3D 结果打标契约测试补齐 preview 与 imageToModel 分支

- textToModel 用例补 preview 产物的相等断言
- 新增对称的 imageToModel 用例，守住 tag 路由与分支字段
- 裸字符串 source 的负例改为点名 Model3dGenerationSource 并单独反序列化 source 值

server-rs/crates/shared-contracts/tests/model3d_api_request_contract.rs

@@ -1,7 +1,8 @@
 use serde_json::json;
 use shared_contracts::model3d::Model3dGenerationResult;
 use shared_contracts::model3d::common::{
-    Model3dGeneratedArtifact, Model3dGenerationTarget, Model3dGenerationTargetRef,
+    Model3dGeneratedArtifact, Model3dGenerationSource, Model3dGenerationTarget,
+    Model3dGenerationTargetRef,
 };
 use shared_contracts::model3d::image_to_model::Model3dImageToModelRequest;
 use shared_contracts::model3d::text_to_model::Model3dTextToModelRequest;
@@ -56,8 +57,18 @@ fn image_source_rejects_ambiguous_and_raw_input() {
         "generation": { "model": "v3.1-20260211" },
         "target": { "kind": "assetLibrary", "folderId": "folder-1", "label": "木椅" }
     });
-    serde_json::from_value::<Model3dImageToModelRequest>(raw_input)
+    let error = serde_json::from_value::<Model3dImageToModelRequest>(raw_input)
         .expect_err("裸字符串图片输入应被拒绝");
+    // 拒绝必须发生在 source 本身：错误里点名 Model3dGenerationSource，避免将来
+    // generation / target 的必填变化把这条负例“顶替”成通过。
+    assert!(
+        error.to_string().contains("Model3dGenerationSource"),
+        "裸字符串 source 的报错应点名 Model3dGenerationSource，实际为：{error}"
+    );
+
+    // 同样把 source 单独反序列化一遍，锁死被拒的是图片输入的形状本身。
+    serde_json::from_value::<Model3dGenerationSource>(json!("https://example.com/a.png"))
+        .expect_err("裸字符串 source 值应被拒绝");
 }
 
 #[test]
@@ -113,4 +124,60 @@ fn generation_result_is_tagged_per_endpoint() {
             sha256: "0f1e".into(),
         }
     );
+    assert_eq!(
+        text.preview,
+        Model3dGeneratedArtifact {
+            object_key: "models/res-1.webp".into(),
+            content_type: "image/webp".into(),
+            content_length: 20_480,
+            sha256: "2a3b".into(),
+        }
+    );
+
+    // 对称覆盖 imageToModel 分支：tag 路由与分支字段都要单独守住。
+    let image_result: Model3dGenerationResult = serde_json::from_value(json!({
+        "kind": "imageToModel",
+        "target": { "kind": "projectResource", "resourceId": "res-2" },
+        "model": {
+            "objectKey": "models/res-2.glb",
+            "contentType": "model/gltf-binary",
+            "contentLength": 41_636_077_u64,
+            "sha256": "3c4d"
+        },
+        "preview": {
+            "objectKey": "models/res-2.webp",
+            "contentType": "image/webp",
+            "contentLength": 20_481_u64,
+            "sha256": "4e5f"
+        }
+    }))
+    .expect("按端点的结果应可反序列化");
+
+    let Model3dGenerationResult::ImageToModel(image) = image_result else {
+        panic!("kind=imageToModel 不应解成 textToModel 分支");
+    };
+    assert_eq!(
+        image.target,
+        Model3dGenerationTargetRef::ProjectResource {
+            resource_id: "res-2".into()
+        }
+    );
+    assert_eq!(
+        image.model,
+        Model3dGeneratedArtifact {
+            object_key: "models/res-2.glb".into(),
+            content_type: "model/gltf-binary".into(),
+            content_length: 41_636_077,
+            sha256: "3c4d".into(),
+        }
+    );
+    assert_eq!(
+        image.preview,
+        Model3dGeneratedArtifact {
+            object_key: "models/res-2.webp".into(),
+            content_type: "image/webp".into(),
+            content_length: 20_481,
+            sha256: "4e5f".into(),
+        }
+    );
 }