feat: add draft state schema projection helper

src/wf_api/schema_projection.py

@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+from copy import deepcopy
+from typing import Any
+
+from jsonschema import Draft202012Validator, SchemaError
+
+JsonObject = dict[str, Any]
+
+
+def project_output_property_to_state_schema(
+    *,
+    state_schema: JsonObject,
+    output_schema: JsonObject,
+    output_field: str,
+    state_field: str,
+) -> JsonObject:
+    """Project one capability output property schema into workflow state schema.
+
+    Capability output schemas may use local references such as
+    ``{"$ref": "#/$defs/Snapshot"}``. Copying only the property schema would
+    create dangling references, so this helper also merges local definition
+    blocks and rejects conflicting definition names.
+    """
+    _check_schema("state_schema", state_schema)
+    _check_schema("output_schema", output_schema)
+    output_properties = output_schema.get("properties")
+    if not isinstance(output_properties, dict) or output_field not in output_properties:
+        raise ValueError(f"output field {output_field!r} is not declared")
+    output_property = output_properties[output_field]
+    if not isinstance(output_property, dict):
+        raise ValueError(f"output field {output_field!r} is not a JSON Schema object")
+
+    projected = deepcopy(state_schema)
+    projected.setdefault("type", "object")
+    properties = projected.setdefault("properties", {})
+    if not isinstance(properties, dict):
+        raise ValueError("state_schema.properties must be an object")
+    properties[state_field] = deepcopy(output_property)
+
+    _merge_definition_block(projected, output_schema, "$defs")
+    _merge_definition_block(projected, output_schema, "definitions")
+    _check_schema("projected state_schema", projected)
+    return projected
+
+
+def _check_schema(name: str, schema: JsonObject) -> None:
+    try:
+        Draft202012Validator.check_schema(schema)
+    except SchemaError as exc:
+        raise ValueError(f"{name} is not valid JSON Schema: {exc.message}") from exc
+
+
+def _merge_definition_block(
+    target_schema: JsonObject,
+    source_schema: JsonObject,
+    key: str,
+) -> None:
+    source_defs = source_schema.get(key)
+    if source_defs is None:
+        return
+    if not isinstance(source_defs, dict):
+        raise ValueError(f"output_schema.{key} must be an object")
+    target_defs = target_schema.setdefault(key, {})
+    if not isinstance(target_defs, dict):
+        raise ValueError(f"state_schema.{key} must be an object")
+    for name, definition in source_defs.items():
+        if name in target_defs and target_defs[name] != definition:
+            raise ValueError(f"conflicting {key}.{name}")
+        target_defs[name] = deepcopy(definition)