diff --git a/backend-java/src/main/java/com/nanri/aiimage/modules/softwareversion/service/support/PublicVersionLookup.java b/backend-java/src/main/java/com/nanri/aiimage/modules/softwareversion/service/support/PublicVersionLookup.java
new file mode 100644
index 00000000..83da6cd6
--- /dev/null
+++ b/backend-java/src/main/java/com/nanri/aiimage/modules/softwareversion/service/support/PublicVersionLookup.java
@@ -0,0 +1,74 @@
+package com.nanri.aiimage.modules.softwareversion.service.support;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * 客户端公开版本查询纯逻辑（module 09）：空语义、created_at DESC + id 稳定排序、
+ * 无 ApiResponse 包装；供 PublicVersionController/契约测试复用。
+ */
+public final class PublicVersionLookup {
+
+    /** web_config 版本记录投影(id 用于同时间稳定排序)。 */
+    public record WebVersion(Long id, String version, String fileUrl, LocalDateTime createdAt) {
+    }
+
+    private PublicVersionLookup() {
+    }
+
+    /** 取最新版本记录：created_at DESC，同一时间按 id 倒序稳定；空/无有效回 null。 */
+    public static WebVersion selectLatest(List<WebVersion> rows) {
+        if (rows == null || rows.isEmpty()) {
+            return null;
+        }
+        List<WebVersion> list = new ArrayList<>(rows);
+        list.sort((a, b) -> {
+            int time = compareTime(b.createdAt(), a.createdAt());
+            if (time != 0) {
+                return time;
+            }
+            long ai = a.id() == null ? 0L : a.id();
+            long bi = b.id() == null ? 0L : b.id();
+            return Long.compare(bi, ai);
+        });
+        return list.get(0);
+    }
+
+    private static int compareTime(LocalDateTime a, LocalDateTime b) {
+        if (a == null && b == null) {
+            return 0;
+        }
+        if (a == null) {
+            return -1;
+        }
+        if (b == null) {
+            return 1;
+        }
+        return a.compareTo(b);
+    }
+
+    /** 当前服务版本响应：保留 version/desc/url 字段(可为空字符串)，不包装 ApiResponse。 */
+    public static Map<String, Object> currentVersionResponse(String version, String desc, String url) {
+        Map<String, Object> map = new LinkedHashMap<>();
+        map.put("version", version == null ? "" : version);
+        map.put("desc", desc == null ? "" : desc);
+        map.put("url", url == null ? "" : url);
+        return map;
+    }
+
+    /** 最新版本响应：无记录返回 version=null,file_url=null(客户端语义)。 */
+    public static Map<String, Object> latestVersionResponse(WebVersion latest) {
+        Map<String, Object> map = new LinkedHashMap<>();
+        if (latest == null) {
+            map.put("version", null);
+            map.put("file_url", null);
+            return map;
+        }
+        map.put("version", latest.version());
+        map.put("file_url", latest.fileUrl());
+        return map;
+    }
+}
diff --git a/backend-java/src/test/java/com/nanri/aiimage/modules/softwareversion/service/support/Task161Test.java b/backend-java/src/test/java/com/nanri/aiimage/modules/softwareversion/service/support/Task161Test.java
new file mode 100644
index 00000000..438feb34
--- /dev/null
+++ b/backend-java/src/test/java/com/nanri/aiimage/modules/softwareversion/service/support/Task161Test.java
@@ -0,0 +1,63 @@
+package com.nanri.aiimage.modules.softwareversion.service.support;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/** task-161：冻结 /api/version 响应契约(version/desc/url 保留且无 ApiResponse 包装)。 */
+class Task161Test {
+
+    @Test
+    void test_task_161_freeze_public_version_normal_primary_path() {
+        Map<String, Object> resp = PublicVersionLookup.currentVersionResponse("1.0.46", "x", "https://a");
+        assertEquals("1.0.46", resp.get("version"));
+        assertEquals("x", resp.get("desc"));
+        assertEquals("https://a", resp.get("url"));
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_normal_variant_input() {
+        Map<String, Object> resp = PublicVersionLookup.currentVersionResponse(null, null, null);
+        assertEquals("", resp.get("version"));
+        assertEquals("", resp.get("desc"));
+        assertEquals("", resp.get("url"));
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_repeated_is_idempotent() {
+        assertTrue(PublicVersionLookup.currentVersionResponse("v", "d", "u")
+                .equals(PublicVersionLookup.currentVersionResponse("v", "d", "u")));
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_boundary_empty_input() {
+        assertTrue(PublicVersionLookup.currentVersionResponse("", "", "").values().stream().allMatch(v -> "".equals(v)));
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_boundary_single_item() {
+        Map<String, Object> resp = PublicVersionLookup.currentVersionResponse("1.0.0", "", "");
+        assertEquals(3, resp.size());
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_boundary_limit_or_missing_field() {
+        assertFalse(PublicVersionLookup.currentVersionResponse("v", "d", "u").containsKey("success"), "公开接口不包装信封");
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_invalid_input_rejected() {
+        Map<String, Object> resp = PublicVersionLookup.currentVersionResponse("1", "a", "b");
+        assertEquals("1", resp.get("version"), "version 不被转数字");
+    }
+
+    @Test
+    void test_task_161_freeze_public_version_dependency_failure_returns_actionable_message() {
+        // 保留字段即使为空；desc/url 不能丢弃
+        assertEquals(3, PublicVersionLookup.currentVersionResponse("v", "", "").keySet().size());
+    }
+}