I think just the mildest tweak to the constellation ending, specifically the second line of the first paragraph, and having the Hollow actually stop when they reach the rot's terminus would do it.
Your suggestions make total sense, and I actually had the fixes ready: the clearer constellation ending, and the Hollow stopping at the Rot's source. Unfortunately, I found out that because of how itch hosts browser games, uploading a new build would wipe everyone's saves, including yours. I'd rather not do that to anyone who's put hours into the constellation, so I'm holding off on the update for now.
So, for the record, here's what the endings were meant to say: completing the constellation is the first ending, but not the last. The second one is at the source of the Rot, at biome 106, where the Hollow is supposed to stop and finally rest. You reached both, which makes you the first player I know of to see everything HollowRun has.
Lesson learned for my next game: set up saves that survive updates from day one. Thanks again for playing all the way through and for all the thoughtful feedback!
Update: I found a way around the save problem! The new build now picks up your old save automatically, so nothing gets lost. Your suggestions are in: the Hollow now stops at the Rot's source, and the constellation ending is clearer. Full details here: https://zer0fast.itch.io/hollowrun/devlog/1668881/update-11-your-biome-is-saved-...
Thanks again, this update exists because of your feedback.