fix(observability): pass err via { error } in initErrorRoutes for Winston dedup (#3657)

logger.error(err.stack) passed a string → PostHogErrorTransport couldn't
read posthogCaptured → 2 $exception events per uncaught express error.
Fixes #3656. Adds unit test for info.error dedup path.

Author: PierreBrisorgueil

lib/services/express.js

@@ -265,7 +265,7 @@ const initModulesServerRoutes = async (app) => {
 const initErrorRoutes = (app) => {
   app.use((err, req, res, next) => {
     if (!err) return next();
-    logger.error(err.stack);
+    logger.error('Unhandled express error', { error: err });
     res.status(err.status || 500).send({
       message: err.message,
       code: err.code,

lib/services/tests/logger.posthog.transport.unit.tests.js

@@ -68,6 +68,16 @@ describe('PostHogErrorTransport:', () => {
     expect(cb).toHaveBeenCalled();
   });
 
+  test('skips when info.error.posthogCaptured is true (dedup via { error: err } meta — express initErrorRoutes path)', () => {
+    const t = new PostHogErrorTransport();
+    const err = Object.assign(new Error('already captured'), { posthogCaptured: true });
+    const info = { level: 'error', message: 'Unhandled express error', error: err };
+    const cb = jest.fn();
+    t.log(info, cb);
+    expect(captureExceptionMock).not.toHaveBeenCalled();
+    expect(cb).toHaveBeenCalled();
+  });
+
   test('sets posthogCaptured = true on the source Error after forwarding', () => {
     const t = new PostHogErrorTransport();
     const err = new Error('boom');