fix(网关): 修复工具续链校验与存储策略

完善 function_call_output 续链校验与引用匹配
续链场景强制 store=true，过滤 input 时避免副作用
补充续链判断与过滤相关单元测试

测试: go test ./...

backend/internal/service/openai_tool_continuation_test.go

@@ -0,0 +1,98 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNeedsToolContinuationSignals(t *testing.T) {
+	// 覆盖所有触发续链的信号来源，确保判定逻辑完整。
+	cases := []struct {
+		name string
+		body map[string]any
+		want bool
+	}{
+		{name: "nil", body: nil, want: false},
+		{name: "previous_response_id", body: map[string]any{"previous_response_id": "resp_1"}, want: true},
+		{name: "previous_response_id_blank", body: map[string]any{"previous_response_id": "  "}, want: false},
+		{name: "function_call_output", body: map[string]any{"input": []any{map[string]any{"type": "function_call_output"}}}, want: true},
+		{name: "item_reference", body: map[string]any{"input": []any{map[string]any{"type": "item_reference"}}}, want: true},
+		{name: "tools", body: map[string]any{"tools": []any{map[string]any{"type": "function"}}}, want: true},
+		{name: "tools_empty", body: map[string]any{"tools": []any{}}, want: false},
+		{name: "tools_invalid", body: map[string]any{"tools": "bad"}, want: false},
+		{name: "tool_choice", body: map[string]any{"tool_choice": "auto"}, want: true},
+		{name: "tool_choice_object", body: map[string]any{"tool_choice": map[string]any{"type": "function"}}, want: true},
+		{name: "tool_choice_empty_object", body: map[string]any{"tool_choice": map[string]any{}}, want: false},
+		{name: "none", body: map[string]any{"input": []any{map[string]any{"type": "text", "text": "hi"}}}, want: false},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, NeedsToolContinuation(tt.body))
+		})
+	}
+}
+
+func TestHasFunctionCallOutput(t *testing.T) {
+	// 仅当 input 中存在 function_call_output 才视为续链输出。
+	require.False(t, HasFunctionCallOutput(nil))
+	require.True(t, HasFunctionCallOutput(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output"}},
+	}))
+	require.False(t, HasFunctionCallOutput(map[string]any{
+		"input": "text",
+	}))
+}
+
+func TestHasToolCallContext(t *testing.T) {
+	// tool_call/function_call 必须包含 call_id，才能作为可关联上下文。
+	require.False(t, HasToolCallContext(nil))
+	require.True(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "tool_call", "call_id": "call_1"}},
+	}))
+	require.True(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "function_call", "call_id": "call_2"}},
+	}))
+	require.False(t, HasToolCallContext(map[string]any{
+		"input": []any{map[string]any{"type": "tool_call"}},
+	}))
+}
+
+func TestFunctionCallOutputCallIDs(t *testing.T) {
+	// 仅提取非空 call_id，去重后返回。
+	require.Empty(t, FunctionCallOutputCallIDs(nil))
+	callIDs := FunctionCallOutputCallIDs(map[string]any{
+		"input": []any{
+			map[string]any{"type": "function_call_output", "call_id": "call_1"},
+			map[string]any{"type": "function_call_output", "call_id": ""},
+			map[string]any{"type": "function_call_output", "call_id": "call_1"},
+		},
+	})
+	require.ElementsMatch(t, []string{"call_1"}, callIDs)
+}
+
+func TestHasFunctionCallOutputMissingCallID(t *testing.T) {
+	require.False(t, HasFunctionCallOutputMissingCallID(nil))
+	require.True(t, HasFunctionCallOutputMissingCallID(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output"}},
+	}))
+	require.False(t, HasFunctionCallOutputMissingCallID(map[string]any{
+		"input": []any{map[string]any{"type": "function_call_output", "call_id": "call_1"}},
+	}))
+}
+
+func TestHasItemReferenceForCallIDs(t *testing.T) {
+	// item_reference 需要覆盖所有 call_id 才视为可关联上下文。
+	require.False(t, HasItemReferenceForCallIDs(nil, []string{"call_1"}))
+	require.False(t, HasItemReferenceForCallIDs(map[string]any{}, []string{"call_1"}))
+	req := map[string]any{
+		"input": []any{
+			map[string]any{"type": "item_reference", "id": "call_1"},
+			map[string]any{"type": "item_reference", "id": "call_2"},
+		},
+	}
+	require.True(t, HasItemReferenceForCallIDs(req, []string{"call_1"}))
+	require.True(t, HasItemReferenceForCallIDs(req, []string{"call_1", "call_2"}))
+	require.False(t, HasItemReferenceForCallIDs(req, []string{"call_1", "call_3"}))
+}