fix: reduce redundant work during chat and note startup

Avoid hidden activity renders, no-op message saves and attachment scans when pinning conversations. Reuse note body inspection and skip unchanged attachment reference writes while preserving recovery and cleanup behavior.

Skip unnecessary Markdown normalization and memoize subagent lookups without delaying live rich text. Add storage operation counts and real Electron rendering equivalence benchmarks; full-render speedup remains unproven.

Validation: 5397 tests passed, 84 skipped; typecheck passed. Lint passed excluding two existing untracked sidebar probe files.

Release note: Reduce repeated rendering and disk work during chat, conversation pinning and note startup while preserving existing content and interactions.

docs/features/document-processing/implementation.md

@@ -64,6 +64,10 @@ Main 先保存资产，再保存草稿或接受队列；消息、分支建立独
 会话删除、项目删除及清空数据均核对引用，启动回收已无归属的记录和孤立 UUID 目录。
 清理失败保留无引用数据库记录供下次重试，不回滚已接受的草稿。
 
+引用保存按输入顺序去重并查询资产。已有引用的顺序、会话归属均相同，且资产无需从临时目录
+转存时，直接返回，不重复开启写事务或删除、插入引用。空引用同样适用；顺序、归属或附件
+发生变化时仍按原事务更新，临时资产仍须转存。
+
 助手库 schema 39 标记新附件元数据，阻止旧客户端将其当旧格式读取；没有批量改写历史附件。
 知识库 schema 13 新增 `metadata.parsedResultId` 表达式索引，结果按主键定位，不扫描全部文档。
 知识库新结果先写入独立 resultId 目录，数据库正文/chunks 发布成功后替换引用，再清理旧目录。