feat: implement AfterTool tail tool calls (#18486)

packages/core/src/hooks/hookEventHandler.ts

@@ -76,12 +76,16 @@ export class HookEventHandler {
     toolName: string,
     toolInput: Record<string, unknown>,
     mcpContext?: McpToolContext,
+    originalRequestName?: string,
   ): Promise<AggregatedHookResult> {
     const input: BeforeToolInput = {
       ...this.createBaseInput(HookEventName.BeforeTool),
       tool_name: toolName,
       tool_input: toolInput,
       ...(mcpContext && { mcp_context: mcpContext }),
+      ...(originalRequestName && {
+        original_request_name: originalRequestName,
+      }),
     };
 
     const context: HookEventContext = { toolName };
@@ -97,6 +101,7 @@ export class HookEventHandler {
     toolInput: Record<string, unknown>,
     toolResponse: Record<string, unknown>,
     mcpContext?: McpToolContext,
+    originalRequestName?: string,
   ): Promise<AggregatedHookResult> {
     const input: AfterToolInput = {
       ...this.createBaseInput(HookEventName.AfterTool),
@@ -104,6 +109,9 @@ export class HookEventHandler {
       tool_input: toolInput,
       tool_response: toolResponse,
       ...(mcpContext && { mcp_context: mcpContext }),
+      ...(originalRequestName && {
+        original_request_name: originalRequestName,
+      }),
     };
 
     const context: HookEventContext = { toolName };

packages/core/src/hooks/hookSystem.ts

@@ -368,12 +368,14 @@ export class HookSystem {
     toolName: string,
     toolInput: Record<string, unknown>,
     mcpContext?: McpToolContext,
+    originalRequestName?: string,
   ): Promise<DefaultHookOutput | undefined> {
     try {
       const result = await this.hookEventHandler.fireBeforeToolEvent(
         toolName,
         toolInput,
         mcpContext,
+        originalRequestName,
       );
       return result.finalOutput;
     } catch (error) {
@@ -391,6 +393,7 @@ export class HookSystem {
       error: unknown;
     },
     mcpContext?: McpToolContext,
+    originalRequestName?: string,
   ): Promise<DefaultHookOutput | undefined> {
     try {
       const result = await this.hookEventHandler.fireAfterToolEvent(
@@ -398,6 +401,7 @@ export class HookSystem {
         toolInput,
         toolResponse as Record<string, unknown>,
         mcpContext,
+        originalRequestName,
       );
       return result.finalOutput;
     } catch (error) {

packages/core/src/hooks/types.ts

@@ -253,6 +253,33 @@ export class DefaultHookOutput implements HookOutput {
   shouldClearContext(): boolean {
     return false;
   }
+
+  /**
+   * Optional request to execute another tool immediately after this one.
+   * The result of this tail call will replace the original tool's response.
+   */
+  getTailToolCallRequest():
+    | {
+        name: string;
+        args: Record<string, unknown>;
+      }
+    | undefined {
+    if (
+      this.hookSpecificOutput &&
+      'tailToolCallRequest' in this.hookSpecificOutput
+    ) {
+      const request = this.hookSpecificOutput['tailToolCallRequest'];
+      if (
+        typeof request === 'object' &&
+        request !== null &&
+        !Array.isArray(request)
+      ) {
+        // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
+        return request as { name: string; args: Record<string, unknown> };
+      }
+    }
+    return undefined;
+  }
 }
 
 /**
@@ -430,6 +457,7 @@ export interface BeforeToolInput extends HookInput {
   tool_name: string;
   tool_input: Record<string, unknown>;
   mcp_context?: McpToolContext; // Only present for MCP tools
+  original_request_name?: string;
 }
 
 /**
@@ -450,6 +478,7 @@ export interface AfterToolInput extends HookInput {
   tool_input: Record<string, unknown>;
   tool_response: Record<string, unknown>;
   mcp_context?: McpToolContext; // Only present for MCP tools
+  original_request_name?: string;
 }
 
 /**
@@ -459,6 +488,14 @@ export interface AfterToolOutput extends HookOutput {
   hookSpecificOutput?: {
     hookEventName: 'AfterTool';
     additionalContext?: string;
+    /**
+     * Optional request to execute another tool immediately after this one.
+     * The result of this tail call will replace the original tool's response.
+     */
+    tailToolCallRequest?: {
+      name: string;
+      args: Record<string, unknown>;
+    };
   };
 }