diff --git a/bunfig.toml b/bunfig.toml
new file mode 100644
index 00000000..dbf0d8f5
--- /dev/null
+++ b/bunfig.toml
@@ -0,0 +1,7 @@
+[test]
+# Force each test file into its own worker process.
+# Prevents mock.module() calls (which are permanent within a worker)
+# from leaking across test files in parallel runs.
+# Note: smol=true increases test startup time by spawning one Bun process per file.
+# See: https://github.com/thedotmack/claude-mem/issues/1299
+smol = true
diff --git a/tests/hooks/context-reinjection-guard.test.ts b/tests/hooks/context-reinjection-guard.test.ts
index 6d84e278..0db5f2fd 100644
--- a/tests/hooks/context-reinjection-guard.test.ts
+++ b/tests/hooks/context-reinjection-guard.test.ts
@@ -38,10 +38,6 @@ mock.module('../../src/shared/worker-utils.js', () => ({
   },
 }));
 
-mock.module('../../src/utils/project-name.js', () => ({
-  getProjectName: () => 'test-project',
-}));
-
 mock.module('../../src/utils/project-filter.js', () => ({
   isProjectExcluded: () => false,
 }));
diff --git a/tests/utils/project-name-isolation.test.ts b/tests/utils/project-name-isolation.test.ts
new file mode 100644
index 00000000..7c08e04c
--- /dev/null
+++ b/tests/utils/project-name-isolation.test.ts
@@ -0,0 +1,28 @@
+/**
+ * Regression test for mock.module() worker pollution (#1299)
+ *
+ * context-reinjection-guard.test.ts used to call mock.module('../../src/utils/project-name.js', ...)
+ * at the top level, which permanently stubbed getProjectName to return 'test-project'
+ * for every subsequent import in the same Bun worker process.
+ *
+ * Without bunfig.toml [test] smol=true, this test would fail when Bun scheduled
+ * it in the same worker as context-reinjection-guard.test.ts, because the module
+ * was mocked before these tests ran and getProjectName() returned 'test-project'
+ * instead of the real extracted basename.
+ */
+import { describe, it, expect } from 'bun:test';
+import { getProjectName } from '../../src/utils/project-name.js';
+
+describe('getProjectName mock isolation (#1299)', () => {
+  it('returns real basename, not the leaked test-project mock', () => {
+    expect(getProjectName('/real/path/to/my-project')).toBe('my-project');
+  });
+
+  it('returns unknown-project for empty string (real implementation)', () => {
+    expect(getProjectName('')).toBe('unknown-project');
+  });
+
+  it('returns real basename from nested path', () => {
+    expect(getProjectName('/home/user/code/awesome-app')).toBe('awesome-app');
+  });
+});