feat(translator): sanitize parametersJsonSchema in OpenAI to Gemini request handling

- Applied `CleanJSONSchemaForGemini` to ensure compatibility by removing unsupported fields and cleaning schema requirements.
- Added test cases to validate schema transformation, ensuring only necessary `required` fields are retained.
- Enhanced both request and response flows to consistently clean and sanitize tool parameter schemas.

Closes: #3863

internal/translator/gemini/openai/chat-completions/gemini_openai_request.go

@@ -363,6 +363,9 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 					fnRawBytes := []byte(fnRaw)
 					fnRawBytes, _ = sjson.SetBytes(fnRawBytes, "name", util.SanitizeFunctionName(fn.Get("name").String()))
 					fnRaw = string(fnRawBytes)
+					if parameters := gjson.Get(fnRaw, "parametersJsonSchema"); parameters.Exists() {
+						fnRaw, _ = sjson.SetRaw(fnRaw, "parametersJsonSchema", util.CleanJSONSchemaForGemini(parameters.Raw))
+					}
 					fnRaw, _ = sjson.Delete(fnRaw, "strict")
 					if !hasFunction {
 						functionToolNode, _ = sjson.SetRawBytes(functionToolNode, "functionDeclarations", []byte("[]"))

internal/translator/gemini/openai/chat-completions/gemini_openai_request_test.go

@@ -58,3 +58,46 @@ func TestConvertOpenAIRequestToGeminiPreservesInputAudio(t *testing.T) {
 		t.Fatalf("audio data = %q, want %q", got, "SUQzBA==")
 	}
 }
+
+func TestConvertOpenAIRequestToGeminiCleansToolSchemaRequiredFields(t *testing.T) {
+	inputJSON := `{
+		"model": "gemini-2.0-flash",
+		"messages": [{"role": "user", "content": "hi"}],
+		"tools": [{
+			"type": "function",
+			"function": {
+				"name": "search_company",
+				"description": "Search",
+				"parameters": {
+					"type": "object",
+					"title": "SearchCompany",
+					"properties": {
+						"country": {"type": "string"},
+						"industry": {"type": "string"}
+					},
+					"required": ["country", "industry", "stale_field", "another_stale"]
+				}
+			}
+		}]
+	}`
+
+	output := ConvertOpenAIRequestToGemini("gemini-2.0-flash", []byte(inputJSON), false)
+	schema := gjson.GetBytes(output, "tools.0.functionDeclarations.0.parametersJsonSchema")
+
+	if !schema.Exists() {
+		t.Fatalf("parametersJsonSchema missing. Output: %s", output)
+	}
+	if schema.Get("title").Exists() {
+		t.Fatalf("schema title should be removed. Output: %s", output)
+	}
+	required := schema.Get("required").Array()
+	if len(required) != 2 {
+		t.Fatalf("required length = %d, want 2. Schema: %s", len(required), schema.Raw)
+	}
+	if got := required[0].String(); got != "country" {
+		t.Fatalf("required[0] = %q, want country. Schema: %s", got, schema.Raw)
+	}
+	if got := required[1].String(); got != "industry" {
+		t.Fatalf("required[1] = %q, want industry. Schema: %s", got, schema.Raw)
+	}
+}

internal/translator/gemini/openai/responses/gemini_openai-responses_request.go

@@ -395,7 +395,7 @@ func ConvertOpenAIResponsesRequestToGemini(modelName string, inputRawJSON []byte
 					funcDecl, _ = sjson.SetBytes(funcDecl, "description", desc.String())
 				}
 				if params := tool.Get("parameters"); params.Exists() {
-					funcDecl, _ = sjson.SetRawBytes(funcDecl, "parametersJsonSchema", []byte(params.Raw))
+					funcDecl, _ = sjson.SetRawBytes(funcDecl, "parametersJsonSchema", []byte(util.CleanJSONSchemaForGemini(params.Raw)))
 				}
 
 				geminiTools, _ = sjson.SetRawBytes(geminiTools, "0.functionDeclarations.-1", funcDecl)

internal/translator/gemini/openai/responses/gemini_openai-responses_request_test.go

@@ -245,6 +245,47 @@ func TestConvertOpenAIResponsesRequestToGemini_SystemAndDeveloperRoles(t *testin
 	}
 }
 
+func TestConvertOpenAIResponsesRequestToGeminiCleansToolSchemaRequiredFields(t *testing.T) {
+	inputJSON := `{
+		"model": "gemini-2.0-flash",
+		"input": "hi",
+		"tools": [{
+			"type": "function",
+			"name": "search_company",
+			"description": "Search",
+			"parameters": {
+				"type": "object",
+				"title": "SearchCompany",
+				"properties": {
+					"country": {"type": "string"},
+					"industry": {"type": "string"}
+				},
+				"required": ["country", "industry", "stale_field", "another_stale"]
+			}
+		}]
+	}`
+
+	output := ConvertOpenAIResponsesRequestToGemini("gemini-2.0-flash", []byte(inputJSON), false)
+	schema := gjson.GetBytes(output, "tools.0.functionDeclarations.0.parametersJsonSchema")
+
+	if !schema.Exists() {
+		t.Fatalf("parametersJsonSchema missing. Output: %s", output)
+	}
+	if schema.Get("title").Exists() {
+		t.Fatalf("schema title should be removed. Output: %s", output)
+	}
+	required := schema.Get("required").Array()
+	if len(required) != 2 {
+		t.Fatalf("required length = %d, want 2. Schema: %s", len(required), schema.Raw)
+	}
+	if got := required[0].String(); got != "country" {
+		t.Fatalf("required[0] = %q, want country. Schema: %s", got, schema.Raw)
+	}
+	if got := required[1].String(); got != "industry" {
+		t.Fatalf("required[1] = %q, want industry. Schema: %s", got, schema.Raw)
+	}
+}
+
 func validResponsesGPTReasoningSignature() string {
 	raw := make([]byte, 1+8+16+16+32)
 	raw[0] = 0x80