fix: default empty input_json_delta arguments to {} for tool call parsing

relay/channel/claude/relay-claude.go

@@ -451,11 +451,17 @@ func StreamResponseClaude2OpenAI(claudeResponse *dto.ClaudeResponse) *dto.ChatCo
 			choice.Delta.Content = claudeResponse.Delta.Text
 			switch claudeResponse.Delta.Type {
 			case "input_json_delta":
+				arguments := "{}"
+				if claudeResponse.Delta.PartialJson != nil {
+					if partial := strings.TrimSpace(*claudeResponse.Delta.PartialJson); partial != "" {
+						arguments = partial
+					}
+				}
 				tools = append(tools, dto.ToolCallResponse{
 					Type:  "function",
 					Index: common.GetPointer(fcIdx),
 					Function: dto.FunctionResponse{
-						Arguments: *claudeResponse.Delta.PartialJson,
+						Arguments: arguments,
 					},
 				})
 			case "signature_delta":

relay/channel/claude/relay_claude_test.go

@@ -215,3 +215,41 @@ func TestRequestOpenAI2ClaudeMessage_AssistantToolCallWithMalformedArguments(t *
 	require.True(t, ok)
 	assert.Empty(t, inputObj)
 }
+
+func TestStreamResponseClaude2OpenAI_EmptyInputJSONDeltaFallback(t *testing.T) {
+	empty := ""
+	resp := &dto.ClaudeResponse{
+		Type:  "content_block_delta",
+		Index: func() *int { v := 1; return &v }(),
+		Delta: &dto.ClaudeMediaMessage{
+			Type:        "input_json_delta",
+			PartialJson: &empty,
+		},
+	}
+
+	chunk := StreamResponseClaude2OpenAI(resp)
+	require.NotNil(t, chunk)
+	require.Len(t, chunk.Choices, 1)
+	require.NotNil(t, chunk.Choices[0].Delta.ToolCalls)
+	require.Len(t, chunk.Choices[0].Delta.ToolCalls, 1)
+	assert.Equal(t, "{}", chunk.Choices[0].Delta.ToolCalls[0].Function.Arguments)
+}
+
+func TestStreamResponseClaude2OpenAI_NonEmptyInputJSONDeltaPreserved(t *testing.T) {
+	partial := `{"timezone":"Asia/Shanghai"}`
+	resp := &dto.ClaudeResponse{
+		Type:  "content_block_delta",
+		Index: func() *int { v := 1; return &v }(),
+		Delta: &dto.ClaudeMediaMessage{
+			Type:        "input_json_delta",
+			PartialJson: &partial,
+		},
+	}
+
+	chunk := StreamResponseClaude2OpenAI(resp)
+	require.NotNil(t, chunk)
+	require.Len(t, chunk.Choices, 1)
+	require.NotNil(t, chunk.Choices[0].Delta.ToolCalls)
+	require.Len(t, chunk.Choices[0].Delta.ToolCalls, 1)
+	assert.Equal(t, partial, chunk.Choices[0].Delta.ToolCalls[0].Function.Arguments)
+}