抠图背景色只作内部 screenColorHex 元数据，不再暴露进用户可见 fields

apply_editor_screen_background_decision_to_generation_inputs 之前会往
generationInputs.fields 追加「抠图背景色」条目，把内部自动决策/兜底细节
暴露给用户，违反「用户可见输入快照不记录抠图背景色/抠图模型」的产品契约（P2）。

- 去掉 fields 注入，只保留顶层内部可追踪元数据 screenColorHex（不进用户快照）。
- 删除因此变成死代码的 format_editor_screen_background_decision_input 及其 import。
- 重写两个单测：断言 fields 不被注入/不被修改，只写 screenColorHex。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server-rs/crates/api-server/src/editor_project.rs

@@ -64,8 +64,7 @@ use crate::{
     },
     editor_screen_background_decision::{
         EditorScreenBackgroundDecision, EditorScreenBackgroundDecisionInput,
-        EditorScreenBackgroundDecisionKind, format_editor_screen_background_decision_input,
-        resolve_editor_screen_background_color,
+        EditorScreenBackgroundDecisionKind, resolve_editor_screen_background_color,
     },
     generated_image_assets::{
         GeneratedImageAssetAdapter, GeneratedImageAssetDataUrl,
@@ -1673,18 +1672,8 @@ pub(crate) fn apply_editor_screen_background_decision_to_generation_inputs(
         Some(other) => return Some(other),
         None => json!({ "fields": [], "references": [] }),
     };
-    let resolved_value = format_editor_screen_background_decision_input(decision);
-    if let Some(fields) = value.get_mut("fields").and_then(Value::as_array_mut) {
-        if let Some(field) = fields
-            .iter_mut()
-            .find(|field| field.get("title").and_then(Value::as_str) == Some("抠图背景色"))
-        {
-            field["value"] = Value::String(resolved_value);
-        } else {
-            fields.push(json!({ "title": "抠图背景色", "value": resolved_value }));
-        }
-    }
-    // 结构化背景色，供旧背景色先验等程序化消费；展示字段的中文格式不可作解析依据。
+    // 抠图背景色是内部自动决策 / 兜底细节，产品契约要求不进用户可见的 generationInputs.fields；
+    // 只写顶层内部可追踪元数据 screenColorHex（不属于用户输入快照，前端展示不读取）。
     value["screenColorHex"] = Value::String(decision.color.hex.to_string());
     Some(value)
 }
@@ -5680,9 +5669,10 @@ mod tests {
     }
 
     #[test]
-    fn screen_background_decision_generation_inputs_record_structured_hex() {
+    fn screen_background_decision_records_hex_without_touching_visible_fields() {
         let decision = manual_screen_background_decision("#B0C2E0");
 
+        // 用户可见的 fields 不被注入抠图背景色，只写内部 screenColorHex。
         let updated = apply_editor_screen_background_decision_to_generation_inputs(
             Some(json!({
                 "fields": [{ "title": "角色设定", "value": "红发骑士" }],
@@ -5694,19 +5684,17 @@ mod tests {
         assert_eq!(updated["screenColorHex"], json!("#B0C2E0"));
         assert_eq!(
             updated["fields"],
-            json!([
-                { "title": "角色设定", "value": "红发骑士" },
-                { "title": "抠图背景色", "value": "浅钢蓝 #B0C2E0" },
-            ]),
+            json!([{ "title": "角色设定", "value": "红发骑士" }]),
         );
 
+        // 无 generation_inputs 时创建骨架并写入内部元数据，fields 保持为空。
         let created =
             apply_editor_screen_background_decision_to_generation_inputs(None, Some(&decision))
                 .expect("missing generation inputs should still record the decision");
         assert_eq!(
             created,
             json!({
-                "fields": [{ "title": "抠图背景色", "value": "浅钢蓝 #B0C2E0" }],
+                "fields": [],
                 "references": [],
                 "screenColorHex": "#B0C2E0",
             }),
@@ -5714,9 +5702,10 @@ mod tests {
     }
 
     #[test]
-    fn screen_background_decision_generation_inputs_overwrite_existing_display_field() {
+    fn screen_background_decision_leaves_existing_visible_fields_untouched() {
         let decision = manual_screen_background_decision("#CFEFFF");
 
+        // 即使旧数据的 fields 里残留了抠图背景色，后端也不修改用户可见字段。
         let updated = apply_editor_screen_background_decision_to_generation_inputs(
             Some(json!({
                 "fields": [{ "title": "抠图背景色", "value": "旧值" }],
@@ -5727,7 +5716,7 @@ mod tests {
         .expect("generation inputs should be preserved");
         assert_eq!(
             updated["fields"],
-            json!([{ "title": "抠图背景色", "value": "浅雾蓝 #CFEFFF" }]),
+            json!([{ "title": "抠图背景色", "value": "旧值" }]),
         );
         assert_eq!(updated["screenColorHex"], json!("#CFEFFF"));
     }

server-rs/crates/api-server/src/editor_screen_background_decision.rs

@@ -278,22 +278,6 @@ pub(crate) fn is_auto_screen_background_color(value: Option<&str>) -> bool {
         .unwrap_or(true)
 }
 
-pub(crate) fn format_editor_screen_background_decision_input(
-    decision: &EditorScreenBackgroundDecision,
-) -> String {
-    let resolved = format!("{} {}", decision.color.label, decision.color.hex);
-    match decision.mode {
-        EditorScreenBackgroundDecisionMode::Manual => resolved,
-        EditorScreenBackgroundDecisionMode::Auto => {
-            if decision.fallback {
-                format!("自动 -> {resolved}（兜底）")
-            } else {
-                format!("自动 -> {resolved}")
-            }
-        }
-    }
-}
-
 fn editor_screen_background_decision_system_prompt() -> &'static str {
     "你是游戏素材生图的抠图背景色决策器。根据任务和用户输入，从候选列表中选择一个最不容易与主体混淆、最适合后续扣除的纯色背景。如果附带了主体参考图，必须以图中主体（含服饰、道具、光效）的实际配色为准，选择色相距离最远的候选色，忽略图中已有的背景或透明区域。只能返回 JSON：{\"hex\":\"#RRGGBB\"}。不要解释，不要返回候选列表外的颜色。"
 }