fix(core): sandbox path resolution in Plan Mode to prevent hallucinations and traversal

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

@@ -35,19 +35,13 @@ describe('planUtils', () => {
       const fullPath = path.join(tempRootDir, planPath);
       fs.writeFileSync(fullPath, '# My Plan');
 
-      const result = await validatePlanPath(planPath, plansDir, tempRootDir);
+      const result = await validatePlanPath(planPath, plansDir);
       expect(result).toBeNull();
     });
 
-    it('should return error for path traversal', async () => {
-      const planPath = path.join('..', 'secret.txt');
-      const result = await validatePlanPath(planPath, plansDir, tempRootDir);
-      expect(result).toContain('Access denied');
-    });
-
     it('should return error for non-existent file', async () => {
       const planPath = path.join('plans', 'ghost.md');
-      const result = await validatePlanPath(planPath, plansDir, tempRootDir);
+      const result = await validatePlanPath(planPath, plansDir);
       expect(result).toContain('Plan file does not exist');
     });
 
@@ -60,11 +54,7 @@ describe('planUtils', () => {
       // Create a symbolic link pointing outside the plans directory
       fs.symlinkSync(outsideFile, fullMaliciousPath);
 
-      const result = await validatePlanPath(
-        maliciousPath,
-        plansDir,
-        tempRootDir,
-      );
+      const result = await validatePlanPath(maliciousPath, plansDir);
       expect(result).toContain('Access denied');
     });
   });

packages/core/src/utils/planUtils.ts

@@ -13,8 +13,8 @@ import { isSubpath, resolveToRealPath } from './paths.js';
  * Shared between backend tools and CLI UI for consistency.
  */
 export const PlanErrorMessages = {
-  PATH_ACCESS_DENIED:
-    'Access denied: plan path must be within the designated plans directory.',
+  PATH_ACCESS_DENIED: (planPath: string, plansDir: string) =>
+    `Access denied: plan path (${planPath}) must be within the designated plans directory (${plansDir}).`,
   FILE_NOT_FOUND: (path: string) =>
     `Plan file does not exist: ${path}. You must create the plan file before requesting approval.`,
   FILE_EMPTY:
@@ -32,14 +32,14 @@ export const PlanErrorMessages = {
 export async function validatePlanPath(
   planPath: string,
   plansDir: string,
-  targetDir: string,
 ): Promise<string | null> {
-  const resolvedPath = path.resolve(targetDir, planPath);
+  const safeFilename = path.basename(planPath);
+  const resolvedPath = path.resolve(plansDir, safeFilename);
   const realPath = resolveToRealPath(resolvedPath);
   const realPlansDir = resolveToRealPath(plansDir);
 
   if (!isSubpath(realPlansDir, realPath)) {
-    return PlanErrorMessages.PATH_ACCESS_DENIED;
+    return PlanErrorMessages.PATH_ACCESS_DENIED(planPath, realPlansDir);
   }
 
   if (!(await fileExists(resolvedPath))) {