修复 AGC Rust shard 4 的两个 CI 失败测试

- direct_registered_taonier_runtime_image_paths 通用平台图兜底补齐 canonical 切片排除：assets/art-spritesheet-slices/ 下的切片只经完整 manifest/receipt/内容校验放行，内容被篡改的切片不再绕过完成门禁
- direct_completion_scans_npm_scene_modules 测试改为保留 fixture 有效切片，不再依赖被修复的兜底漏洞
- mixed_project_history_rows 过时测试按 d48d09905 收紧后的契约改为断言 DirectProject 链对 legacy 行失败关闭

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

@@ -2555,6 +2555,15 @@ fn direct_registered_taonier_runtime_image_paths(root: &Path) -> Vec<String> {
                     .generation_route
                     .as_deref()
                     .is_some_and(|route| route.starts_with("/api/external/v1/editor/"))
+                // Canonical slices are admitted only through
+                // `direct_registered_taonier_slice_paths` after the full slice
+                // manifest/receipt/content validation. This generic fallback
+                // must not re-admit a slice whose bytes no longer match the
+                // registered receipt.
+                && !(asset.kind == "art-spritesheet-slice"
+                    && asset
+                        .local_path
+                        .starts_with("assets/art-spritesheet-slices/"))
         })
         .filter_map(|asset| {
             let path = direct_normalized_project_asset_path(&asset.local_path)?;
@@ -8220,11 +8229,6 @@ mod tests {
             "const player = new Image(); player.src = '/assets/art-spritesheet-slices/player.png';",
         )
         .expect("scene");
-        std::fs::write(
-            root.join("assets/art-spritesheet-slices/player.png"),
-            tiny_opaque_png(),
-        )
-        .expect("slice");
 
         assert_eq!(
             direct_game_sources_referenced_taonier_assets(&root),

apps/ai-game-creator-shell/src-tauri/src/project/conversation/tests.rs

@@ -272,7 +272,7 @@ fn project_history_skips_direct_project_rows_but_keeps_other_broken_rows_failing
 }
 
 #[test]
-fn mixed_project_history_rows_stay_readable_from_both_sides() {
+fn mixed_project_history_rows_read_by_generic_chain_but_fail_closed_for_direct_project() {
     let root = unique_conversation_test_root();
     init_local_game_project_at(&root, "project-1", "写侧统一测试").expect("init project");
     write_project_history(&root, &[DIRECT_PROJECT_ROW]);
@@ -309,19 +309,12 @@ fn mixed_project_history_rows_stay_readable_from_both_sides() {
         vec!["模式切换后由通用写入器补写的回复", "带 id 的旧格式回复"]
     );
 
-    // 反向：DirectProject 链把同一份文件里的两种行都读出来，混合文件不构成毒化。
-    let direct_items = crate::agent::read_direct_project_history_items_at(&root)
-        .expect("DirectProject must keep reading the mixed history");
-    assert_eq!(
-        direct_items
-            .iter()
-            .map(|item| item["content"][0]["text"].as_str().unwrap_or_default())
-            .collect::<Vec<_>>(),
-        vec![
-            "再加一个按钮",
-            "模式切换后由通用写入器补写的回复",
-            "带 id 的旧格式回复",
-        ]
+    // 反向：DirectProject 链只接受 response_item 信封，混合文件里的 legacy 行让它失败关闭。
+    let error = crate::agent::read_direct_project_history_items_at(&root)
+        .expect_err("DirectProject must fail closed on legacy rows");
+    assert!(
+        error.starts_with("DirectProject 历史记录类型无效"),
+        "{error}"
     );
 
     std::fs::remove_dir_all(root).ok();