fix: hold the data trees for the whole pipeline

The pipeline held its output directory for the run but let each step
lock the data directory trees on its own, so another session's
refresh could swap a tree between the packs and the manifests. The
trees are now held shared from right after the pipeline's own
refresh until it exits.

tests/test_artifact_lock.py

@@ -207,5 +207,19 @@ class HeldLockTest(unittest.TestCase):
         self.assertIn("hold_artifact_lock(args.output_dir)", source)
 
 
+class PipelineHoldsTheDataTrees(unittest.TestCase):
+    """The pipeline held dist/ for the whole run but not the data directory
+    trees: a refresh from another session could swap one between the packs
+    and the manifests, which then described two revisions of it."""
+
+    def test_the_trees_are_held_after_the_refresh_and_before_verify(self):
+        source = (Path(__file__).resolve().parents[1] / "scripts" / "pipeline.py").read_text()
+        refresh = source.index('"scripts/refresh_data_dirs.py"')
+        hold = source.index("hold_data_dirs(held,")
+        verify = source.index('"scripts/verify.py", "--all"')
+        self.assertLess(refresh, hold)
+        self.assertLess(hold, verify)
+
+
 if __name__ == "__main__":
     unittest.main()