diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index e4c0fef6eb..50af69f022 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -1349,6 +1349,7 @@ export class Config implements McpContext {
 
   setSessionId(sessionId: string): void {
     this.sessionId = sessionId;
+    this.storage.setSessionId(sessionId);
   }
 
   setTerminalBackground(terminalBackground: string | undefined): void {
diff --git a/packages/core/src/config/storage.test.ts b/packages/core/src/config/storage.test.ts
index 15b49d12f1..06ea04be33 100644
--- a/packages/core/src/config/storage.test.ts
+++ b/packages/core/src/config/storage.test.ts
@@ -13,6 +13,7 @@ vi.unmock('./storageMigration.js');
 import * as os from 'node:os';
 import * as path from 'node:path';
 import * as fs from 'node:fs';
+import { sessionId as defaultSessionId } from '../utils/session.js';
 
 vi.mock('fs', async (importOriginal) => {
   const actual = await importOriginal<typeof import('fs')>();
@@ -161,10 +162,10 @@ describe('Storage – additional helpers', () => {
     expect(Storage.getGlobalBinDir()).toBe(expected);
   });
 
-  it('getProjectTempPlansDir returns ~/.gemini/tmp/<identifier>/plans when no sessionId is provided', async () => {
+  it('getProjectTempPlansDir returns ~/.gemini/tmp/<identifier>/<defaultSessionId>/plans when no sessionId is provided', async () => {
     await storage.initialize();
     const tempDir = storage.getProjectTempDir();
-    const expected = path.join(tempDir, 'plans');
+    const expected = path.join(tempDir, defaultSessionId, 'plans');
     expect(storage.getProjectTempPlansDir()).toBe(expected);
   });
 
diff --git a/packages/core/src/config/storage.ts b/packages/core/src/config/storage.ts
index 10e88543ba..e903662607 100644
--- a/packages/core/src/config/storage.ts
+++ b/packages/core/src/config/storage.ts
@@ -16,6 +16,7 @@ import {
   resolveToRealPath,
   normalizePath,
 } from '../utils/paths.js';
+import { sessionId as defaultSessionId } from '../utils/session.js';
 import { ProjectRegistry } from './projectRegistry.js';
 import { StorageMigration } from './storageMigration.js';
 
@@ -28,16 +29,20 @@ export const AUTO_SAVED_POLICY_FILENAME = 'auto-saved.toml';
 
 export class Storage {
   private readonly targetDir: string;
-  private readonly sessionId: string | undefined;
+  private sessionId: string;
   private projectIdentifier: string | undefined;
   private initPromise: Promise<void> | undefined;
   private customPlansDir: string | undefined;
 
-  constructor(targetDir: string, sessionId?: string) {
+  constructor(targetDir: string, sessionId: string = defaultSessionId) {
     this.targetDir = targetDir;
     this.sessionId = sessionId;
   }
 
+  setSessionId(sessionId: string): void {
+    this.sessionId = sessionId;
+  }
+
   setCustomPlansDir(dir: string | undefined): void {
     this.customPlansDir = dir;
   }
@@ -280,10 +285,7 @@ export class Storage {
   }
 
   getProjectTempPlansDir(): string {
-    if (this.sessionId) {
-      return path.join(this.getProjectTempDir(), this.sessionId, 'plans');
-    }
-    return path.join(this.getProjectTempDir(), 'plans');
+    return path.join(this.getProjectTempDir(), this.sessionId, 'plans');
   }
 
   getProjectTempTrackerDir(): string {
@@ -311,10 +313,7 @@ export class Storage {
   }
 
   getProjectTempTasksDir(): string {
-    if (this.sessionId) {
-      return path.join(this.getProjectTempDir(), this.sessionId, 'tasks');
-    }
-    return path.join(this.getProjectTempDir(), 'tasks');
+    return path.join(this.getProjectTempDir(), this.sessionId, 'tasks');
   }
 
   async listProjectChatFiles(): Promise<