msglist: Fetch newer messages despite previous muted batch #1989
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The nested `try` block doesn't seem to be making any difference, so good to remove.
This change is necessary when there is a need to fetch more messages in both directions, older and newer, and when fetching in one direction avoids fetching in another direction at the same time, because of the `if (busyFetchingNewer) return` line in both `fetchOlder` and `fetchNewer`. This scenario happens when a conversation is opened in its first unread, such that the number of messages in the initial batch is so low (because they're muted in one way or another) that it's already past the certain point where the scroll metrics listener in the widget code triggers both `fetchOlder` and `fetchNewer`. In 2025-11, that code first calls `fetchOlder` then `fetchNewer`, and for the reason mentioned above, `fetchNewer` will not fetch any new messages. But that's fine, because as soon as older messages from `fetchOlder` arrives, there will be a change in the scroll metrics, so `fetchNewer` will be called again, fetching new messages. But imagine if the number of messages in the initial batch occupies less than a screenful, and then `fetchOlder` returns no messages or a few messages that combined with the initial batch messages are still less than a screenful; in that case, there will be no change in the scroll metrics to call `fetchNewer`. With the three fetch request types being separated, especially the two request types for older and newer messages, each direction can fetch more messages independently without interfering with one another. Another benefit of this change is that if there's a backoff in one direction, it will not affect the other one. Fixes: zulip#1256
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Fixes: #1256
Screen recordings
First batch - Empty
Before
Empty.first.batch.-.Before.mov
After
Empty.first.batch.-.After.mov
First batch - Less than a screenful
Before
First.batch.with.few.messages.-.Before.mov
After
First.batch.with.few.messages.-.After.mov