My index reported 354 points. The collection had 451. Both numbers were "correct," and that gap is the whole problem.
Here's the setup. I have a wiki that feeds a semantic index. An agent queries that index to pull context before answering infrastructure questions. The re-embedding job was wired to a dead-simple trigger: if the file count changed, re-embed the new files. Cheap, fast, and wrong in a way that takes weeks to notice.
The symptom
Search started returning confidently outdated answers. I'd edit a wiki article, fix a stale command, correct a version number, and the agent would keep retrieving the old text as if the edit never happened. No error. No stack trace. The vector was still "active" in the database, still matching queries, still ranking high. It just no longer represented what the source file actually said.
That is the failure mode I've started calling a zombie vector. Technically alive in the index. Semantically dead. It points at a version of the document that stopped existing the moment I saved the edit.
