fix: address review feedback and fix critical bugs in context usage feature

- Add missing `get_context_usage` route in ControlDispatcher (SDK calls would throw)
- Fix `executionMode` defaulting: use `?? 'interactive'` to match other commands
- Validate dynamic import of `collectContextData` before invoking
- Preserve original error message in handleGetContextUsage catch block
- Add ControlDispatcher test for get_context_usage routing
- Add JSDoc comment for context command in non-interactive allowlist

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wenshao

packages/cli/src/nonInteractive/control/ControlDispatcher.test.ts

@@ -18,6 +18,7 @@ import type {
   CLIControlInterruptRequest,
   CLIControlSetModelRequest,
   CLIControlSupportedCommandsRequest,
+  CLIControlGetContextUsageRequest,
 } from '../types.js';
 
 /**
@@ -242,6 +243,41 @@ describe('ControlDispatcher', () => {
       });
     });
 
+    it('should route get_context_usage request to system controller', async () => {
+      const request: CLIControlRequest = {
+        type: 'control_request',
+        request_id: 'req-ctx',
+        request: {
+          subtype: 'get_context_usage',
+          show_details: false,
+        } as CLIControlGetContextUsageRequest,
+      };
+
+      const mockResponse = {
+        subtype: 'get_context_usage',
+        totalTokens: 1000,
+      };
+
+      vi.mocked(mockSystemController.handleRequest).mockResolvedValue(
+        mockResponse,
+      );
+
+      await dispatcher.dispatch(request);
+
+      expect(mockSystemController.handleRequest).toHaveBeenCalledWith(
+        request.request,
+        'req-ctx',
+      );
+      expect(mockContext.streamJson.send).toHaveBeenCalledWith({
+        type: 'control_response',
+        response: {
+          subtype: 'success',
+          request_id: 'req-ctx',
+          response: mockResponse,
+        },
+      });
+    });
+
     it('should send error response when controller throws error', async () => {
       const request: CLIControlRequest = {
         type: 'control_request',

packages/cli/src/nonInteractive/control/ControlDispatcher.ts

@@ -14,7 +14,7 @@
  * which wraps these controllers with a stable programmatic API.
  *
  * Controllers:
- * - SystemController: initialize, interrupt, set_model, supported_commands
+ * - SystemController: initialize, interrupt, set_model, supported_commands, get_context_usage
  * - PermissionController: can_use_tool, set_permission_mode
  * - SdkMcpController: mcp_server_status (mcp_message handled via callback)
  * - HookController: hook_callback
@@ -380,6 +380,7 @@ export class ControlDispatcher implements IPendingRequestRegistry {
       case 'interrupt':
       case 'set_model':
       case 'supported_commands':
+      case 'get_context_usage':
         return this.systemController;
 
       case 'can_use_tool':

packages/cli/src/nonInteractive/control/controllers/systemController.ts

@@ -82,11 +82,12 @@ export class SystemController extends BaseController {
     }
 
     try {
-      const { collectContextData } = await import(
-        '../../../ui/commands/contextCommand.js'
-      );
+      const mod = await import('../../../ui/commands/contextCommand.js');
+      if (typeof mod.collectContextData !== 'function') {
+        throw new Error('collectContextData is not available');
+      }
       const showDetails = payload.show_details ?? false;
-      const contextUsageItem = await collectContextData(
+      const contextUsageItem = await mod.collectContextData(
         this.context.config,
         showDetails,
       );
@@ -96,11 +97,13 @@ export class SystemController extends BaseController {
         ...contextUsageItem,
       };
     } catch (error) {
+      const errorMessage =
+        error instanceof Error ? error.message : 'Failed to get context usage';
       debugLogger.error(
         '[SystemController] Failed to get context usage:',
         error,
       );
-      throw new Error('Failed to get context usage');
+      throw new Error(errorMessage);
     }
   }
 

packages/cli/src/nonInteractiveCliCommands.ts

@@ -37,6 +37,7 @@ const debugLogger = createDebugLogger('NON_INTERACTIVE_COMMANDS');
  * - init: Initialize project configuration
  * - summary: Generate session summary
  * - compress: Compress conversation history
+ * - context: Show context window usage (read-only diagnostic)
  */
 export const ALLOWED_BUILTIN_COMMANDS_NON_INTERACTIVE = [
   'init',

packages/cli/src/ui/commands/contextCommand.ts

@@ -319,9 +319,10 @@ export const contextCommand: SlashCommand = {
     const showDetails =
       args?.trim().toLowerCase() === 'detail' ||
       args?.trim().toLowerCase() === '-d';
+    const executionMode = context.executionMode ?? 'interactive';
     const { config } = context.services;
     if (!config) {
-      if (context.executionMode === 'interactive') {
+      if (executionMode === 'interactive') {
         context.ui.addItem(
           {
             type: MessageType.ERROR,
@@ -340,7 +341,7 @@ export const contextCommand: SlashCommand = {
 
     const contextUsageItem = await collectContextData(config, showDetails);
 
-    if (context.executionMode === 'interactive') {
+    if (executionMode === 'interactive') {
       context.ui.addItem(contextUsageItem, Date.now());
       return;
     } else {