diff --git a/tests/setup.ts b/tests/setup.ts
new file mode 100644
index 00000000..b4f27206
--- /dev/null
+++ b/tests/setup.ts
@@ -0,0 +1,13 @@
+// Copyright 2026 Layne Penney
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/**
+ * Vitest global setup.
+ *
+ * Removes workspace-specific environment variables that interfere with
+ * test isolation.  CODI_HOME is set by envsetup.sh to point at the
+ * workspace .codi directory, but tests expect the default home-relative
+ * path (~/.codi).
+ */
+
+delete process.env.CODI_HOME;
diff --git a/vitest.config.ts b/vitest.config.ts
index c25688dd..2faf826b 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -4,6 +4,7 @@ export default defineConfig({
   test: {
     environment: 'node',
     globals: true,
+    setupFiles: ['tests/setup.ts'],
     include: ['tests/**/*.test.ts', 'tests/**/*.test.tsx'],
     // Default timeout (increased for e2e tests in their own files)
     testTimeout: 10000,