diff --git a/app/api/projects/[projectId]/members/route.ts b/app/api/projects/[projectId]/members/route.ts
index 642306f..cd11988 100644
--- a/app/api/projects/[projectId]/members/route.ts
+++ b/app/api/projects/[projectId]/members/route.ts
@@ -1,9 +1,9 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { getCurrentUser } from '@/lib/auth/getCurrentUser';
 import { createProjectService, createUserRepository } from '@/lib/api/services';
+import { validateProjectMemberRole } from '@/lib/validators/projectValidator';
 import { UnauthorizedError, NotFoundError } from '@/lib/errors';
 import { handleApiError, jsonError } from '@/lib/api/handleError';
-import type { ProjectMemberRole } from '@/lib/types';
 
 export const runtime = 'nodejs';
 
@@ -44,9 +44,9 @@ export async function POST(
   }
 
   const email = String(body.email ?? '');
-  const role = (
+  const role = validateProjectMemberRole(
     typeof body.role === 'string' ? body.role : 'member'
-  ) as ProjectMemberRole;
+  );
 
   // メールアドレスからユーザーを解決する
   const targetUser = createUserRepository().findByEmail(email);
diff --git a/lib/auth/session.ts b/lib/auth/session.ts
index 8346fa0..097af27 100644
--- a/lib/auth/session.ts
+++ b/lib/auth/session.ts
@@ -50,8 +50,15 @@ export function verifySessionToken(token: string): number | null {
   try {
     const payload = JSON.parse(
       Buffer.from(encoded, 'base64url').toString('utf-8')
-    ) as { uid?: unknown };
+    ) as { uid?: unknown; iat?: unknown };
     if (typeof payload.uid !== 'number') return null;
+    // サーバ側でも有効期限を検証する(クッキーのmaxAgeだけに依存しない)
+    if (
+      typeof payload.iat !== 'number' ||
+      Date.now() - payload.iat > SESSION_MAX_AGE_SECONDS * 1000
+    ) {
+      return null;
+    }
     return payload.uid;
   } catch {
     return null;
diff --git a/lib/validators/projectValidator.ts b/lib/validators/projectValidator.ts
index b47592e..72fe9a0 100644
--- a/lib/validators/projectValidator.ts
+++ b/lib/validators/projectValidator.ts
@@ -1,5 +1,5 @@
 import { ValidationError } from '@/lib/errors';
-import type { ProjectStatus } from '@/lib/types';
+import type { ProjectMemberRole, ProjectStatus } from '@/lib/types';
 
 const MAX_NAME_LENGTH = 200;
 const MAX_DESCRIPTION_LENGTH = 2000;
@@ -9,6 +9,7 @@ const VALID_STATUSES: ProjectStatus[] = [
   'completed',
   'archived',
 ];
+const VALID_MEMBER_ROLES: ProjectMemberRole[] = ['admin', 'member', 'guest'];
 
 export interface ProjectCreateInput {
   name: string;
@@ -64,3 +65,10 @@ export function validateProjectUpdate(input: ProjectUpdateInput): void {
     throw new ValidationError('無効なステータスです', 'status');
   }
 }
+
+export function validateProjectMemberRole(role: string): ProjectMemberRole {
+  if (!VALID_MEMBER_ROLES.includes(role as ProjectMemberRole)) {
+    throw new ValidationError('無効なメンバーロールです', 'role');
+  }
+  return role as ProjectMemberRole;
+}
diff --git a/tests/unit/lib/auth/session.test.ts b/tests/unit/lib/auth/session.test.ts
index ac30155..3d7cc2c 100644
--- a/tests/unit/lib/auth/session.test.ts
+++ b/tests/unit/lib/auth/session.test.ts
@@ -1,6 +1,18 @@
 import { describe, it, expect } from 'vitest';
+import crypto from 'node:crypto';
 import { createSessionToken, verifySessionToken } from '@/lib/auth/session';
 
+function forgeToken(uid: number, iat: number): string {
+  const secret = process.env.SESSION_SECRET!;
+  const payload = JSON.stringify({ uid, iat });
+  const encoded = Buffer.from(payload, 'utf-8').toString('base64url');
+  const signature = crypto
+    .createHmac('sha256', secret)
+    .update(encoded)
+    .digest('base64url');
+  return `${encoded}.${signature}`;
+}
+
 describe('session token', () => {
   it('round-trips a user id through create and verify', () => {
     const token = createSessionToken(42);
@@ -34,6 +46,15 @@ describe('session token', () => {
     expect(verifySessionToken('')).toBeNull();
   });
 
+  it('returns null for an expired token (stale iat)', () => {
+    const eightDaysAgo = Date.now() - 8 * 24 * 60 * 60 * 1000;
+    expect(verifySessionToken(forgeToken(42, eightDaysAgo))).toBeNull();
+  });
+
+  it('accepts a freshly-issued token', () => {
+    expect(verifySessionToken(forgeToken(42, Date.now()))).toBe(42);
+  });
+
   it('returns null when the payload uid is not a number', () => {
     const encoded = Buffer.from(
       JSON.stringify({ uid: 'not-a-number', iat: Date.now() })
diff --git a/vitest.config.ts b/vitest.config.ts
index 4318b8b..e697520 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -22,11 +22,14 @@ export default defineConfig({
     coverage: {
       provider: 'v8',
       reporter: ['text', 'json', 'html'],
+      include: ['repositories/**', 'services/**'],
       exclude: [
         'node_modules/**',
         'dist/**',
         '.next/**',
         '.steering/**',
+        'app/**',
+        'components/**',
         '**/*.config.{ts,js,mjs}',
         '**/types/**',
         'tests/**',