feat(agent): implement tool-controlled display protocol (Steps 2-3)

packages/cli/src/nonInteractiveCliAgentSession.ts

@@ -37,6 +37,7 @@ import {
   LegacyAgentSession,
   ToolErrorType,
   geminiPartsToContentParts,
+  displayContentToString,
   debugLogger,
 } from '@google/gemini-cli-core';
 
@@ -470,7 +471,8 @@ export async function runNonInteractive({
           case 'tool_response': {
             textOutput.ensureTrailingNewline();
             if (streamFormatter) {
-              const displayText = getTextContent(event.displayContent);
+              const display = event.display?.result;
+              const displayText = displayContentToString(display);
               const errorMsg = getTextContent(event.content) ?? 'Tool error';
               streamFormatter.emitEvent({
                 type: JsonStreamEventType.TOOL_RESULT,
@@ -490,7 +492,8 @@ export async function runNonInteractive({
               });
             }
             if (event.isError) {
-              const displayText = getTextContent(event.displayContent);
+              const display = event.display?.result;
+              const displayText = displayContentToString(display);
               const errorMsg = getTextContent(event.content) ?? 'Tool error';
 
               if (event.data?.['errorType'] === ToolErrorType.STOP_EXECUTION) {

packages/cli/src/ui/hooks/useAgentStream.ts

@@ -10,6 +10,7 @@ import {
   MessageSenderType,
   debugLogger,
   geminiPartsToContentParts,
+  displayContentToString,
   parseThought,
   CoreToolCallStatus,
   type ApprovalMode,
@@ -197,6 +198,7 @@ export const useAgentStream = ({
             name: displayName,
             originalRequestName: event.name,
             description: desc,
+            display: event.display,
             status: CoreToolCallStatus.Scheduled,
             isClientInitiated: false,
             renderOutputAsMarkdown: isOutputMarkdown,
@@ -222,10 +224,9 @@ export const useAgentStream = ({
               else if (evtStatus === 'success')
                 status = CoreToolCallStatus.Success;
 
+              const display = event.display?.result;
               const liveOutput =
-                event.displayContent?.[0]?.type === 'text'
-                  ? event.displayContent[0].text
-                  : tc.resultDisplay;
+                displayContentToString(display) ?? tc.resultDisplay;
               const progressMessage =
                 legacyState?.progressMessage ?? tc.progressMessage;
               const progress = legacyState?.progress ?? tc.progress;
@@ -237,6 +238,9 @@ export const useAgentStream = ({
               return {
                 ...tc,
                 status,
+                display: event.display
+                  ? { ...tc.display, ...event.display }
+                  : tc.display,
                 resultDisplay: liveOutput,
                 progressMessage,
                 progress,
@@ -255,16 +259,18 @@ export const useAgentStream = ({
 
               const legacyState = event._meta?.legacyState;
               const outputFile = legacyState?.outputFile;
+              const display = event.display?.result;
               const resultDisplay =
-                event.displayContent?.[0]?.type === 'text'
-                  ? event.displayContent[0].text
-                  : tc.resultDisplay;
+                displayContentToString(display) ?? tc.resultDisplay;
 
               return {
                 ...tc,
                 status: event.isError
                   ? CoreToolCallStatus.Error
                   : CoreToolCallStatus.Success,
+                display: event.display
+                  ? { ...tc.display, ...event.display }
+                  : tc.display,
                 resultDisplay,
                 outputFile,
               };

packages/cli/src/ui/types.ts

@@ -11,6 +11,7 @@ import {
   type ThoughtSummary,
   type SerializableConfirmationDetails,
   type ToolResultDisplay,
+  type ToolDisplay,
   type RetrieveUserQuotaResponse,
   type SkillDefinition,
   type AgentDefinition,
@@ -121,6 +122,7 @@ export interface IndividualToolCallDisplay {
   name: string;
   args?: Record<string, unknown>;
   description: string;
+  display?: ToolDisplay;
   resultDisplay: ToolResultDisplay | undefined;
   status: CoreToolCallStatus;
   // True when the tool was initiated directly by the user (slash/@/shell flows).

packages/core/src/agent/content-utils.test.ts

@@ -8,7 +8,6 @@ import { describe, expect, it } from 'vitest';
 import {
   geminiPartsToContentParts,
   contentPartsToGeminiParts,
-  toolResultDisplayToContentParts,
   buildToolResponseData,
 } from './content-utils.js';
 import type { Part } from '@google/genai';
@@ -200,27 +199,6 @@ describe('contentPartsToGeminiParts', () => {
   });
 });
 
-describe('toolResultDisplayToContentParts', () => {
-  it('returns undefined for undefined', () => {
-    expect(toolResultDisplayToContentParts(undefined)).toBeUndefined();
-  });
-
-  it('returns undefined for null', () => {
-    expect(toolResultDisplayToContentParts(null)).toBeUndefined();
-  });
-
-  it('handles string resultDisplay as-is', () => {
-    const result = toolResultDisplayToContentParts('File written');
-    expect(result).toEqual([{ type: 'text', text: 'File written' }]);
-  });
-
-  it('stringifies object resultDisplay', () => {
-    const display = { type: 'FileDiff', oldPath: 'a.ts', newPath: 'b.ts' };
-    const result = toolResultDisplayToContentParts(display);
-    expect(result).toEqual([{ type: 'text', text: JSON.stringify(display) }]);
-  });
-});
-
 describe('buildToolResponseData', () => {
   it('preserves outputFile and contentLength', () => {
     const result = buildToolResponseData({

packages/core/src/agent/content-utils.ts

@@ -101,24 +101,6 @@ export function contentPartsToGeminiParts(content: ContentPart[]): Part[] {
   return result;
 }
 
-/**
- * Converts a ToolCallResponseInfo.resultDisplay value into ContentPart[].
- * Handles string, object-valued (FileDiff, SubagentProgress, etc.),
- * and undefined resultDisplay consistently.
- */
-export function toolResultDisplayToContentParts(
-  resultDisplay: unknown,
-): ContentPart[] | undefined {
-  if (resultDisplay === undefined || resultDisplay === null) {
-    return undefined;
-  }
-  const text =
-    typeof resultDisplay === 'string'
-      ? resultDisplay
-      : JSON.stringify(resultDisplay);
-  return [{ type: 'text', text }];
-}
-
 /**
  * Builds the data record for a tool_response AgentEvent, preserving
  * all available metadata from the ToolCallResponseInfo.

packages/core/src/agent/event-translator.test.ts

@@ -155,9 +155,10 @@ describe('translateEvent', () => {
       expect(resp.content).toEqual([
         { type: 'text', text: 'Permission denied to write' },
       ]);
-      expect(resp.displayContent).toEqual([
-        { type: 'text', text: 'Permission denied' },
-      ]);
+      expect(resp.display?.result).toEqual({
+        type: 'text',
+        text: 'Permission denied',
+      });
       expect(resp.data).toEqual({ errorType: 'permission_denied' });
     });
 
@@ -200,9 +201,12 @@ describe('translateEvent', () => {
       };
       const result = translateEvent(event, state);
       const resp = result[0] as AgentEvent<'tool_response'>;
-      expect(resp.displayContent).toEqual([
-        { type: 'text', text: JSON.stringify(objectDisplay) },
-      ]);
+      expect(resp.display?.result).toEqual({
+        type: 'diff',
+        path: '/tmp/test.txt',
+        beforeText: 'a',
+        afterText: 'b',
+      });
     });
 
     it('passes through string resultDisplay as-is', () => {
@@ -220,9 +224,10 @@ describe('translateEvent', () => {
       };
       const result = translateEvent(event, state);
       const resp = result[0] as AgentEvent<'tool_response'>;
-      expect(resp.displayContent).toEqual([
-        { type: 'text', text: 'Command output text' },
-      ]);
+      expect(resp.display?.result).toEqual({
+        type: 'text',
+        text: 'Command output text',
+      });
     });
 
     it('preserves outputFile and contentLength in data', () => {

packages/core/src/agent/event-translator.ts

@@ -25,12 +25,13 @@ import type {
   ErrorData,
   Usage,
   AgentEventType,
+  ToolDisplay,
 } from './types.js';
 import {
   geminiPartsToContentParts,
-  toolResultDisplayToContentParts,
   buildToolResponseData,
 } from './content-utils.js';
+import { toolResultDisplayToDisplayContent } from './tool-display-utils.js';
 
 // ---------------------------------------------------------------------------
 // Translation State
@@ -241,10 +242,14 @@ export function translateEvent(
 
     case GeminiEventType.ToolCallResponse: {
       ensureStreamStart(state, out);
-      const displayContent = toolResultDisplayToContentParts(
-        event.value.resultDisplay,
-      );
       const data = buildToolResponseData(event.value);
+      const display: ToolDisplay | undefined = event.value.resultDisplay
+        ? {
+            result: toolResultDisplayToDisplayContent(
+              event.value.resultDisplay,
+            ),
+          }
+        : undefined;
       out.push(
         makeEvent('tool_response', state, {
           requestId: event.value.callId,
@@ -253,7 +258,7 @@ export function translateEvent(
             ? [{ type: 'text', text: event.value.error.message }]
             : geminiPartsToContentParts(event.value.responseParts),
           isError: event.value.error !== undefined,
-          ...(displayContent ? { displayContent } : {}),
+          ...(display ? { display } : {}),
           ...(data ? { data } : {}),
         }),
       );

packages/core/src/agent/legacy-agent-session.test.ts

@@ -489,9 +489,10 @@ describe('LegacyAgentSession', () => {
       expect(toolResp?.content).toEqual([
         { type: 'text', text: 'Permission denied' },
       ]);
-      expect(toolResp?.displayContent).toEqual([
-        { type: 'text', text: 'Error display' },
-      ]);
+      expect(toolResp?.display?.result).toEqual({
+        type: 'text',
+        text: 'Error display',
+      });
     });
 
     it('stops on STOP_EXECUTION tool error', async () => {

packages/core/src/agent/legacy-agent-session.ts

@@ -23,8 +23,8 @@ import {
   buildToolResponseData,
   contentPartsToGeminiParts,
   geminiPartsToContentParts,
-  toolResultDisplayToContentParts,
 } from './content-utils.js';
+import { populateToolDisplay } from './tool-display-utils.js';
 import { AgentSession } from './agent-session.js';
 import {
   createTranslationState,
@@ -262,9 +262,12 @@ export class LegacyAgentProtocol implements AgentProtocol {
         const content: ContentPart[] = response.error
           ? [{ type: 'text', text: response.error.message }]
           : geminiPartsToContentParts(response.responseParts);
-        const displayContent = toolResultDisplayToContentParts(
-          response.resultDisplay,
-        );
+        const display = populateToolDisplay({
+          name: request.name,
+          invocation: 'invocation' in tc ? tc.invocation : undefined,
+          resultDisplay: response.resultDisplay,
+          displayName: 'tool' in tc ? tc.tool?.displayName : undefined,
+        });
         const data = buildToolResponseData(response);
 
         this._emit([
@@ -273,7 +276,7 @@ export class LegacyAgentProtocol implements AgentProtocol {
             name: request.name,
             content,
             isError: response.error !== undefined,
-            ...(displayContent ? { displayContent } : {}),
+            ...(display ? { display } : {}),
             ...(data ? { data } : {}),
           }),
         ]);