Implement support for tool input modification (#15492)

packages/core/src/hooks/hookAggregator.ts

@@ -158,6 +158,14 @@ export class HookAggregator {
         merged.suppressOutput = true;
       }
 
+      // Merge hookSpecificOutput
+      if (output.hookSpecificOutput) {
+        merged.hookSpecificOutput = {
+          ...(merged.hookSpecificOutput || {}),
+          ...output.hookSpecificOutput,
+        };
+      }
+
       // Collect additional context from hook-specific outputs
       this.extractAdditionalContext(output, additionalContexts);
     }

packages/core/src/hooks/hookRunner.ts

@@ -15,6 +15,7 @@ import type {
   BeforeAgentInput,
   BeforeModelInput,
   BeforeModelOutput,
+  BeforeToolInput,
 } from './types.js';
 import type { LLMRequest } from './hookTranslator.js';
 import { debugLogger } from '../utils/debugLogger.js';
@@ -190,6 +191,20 @@ export class HookRunner {
           }
           break;
 
+        case HookEventName.BeforeTool:
+          if ('tool_input' in hookOutput.hookSpecificOutput) {
+            const newToolInput = hookOutput.hookSpecificOutput[
+              'tool_input'
+            ] as Record<string, unknown>;
+            if (newToolInput && 'tool_input' in modifiedInput) {
+              (modifiedInput as BeforeToolInput).tool_input = {
+                ...(modifiedInput as BeforeToolInput).tool_input,
+                ...newToolInput,
+              };
+            }
+          }
+          break;
+
         default:
           // For other events, no special input modification is needed
           break;

packages/core/src/hooks/types.test.ts

@@ -13,6 +13,7 @@ import {
   AfterModelHookOutput,
   HookEventName,
   HookType,
+  BeforeToolHookOutput,
 } from './types.js';
 import { defaultHookTranslator } from './hookTranslator.js';
 import type {
@@ -92,6 +93,11 @@ describe('Hook Output Classes', () => {
       const output = createHookOutput(HookEventName.BeforeToolSelection, {});
       expect(output).toBeInstanceOf(BeforeToolSelectionHookOutput);
     });
+
+    it('should return BeforeToolHookOutput for BeforeTool event', () => {
+      const output = createHookOutput(HookEventName.BeforeTool, {});
+      expect(output).toBeInstanceOf(BeforeToolHookOutput);
+    });
   });
 
   describe('DefaultHookOutput', () => {

packages/core/src/hooks/types.ts

@@ -133,6 +133,8 @@ export function createHookOutput(
       return new AfterModelHookOutput(data);
     case 'BeforeToolSelection':
       return new BeforeToolSelectionHookOutput(data);
+    case 'BeforeTool':
+      return new BeforeToolHookOutput(data);
     default:
       return new DefaultHookOutput(data);
   }
@@ -236,7 +238,24 @@ export class DefaultHookOutput implements HookOutput {
 /**
  * Specific hook output class for BeforeTool events.
  */
-export class BeforeToolHookOutput extends DefaultHookOutput {}
+export class BeforeToolHookOutput extends DefaultHookOutput {
+  /**
+   * Get modified tool input if provided by hook
+   */
+  getModifiedToolInput(): Record<string, unknown> | undefined {
+    if (this.hookSpecificOutput && 'tool_input' in this.hookSpecificOutput) {
+      const input = this.hookSpecificOutput['tool_input'];
+      if (
+        typeof input === 'object' &&
+        input !== null &&
+        !Array.isArray(input)
+      ) {
+        return input as Record<string, unknown>;
+      }
+    }
+    return undefined;
+  }
+}
 
 /**
  * Specific hook output class for BeforeModel events
@@ -368,6 +387,7 @@ export interface BeforeToolInput extends HookInput {
 export interface BeforeToolOutput extends HookOutput {
   hookSpecificOutput?: {
     hookEventName: 'BeforeTool';
+    tool_input?: Record<string, unknown>;
   };
 }