diff --git a/packages/core/src/tools/edit.test.ts b/packages/core/src/tools/edit.test.ts
index 84086bbd69..897824e00c 100644
--- a/packages/core/src/tools/edit.test.ts
+++ b/packages/core/src/tools/edit.test.ts
@@ -1371,6 +1371,14 @@ function doIt() {
   });
 
   describe('plan mode', () => {
+    beforeEach(() => {
+      vi.mocked(mockConfig.isPlanMode).mockReturnValue(true);
+    });
+
+    afterEach(() => {
+      vi.mocked(mockConfig.isPlanMode).mockReturnValue(false);
+    });
+
     it('should allow edits to plans directory when isPlanMode is true', async () => {
       const mockProjectTempDir = path.join(tempDir, 'project');
       fs.mkdirSync(mockProjectTempDir);
@@ -1380,8 +1388,6 @@ function doIt() {
 
       const plansDir = path.join(mockProjectTempDir, 'plans');
       fs.mkdirSync(plansDir);
-
-      vi.mocked(mockConfig.isPlanMode).mockReturnValue(true);
       vi.mocked(mockConfig.storage.getPlansDir).mockReturnValue(plansDir);
 
       const filePath = 'test-file.txt';
@@ -1408,5 +1414,77 @@ function doIt() {
 
       fs.rmSync(plansDir, { recursive: true, force: true });
     });
+
+    it('should preserve nested directory structure within the plans directory in Plan Mode', async () => {
+      const mockProjectTempDir = path.join(tempDir, 'project');
+      fs.mkdirSync(mockProjectTempDir);
+      vi.mocked(mockConfig.storage.getProjectTempDir).mockReturnValue(
+        mockProjectTempDir,
+      );
+
+      const plansDir = path.join(mockProjectTempDir, 'plans');
+      fs.mkdirSync(plansDir);
+      vi.mocked(mockConfig.storage.getPlansDir).mockReturnValue(plansDir);
+
+      const nestedDir = path.join(plansDir, 'tracks', 'fibsqrt_20260519');
+      fs.mkdirSync(nestedDir, { recursive: true });
+
+      const planFilePath = path.join(nestedDir, 'spec.md');
+      const initialContent = 'some initial content';
+      fs.writeFileSync(planFilePath, initialContent, 'utf8');
+
+      const params: EditToolParams = {
+        file_path: 'tracks/fibsqrt_20260519/spec.md',
+        instruction: 'Replace initial with new',
+        old_string: 'initial',
+        new_string: 'new',
+      };
+
+      const invocation = tool.build(params);
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+
+      expect(result.llmContent).toMatch(/Successfully modified file/);
+      expect(fs.readFileSync(planFilePath, 'utf8')).toBe('some new content');
+
+      fs.rmSync(plansDir, { recursive: true, force: true });
+    });
+
+    it('should strip the leading plansDir folder name segment if present in path', async () => {
+      const mockProjectTempDir = path.join(tempDir, 'project');
+      fs.mkdirSync(mockProjectTempDir);
+      vi.mocked(mockConfig.storage.getProjectTempDir).mockReturnValue(
+        mockProjectTempDir,
+      );
+
+      const plansDir = path.join(mockProjectTempDir, 'plans');
+      fs.mkdirSync(plansDir);
+      vi.mocked(mockConfig.storage.getPlansDir).mockReturnValue(plansDir);
+
+      const nestedDir = path.join(plansDir, 'tracks', 'fibsqrt_20260519');
+      fs.mkdirSync(nestedDir, { recursive: true });
+
+      const planFilePath = path.join(nestedDir, 'spec.md');
+      const initialContent = 'some initial content';
+      fs.writeFileSync(planFilePath, initialContent, 'utf8');
+
+      const params: EditToolParams = {
+        file_path: 'plans/tracks/fibsqrt_20260519/spec.md',
+        instruction: 'Replace initial with new',
+        old_string: 'initial',
+        new_string: 'new',
+      };
+
+      const invocation = tool.build(params);
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+
+      expect(result.llmContent).toMatch(/Successfully modified file/);
+      expect(fs.readFileSync(planFilePath, 'utf8')).toBe('some new content');
+
+      fs.rmSync(plansDir, { recursive: true, force: true });
+    });
   });
 });
diff --git a/packages/core/src/tools/edit.ts b/packages/core/src/tools/edit.ts
index c00ea4c0da..cbf151bfc7 100644
--- a/packages/core/src/tools/edit.ts
+++ b/packages/core/src/tools/edit.ts
@@ -28,6 +28,7 @@ import { buildFilePathArgsPattern } from '../policy/utils.js';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
 import { ToolErrorType } from './tool-error.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
+import { resolvePlanPath } from '../utils/planUtils.js';
 import { isNodeError } from '../utils/errors.js';
 import { correctPath } from '../utils/pathCorrector.js';
 import type { Config } from '../config/config.js';
diff --git a/packages/core/src/tools/exit-plan-mode.test.ts b/packages/core/src/tools/exit-plan-mode.test.ts
index 3501d9df56..4eaaca3b2b 100644
--- a/packages/core/src/tools/exit-plan-mode.test.ts
+++ b/packages/core/src/tools/exit-plan-mode.test.ts
@@ -515,5 +515,28 @@ Ask the user for specific feedback on how to improve the plan.`,
       });
       expect(result).toBeNull();
     });
+
+    it('should accept nested valid path within plans directory', () => {
+      const nestedDir = path.join(mockPlansDir, 'tracks', 'fibsqrt_20260519');
+      fs.mkdirSync(nestedDir, { recursive: true });
+      fs.writeFileSync(path.join(nestedDir, 'spec.md'), '# Content');
+
+      const result = tool.validateToolParams({
+        plan_filename: 'tracks/fibsqrt_20260519/spec.md',
+      });
+      expect(result).toBeNull();
+    });
+
+    it('should strip the leading plansDir folder name segment if present in path', () => {
+      const plansDirName = path.basename(mockPlansDir);
+      const nestedDir = path.join(mockPlansDir, 'tracks', 'fibsqrt_20260519');
+      fs.mkdirSync(nestedDir, { recursive: true });
+      fs.writeFileSync(path.join(nestedDir, 'spec.md'), '# Content');
+
+      const result = tool.validateToolParams({
+        plan_filename: `${plansDirName}/tracks/fibsqrt_20260519/spec.md`,
+      });
+      expect(result).toBeNull();
+    });
   });
 });
diff --git a/packages/core/src/tools/exit-plan-mode.ts b/packages/core/src/tools/exit-plan-mode.ts
index e88723a777..5318e56889 100644
--- a/packages/core/src/tools/exit-plan-mode.ts
+++ b/packages/core/src/tools/exit-plan-mode.ts
@@ -227,7 +227,7 @@ export class ExitPlanModeInvocation extends BaseToolInvocation<
 
       return {
         llmContent: `${exitMessage}
-
+ 
 The approved implementation plan is stored at: ${resolvedPlanPath}
 Read and follow the plan strictly during implementation.`,
         returnDisplay: `Plan approved: ${resolvedPlanPath}`,
@@ -237,7 +237,7 @@ Read and follow the plan strictly during implementation.`,
       if (feedback) {
         return {
           llmContent: `Plan rejected. User feedback: ${feedback}
-
+ 
 The plan is stored at: ${resolvedPlanPath}
 Revise the plan based on the feedback.`,
           returnDisplay: `Feedback: ${feedback}`,
@@ -245,7 +245,7 @@ Revise the plan based on the feedback.`,
       } else {
         return {
           llmContent: `Plan rejected. No feedback provided.
-
+ 
 The plan is stored at: ${resolvedPlanPath}
 Ask the user for specific feedback on how to improve the plan.`,
           returnDisplay: 'Rejected (no feedback)',
diff --git a/packages/core/src/tools/write-file.test.ts b/packages/core/src/tools/write-file.test.ts
index b35d26fe20..e276f1f792 100644
--- a/packages/core/src/tools/write-file.test.ts
+++ b/packages/core/src/tools/write-file.test.ts
@@ -110,6 +110,7 @@ const mockConfigInternal = {
   getActiveModel: () => 'test-model',
   storage: {
     getProjectTempDir: vi.fn().mockReturnValue('/tmp/project'),
+    getPlansDir: vi.fn().mockReturnValue('/tmp/plans'),
   },
 };
 
@@ -148,6 +149,7 @@ describe('WriteFileTool', () => {
     const workspaceContext = new WorkspaceContext(rootDir, [plansDir]);
     const mockStorage = {
       getProjectTempDir: vi.fn().mockReturnValue('/tmp/project'),
+      getPlansDir: vi.fn().mockReturnValue(plansDir),
     };
 
     mockConfig = {
@@ -1146,4 +1148,34 @@ describe('WriteFileTool', () => {
       expect(fs.readFileSync(expectedWritePath, 'utf8')).toBe('nested content');
     });
   });
+
+  describe('Plan Mode path resolution', () => {
+    beforeEach(() => {
+      vi.mocked(mockConfigInternal.isPlanMode).mockReturnValue(true);
+      vi.mocked(mockConfigInternal.storage.getPlansDir).mockReturnValue(
+        plansDir,
+      );
+    });
+
+    afterEach(() => {
+      vi.mocked(mockConfigInternal.isPlanMode).mockReturnValue(false);
+    });
+
+    it('should preserve nested directory structure within the plans directory', () => {
+      const planFilePath = 'tracks/fibsqrt_20260519/spec.md';
+      const params = { file_path: planFilePath, content: '# Spec' };
+      const invocation = tool.build(params);
+
+      expect(
+        (invocation as unknown as { resolvedPath: string }).resolvedPath,
+      ).toBe(path.resolve(plansDir, 'tracks/fibsqrt_20260519/spec.md'));
+    });
+
+    it('should strip the leading plansDir folder name segment if present in path', () => {
+      const plansDirName = path.basename(plansDir);
+      const planFilePath = `${plansDirName}/tracks/fibsqrt_20260519/spec.md`;
+      const params = { file_path: planFilePath, content: '# Spec' };
+      const invocation = tool.build(params);
+    });
+  });
 });
diff --git a/packages/core/src/tools/write-file.ts b/packages/core/src/tools/write-file.ts
index 9ec19b879f..080b3f1bf8 100644
--- a/packages/core/src/tools/write-file.ts
+++ b/packages/core/src/tools/write-file.ts
@@ -29,6 +29,7 @@ import {
 import { buildFilePathArgsPattern } from '../policy/utils.js';
 import { ToolErrorType } from './tool-error.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
+import { resolvePlanPath } from '../utils/planUtils.js';
 import { getErrorMessage, isNodeError } from '../utils/errors.js';
 import { ensureCorrectFileContent } from '../utils/editCorrector.js';
 import { detectLineEnding } from '../utils/textUtils.js';
diff --git a/packages/core/src/utils/planUtils.test.ts b/packages/core/src/utils/planUtils.test.ts
index a8340d596a..5cf6ce0bc8 100644
--- a/packages/core/src/utils/planUtils.test.ts
+++ b/packages/core/src/utils/planUtils.test.ts
@@ -8,7 +8,11 @@ import { describe, it, expect, beforeEach, afterEach } from 'vitest';
 import path from 'node:path';
 import * as fs from 'node:fs';
 import os from 'node:os';
-import { validatePlanPath, validatePlanContent } from './planUtils.js';
+import {
+  validatePlanPath,
+  validatePlanContent,
+  resolvePlanPath,
+} from './planUtils.js';
 
 describe('planUtils', () => {
   let tempRootDir: string;
@@ -63,6 +67,55 @@ describe('planUtils', () => {
       );
       expect(result).toContain('Access denied');
     });
+
+    it('should validate a nested path within the plans directory', async () => {
+      const nestedDir = path.join(plansDir, 'tracks', 'fibsqrt_20260519');
+      fs.mkdirSync(nestedDir, { recursive: true });
+      const planPath = path.join('tracks', 'fibsqrt_20260519', 'spec.md');
+      const fullPath = path.join(plansDir, planPath);
+      fs.writeFileSync(fullPath, '# Nested Spec');
+
+      const result = await validatePlanPath(planPath, plansDir, tempRootDir);
+      expect(result).toBeNull();
+    });
+  });
+
+  describe('resolvePlanPath', () => {
+    it('should resolve simple filenames relative to plansDir', () => {
+      const result = resolvePlanPath(
+        'implementation_plan.md',
+        plansDir,
+        tempRootDir,
+      );
+      expect(result).toBe(path.join(plansDir, 'implementation_plan.md'));
+    });
+
+    it('should preserve subdirectories if already inside plansDir', () => {
+      const planPath = path.join(
+        'plans',
+        'tracks',
+        'fibsqrt_20260519',
+        'spec.md',
+      );
+      const result = resolvePlanPath(planPath, plansDir, tempRootDir);
+      expect(result).toBe(
+        path.join(plansDir, 'tracks', 'fibsqrt_20260519', 'spec.md'),
+      );
+    });
+
+    it('should resolve paths relative to plansDir if they contain subdirectories', () => {
+      const planPath = path.join('tracks', 'fibsqrt_20260519', 'spec.md');
+      const result = resolvePlanPath(planPath, plansDir, tempRootDir);
+      expect(result).toBe(
+        path.join(plansDir, 'tracks', 'fibsqrt_20260519', 'spec.md'),
+      );
+    });
+
+    it('should fallback to safe basename when escaping', () => {
+      const planPath = '../../escaped.md';
+      const result = resolvePlanPath(planPath, plansDir, tempRootDir);
+      expect(result).toBe(path.join(plansDir, 'escaped.md'));
+    });
   });
 
   describe('validatePlanContent', () => {
diff --git a/packages/core/src/utils/planUtils.ts b/packages/core/src/utils/planUtils.ts
index 8060fbfd51..a1a869edd0 100644
--- a/packages/core/src/utils/planUtils.ts
+++ b/packages/core/src/utils/planUtils.ts
@@ -22,14 +22,6 @@ export const PlanErrorMessages = {
   READ_FAILURE: (detail: string) => `Failed to read plan file: ${detail}`,
 } as const;
 
-/**
- * Resolves a plan file path and strictly validates it against the plans directory boundary.
- * Useful for tools that need to write or read plans.
- * @param planPath The untrusted file path provided by the model.
- * @param plansDir The authorized project plans directory.
- * @returns The safely resolved path string.
- * @throws Error if the path is empty, malicious, or escapes boundaries.
- */
 export function resolveAndValidatePlanPath(
   planPath: string,
   plansDir: string,
@@ -40,38 +32,59 @@ export function resolveAndValidatePlanPath(
     throw new Error('Plan file path must be non-empty.');
   }
 
-  // 1. Handle case where agent provided an absolute path
-  if (path.isAbsolute(trimmedPath)) {
-    if (
-      isSubpath(resolveToRealPath(plansDir), resolveToRealPath(trimmedPath))
-    ) {
-      return trimmedPath;
+  const realPlansDir = resolveToRealPath(plansDir);
+  const plansDirName = path.basename(plansDir);
+
+  let normalizedPlanPath = trimmedPath;
+  if (!path.isAbsolute(trimmedPath)) {
+    const segments = trimmedPath.split(/[\\/]+/);
+    if (segments.length > 1 && segments[0] === plansDirName) {
+      normalizedPlanPath = segments.slice(1).join(path.sep);
     }
   }
 
-  // 2. Handle case where agent provided a path relative to the project root
-  const resolvedFromProjectRoot = path.resolve(projectRoot, trimmedPath);
-  if (
-    isSubpath(
-      resolveToRealPath(plansDir),
-      resolveToRealPath(resolvedFromProjectRoot),
-    )
-  ) {
-    return resolvedFromProjectRoot;
+  // 1. Handle case where agent provided an absolute path
+  if (path.isAbsolute(normalizedPlanPath)) {
+    try {
+      const realResolved = resolveToRealPath(normalizedPlanPath);
+      if (isSubpath(realPlansDir, realResolved)) {
+        return normalizedPlanPath;
+      }
+    } catch {
+      // Fall through if resolveToRealPath fails
+    }
   }
 
-  // 3. Handle default case where agent provided a path relative to the plans directory
-  const resolvedPath = path.resolve(plansDir, trimmedPath);
-  const realPath = resolveToRealPath(resolvedPath);
-  const realPlansDir = resolveToRealPath(plansDir);
-
-  if (!isSubpath(realPlansDir, realPath)) {
-    throw new Error(
-      PlanErrorMessages.PATH_ACCESS_DENIED(trimmedPath, plansDir),
-    );
+  // 2. Try resolving relative to project root
+  const resolvedFromProjectRoot = path.resolve(projectRoot, normalizedPlanPath);
+  try {
+    const realResolved = resolveToRealPath(resolvedFromProjectRoot);
+    if (isSubpath(realPlansDir, realResolved)) {
+      return resolvedFromProjectRoot;
+    }
+  } catch {
+    const directResolved = path.resolve(resolvedFromProjectRoot);
+    if (isSubpath(realPlansDir, directResolved)) {
+      return resolvedFromProjectRoot;
+    }
   }
 
-  return resolvedPath;
+  // 3. Try resolving relative to plansDir
+  const resolvedFromPlansDir = path.resolve(plansDir, normalizedPlanPath);
+  try {
+    const realResolved = resolveToRealPath(resolvedFromPlansDir);
+    if (isSubpath(realPlansDir, realResolved)) {
+      return resolvedFromPlansDir;
+    }
+  } catch {
+    const directResolved = path.resolve(resolvedFromPlansDir);
+    if (isSubpath(realPlansDir, directResolved)) {
+      return resolvedFromPlansDir;
+    }
+  }
+
+  // Fallback boundary check: if still not a subpath, throw PATH_ACCESS_DENIED
+  throw new Error(PlanErrorMessages.PATH_ACCESS_DENIED(trimmedPath, plansDir));
 }
 
 /**