It reproduces only on Horizon - on Foundation I didn’t see the reply branch carrying
over between topics.
But I don’t think it’s simply absent on Foundation; it looks more like it comes down to
how navigation works there. The difference I noticed:
- Horizon: when I click a related topic (or open any topic from the list), the topic
appears instantly, with no loading indicator. This instant navigation is exactly when
the branch carry-over shows up, after 2+ clicks in a row. - Foundation: the topic also appears instantly at first (same as Horizon), but then after
~200-400ms a loading screen with animated dots appears and the topic loads again - so there’s a second, self-triggered load right after the fast open.
So it seems the bug surfaces specifically because of the “instant” navigation, where the
previous topic’s state isn’t reset. On Foundation that follow-up load apparently resets
the state and masks the problem. In other words: on Horizon the instant nested-topic
navigation doesn’t reset the previous topic’s post stream / message-bus subscription,
whereas Foundation’s flow does it via that second load.
Separately, while testing on Horizon: in the nested view I occasionally get a tiny layout
shift. I open a topic, start scrolling down, and as the screen reaches the replies a quick
micro-shift can happen - not every time, but fairly often. Might be related, might be a
separate minor thing; flagging it just in case.