feat(plan): handle inconsistency in schedulers (#17813)

packages/core/src/scheduler/policy.ts

@@ -4,10 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import { ToolErrorType } from '../tools/tool-error.js';
 import {
   ApprovalMode,
   PolicyDecision,
   type CheckResult,
+  type PolicyRule,
 } from '../policy/types.js';
 import type { Config } from '../config/config.js';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
@@ -24,6 +26,30 @@ import { DiscoveredMCPTool } from '../tools/mcp-tool.js';
 import { EDIT_TOOL_NAMES } from '../tools/tool-names.js';
 import type { ValidatingToolCall } from './types.js';
 
+export const PLAN_MODE_DENIAL_MESSAGE =
+  'You are in Plan Mode - adjust your prompt to only use read and search tools.';
+
+/**
+ * Helper to determine the error message and type for a policy denial.
+ */
+export function getPolicyDenialError(
+  config: Config,
+  rule?: PolicyRule,
+): { errorMessage: string; errorType: ToolErrorType } {
+  if (config.getApprovalMode() === ApprovalMode.PLAN) {
+    return {
+      errorMessage: PLAN_MODE_DENIAL_MESSAGE,
+      errorType: ToolErrorType.STOP_EXECUTION,
+    };
+  }
+
+  const denyMessage = rule?.denyMessage ? ` ${rule.denyMessage}` : '';
+  return {
+    errorMessage: `Tool execution denied by policy.${denyMessage}`,
+    errorType: ToolErrorType.POLICY_VIOLATION,
+  };
+}
+
 /**
  * Queries the system PolicyEngine to determine tool allowance.
  * @returns The PolicyDecision.