Gateway: drop strict on a tool whose schema cannot meet strict mode instead of failing the call with 400

Chat clients such as AIRI send strict: true with looser schemas; the Responses
upstream answers 400 unless every object has additionalProperties false and
every property is required. The transpiler now downgrades that tool to
non-strict and reports it in the warnings list.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/unit/services/openai_gateway/responses.py

@@ -83,7 +83,11 @@ def test_chat_to_responses_pins_strict_explicitly():
                     "function": {
                         "name": "f",
                         "strict": True,
-                        "parameters": {"type": "object"},
+                        "parameters": {
+                            "type": "object",
+                            "properties": {},
+                            "additionalProperties": False,
+                        },
                     },
                 }
             ],
@@ -92,6 +96,55 @@ def test_chat_to_responses_pins_strict_explicitly():
     assert resp["tools"][0]["strict"] is True
 
 
+def test_chat_to_responses_drops_strict_the_schema_cannot_meet():
+    def tool(parameters):
+        return {
+            "type": "function",
+            "function": {"name": "f", "strict": True, "parameters": parameters},
+        }
+
+    nested_open = {
+        "type": "object",
+        "properties": {
+            "words": {
+                "type": "array",
+                "items": {
+                    "type": "object",
+                    "properties": {"text": {"type": "string"}},
+                    "required": ["text"],
+                },
+            }
+        },
+        "required": ["words"],
+        "additionalProperties": False,
+    }
+    optional_property = {
+        "type": "object",
+        "properties": {"a": {"type": "string"}},
+        "additionalProperties": False,
+    }
+    for parameters in (nested_open, optional_property, {"type": "object"}):
+        resp, warn = chat_to_responses(
+            {
+                "model": "m",
+                "messages": [{"role": "user", "content": "hi"}],
+                "tools": [tool(parameters)],
+            }
+        )
+        assert resp["tools"][0]["strict"] is False
+        assert any("dropped strict" in w for w in warn)
+    nested_open["properties"]["words"]["items"]["additionalProperties"] = False
+    resp, warn = chat_to_responses(
+        {
+            "model": "m",
+            "messages": [{"role": "user", "content": "hi"}],
+            "tools": [tool(nested_open)],
+        }
+    )
+    assert resp["tools"][0]["strict"] is True
+    assert not any("dropped strict" in w for w in warn)
+
+
 def test_chat_to_responses_warns_on_drops_and_unknowns():
     resp, warn = chat_to_responses(
         _chat_body(n=2, stop=["x"], seed=1, wat_field=True)