fix(anthropic): drop empty Read.pages in responses-to-anthropic tool input

backend/internal/pkg/apicompat/anthropic_responses_test.go

@@ -258,6 +258,48 @@ func TestResponsesToAnthropic_ToolUse(t *testing.T) {
 	assert.Equal(t, "tool_use", anth.Content[1].Type)
 	assert.Equal(t, "call_1", anth.Content[1].ID)
 	assert.Equal(t, "get_weather", anth.Content[1].Name)
+	assert.JSONEq(t, `{"city":"NYC"}`, string(anth.Content[1].Input))
+}
+
+func TestResponsesToAnthropic_ReadToolDropsEmptyPages(t *testing.T) {
+	resp := &ResponsesResponse{
+		ID:     "resp_read",
+		Model:  "gpt-5.5",
+		Status: "completed",
+		Output: []ResponsesOutput{
+			{
+				Type:      "function_call",
+				CallID:    "call_read",
+				Name:      "Read",
+				Arguments: `{"file_path":"/tmp/demo.py","limit":2000,"offset":0,"pages":""}`,
+			},
+		},
+	}
+
+	anth := ResponsesToAnthropic(resp, "claude-opus-4-6")
+	require.Len(t, anth.Content, 1)
+	assert.Equal(t, "tool_use", anth.Content[0].Type)
+	assert.JSONEq(t, `{"file_path":"/tmp/demo.py","limit":2000,"offset":0}`, string(anth.Content[0].Input))
+}
+
+func TestResponsesToAnthropic_PreservesEmptyStringsForOtherTools(t *testing.T) {
+	resp := &ResponsesResponse{
+		ID:     "resp_other",
+		Model:  "gpt-5.5",
+		Status: "completed",
+		Output: []ResponsesOutput{
+			{
+				Type:      "function_call",
+				CallID:    "call_other",
+				Name:      "Search",
+				Arguments: `{"query":""}`,
+			},
+		},
+	}
+
+	anth := ResponsesToAnthropic(resp, "claude-opus-4-6")
+	require.Len(t, anth.Content, 1)
+	assert.JSONEq(t, `{"query":""}`, string(anth.Content[0].Input))
 }
 
 func TestResponsesToAnthropic_Reasoning(t *testing.T) {
@@ -472,6 +514,41 @@ func TestStreamingToolCall(t *testing.T) {
 	assert.Equal(t, "tool_use", events[0].Delta.StopReason)
 }
 
+func TestStreamingReadToolDropsEmptyPages(t *testing.T) {
+	state := NewResponsesEventToAnthropicState()
+
+	ResponsesEventToAnthropicEvents(&ResponsesStreamEvent{
+		Type:     "response.created",
+		Response: &ResponsesResponse{ID: "resp_read_stream", Model: "gpt-5.5"},
+	}, state)
+
+	events := ResponsesEventToAnthropicEvents(&ResponsesStreamEvent{
+		Type:        "response.output_item.added",
+		OutputIndex: 0,
+		Item:        &ResponsesOutput{Type: "function_call", CallID: "call_read", Name: "Read"},
+	}, state)
+	require.Len(t, events, 1)
+	assert.Equal(t, "content_block_start", events[0].Type)
+
+	events = ResponsesEventToAnthropicEvents(&ResponsesStreamEvent{
+		Type:        "response.function_call_arguments.delta",
+		OutputIndex: 0,
+		Delta:       `{"file_path":"/tmp/demo.py","limit":2000,"offset":0,"pages":""}`,
+	}, state)
+	assert.Len(t, events, 0)
+
+	events = ResponsesEventToAnthropicEvents(&ResponsesStreamEvent{
+		Type:        "response.function_call_arguments.done",
+		OutputIndex: 0,
+		Arguments:   `{"file_path":"/tmp/demo.py","limit":2000,"offset":0,"pages":""}`,
+	}, state)
+	require.Len(t, events, 2)
+	assert.Equal(t, "content_block_delta", events[0].Type)
+	assert.Equal(t, "input_json_delta", events[0].Delta.Type)
+	assert.JSONEq(t, `{"file_path":"/tmp/demo.py","limit":2000,"offset":0}`, events[0].Delta.PartialJSON)
+	assert.Equal(t, "content_block_stop", events[1].Type)
+}
+
 func TestStreamingReasoning(t *testing.T) {
 	state := NewResponsesEventToAnthropicState()