Integrator: Enforce unique destination transfers, disallow overwrites in queued transfers (#4662)

* Fix #4656: Enforce unique destination transfer in Integrator

Note that this is per instance - it doesn't validate cross-instance destinations in the context

* Use explicit DuplicateDestinationError and raise as KnownPublishError

openpype/plugins/publish/integrate.py

@@ -24,7 +24,10 @@ from openpype.client import (
     get_version_by_name,
 )
 from openpype.lib import source_hash
-from openpype.lib.file_transaction import FileTransaction
+from openpype.lib.file_transaction import (
+    FileTransaction,
+    DuplicateDestinationError
+)
 from openpype.pipeline.publish import (
     KnownPublishError,
     get_publish_template_name,
@@ -170,9 +173,18 @@ class IntegrateAsset(pyblish.api.InstancePlugin):
             ).format(instance.data["family"]))
             return
 
-        file_transactions = FileTransaction(log=self.log)
+        file_transactions = FileTransaction(log=self.log,
+                                            # Enforce unique transfers
+                                            allow_queue_replacements=False)
         try:
             self.register(instance, file_transactions, filtered_repres)
+        except DuplicateDestinationError as exc:
+            # Raise DuplicateDestinationError as KnownPublishError
+            # and rollback the transactions
+            file_transactions.rollback()
+            six.reraise(KnownPublishError,
+                        KnownPublishError(exc),
+                        sys.exc_info()[2])
         except Exception:
             # clean destination
             # todo: preferably we'd also rollback *any* changes to the database