refactor(core): introduce InjectionService with source-aware injection and backend-native background completions (#22544)

packages/core/src/config/injectionService.test.ts

@@ -0,0 +1,139 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi } from 'vitest';
+import { InjectionService } from './injectionService.js';
+
+describe('InjectionService', () => {
+  it('is disabled by default and ignores user_steering injections', () => {
+    const service = new InjectionService(() => false);
+    service.addInjection('this hint should be ignored', 'user_steering');
+    expect(service.getInjections()).toEqual([]);
+    expect(service.getLatestInjectionIndex()).toBe(-1);
+  });
+
+  it('stores trimmed injections and exposes them via indexing when enabled', () => {
+    const service = new InjectionService(() => true);
+
+    service.addInjection('  first hint  ', 'user_steering');
+    service.addInjection('second hint', 'user_steering');
+    service.addInjection('   ', 'user_steering');
+
+    expect(service.getInjections()).toEqual(['first hint', 'second hint']);
+    expect(service.getLatestInjectionIndex()).toBe(1);
+    expect(service.getInjectionsAfter(-1)).toEqual([
+      'first hint',
+      'second hint',
+    ]);
+    expect(service.getInjectionsAfter(0)).toEqual(['second hint']);
+    expect(service.getInjectionsAfter(1)).toEqual([]);
+  });
+
+  it('notifies listeners when an injection is added', () => {
+    const service = new InjectionService(() => true);
+    const listener = vi.fn();
+    service.onInjection(listener);
+
+    service.addInjection('new hint', 'user_steering');
+
+    expect(listener).toHaveBeenCalledWith('new hint', 'user_steering');
+  });
+
+  it('does NOT notify listeners after they are unregistered', () => {
+    const service = new InjectionService(() => true);
+    const listener = vi.fn();
+    service.onInjection(listener);
+    service.offInjection(listener);
+
+    service.addInjection('ignored hint', 'user_steering');
+
+    expect(listener).not.toHaveBeenCalled();
+  });
+
+  it('should clear all injections', () => {
+    const service = new InjectionService(() => true);
+    service.addInjection('hint 1', 'user_steering');
+    service.addInjection('hint 2', 'user_steering');
+    expect(service.getInjections()).toHaveLength(2);
+
+    service.clear();
+    expect(service.getInjections()).toHaveLength(0);
+    expect(service.getLatestInjectionIndex()).toBe(-1);
+  });
+
+  describe('source-specific behavior', () => {
+    it('notifies listeners with source for user_steering', () => {
+      const service = new InjectionService(() => true);
+      const listener = vi.fn();
+      service.onInjection(listener);
+
+      service.addInjection('steering hint', 'user_steering');
+
+      expect(listener).toHaveBeenCalledWith('steering hint', 'user_steering');
+    });
+
+    it('notifies listeners with source for background_completion', () => {
+      const service = new InjectionService(() => true);
+      const listener = vi.fn();
+      service.onInjection(listener);
+
+      service.addInjection('bg output', 'background_completion');
+
+      expect(listener).toHaveBeenCalledWith(
+        'bg output',
+        'background_completion',
+      );
+    });
+
+    it('accepts background_completion even when model steering is disabled', () => {
+      const service = new InjectionService(() => false);
+      const listener = vi.fn();
+      service.onInjection(listener);
+
+      service.addInjection('bg output', 'background_completion');
+
+      expect(listener).toHaveBeenCalledWith(
+        'bg output',
+        'background_completion',
+      );
+      expect(service.getInjections()).toEqual(['bg output']);
+    });
+
+    it('filters injections by source when requested', () => {
+      const service = new InjectionService(() => true);
+      service.addInjection('hint', 'user_steering');
+      service.addInjection('bg output', 'background_completion');
+      service.addInjection('hint 2', 'user_steering');
+
+      expect(service.getInjections('user_steering')).toEqual([
+        'hint',
+        'hint 2',
+      ]);
+      expect(service.getInjections('background_completion')).toEqual([
+        'bg output',
+      ]);
+      expect(service.getInjections()).toEqual(['hint', 'bg output', 'hint 2']);
+
+      expect(service.getInjectionsAfter(0, 'user_steering')).toEqual([
+        'hint 2',
+      ]);
+      expect(service.getInjectionsAfter(0, 'background_completion')).toEqual([
+        'bg output',
+      ]);
+    });
+
+    it('rejects user_steering when model steering is disabled', () => {
+      const service = new InjectionService(() => false);
+      const listener = vi.fn();
+      service.onInjection(listener);
+
+      service.addInjection('steering hint', 'user_steering');
+
+      expect(listener).not.toHaveBeenCalled();
+      expect(service.getInjections()).toEqual([]);
+    });
+  });
+});