显式 Codex 返回不再往项目主对话投影旧格式行

- direct_tools_mcp.rs：删除 conversation.record_codex_response 末尾往 project.jsonl 追加 legacy 行的投影，它写的是 {schemaVersion:game-creator-conversation.v1,...} 旧行，会毒化共用该文件的 DirectProject 历史
- 顺带删掉只为那条投影存在的 key/message_id 计算与描述它的注释，不留墓碑
- 该工具的事实来源仍是自己的只读 journal .agent/conversations/codex-responses.jsonl，返回内容与 conversation.list/read 行为不变
- 补断言：record_codex_response 只写 codex-responses.jsonl，project.jsonl 保持为空

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

@@ -1247,8 +1247,6 @@ fn external_mcp_record_response(root: &Path, arguments: &Value) -> Value {
         Err(error) => return mcp_tool_result(error, Vec::new(), true),
     };
     let redacted = redact_external_mcp_response(&content);
-    let key = format!("{request_id}\u{0}{sequence}");
-    let message_id = format!("external-codex-{:x}", Sha256::digest(key.as_bytes()));
     let guard = EXTERNAL_MCP_JOURNAL_LOCK
         .get_or_init(|| Mutex::new(()))
         .lock();
@@ -1358,29 +1356,6 @@ fn external_mcp_record_response(root: &Path, arguments: &Value) -> Value {
             true,
         );
     }
-    // Reuse the existing conversation projection so the current UI can read
-    // the explicit external response without treating it as business truth.
-    if let Err(error) = append_local_conversation_message_for_session_idempotent_at(
-        root,
-        None,
-        None,
-        LocalConversationMessage {
-            role: "assistant".to_string(),
-            content: record
-                .get("content")
-                .and_then(Value::as_str)
-                .unwrap_or_default()
-                .to_string(),
-            agent_id: None,
-        },
-        &message_id,
-    ) {
-        return mcp_tool_result(
-            format!("Codex 返回已写入但对话投影失败：{error}"),
-            Vec::new(),
-            true,
-        );
-    }
     records.push(record.clone());
     mcp_tool_result(record.to_string(), Vec::new(), false)
 }
@@ -2280,4 +2255,33 @@ mod tests {
         }))
         .is_err());
     }
+
+    #[test]
+    fn recorded_codex_response_only_writes_its_own_journal() {
+        let temporary = crate::tests::canonical_test_tempdir("direct-tools-record-response-");
+        let root = temporary.path();
+        init_local_game_project_at(root, "direct-tools-record", "Codex 返回记录测试")
+            .expect("init project");
+
+        let result = external_mcp_record_response(
+            root,
+            &json!({
+                "requestId": "req-1",
+                "sequence": 0,
+                "content": "已完成的返回正文"
+            }),
+        );
+        assert_eq!(result.get("isError"), Some(&json!(false)), "{result}");
+
+        let journal = root.join(".agent/conversations/codex-responses.jsonl");
+        let journal_text = std::fs::read_to_string(&journal).expect("read codex responses journal");
+        assert!(journal_text.contains("已完成的返回正文"), "{journal_text}");
+
+        let project_history = root.join(".agent/conversations/project.jsonl");
+        let project_history_text = std::fs::read_to_string(&project_history).unwrap_or_default();
+        assert_eq!(
+            project_history_text, "",
+            "显式 Codex 返回不能再往项目主对话写 legacy 行"
+        );
+    }
 }