diff --git a/apps/api/src/index.ts b/apps/api/src/index.ts
index 2a2bb41..adcb861 100644
--- a/apps/api/src/index.ts
+++ b/apps/api/src/index.ts
@@ -62,11 +62,12 @@ app.route('/api/me', meRouter)
 app.route('/api/events', eventsRouter)
 app.route('/api/sse', sseRouter)
 
-// Start the CalDAV broker poller (5-min cron, D-13 ctag change-detection)
-// Runs in the background — errors are caught and logged per-credential (T-03-04)
-startBrokerPoller()
-// Drain the D-05 outbox every 15s: dispatches pending CalDAV writes to Fastmail
-startOutboxWorker()
+// WR-04: background worker startup (cron schedules) moved into the isMainModule()
+// guard below. Calling them at top level registered real node-cron schedules whenever
+// ./index.js was imported — the route tests import `app` from here, so the poller/outbox
+// drain fired during the test run, touched the mocked DB/CalDAV layers nondeterministically,
+// and left open handles that blocked clean process exit. They now start only when the
+// module is the process entrypoint.
 
 // Serve React PWA static assets from ./public (Vite build output).
 // MUST serve the whole ./public tree, not just /assets/* — root-level PWA files
@@ -97,8 +98,16 @@ function isMainModule(): boolean {
   }
 }
 
-// Only start the HTTP server when this module is run directly (not imported in tests)
+// Only start the HTTP server AND background workers when this module is run directly
+// (not imported in tests). WR-04: gating the cron schedules here keeps them out of the
+// test process.
 if (isMainModule()) {
+  // Start the CalDAV broker poller (5-min cron, D-13 ctag change-detection).
+  // Runs in the background — errors are caught and logged per-credential (T-03-04).
+  startBrokerPoller()
+  // Drain the D-05 outbox every 15s: dispatches pending CalDAV writes to Fastmail.
+  startOutboxWorker()
+
   serve({ fetch: app.fetch, port: 3000 }, (info) => {
     console.log(`FamilySync API running on http://localhost:${info.port}`)
   })