objectstore: clamp mtime on commit

When we commit objects to the store and there is a `source_epoch`
set on the `Object`, clamp the mtime. This is needed because it
is possible that the object corresponds to the last stage of a
pipeline[1] and it could later directly be exported without going
through `finalize` again. Also we are doing in on object itself
and not the cloned path so that resuming and checkpointing will
behave identical.

[1] not even necessarily the pipeline we are currently building.

osbuild/objectstore.py

@@ -423,6 +423,10 @@ class ObjectStore(contextlib.AbstractContextManager):
 
         with self.cache.store(object_id) as name:
             path = os.path.join(self.cache, name)
+            # we clamp the mtime of `obj` itself so that it
+            # resuming a snapshop and building with a snapshot
+            # goes through the same code path
+            obj.clamp_mtime()
             obj.clone(path)
 
     def cleanup(self):