
+
+      // logAgentStartEvent uses the non-async enqueueLogEvent path
+      logger?.logAgentStartEvent(event);
+
+      const events = getEvents(logger!);
+      expect(events.length).toBe(1);
+      // exp.gws_experiment should NOT be present for non-async events
+      expect(events[0][0].exp).toBeUndefined();
     });
   });
 
diff --git a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
index 443f9365c9..f3fc7e1347 100644
--- a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
+++ b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
@@ -106,6 +106,9 @@ export interface LogResponse {
 export interface LogEventEntry {
   event_time_ms: number;
   source_extension_json: string;
+  exp?: {
+    gws_experiment: number[];
+  };
 }
 
 export interface EventValue {
@@ -250,7 +253,7 @@ export class ClearcutLogger {
     ClearcutLogger.instance = undefined;
   }
 
-  enqueueHelper(event: LogEvent): void {
+  enqueueHelper(event: LogEvent, experimentIds?: number[]): void {
     // Manually handle overflow for FixedDeque, which throws when full.
     const wasAtCapacity = this.events.size >= MAX_EVENTS;
 
@@ -258,12 +261,18 @@ export class ClearcutLogger {
       this.events.shift(); // Evict oldest element to make space.
     }
 
-    this.events.push([
-      {
-        event_time_ms: Date.now(),
-        source_extension_json: safeJsonStringify(event),
-      },
-    ]);
+    const logEventEntry: LogEventEntry = {
+      event_time_ms: Date.now(),
+      source_extension_json: safeJsonStringify(event),
+    };
+
+    if (experimentIds !== undefined) {
+      logEventEntry.exp = {
+        gws_experiment: experimentIds,
+      };
+    }
+
+    this.events.push([logEventEntry]);
 
     if (wasAtCapacity && this.config?.getDebugMode()) {
       debugLogger.debug(
@@ -298,7 +307,7 @@ export class ClearcutLogger {
           event.event_metadata = [[...event.event_metadata[0], ...exp_id_data]];
         }
 
-        this.enqueueHelper(event);
+        this.enqueueHelper(event, experiments?.experimentIds);
       });
     } catch (error) {
       debugLogger.warn('ClearcutLogger: Failed to enqueue log event.', error);