让提取提示词序列化错误可恢复

将提取提示词生成改为返回带上下文的错误。

apps/ai-game-creator-shell/src-tauri/src/ui_editor/commands/separation/prompt/extract.rs

@@ -45,7 +45,7 @@ pub(crate) fn gen_extract_prompt(
     state: &SeparationState,
     tree: &SeparationTree,
     batch: &[&SeparationNode],
-) -> String {
+) -> Result<String, String> {
     let mut result = r#"
     This is a UI design image, not a normal photo/illustration. Extract it strictly as UI elements/layers, not as a generic foreground/background extraction.
     Treat distinct UI element as its own layer with hard, clean, pixel-accurate edges and full transparency outside the element.
@@ -78,12 +78,12 @@ pub(crate) fn gen_extract_prompt(
         ui_layer_tree: project_node(&tree.root, &target_ids, &terminal_ids, &mut index),
     };
     let yaml = serde_yaml::to_string(&document)
-        .expect("UI separation extract prompt projection must be serializable");
+        .map_err(|error| format!("UI separation extract prompt projection failed: {error}"))?;
 
     result.push_str("```yaml\n");
     result.push_str(&yaml);
     result.push_str("```\n");
-    result
+    Ok(result)
 }
 
 fn project_node(

apps/ai-game-creator-shell/src-tauri/src/ui_editor/commands/separation/workflow/mod.rs

@@ -127,7 +127,7 @@ pub(crate) async fn separate_ui_impl(
                 break;
             }
             let batch = batch_nodes.iter().collect::<Vec<_>>();
-            let prompt = gen_extract_prompt(&separation, current_tree, &batch);
+            let prompt = gen_extract_prompt(&separation, current_tree, &batch)?;
             app_log!(
                 "ui_separation.batch_start tree_index={} batch_index={} nodes={} area_px={} image_edit_dimension_px={} prompt_chars={} rework_total={}",
                 tree_index, batch_index, batch.len(), batch_area_px, image_edit_dimension_px,