bug(ux): update context percentage when /clear command is run (#4162)

Co-authored-by: matt korwel <matt.korwel@gmail.com>

packages/core/src/telemetry/uiTelemetry.test.ts

@@ -508,4 +508,116 @@ describe('UiTelemetryService', () => {
       expect(tools.byName['tool_B'].count).toBe(1);
     });
   });
+
+  describe('resetLastPromptTokenCount', () => {
+    it('should reset the last prompt token count to 0', () => {
+      // First, set up some initial token count
+      const event = {
+        'event.name': EVENT_API_RESPONSE,
+        model: 'gemini-2.5-pro',
+        duration_ms: 500,
+        input_token_count: 100,
+        output_token_count: 200,
+        total_token_count: 300,
+        cached_content_token_count: 50,
+        thoughts_token_count: 20,
+        tool_token_count: 30,
+      } as ApiResponseEvent & { 'event.name': typeof EVENT_API_RESPONSE };
+
+      service.addEvent(event);
+      expect(service.getLastPromptTokenCount()).toBe(100);
+
+      // Now reset the token count
+      service.resetLastPromptTokenCount();
+      expect(service.getLastPromptTokenCount()).toBe(0);
+    });
+
+    it('should emit an update event when resetLastPromptTokenCount is called', () => {
+      const spy = vi.fn();
+      service.on('update', spy);
+
+      // Set up initial token count
+      const event = {
+        'event.name': EVENT_API_RESPONSE,
+        model: 'gemini-2.5-pro',
+        duration_ms: 500,
+        input_token_count: 100,
+        output_token_count: 200,
+        total_token_count: 300,
+        cached_content_token_count: 50,
+        thoughts_token_count: 20,
+        tool_token_count: 30,
+      } as ApiResponseEvent & { 'event.name': typeof EVENT_API_RESPONSE };
+
+      service.addEvent(event);
+      spy.mockClear(); // Clear the spy to focus on the reset call
+
+      service.resetLastPromptTokenCount();
+
+      expect(spy).toHaveBeenCalledOnce();
+      const { metrics, lastPromptTokenCount } = spy.mock.calls[0][0];
+      expect(metrics).toBeDefined();
+      expect(lastPromptTokenCount).toBe(0);
+    });
+
+    it('should not affect other metrics when resetLastPromptTokenCount is called', () => {
+      // Set up initial state with some metrics
+      const event = {
+        'event.name': EVENT_API_RESPONSE,
+        model: 'gemini-2.5-pro',
+        duration_ms: 500,
+        input_token_count: 100,
+        output_token_count: 200,
+        total_token_count: 300,
+        cached_content_token_count: 50,
+        thoughts_token_count: 20,
+        tool_token_count: 30,
+      } as ApiResponseEvent & { 'event.name': typeof EVENT_API_RESPONSE };
+
+      service.addEvent(event);
+
+      const metricsBefore = service.getMetrics();
+
+      service.resetLastPromptTokenCount();
+
+      const metricsAfter = service.getMetrics();
+
+      // Metrics should be unchanged
+      expect(metricsAfter).toEqual(metricsBefore);
+
+      // Only the last prompt token count should be reset
+      expect(service.getLastPromptTokenCount()).toBe(0);
+    });
+
+    it('should work correctly when called multiple times', () => {
+      const spy = vi.fn();
+      service.on('update', spy);
+
+      // Set up initial token count
+      const event = {
+        'event.name': EVENT_API_RESPONSE,
+        model: 'gemini-2.5-pro',
+        duration_ms: 500,
+        input_token_count: 100,
+        output_token_count: 200,
+        total_token_count: 300,
+        cached_content_token_count: 50,
+        thoughts_token_count: 20,
+        tool_token_count: 30,
+      } as ApiResponseEvent & { 'event.name': typeof EVENT_API_RESPONSE };
+
+      service.addEvent(event);
+      expect(service.getLastPromptTokenCount()).toBe(100);
+
+      // Reset once
+      service.resetLastPromptTokenCount();
+      expect(service.getLastPromptTokenCount()).toBe(0);
+
+      // Reset again - should still be 0 and still emit event
+      spy.mockClear();
+      service.resetLastPromptTokenCount();
+      expect(service.getLastPromptTokenCount()).toBe(0);
+      expect(spy).toHaveBeenCalledOnce();
+    });
+  });
 });

packages/core/src/telemetry/uiTelemetry.ts

@@ -133,6 +133,14 @@ export class UiTelemetryService extends EventEmitter {
     return this.#lastPromptTokenCount;
   }
 
+  resetLastPromptTokenCount(): void {
+    this.#lastPromptTokenCount = 0;
+    this.emit('update', {
+      metrics: this.#metrics,
+      lastPromptTokenCount: this.#lastPromptTokenCount,
+    });
+  }
+
   private getOrCreateModelMetrics(modelName: string): ModelMetrics {
     if (!this.#metrics.models[modelName]) {
       this.#metrics.models[modelName] = createInitialModelMetrics();