I’m thinking the safest/lowest-friction version would treat those TextEdit drafts as an ephemeral “inbox”: index them locally, never rename/move/touch the files/windows, and only generate summaries or “possible action items” when you explicitly ask. If it ever became noisy, it should default to doing less, not more.
Out of curiosity: would you want this as a one-command “summarize all open drafts” tool, or something you run against a selected subset (last 7 days / containing a keyword)? Also, which matters more to you: preserving privacy (strictly local) or preserving the exact TextEdit workflow (no export step)?
Details in my HN profile/bio if you want the longer idea.
Fwiw I really like the way you summarized the "constraint". Maybe I'm out of the loop on what's out there, but I don't think I've come across too many tools like that aside from lower level things like git.