feat(hooks): simplify hook firing with HookSystem wrapper methods (#15982)

Co-authored-by: Ishaan Gupta <ishaankone@gmail.com>

packages/cli/src/gemini.test.tsx

@@ -269,6 +269,7 @@ describe('gemini.tsx main function', () => {
           subscribe: vi.fn(),
         }),
         getEnableHooks: () => false,
+        getHookSystem: () => undefined,
         getToolRegistry: vi.fn(),
         getContentGeneratorConfig: vi.fn(),
         getModel: () => 'gemini-pro',
@@ -505,6 +506,7 @@ describe('gemini.tsx main function kitty protocol', () => {
         subscribe: vi.fn(),
       }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       getToolRegistry: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getModel: () => 'gemini-pro',
@@ -609,6 +611,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -692,6 +695,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -760,6 +764,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -843,6 +848,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -923,6 +929,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -997,6 +1004,7 @@ describe('gemini.tsx main function kitty protocol', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),
@@ -1170,6 +1178,7 @@ describe('gemini.tsx main function exit codes', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       getToolRegistry: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getModel: () => 'gemini-pro',
@@ -1234,6 +1243,7 @@ describe('gemini.tsx main function exit codes', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: () => false,
+      getHookSystem: () => undefined,
       getToolRegistry: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getModel: () => 'gemini-pro',

packages/cli/src/gemini.tsx

@@ -64,8 +64,6 @@ import {
   ExitCodes,
   SessionStartSource,
   SessionEndReason,
-  fireSessionStartHook,
-  fireSessionEndHook,
   getVersion,
 } from '@google/gemini-cli-core';
 import {
@@ -491,11 +489,9 @@ export async function main() {
 
     // Register SessionEnd hook to fire on graceful exit
     // This runs before telemetry shutdown in runExitCleanup()
-    if (config.getEnableHooks() && messageBus) {
     registerCleanup(async () => {
-        await fireSessionEndHook(messageBus, SessionEndReason.Exit);
+      await config.getHookSystem()?.fireSessionEndEvent(SessionEndReason.Exit);
     });
-    }
 
     // Cleanup sessions after config initialization
     try {
@@ -646,35 +642,28 @@ export async function main() {
 
     // Fire SessionStart hook through MessageBus (only if hooks are enabled)
     // Must be called AFTER config.initialize() to ensure HookRegistry is loaded
-    const hooksEnabled = config.getEnableHooks();
-    const hookMessageBus = config.getMessageBus();
-    if (hooksEnabled && hookMessageBus) {
     const sessionStartSource = resumedSessionData
       ? SessionStartSource.Resume
       : SessionStartSource.Startup;
-      const result = await fireSessionStartHook(
+    const result = await config
-        hookMessageBus,
+      .getHookSystem()
-        sessionStartSource,
+      ?.fireSessionStartEvent(sessionStartSource);
-      );
 
-      if (result) {
+    if (result?.finalOutput) {
-        if (result.systemMessage) {
+      if (result.finalOutput.systemMessage) {
-          writeToStderr(result.systemMessage + '\n');
+        writeToStderr(result.finalOutput.systemMessage + '\n');
       }
-        const additionalContext = result.getAdditionalContext();
+      const additionalContext = result.finalOutput.getAdditionalContext();
       if (additionalContext) {
         // Prepend context to input (System Context -> Stdin -> Question)
-          input = input
+        input = input ? `${additionalContext}\n\n${input}` : additionalContext;
-            ? `${additionalContext}\n\n${input}`
-            : additionalContext;
       }
     }
 
     // Register SessionEnd hook for graceful exit
     registerCleanup(async () => {
-        await fireSessionEndHook(hookMessageBus, SessionEndReason.Exit);
+      await config.getHookSystem()?.fireSessionEndEvent(SessionEndReason.Exit);
     });
-    }
 
     if (!input) {
       debugLogger.error(

packages/cli/src/gemini_cleanup.test.tsx

@@ -189,6 +189,7 @@ describe('gemini.tsx main function cleanup', () => {
       getPolicyEngine: vi.fn(),
       getMessageBus: () => ({ subscribe: vi.fn() }),
       getEnableHooks: vi.fn(() => false),
+      getHookSystem: () => undefined,
       initialize: vi.fn(),
       getContentGeneratorConfig: vi.fn(),
       getMcpServers: () => ({}),

packages/core/src/hooks/hookSystem.ts

@@ -14,11 +14,17 @@ import type { HookRegistryEntry } from './hookRegistry.js';
 import { logs, type Logger } from '@opentelemetry/api-logs';
 import { SERVICE_NAME } from '../telemetry/constants.js';
 import { debugLogger } from '../utils/debugLogger.js';
-
+import type {
+  SessionStartSource,
+  SessionEndReason,
+  PreCompressTrigger,
+} from './types.js';
+import type { AggregatedHookResult } from './hookAggregator.js';
 /**
  * Main hook system that coordinates all hook-related functionality
  */
 export class HookSystem {
+  private readonly config: Config;
   private readonly hookRegistry: HookRegistry;
   private readonly hookRunner: HookRunner;
   private readonly hookAggregator: HookAggregator;
@@ -26,6 +32,7 @@ export class HookSystem {
   private readonly hookEventHandler: HookEventHandler;
 
   constructor(config: Config) {
+    this.config = config;
     const logger: Logger = logs.getLogger(SERVICE_NAME);
     const messageBus = config.getMessageBus();
 
@@ -79,4 +86,35 @@ export class HookSystem {
   getAllHooks(): HookRegistryEntry[] {
     return this.hookRegistry.getAllHooks();
   }
+
+  /**
+   * Fire hook events directly
+   * Returns undefined if hooks are disabled
+   */
+  async fireSessionStartEvent(
+    source: SessionStartSource,
+  ): Promise<AggregatedHookResult | undefined> {
+    if (!this.config.getEnableHooks()) {
+      return undefined;
+    }
+    return this.hookEventHandler.fireSessionStartEvent(source);
+  }
+
+  async fireSessionEndEvent(
+    reason: SessionEndReason,
+  ): Promise<AggregatedHookResult | undefined> {
+    if (!this.config.getEnableHooks()) {
+      return undefined;
+    }
+    return this.hookEventHandler.fireSessionEndEvent(reason);
+  }
+
+  async firePreCompressEvent(
+    trigger: PreCompressTrigger,
+  ): Promise<AggregatedHookResult | undefined> {
+    if (!this.config.getEnableHooks()) {
+      return undefined;
+    }
+    return this.hookEventHandler.firePreCompressEvent(trigger);
+  }
 }