REX
comment on a document, and talk each comment through with an agent
2026
- Point, don't pasteReviewing a document with an AI still means copying a paragraph into a chat, explaining where it came from, and carrying the answer back by hand. REX puts the conversation on the document instead — every comment is a thread, the thread stays attached to its passage, and nothing reaches your file until you approve it.
- A wrong place is worse than no placeA broken anchor does not fail. It lands somewhere, reports `ok`, and paints a highlight that looks exactly like a correct one. How REX keeps a comment on its passage while the document is edited, the three times it lied anyway, and the rule that came out of it: orphan before you guess.
- A comment is a conversation that waits for youEvery REX comment is its own thread with its own agent session, stored on the document rather than in a chat window. What is stored and what is derived, how four SDKs resume a conversation four different ways, and the resume that was silently broken until a debug report asked the filesystem instead of the SDK.
- A question cannot change your fileREX makes one safety promise: ASK cannot write, ACT edits a copy, and only Approve touches your file. Three times it broke without a sound — a line gone under "Applied to 0 file(s)", a committed file deleted under a notice saying it was put back, a copy removed while the agent was reading it — and what an allowlist, four SDKs and a repository's own settings file taught me about where a boundary actually is.
- Binary files differThe ACT loop ends in a diff you approve, and on a .pptx that diff is two words. So the agent writes a plan, REX performs it on a copy, and the checker has to prove not only that the change happened but that nothing else did — plus the three numbers I measured wrong on the way.