Property type comparison mutates schemas that combine a `type` list with `anyOf`

[fede-kamel]

Description

Comparing two property schemas, or checking whether one is castable to the other, silently mutates a schema that combines a type list with anyOf: the entries of type are appended to the schema's own anyOf list. The schema keeps growing on every comparison.

Reproduction

from pyagentspec.property import json_schemas_have_same_type

schema_a = {"type": ["integer", "null"], "anyOf": [{"type": "string"}]}
schema_b = {"anyOf": [{"type": "string"}, {"type": "integer"}, {"type": "null"}]}

json_schemas_have_same_type(schema_a, schema_b)
print(schema_a)
# {'type': ['integer', 'null'], 'anyOf': [{'type': 'string'}, {'type': 'integer'}, {'type': 'null'}]}
#                                        ^ two entries were appended to the caller's schema

json_schemas_have_same_type(schema_a, schema_b)
print(len(schema_a["anyOf"]))   # 5

The same happens through json_schema_is_castable_to and value_is_of_compatible_type, which are called during Flow / DataFlowEdge validation, so a Property.json_schema can change as a side effect of building a flow.

Expected behavior

Type comparison is read-only; the input schemas are left untouched.

Root cause

_normalize_json_schema_union_types in pyagentspec/src/pyagentspec/property.py uses all_types = schema.get("anyOf", []) as the accumulator of normalized types and then appends to it, so when the schema already has an anyOf list the appends go into the caller's list.

Environment

• pyagentspec main (26.4.0.dev0), Python 3.12