diff --git a/packages/cli/src/utils/sandbox.test.ts b/packages/cli/src/utils/sandbox.test.ts
index ef972a4a0b..1dda7b355a 100644
--- a/packages/cli/src/utils/sandbox.test.ts
+++ b/packages/cli/src/utils/sandbox.test.ts
@@ -8,8 +8,13 @@ import { vi, describe, it, expect, beforeEach, afterEach } from 'vitest';
 import { spawn, exec, execFile, execSync } from 'node:child_process';
 import os from 'node:os';
 import fs from 'node:fs';
+import path from 'node:path';
 import { start_sandbox } from './sandbox.js';
-import { FatalSandboxError, type SandboxConfig } from '@google/gemini-cli-core';
+import {
+  FatalSandboxError,
+  homedir,
+  type SandboxConfig,
+} from '@google/gemini-cli-core';
 import { createMockSandboxConfig } from '@google/gemini-cli-test-utils';
 import { EventEmitter } from 'node:events';
 
@@ -133,6 +138,7 @@ describe('sandbox', () => {
   afterEach(() => {
     process.env = originalEnv;
     process.argv = originalArgv;
+    vi.unstubAllEnvs();
   });
 
   describe('start_sandbox', () => {
@@ -171,6 +177,105 @@ describe('sandbox', () => {
       );
     });
 
+    it('should resolve custom seatbelt profile from user home directory', async () => {
+      vi.mocked(os.platform).mockReturnValue('darwin');
+      vi.stubEnv('SEATBELT_PROFILE', 'custom-test');
+      vi.mocked(fs.existsSync).mockImplementation((p) =>
+        String(p).includes(
+          path.join(homedir(), '.gemini', 'sandbox-macos-custom-test.sb'),
+        ),
+      );
+      const config: SandboxConfig = createMockSandboxConfig({
+        command: 'sandbox-exec',
+        image: 'some-image',
+      });
+
+      interface MockProcess extends EventEmitter {
+        stdout: EventEmitter;
+        stderr: EventEmitter;
+      }
+      const mockSpawnProcess = new EventEmitter() as MockProcess;
+      mockSpawnProcess.stdout = new EventEmitter();
+      mockSpawnProcess.stderr = new EventEmitter();
+      vi.mocked(spawn).mockReturnValue(
+        mockSpawnProcess as unknown as ReturnType<typeof spawn>,
+      );
+
+      const promise = start_sandbox(config, [], undefined, ['arg1']);
+
+      setTimeout(() => {
+        mockSpawnProcess.emit('close', 0);
+      }, 10);
+
+      await expect(promise).resolves.toBe(0);
+      expect(spawn).toHaveBeenCalledWith(
+        'sandbox-exec',
+        expect.any(Array),
+        expect.objectContaining({ stdio: 'inherit' }),
+      );
+      const spawnArgs = vi.mocked(spawn).mock.calls[0]?.[1];
+      expect(spawnArgs).toEqual(
+        expect.arrayContaining(['-f', expect.any(String)]),
+      );
+      const profileArg = spawnArgs?.[spawnArgs.indexOf('-f') + 1];
+      expect(profileArg).toEqual(
+        expect.stringContaining(
+          path.join(homedir(), '.gemini', 'sandbox-macos-custom-test.sb'),
+        ),
+      );
+    });
+
+    it('should fall back to project .gemini directory when user profile is missing', async () => {
+      vi.mocked(os.platform).mockReturnValue('darwin');
+      vi.stubEnv('SEATBELT_PROFILE', 'custom-test');
+      vi.mocked(fs.existsSync).mockImplementation((p) => {
+        const s = String(p);
+        return (
+          s.includes(path.join('.gemini', 'sandbox-macos-custom-test.sb')) &&
+          !s.includes(path.join(homedir(), '.gemini'))
+        );
+      });
+      const config: SandboxConfig = createMockSandboxConfig({
+        command: 'sandbox-exec',
+        image: 'some-image',
+      });
+
+      interface MockProcess extends EventEmitter {
+        stdout: EventEmitter;
+        stderr: EventEmitter;
+      }
+      const mockSpawnProcess = new EventEmitter() as MockProcess;
+      mockSpawnProcess.stdout = new EventEmitter();
+      mockSpawnProcess.stderr = new EventEmitter();
+      vi.mocked(spawn).mockReturnValue(
+        mockSpawnProcess as unknown as ReturnType<typeof spawn>,
+      );
+
+      const promise = start_sandbox(config, [], undefined, ['arg1']);
+
+      setTimeout(() => {
+        mockSpawnProcess.emit('close', 0);
+      }, 10);
+
+      await expect(promise).resolves.toBe(0);
+      expect(spawn).toHaveBeenCalledWith(
+        'sandbox-exec',
+        expect.any(Array),
+        expect.objectContaining({ stdio: 'inherit' }),
+      );
+      const spawnArgs = vi.mocked(spawn).mock.calls[0]?.[1];
+      expect(spawnArgs).toEqual(
+        expect.arrayContaining(['-f', expect.any(String)]),
+      );
+      const profileArg = spawnArgs?.[spawnArgs.indexOf('-f') + 1];
+      expect(profileArg).toEqual(
+        expect.stringContaining(
+          path.join('.gemini', 'sandbox-macos-custom-test.sb'),
+        ),
+      );
+      expect(profileArg).not.toContain(homedir());
+    });
+
     it('should throw FatalSandboxError if seatbelt profile is missing', async () => {
       vi.mocked(os.platform).mockReturnValue('darwin');
       vi.mocked(fs.existsSync).mockReturnValue(false);
diff --git a/packages/cli/src/utils/sandbox.ts b/packages/cli/src/utils/sandbox.ts
index dbd2ec64e3..6001725cdd 100644
--- a/packages/cli/src/utils/sandbox.ts
+++ b/packages/cli/src/utils/sandbox.ts
@@ -68,9 +68,17 @@ export async function start_sandbox(
       let profileFile = fileURLToPath(
         new URL(`sandbox-macos-${profile}.sb`, import.meta.url),
       );
-      // if profile name is not recognized, then look for file under project settings directory
+      // if profile name is not recognized, look in user-level ~/.gemini first,
+      // then fall back to project-level .gemini. path.basename() strips any
+      // directory separators to prevent path traversal via SEATBELT_PROFILE.
       if (!BUILTIN_SEATBELT_PROFILES.includes(profile)) {
-        profileFile = path.join(GEMINI_DIR, `sandbox-macos-${profile}.sb`);
+        const safeProfile = path.basename(profile);
+        const fileName = `sandbox-macos-${safeProfile}.sb`;
+        const userProfileFile = path.join(homedir(), GEMINI_DIR, fileName);
+        const projectProfileFile = path.join(GEMINI_DIR, fileName);
+        profileFile = fs.existsSync(userProfileFile)
+          ? userProfileFile
+          : projectProfileFile;
       }
       if (!fs.existsSync(profileFile)) {
         throw new FatalSandboxError(