fix: remove dead _part_integrity attribute, add iteration comment

_part_integrity was set in __init__, copy constructor, and cascade()
but never read — part_integrity flows as a function argument to
_propagate_restrictions(), not through instance state.

Add comment explaining the 50-iteration safety limit in
load_all_downstream() (cross-schema FK chains could theoretically
cycle, unlike the DAG within a schema).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/dependencies.py

@@ -242,8 +242,10 @@ def load_all_downstream(self) -> None:
             self.load()
             return
 
-        max_iterations = 50
-        for _ in range(max_iterations):
+        # Safety limit: cross-schema FK chains are typically 3-5 deep.
+        # Unlike the DAG within a schema, cross-schema references could
+        # theoretically form cycles, so we cap iterations.
+        for _ in range(50):
             schemas_list = ", ".join(adapter.quote_string(s) for s in known_schemas)
             result = self._conn.query(adapter.find_downstream_schemas_sql(schemas_list))
             new_schemas = {row[0] for row in result} - known_schemas

src/datajoint/diagram.py

@@ -99,7 +99,6 @@ def __init__(self, source, context=None) -> None:
             self._cascade_restrictions = copy_module.deepcopy(source._cascade_restrictions)
             self._restrict_conditions = copy_module.deepcopy(source._restrict_conditions)
             self._restriction_attrs = copy_module.deepcopy(source._restriction_attrs)
-            self._part_integrity = source._part_integrity
             super().__init__(source)
             return
 
@@ -127,7 +126,6 @@ def __init__(self, source, context=None) -> None:
         self._cascade_restrictions = {}
         self._restrict_conditions = {}
         self._restriction_attrs = {}
-        self._part_integrity = "enforce"
 
         # Enumerate nodes from all the items in the list
         self.nodes_to_show = set()
@@ -357,7 +355,7 @@ def cascade(cls, table_expr, part_integrity="enforce"):
         result._cascade_restrictions = {}
         result._restrict_conditions = {}
         result._restriction_attrs = {}
-        result._part_integrity = part_integrity
+
         # Include seed + all descendants
         descendants = set(nx.descendants(result, node)) | {node}
         result.nodes_to_show = descendants