修复策划工具乱序局部修改导致的中断

按原文位置排序并顺序拼接补丁，避免替换偏移失效。
新增乱序、中文与长度变化的局部修改回归测试。
同步策划 Agent 批量局部修改技术说明。

apps/ai-game-creator-shell/src-tauri/src/agent/design_tools.rs

@@ -380,11 +380,16 @@ pub(crate) fn execute_design_file_tool(
                 }
                 return Err(details.join("\n"));
             }
-            let mut updated = content.clone();
-            for (index, start, end) in matches.into_iter().rev() {
+            matches.sort_unstable_by_key(|(_, start, _)| *start);
+            let mut updated = String::with_capacity(content.len());
+            let mut cursor = 0;
+            for (index, start, end) in matches {
                 let (_, new) = &normalized[index];
-                updated.replace_range(start..end, new);
+                updated.push_str(&content[cursor..start]);
+                updated.push_str(new);
+                cursor = end;
             }
+            updated.push_str(&content[cursor..]);
             if updated == content {
                 return Err(format!("没有产生修改：{display}"));
             }
@@ -834,6 +839,35 @@ mod tests {
         assert!(!root.join("design_artifacts/notes").exists());
     }
 
+    #[test]
+    fn patch_file_applies_out_of_order_edits_with_changing_utf8_lengths() {
+        let temp = test_root();
+        let root = temp.path();
+        execute_design_file_tool(
+            root,
+            "write_file",
+            &json!({"path":"notes/design.md","content":"开头\n甲\n保留一\n乙乙\n保留二\n丙\n结尾"}),
+        )
+        .expect("write");
+        execute_design_file_tool(
+            root,
+            "patch_file",
+            &json!({
+                "path":"notes/design.md",
+                "edits":[
+                    {"old_text":"丙","new_text":"新的结论"},
+                    {"old_text":"甲","new_text":"扩展A"},
+                    {"old_text":"乙乙","new_text":"乙"}
+                ]
+            }),
+        )
+        .expect("patch out of order");
+        assert_eq!(
+            fs::read_to_string(root.join("design_artifacts/notes/design.md")).expect("read disk"),
+            "开头\n扩展A\n保留一\n乙\n保留二\n新的结论\n结尾"
+        );
+    }
+
     #[test]
     fn phase_context_injects_current_skill_only() {
         let resources = DesignResources::new(pack_root()).expect("pack");