fix(builder): align backend contracts and fixtures with main CI

api/services/dify_builder/native_api_string_input_binding.py

@@ -8,7 +8,6 @@ The caller supplies its existing placeholder grammar; no runtime lookup occurs.
 from collections import Counter
 from collections.abc import Mapping, Sequence
 from re import Pattern
-from typing import cast
 
 from services.dify_builder.native_api_output_contract import is_native_api_tool
 
@@ -30,7 +29,7 @@ def normalize_native_api_string_bindings(
     Sources, declarations and original binding objects are never mutated.
     """
     raw = tool_data.get("tool_parameters")
-    bindings = dict(cast(Mapping[str, object], raw)) if isinstance(raw, Mapping) else {}
+    bindings: dict[str, object] = dict(raw) if isinstance(raw, Mapping) else {}
     if not is_native_api_tool(tool_data):
         return bindings
 
@@ -40,9 +39,10 @@ def normalize_native_api_string_bindings(
         node_id, data = node.get("id"), node.get("data")
         if not isinstance(node_id, str) or node_counts[node_id] != 1 or not isinstance(data, Mapping):
             continue
-        if data.get("type") != "start" or not isinstance(data.get("variables"), list):
+        raw_variables = data.get("variables")
+        if data.get("type") != "start" or not isinstance(raw_variables, list):
             continue
-        variables = [item for item in cast(list[object], data["variables"]) if isinstance(item, Mapping)]
+        variables = [item for item in raw_variables if isinstance(item, Mapping)]
         counts = Counter(item.get("variable") for item in variables if isinstance(item.get("variable"), str))
         for variable in variables:
             name = variable.get("variable")
@@ -66,7 +66,9 @@ def normalize_native_api_string_bindings(
         selector = binding.get("value")
         if not isinstance(selector, list) or len(selector) != 2 or not all(isinstance(part, str) for part in selector):
             continue
-        source_id, field = cast(list[str], selector)
+        source_id, field = selector
+        assert isinstance(source_id, str)
+        assert isinstance(field, str)
         # A dot inside the direct field would become a different nested selector
         # when the native template resolver splits its placeholder on dots.
         if "." in field or (source_id, field) not in string_selectors: