test(mosaic): control brain config owner binding

packages/mosaic/src/commands/brain-secure-config.spec.ts

@@ -1,4 +1,4 @@
-import { afterEach, describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
 import { chmodSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
@@ -30,6 +30,7 @@ function fixture(): { readonly root: string; readonly directory: string; readonl
 }
 
 afterEach((): void => {
+  vi.restoreAllMocks();
   for (const root of roots.splice(0)) rmSync(root, { recursive: true, force: true });
 });
 
@@ -41,6 +42,19 @@ describe('security-critical brain configuration reads', (): void => {
     expect(secure.readBrainConfigSecure(config.file, config.root)).toBe('{"version":1}\n');
   });
 
+  it('rejects a managed root owned by a UID other than the running principal', async (): Promise<void> => {
+    const secure = await loadSecureConfig();
+    const config = fixture();
+    if (typeof process.getuid !== 'function') throw new Error('test requires POSIX getuid');
+    const processWithUid = process as typeof process & { getuid: () => number };
+    const actualUid = processWithUid.getuid();
+    vi.spyOn(processWithUid, 'getuid').mockReturnValue(actualUid + 1);
+
+    expect(() => secure.readBrainConfigSecure(config.file, config.root)).toThrow(
+      /config-ancestor-owner-unsafe/,
+    );
+  });
+
   it('rejects a group/world-writable policy file', async (): Promise<void> => {
     const secure = await loadSecureConfig();
     const config = fixture();