fix(pg): do not treat Sync as connection ending

packages/pg/lib/connection.js

@@ -195,7 +195,8 @@ class Connection extends EventEmitter {
   }
 
   sync() {
-    this._ending = true
+    // Sync is the extended-query protocol barrier, not a disconnect.
+    // Only end()/Terminate (and connect-timeout teardown) should set _ending.
     this._send(syncBuffer)
   }
 

packages/pg/test/unit/connection/error-tests.js

@@ -29,6 +29,28 @@ suite.test('connection emits ECONNRESET errors during normal operation', functio
   con.stream.emit('error', e)
 })
 
+suite.test('connection emits ECONNRESET errors after Sync (Sync is not disconnect)', function (done) {
+  const con = new Connection({ stream: new MemoryStream() })
+  con.connect()
+  // Extended-query Sync used to incorrectly set _ending and swallow resets (#3769)
+  con.sync()
+  assert.equal(con._ending, false)
+  assert.emits(con, 'error', function (err) {
+    assert.equal(err.code, 'ECONNRESET')
+    done()
+  })
+  const e = new Error('Connection Reset')
+  e.code = 'ECONNRESET'
+  con.stream.emit('error', e)
+})
+
+suite.test('connection does not set _ending when calling sync()', function () {
+  const con = new Connection({ stream: new MemoryStream() })
+  con.connect()
+  con.sync()
+  assert.equal(con._ending, false)
+})
+
 suite.test('connection does not emit ECONNRESET errors during disconnect', function (done) {
   const con = new Connection({ stream: new MemoryStream() })
   con.connect()