fix: address PR feedback for slash commands and background task tracking

Addresses high-priority feedback from the automated code review tool regarding the logic error and inconsistency in `useAgentStream.ts` and `useExecutionLifecycle.ts`.

- `useAgentStream.ts`: Fixed `schedule_tool` fall-through by returning early if the command type is not `submit_prompt`. Prevented history duplication by only adding items not already handled by the slash command processor. Ensured the original raw string is logged.
- `useExecutionLifecycle.ts`: Removed `isActive` guards from the unmount cleanup effect and the `ExecutionLifecycleService.onBackground` listener to prevent background tasks from being incorrectly unsubscribed or missed when switching between Gemini and Agent streams.
- Updated `useAgentStream.test.tsx` to reflect the fixed history logic.

docs/reference/configuration.md

@@ -550,6 +550,24 @@ their corresponding top-level category object in your `settings.json` file.
           "model": "gemini-3-flash-preview"
         }
       },
+      "gemini-3.1-pro-preview": {
+        "extends": "chat-base-3",
+        "modelConfig": {
+          "model": "gemini-3.1-pro-preview"
+        }
+      },
+      "gemini-3.1-pro-preview-customtools": {
+        "extends": "chat-base-3",
+        "modelConfig": {
+          "model": "gemini-3.1-pro-preview-customtools"
+        }
+      },
+      "gemini-3.1-flash-lite-preview": {
+        "extends": "chat-base-3",
+        "modelConfig": {
+          "model": "gemini-3.1-flash-lite-preview"
+        }
+      },
       "gemini-2.5-pro": {
         "extends": "chat-base-2.5",
         "modelConfig": {
@@ -1836,6 +1854,12 @@ their corresponding top-level category object in your `settings.json` file.
   - **Default:** `false`
   - **Requires restart:** Yes
 
+- **`experimental.adk.agentSessionSubagentEnabled`** (boolean):
+  - **Description:** Route subagent invocations through the AgentSession
+    protocol instead of legacy executors.
+  - **Default:** `false`
+  - **Requires restart:** Yes
+
 - **`experimental.enableAgents`** (boolean):
   - **Description:** Enable local and remote subagents.
   - **Default:** `true`

packages/cli/src/config/settingsSchema.test.ts

@@ -571,6 +571,18 @@ describe('SettingsSchema', () => {
       expect(agentSessionNoninteractiveEnabled.description).toBe(
         'Enable non-interactive agent sessions.',
       );
+
+      const agentSessionSubagentEnabled =
+        adk.properties.agentSessionSubagentEnabled;
+      expect(agentSessionSubagentEnabled).toBeDefined();
+      expect(agentSessionSubagentEnabled.type).toBe('boolean');
+      expect(agentSessionSubagentEnabled.category).toBe('Experimental');
+      expect(agentSessionSubagentEnabled.default).toBe(false);
+      expect(agentSessionSubagentEnabled.requiresRestart).toBe(true);
+      expect(agentSessionSubagentEnabled.showInDialog).toBe(false);
+      expect(agentSessionSubagentEnabled.description).toBe(
+        'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+      );
     });
   });
 

packages/cli/src/config/settingsSchema.ts

@@ -2194,6 +2194,16 @@ const SETTINGS_SCHEMA = {
               'Enable the agent session implementation for the interactive CLI.',
             showInDialog: false,
           },
+          agentSessionSubagentEnabled: {
+            type: 'boolean',
+            label: 'Agent Session Subagent Enabled',
+            category: 'Experimental',
+            requiresRestart: true,
+            default: false,
+            description:
+              'Route subagent invocations through the AgentSession protocol instead of legacy executors.',
+            showInDialog: false,
+          },
         },
       },
       enableAgents: {

packages/cli/src/ui/AppContainer.tsx

@@ -1185,6 +1185,7 @@ Logging in with Google... Restarting Gemini CLI to continue.
       useAgentStream({
         agent: streamAgent,
         addItem: historyManager.addItem,
+        handleSlashCommand,
         onCancelSubmit,
         isShellFocused: embeddedShellFocused,
         logger,

packages/cli/src/ui/hooks/useAgentStream.test.tsx

@@ -4,14 +4,14 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import { act } from 'react';
-import type { LegacyAgentProtocol } from '@google/gemini-cli-core';
+import type { AgentProtocol } from '@google/gemini-cli-core';
 import { renderHookWithProviders } from '../../test-utils/render.js';
 
 // --- MOCKS ---
 
-const mockLegacyAgentProtocol = vi.hoisted(() => ({
+const mockAgentProtocol = vi.hoisted(() => ({
   send: vi.fn().mockResolvedValue({ streamId: 'test-stream-id' }),
   subscribe: vi.fn().mockReturnValue(() => {}),
   abort: vi.fn().mockResolvedValue(undefined),
@@ -40,24 +40,31 @@ describe('useAgentStream', () => {
     vi.clearAllMocks();
   });
 
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
   it('should initialize on mount', async () => {
     await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: vi.fn().mockResolvedValue(false),
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
     );
 
-    expect(mockLegacyAgentProtocol.subscribe).toHaveBeenCalled();
+    expect(mockAgentProtocol.subscribe).toHaveBeenCalled();
   });
 
   it('should call agent.send when submitQuery is called', async () => {
+    const mockHandleSlashCommand = vi.fn().mockResolvedValue(false);
     const { result } = await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: mockHandleSlashCommand,
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
@@ -67,7 +74,7 @@ describe('useAgentStream', () => {
       await result.current.submitQuery('hello');
     });
 
-    expect(mockLegacyAgentProtocol.send).toHaveBeenCalledWith({
+    expect(mockAgentProtocol.send).toHaveBeenCalledWith({
       message: { content: [{ type: 'text', text: 'hello' }] },
     });
     expect(mockAddItem).toHaveBeenCalledWith(
@@ -76,17 +83,70 @@ describe('useAgentStream', () => {
     );
   });
 
-  it('should update streamingState based on agent_start and agent_end events', async () => {
+  it('should intercept slash commands and not call agent.send if handled', async () => {
+    const mockHandleSlashCommand = vi
+      .fn()
+      .mockResolvedValue({ type: 'handled' });
     const { result } = await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: mockHandleSlashCommand,
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
     );
 
-    const eventHandler = vi.mocked(mockLegacyAgentProtocol.subscribe).mock
+    await act(async () => {
+      await result.current.submitQuery('/about');
+    });
+
+    expect(mockHandleSlashCommand).toHaveBeenCalledWith('/about');
+    expect(mockAgentProtocol.send).not.toHaveBeenCalled();
+  });
+
+  it('should intercept slash commands and call agent.send with new content if submit_prompt', async () => {
+    const mockHandleSlashCommand = vi.fn().mockResolvedValue({
+      type: 'submit_prompt',
+      content: 'modified prompt',
+    });
+    const { result } = await renderHookWithProviders(() =>
+      useAgentStream({
+        agent: mockAgentProtocol as unknown as AgentProtocol,
+        addItem: mockAddItem,
+        handleSlashCommand: mockHandleSlashCommand,
+        onCancelSubmit: mockOnCancelSubmit,
+        isShellFocused: false,
+      }),
+    );
+
+    await act(async () => {
+      await result.current.submitQuery('/mcp-prompt');
+    });
+
+    expect(mockHandleSlashCommand).toHaveBeenCalledWith('/mcp-prompt');
+    expect(mockAgentProtocol.send).toHaveBeenCalledWith({
+      message: { content: [{ type: 'text', text: 'modified prompt' }] },
+    });
+    expect(mockAddItem).toHaveBeenCalledWith(
+      expect.objectContaining({ type: MessageType.USER, text: '/mcp-prompt' }),
+      expect.any(Number),
+    );
+  });
+
+  it('should update streamingState based on agent_start and agent_end events', async () => {
+    const mockHandleSlashCommand = vi.fn().mockResolvedValue(false);
+    const { result } = await renderHookWithProviders(() =>
+      useAgentStream({
+        agent: mockAgentProtocol as unknown as AgentProtocol,
+        addItem: mockAddItem,
+        handleSlashCommand: mockHandleSlashCommand,
+        onCancelSubmit: mockOnCancelSubmit,
+        isShellFocused: false,
+      }),
+    );
+
+    const eventHandler = vi.mocked(mockAgentProtocol.subscribe).mock
       .calls[0][0];
 
     expect(result.current.streamingState).toBe(StreamingState.Idle);
@@ -116,14 +176,15 @@ describe('useAgentStream', () => {
   it('should accumulate text content and update pendingHistoryItems', async () => {
     const { result } = await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: vi.fn().mockResolvedValue(false),
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
     );
 
-    const eventHandler = vi.mocked(mockLegacyAgentProtocol.subscribe).mock
+    const eventHandler = vi.mocked(mockAgentProtocol.subscribe).mock
       .calls[0][0];
 
     act(() => {
@@ -160,14 +221,15 @@ describe('useAgentStream', () => {
   it('should process thought events and update thought state', async () => {
     const { result } = await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: vi.fn().mockResolvedValue(false),
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
     );
 
-    const eventHandler = vi.mocked(mockLegacyAgentProtocol.subscribe).mock
+    const eventHandler = vi.mocked(mockAgentProtocol.subscribe).mock
       .calls[0][0];
 
     act(() => {
@@ -190,8 +252,9 @@ describe('useAgentStream', () => {
   it('should call agent.abort when cancelOngoingRequest is called', async () => {
     const { result } = await renderHookWithProviders(() =>
       useAgentStream({
-        agent: mockLegacyAgentProtocol as unknown as LegacyAgentProtocol,
+        agent: mockAgentProtocol as unknown as AgentProtocol,
         addItem: mockAddItem,
+        handleSlashCommand: vi.fn().mockResolvedValue(false),
         onCancelSubmit: mockOnCancelSubmit,
         isShellFocused: false,
       }),
@@ -201,7 +264,7 @@ describe('useAgentStream', () => {
       await result.current.cancelOngoingRequest();
     });
 
-    expect(mockLegacyAgentProtocol.abort).toHaveBeenCalled();
+    expect(mockAgentProtocol.abort).toHaveBeenCalled();
     expect(mockOnCancelSubmit).toHaveBeenCalledWith(false, true);
   });
 });

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

@@ -5,12 +5,14 @@
  */
 
 import { useState, useRef, useCallback, useEffect, useMemo } from 'react';
+import { type PartListUnion } from '@google/genai';
 import {
   getErrorMessage,
   MessageSenderType,
   debugLogger,
   geminiPartsToContentParts,
   displayContentToString,
+  partToString,
   parseThought,
   CoreToolCallStatus,
   type ApprovalMode,
@@ -20,15 +22,16 @@ import {
   type AgentEvent,
   type AgentProtocol,
   type Logger,
-  type Part,
 } from '@google/gemini-cli-core';
 import type {
   HistoryItemWithoutId,
   LoopDetectionConfirmationRequest,
   IndividualToolCallDisplay,
   HistoryItemToolDisplayGroup,
+  SlashCommandProcessorResult,
 } from '../types.js';
 import { StreamingState, MessageType } from '../types.js';
+import { isSlashCommand } from '../utils/commandUtils.js';
 import { findLastSafeSplitPoint } from '../utils/markdownUtilities.js';
 import { getToolGroupBorderAppearance } from '../utils/borderStyles.js';
 import { type BackgroundTask } from './useExecutionLifecycle.js';
@@ -41,6 +44,9 @@ import { useKeypress } from './useKeypress.js';
 export interface UseAgentStreamOptions {
   agent?: AgentProtocol;
   addItem: UseHistoryManagerReturn['addItem'];
+  handleSlashCommand: (
+    cmd: string,
+  ) => Promise<SlashCommandProcessorResult | false>;
   onCancelSubmit: (
     shouldRestorePrompt?: boolean,
     clearBuffer?: boolean,
@@ -56,6 +62,7 @@ export interface UseAgentStreamOptions {
 export const useAgentStream = ({
   agent,
   addItem,
+  handleSlashCommand,
   onCancelSubmit,
   isShellFocused,
   logger,
@@ -333,8 +340,8 @@ export const useAgentStream = ({
 
   useKeypress(
     (key) => {
-      if (key.name === 'escape' && !isShellFocused) {
-        void cancelOngoingRequest(false);
+      if (key.ctrl && key.name === 'c') {
+        void cancelOngoingRequest();
         return true;
       }
       return false;
@@ -348,7 +355,7 @@ export const useAgentStream = ({
 
   const submitQuery = useCallback(
     async (
-      query: Part[] | string,
+      query: PartListUnion,
       options?: { isContinuation: boolean },
       _prompt_id?: string,
     ) => {
@@ -360,16 +367,59 @@ export const useAgentStream = ({
 
       geminiMessageBufferRef.current = '';
 
+      let localQuery: PartListUnion = query;
+
       if (!options?.isContinuation) {
-        if (typeof query === 'string') {
-          addItem({ type: MessageType.USER, text: query }, timestamp);
-          void logger?.logMessage(MessageSenderType.USER, query);
+        let shouldAddToHistory = true;
+        if (typeof localQuery === 'string') {
+          const trimmedQuery = localQuery.trim();
+          void logger?.logMessage(MessageSenderType.USER, trimmedQuery);
+
+          if (isSlashCommand(trimmedQuery)) {
+            const slashResult = await handleSlashCommand(trimmedQuery);
+            if (slashResult) {
+              if (slashResult.type === 'submit_prompt') {
+                localQuery = slashResult.content;
+              } else if (slashResult.type === 'schedule_tool') {
+                addItem(
+                  {
+                    type: MessageType.ERROR,
+                    text: `The /${slashResult.toolName} command is not yet supported in Agent mode.`,
+                  },
+                  timestamp,
+                );
+                return;
+              } else {
+                // 'handled' or other types that don't need LLM submission
+                shouldAddToHistory = false;
+                return;
+              }
+            }
+          }
+        }
+
+        if (shouldAddToHistory) {
+          const originalQueryText =
+            typeof query === 'string' ? query : partToString(query);
+
+          addItem(
+            { type: MessageType.USER, text: originalQueryText },
+            timestamp,
+          );
+          if (typeof localQuery !== 'string') {
+            void logger?.logMessage(
+              MessageSenderType.USER,
+              partToString(localQuery),
+            );
+          }
         }
         startNewPrompt();
       }
 
       const parts = geminiPartsToContentParts(
-        typeof query === 'string' ? [{ text: query }] : query,
+        (Array.isArray(localQuery) ? localQuery : [localQuery]).map((p) =>
+          typeof p === 'string' ? { text: p } : p,
+        ),
       );
 
       try {
@@ -384,9 +434,8 @@ export const useAgentStream = ({
         );
       }
     },
-    [agent, addItem, logger, startNewPrompt],
+    [agent, addItem, logger, startNewPrompt, handleSlashCommand],
   );
-
   useEffect(() => {
     if (trackedTools.length > 0) {
       const isNewBatch = !trackedTools.some((tc) =>
@@ -397,6 +446,7 @@ export const useAgentStream = ({
         setIsFirstToolInGroup(true);
       }
     } else if (streamingState === StreamingState.Idle) {
+      // Clear when idle to be ready for next turn
       setPushedToolCallIds(new Set());
       setIsFirstToolInGroup(true);
     }

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

@@ -387,6 +387,11 @@ export const useGeminiStream = (
     [setIsResponding],
   );
 
+  const streamingState = useMemo(
+    () => calculateStreamingState(isResponding, toolCalls),
+    [isResponding, toolCalls],
+  );
+
   const {
     handleShellCommand,
     activeShellPtyId,
@@ -409,11 +414,7 @@ export const useGeminiStream = (
     terminalWidth,
     terminalHeight,
     activeBackgroundExecutionId,
-  );
-
-  const streamingState = useMemo(
-    () => calculateStreamingState(isResponding, toolCalls),
-    [isResponding, toolCalls],
+    streamingState === StreamingState.WaitingForConfirmation,
   );
 
   // Reset tracking when a new batch of tools starts
@@ -599,6 +600,7 @@ export const useGeminiStream = (
     backgroundTasks,
     settings.merged.ui?.compactToolOutput,
   ]);
+
   const pendingToolGroupItems = useMemo((): HistoryItemWithoutId[] => {
     const remainingTools = toolCalls.filter(
       (tc) => !pushedToolCallIds.has(tc.request.callId),
@@ -983,16 +985,28 @@ export const useGeminiStream = (
 
                 if (postSubmitPrompt) {
                   localQueryToSendToGemini = postSubmitPrompt;
+                  addItem(
+                    { type: MessageType.USER, text: trimmedQuery },
+                    userMessageTimestamp,
+                  );
                   return {
                     queryToSend: localQueryToSendToGemini,
                     shouldProceed: true,
                   };
                 }
 
+                addItem(
+                  { type: MessageType.USER, text: trimmedQuery },
+                  userMessageTimestamp,
+                );
                 return { queryToSend: null, shouldProceed: false };
               }
               case 'submit_prompt': {
                 localQueryToSendToGemini = slashCommandResult.content;
+                addItem(
+                  { type: MessageType.USER, text: trimmedQuery },
+                  userMessageTimestamp,
+                );
 
                 return {
                   queryToSend: localQueryToSendToGemini,

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

@@ -93,13 +93,16 @@ export function contentPartsToGeminiParts(content: ContentPart[]): Part[] {
         // References are converted to text for the model
         result.push({ text: part.text });
         break;
-      default:
+      default: {
+        const _exhaustiveCheck: never = part;
+        void _exhaustiveCheck;
         debugLogger.warn(
           `Unhandled ContentPart type: ${JSON.stringify(part)} fallback to serialization`,
         );
         // Serialize unknown ContentPart variants instead of dropping them
         result.push({ text: JSON.stringify(part) });
         break;
+      }
     }
   }
   return result;

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

@@ -324,38 +324,6 @@ describe('Server Config (config.ts)', () => {
     });
   });
 
-  describe('model fallback', () => {
-    it('should fallback to default model when an obsolete model is provided', () => {
-      const config = new Config({
-        ...baseParams,
-        model: 'gemini-pro-latest',
-      });
-      expect(config.getModel()).toBe(DEFAULT_GEMINI_MODEL);
-    });
-
-    it('should fallback to default model when an invalid gemini model is provided', () => {
-      const config = new Config({
-        ...baseParams,
-        model: 'gemini-invalid-model',
-      });
-      expect(config.getModel()).toBe(DEFAULT_GEMINI_MODEL);
-    });
-
-    it('should fallback to default model when setModel is called with an invalid gemini model', () => {
-      const config = new Config(baseParams);
-      config.setModel('gemini-invalid-model');
-      expect(config.getModel()).toBe(DEFAULT_GEMINI_MODEL);
-    });
-
-    it('should allow custom models (non-gemini prefixed)', () => {
-      const config = new Config({
-        ...baseParams,
-        model: 'custom-model',
-      });
-      expect(config.getModel()).toBe('custom-model');
-    });
-  });
-
   describe('setShellExecutionConfig', () => {
     it('should preserve existing shell execution fields that are not being updated', () => {
       const config = new Config({
@@ -2051,7 +2019,6 @@ describe('Server Config (config.ts)', () => {
     expect(configInternal.lastEmittedQuotaRemaining).toBeUndefined();
     expect(configInternal.lastEmittedQuotaLimit).toBeUndefined();
     expect(configInternal.lastQuotaFetchTime).toBe(0);
-    expect(configInternal.hasAccessToPreviewModel).toBeNull();
 
     // Event emission
     expect(emitQuotaSpy).toHaveBeenCalledWith(undefined, undefined, undefined);
@@ -2645,7 +2612,7 @@ describe('Config getHooks', () => {
     targetDir: '/path/to/target',
     debugMode: false,
     sessionId: 'test-session-id',
-    model: 'gemini-2.5-flash',
+    model: 'gemini-pro',
     usageStatisticsEnabled: false,
   };
 
@@ -2894,7 +2861,7 @@ describe('Config getExperiments', () => {
     targetDir: '/path/to/target',
     debugMode: false,
     sessionId: 'test-session-id',
-    model: 'gemini-2.5-flash',
+    model: 'gemini-pro',
     usageStatisticsEnabled: false,
   };
 
@@ -2939,7 +2906,7 @@ describe('Config setExperiments logging', () => {
     targetDir: '/path/to/target',
     debugMode: false,
     sessionId: 'test-session-id',
-    model: 'gemini-2.5-flash',
+    model: 'gemini-pro',
     usageStatisticsEnabled: false,
   };
 

packages/core/src/config/config.ts

@@ -80,12 +80,10 @@ import { tokenLimit } from '../core/tokenLimits.js';
 import {
   DEFAULT_GEMINI_EMBEDDING_MODEL,
   DEFAULT_GEMINI_FLASH_MODEL,
-  DEFAULT_GEMINI_MODEL,
   DEFAULT_GEMINI_MODEL_AUTO,
   isAutoModel,
   isPreviewModel,
   isGemini2Model,
-  isValidModel,
   PREVIEW_GEMINI_FLASH_MODEL,
   resolveModel,
 } from './models.js';
@@ -239,6 +237,7 @@ export interface GemmaModelRouterSettings {
 export interface ADKSettings {
   agentSessionNoninteractiveEnabled?: boolean;
   agentSessionInteractiveEnabled?: boolean;
+  agentSessionSubagentEnabled?: boolean;
 }
 
 export interface ExtensionSetting {
@@ -915,6 +914,7 @@ export class Config implements McpContext, AgentLoopContext {
   private readonly gemmaModelRouter: GemmaModelRouterSettings;
   private readonly agentSessionNoninteractiveEnabled: boolean;
   private readonly agentSessionInteractiveEnabled: boolean;
+  private readonly agentSessionSubagentEnabled: boolean;
 
   private readonly retryFetchErrors: boolean;
   private readonly maxAttempts: number;
@@ -1116,11 +1116,9 @@ export class Config implements McpContext, AgentLoopContext {
     this.cwd = params.cwd ?? process.cwd();
     this.fileDiscoveryService = params.fileDiscoveryService ?? null;
     this.bugCommand = params.bugCommand;
-    this.model = isValidModel(params.model)
-      ? params.model
-      : DEFAULT_GEMINI_MODEL;
+    this.model = params.model;
     this.disableLoopDetection = params.disableLoopDetection ?? false;
-    this._activeModel = this.model;
+    this._activeModel = params.model;
     this.enableAgents = params.enableAgents ?? true;
     this.agents = params.agents ?? {};
     this.disableLLMCorrection = params.disableLLMCorrection ?? true;
@@ -1363,6 +1361,8 @@ export class Config implements McpContext, AgentLoopContext {
       params.adk?.agentSessionNoninteractiveEnabled ?? false;
     this.agentSessionInteractiveEnabled =
       params.adk?.agentSessionInteractiveEnabled ?? false;
+    this.agentSessionSubagentEnabled =
+      params.adk?.agentSessionSubagentEnabled ?? false;
     this.retryFetchErrors = params.retryFetchErrors ?? true;
     this.maxAttempts = Math.min(
       params.maxAttempts ?? DEFAULT_MAX_ATTEMPTS,
@@ -1837,7 +1837,6 @@ export class Config implements McpContext, AgentLoopContext {
     this.modelQuotas.clear();
     this.lastRetrievedQuota = undefined;
     this.lastQuotaFetchTime = 0;
-    this.hasAccessToPreviewModel = null;
 
     // Force an event emission to clear the UI display
     coreEvents.emitQuotaChanged(undefined, undefined, undefined);
@@ -1906,20 +1905,17 @@ export class Config implements McpContext, AgentLoopContext {
   }
 
   setModel(newModel: string, isTemporary: boolean = true): void {
-    const validatedModel = isValidModel(newModel)
-      ? newModel
-      : DEFAULT_GEMINI_MODEL;
-    if (this.model !== validatedModel || this._activeModel !== validatedModel) {
-      this.model = validatedModel;
+    if (this.model !== newModel || this._activeModel !== newModel) {
+      this.model = newModel;
       // When the user explicitly sets a model, that becomes the active model.
-      this._activeModel = validatedModel;
-      coreEvents.emitModelChanged(validatedModel);
+      this._activeModel = newModel;
+      coreEvents.emitModelChanged(newModel);
       this.lastEmittedQuotaRemaining = undefined;
       this.lastEmittedQuotaLimit = undefined;
       this.emitQuotaChangedEvent();
     }
     if (this.onModelChange && !isTemporary) {
-      this.onModelChange(validatedModel);
+      this.onModelChange(newModel);
     }
     this.modelAvailabilityService.reset();
   }
@@ -2581,6 +2577,10 @@ export class Config implements McpContext, AgentLoopContext {
     return this.contextManagement.enabled;
   }
 
+  isAgentSessionSubagentEnabled(): boolean {
+    return this.agentSessionSubagentEnabled;
+  }
+
   getMemoryBoundaryMarkers(): readonly string[] {
     return this.memoryBoundaryMarkers;
   }

packages/core/src/config/defaultModelConfigs.ts

@@ -71,6 +71,24 @@ export const DEFAULT_MODEL_CONFIGS: ModelConfigServiceConfig = {
         model: 'gemini-3-flash-preview',
       },
     },
+    'gemini-3.1-pro-preview': {
+      extends: 'chat-base-3',
+      modelConfig: {
+        model: 'gemini-3.1-pro-preview',
+      },
+    },
+    'gemini-3.1-pro-preview-customtools': {
+      extends: 'chat-base-3',
+      modelConfig: {
+        model: 'gemini-3.1-pro-preview-customtools',
+      },
+    },
+    'gemini-3.1-flash-lite-preview': {
+      extends: 'chat-base-3',
+      modelConfig: {
+        model: 'gemini-3.1-flash-lite-preview',
+      },
+    },
     'gemini-2.5-pro': {
       extends: 'chat-base-2.5',
       modelConfig: {

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

@@ -672,3 +672,35 @@ describe('isActiveModel', () => {
     ).toBe(false);
   });
 });
+
+describe('Gemini 3.1 Config Resolution', () => {
+  it('PREVIEW_GEMINI_3_1_MODEL should resolve to chat-base-3 config (including thinkingLevel)', () => {
+    const resolved = modelConfigService.getResolvedConfig({
+      model: PREVIEW_GEMINI_3_1_MODEL,
+      isChatModel: true,
+    });
+    expect(
+      resolved.generateContentConfig?.thinkingConfig?.thinkingLevel,
+    ).toBeDefined();
+  });
+
+  it('PREVIEW_GEMINI_3_1_CUSTOM_TOOLS_MODEL should resolve to chat-base-3 config (including thinkingLevel)', () => {
+    const resolved = modelConfigService.getResolvedConfig({
+      model: PREVIEW_GEMINI_3_1_CUSTOM_TOOLS_MODEL,
+      isChatModel: true,
+    });
+    expect(
+      resolved.generateContentConfig?.thinkingConfig?.thinkingLevel,
+    ).toBeDefined();
+  });
+
+  it('PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL should resolve to chat-base-3 config (including thinkingLevel)', () => {
+    const resolved = modelConfigService.getResolvedConfig({
+      model: PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL,
+      isChatModel: true,
+    });
+    expect(
+      resolved.generateContentConfig?.thinkingConfig?.thinkingLevel,
+    ).toBeDefined();
+  });
+});

packages/core/src/config/models.ts

@@ -4,8 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { normalizeModelId } from '../utils/modelUtils.js';
-
 export interface ModelResolutionContext {
   useGemini3_1?: boolean;
   useGemini3_1FlashLite?: boolean;
@@ -112,20 +110,6 @@ export function getAutoModelDescription(
   return `Let Gemini CLI decide the best model for the task: ${proModel}, ${flashModel}`;
 }
 
-export function isValidModel(model: string): boolean {
-  const normalized = normalizeModelId(model);
-  return (
-    VALID_GEMINI_MODELS.has(normalized) ||
-    normalized === GEMINI_MODEL_ALIAS_AUTO ||
-    normalized === GEMINI_MODEL_ALIAS_PRO ||
-    normalized === GEMINI_MODEL_ALIAS_FLASH ||
-    normalized === GEMINI_MODEL_ALIAS_FLASH_LITE ||
-    normalized === PREVIEW_GEMINI_MODEL_AUTO ||
-    normalized === DEFAULT_GEMINI_MODEL_AUTO ||
-    !normalized.startsWith('gemini-')
-  );
-}
-
 /**
  * Resolves the requested model alias (e.g., 'auto', 'pro', 'flash', 'flash-lite')
  * to a concrete model name.
@@ -180,7 +164,7 @@ export function resolveModel(
   switch (normalizedModel) {
     case GEMINI_MODEL_ALIAS_AUTO:
     case GEMINI_MODEL_ALIAS_PRO: {
-      if (currentReleaseChannel === 'stable') {
+      if (!hasAccessToPreview) {
         resolved = DEFAULT_GEMINI_MODEL;
         break;
       }
@@ -212,12 +196,7 @@ export function resolveModel(
       break;
     }
     default: {
-      if (!isValidModel(normalizedModel)) {
-        // Fallback to stable default for unknown/obsolete models.
-        resolved = DEFAULT_GEMINI_MODEL;
-      } else {
-        resolved = normalizedModel;
-      }
+      resolved = normalizedModel;
       break;
     }
   }

packages/core/src/services/test-data/resolved-aliases-retry.golden.json

@@ -61,6 +61,42 @@
       "topK": 64
     }
   },
+  "gemini-3.1-pro-preview": {
+    "model": "gemini-3.1-pro-preview",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
+  "gemini-3.1-pro-preview-customtools": {
+    "model": "gemini-3.1-pro-preview-customtools",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
+  "gemini-3.1-flash-lite-preview": {
+    "model": "gemini-3.1-flash-lite-preview",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
   "gemini-2.5-pro": {
     "model": "gemini-2.5-pro",
     "generateContentConfig": {

packages/core/src/services/test-data/resolved-aliases.golden.json

@@ -61,6 +61,42 @@
       "topK": 64
     }
   },
+  "gemini-3.1-pro-preview": {
+    "model": "gemini-3.1-pro-preview",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
+  "gemini-3.1-pro-preview-customtools": {
+    "model": "gemini-3.1-pro-preview-customtools",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
+  "gemini-3.1-flash-lite-preview": {
+    "model": "gemini-3.1-flash-lite-preview",
+    "generateContentConfig": {
+      "temperature": 1,
+      "topP": 0.95,
+      "thinkingConfig": {
+        "includeThoughts": true,
+        "thinkingLevel": "HIGH"
+      },
+      "topK": 64
+    }
+  },
   "gemini-2.5-pro": {
     "model": "gemini-2.5-pro",
     "generateContentConfig": {

packages/core/src/utils/fetch.test.ts

@@ -5,7 +5,7 @@
  */
 
 import { updateGlobalFetchTimeouts } from './fetch.js';
-import { describe, it, expect, vi, beforeEach, afterAll } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import * as dnsPromises from 'node:dns/promises';
 import type { LookupAddress, LookupAllOptions } from 'node:dns';
 import ipaddr from 'ipaddr.js';
@@ -34,18 +34,14 @@ const {
   fetchWithTimeout,
   setGlobalProxy,
 } = await import('./fetch.js');
-
-// Mock global fetch
-const originalFetch = global.fetch;
-global.fetch = vi.fn();
-
 interface ErrorWithCode extends Error {
   code?: string;
 }
 
 describe('fetch utils', () => {
   beforeEach(() => {
-    vi.clearAllMocks();
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    vi.spyOn(global, 'fetch').mockImplementation(vi.fn() as any);
     // Default DNS lookup to return a public IP, or the IP itself if valid
     vi.mocked(
       dnsPromises.lookup as (
@@ -60,8 +56,8 @@ describe('fetch utils', () => {
     });
   });
 
-  afterAll(() => {
-    global.fetch = originalFetch;
+  afterEach(() => {
+    vi.restoreAllMocks();
   });
 
   describe('isAddressPrivate', () => {
@@ -177,7 +173,7 @@ describe('fetch utils', () => {
   });
 
   describe('fetchWithTimeout', () => {
-    it('should handle timeouts', async () => {
+    it('should throw FetchError with ETIMEDOUT on an internal timeout', async () => {
       vi.mocked(global.fetch).mockImplementation(
         (_input, init) =>
           new Promise((_resolve, reject) => {
@@ -198,6 +194,46 @@ describe('fetch utils', () => {
         'Request timed out after 50ms',
       );
     });
+
+    it('should throw an AbortError (not ETIMEDOUT) when the caller signal is aborted', async () => {
+      vi.mocked(global.fetch).mockImplementation(
+        (_input, init) =>
+          new Promise((_resolve, reject) => {
+            const rejectWithAbortError = () => {
+              const error = new Error('The operation was aborted');
+              error.name = 'AbortError';
+              // @ts-expect-error - for mocking purposes
+              error.code = 'ABORT_ERR';
+              reject(error);
+            };
+
+            // Handle the case where the signal is already aborted before
+            // fetch is called (e.g. controller.abort() called synchronously).
+            if (init?.signal?.aborted) {
+              rejectWithAbortError();
+              return;
+            }
+
+            if (init?.signal) {
+              init.signal.addEventListener('abort', rejectWithAbortError, {
+                once: true,
+              });
+            }
+          }),
+      );
+
+      const controller = new AbortController();
+      // Abort the external signal before the request even starts
+      controller.abort();
+
+      const rejection = fetchWithTimeout('http://example.com', 10_000, {
+        signal: controller.signal,
+      });
+
+      await expect(rejection).rejects.toMatchObject({ name: 'AbortError' });
+      // Must NOT be classified as a timeout
+      await expect(rejection).rejects.not.toThrow('timed out');
+    });
   });
 
   describe('setGlobalProxy', () => {

packages/core/src/utils/fetch.ts

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { getErrorMessage, isNodeError } from './errors.js';
+import { getErrorMessage, isAbortError } from './errors.js';
 import { URL } from 'node:url';
 import { Agent, ProxyAgent, setGlobalDispatcher } from 'undici';
 import ipaddr from 'ipaddr.js';
@@ -202,7 +202,15 @@ export async function fetchWithTimeout(
     });
     return response;
   } catch (error) {
-    if (isNodeError(error) && error.code === 'ABORT_ERR') {
+    if (isAbortError(error)) {
+      // If the caller's own signal was already aborted, this is a user-initiated
+      // cancellation (e.g. Ctrl+C), not an internal timeout. Re-throw as a plain
+      // AbortError so the retry layer does NOT treat it as a retryable ETIMEDOUT.
+      if (options?.signal?.aborted) {
+        // Rethrow the original abort reason or the caught error to preserve
+        // the stack trace and any custom abort reason (e.g. from Ctrl+C).
+        throw options.signal.reason ?? error;
+      }
       throw new FetchError(`Request timed out after ${timeout}ms`, 'ETIMEDOUT');
     }
     throw new FetchError(getErrorMessage(error), undefined, { cause: error });