feat(cli/sdk): expose /context usage data in non-interactive mode and SDK API

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

@@ -19,6 +19,7 @@ import type {
   CLIControlInitializeRequest,
   CLIControlSetModelRequest,
   CLIMcpServerConfig,
+  CLIControlGetContextUsageRequest,
 } from '../../types.js';
 import { getAvailableCommands } from '../../../nonInteractiveCliCommands.js';
 import {
@@ -61,11 +62,51 @@ export class SystemController extends BaseController {
       case 'supported_commands':
         return this.handleSupportedCommands(signal);
 
+      case 'get_context_usage':
+        return this.handleGetContextUsage(
+          payload as CLIControlGetContextUsageRequest,
+          signal,
+        );
+
       default:
         throw new Error(`Unsupported request subtype in SystemController`);
     }
   }
 
+  private async handleGetContextUsage(
+    payload: CLIControlGetContextUsageRequest,
+    signal: AbortSignal,
+  ): Promise<Record<string, unknown>> {
+    if (signal.aborted) {
+      throw new Error('Request aborted');
+    }
+
+    try {
+      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 mod.collectContextData(
+        this.context.config,
+        showDetails,
+      );
+
+      return {
+        subtype: 'get_context_usage',
+        ...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(errorMessage);
+    }
+  }
+
   /**
    * Handle initialize request
    *
@@ -212,6 +253,7 @@ export class SystemController extends BaseController {
       can_set_permission_mode:
         typeof this.context.config.setApprovalMode === 'function',
       can_set_model: typeof this.context.config.setModel === 'function',
+      can_get_context_usage: true,
       // SDK MCP servers are supported - messages routed through control plane
       can_handle_mcp_message: true,
     };

packages/cli/src/nonInteractive/types.ts

@@ -407,6 +407,11 @@ export interface CLIControlSupportedCommandsRequest {
   subtype: 'supported_commands';
 }
 
+export interface CLIControlGetContextUsageRequest {
+  subtype: 'get_context_usage';
+  show_details?: boolean;
+}
+
 export type ControlRequestPayload =
   | CLIControlInterruptRequest
   | CLIControlPermissionRequest
@@ -416,7 +421,8 @@ export type ControlRequestPayload =
   | CLIControlMcpMessageRequest
   | CLIControlSetModelRequest
   | CLIControlMcpStatusRequest
-  | CLIControlSupportedCommandsRequest;
+  | CLIControlSupportedCommandsRequest
+  | CLIControlGetContextUsageRequest;
 
 export interface CLIControlRequest {
   type: 'control_request';

packages/cli/src/nonInteractiveCliCommands.ts

@@ -37,13 +37,15 @@ 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',
   'summary',
   'compress',
   'btw',
   'bug',
+  'context',
 ] as const;
 
 /**