diff --git a/server/db.js b/server/db.js
index 6d221cc..b88e974 100644
--- a/server/db.js
+++ b/server/db.js
@@ -133,13 +133,18 @@ export function _resetForTest() {
 }
 
 // ── Boot ──────────────────────────────────────────────────────────────────────
+// Skipped in test environment — parallel Vitest workers would race to open
+// the same file, causing "database is locked". _resetForTest() in beforeEach
+// handles initialisation for every test worker using :memory: instead.
 
-const DB_PATH = process.env.DB_PATH ?? DEFAULT_PATH;
-try {
-  init(DB_PATH);
-} catch (e) {
-  console.error('[catalyst] fatal: could not open database at', DB_PATH);
-  console.error('[catalyst] ensure the data directory exists and is writable by the server process.');
-  console.error(e);
-  process.exit(1);
+if (process.env.NODE_ENV !== 'test') {
+  const DB_PATH = process.env.DB_PATH ?? DEFAULT_PATH;
+  try {
+    init(DB_PATH);
+  } catch (e) {
+    console.error('[catalyst] fatal: could not open database at', DB_PATH);
+    console.error('[catalyst] ensure the data directory exists and is writable by the server process.');
+    console.error(e);
+    process.exit(1);
+  }
 }
diff --git a/tests/db.test.js b/tests/db.test.js
index a61073e..746f2b5 100644
--- a/tests/db.test.js
+++ b/tests/db.test.js
@@ -165,3 +165,23 @@ describe('deleteInstance', () => {
     expect(getInstance(2)).not.toBeNull();
   });
 });
+
+// ── Test environment boot isolation ───────────────────────────────────────────
+
+describe('test environment boot isolation', () => {
+  it('vitest runs with NODE_ENV=test', () => {
+    // Vitest sets NODE_ENV=test automatically. This is the guard condition
+    // that prevents the boot init() from opening the real database file.
+    expect(process.env.NODE_ENV).toBe('test');
+  });
+
+  it('db module loads cleanly in parallel workers without locking the real db file', () => {
+    // Regression: the module-level init(DEFAULT_PATH) used to run unconditionally,
+    // causing "database is locked" when multiple test workers imported db.js at
+    // the same time. process.exit(1) then killed the worker mid-suite.
+    // Fix: boot init is skipped when NODE_ENV=test. _resetForTest() handles setup.
+    // Reaching this line proves the module loaded without calling process.exit.
+    expect(() => _resetForTest()).not.toThrow();
+    expect(getInstances()).toEqual([]);
+  });
+});