Three targeted fixes for the jitter that shows up as soon as a feed
contains nested NoteCompose (reposts, quotes, BechLink previews):
* `calculateBackgroundColor`: only schedule the 5s "new item" fade
LaunchedEffect when the item is actually new and tracks read state.
Inner notes pass `routeForLastRead = null` and were parking a
coroutine for 5s per item, every scroll. Also drop a per-call
`Color.copy(alpha = 0f)` allocation in favor of `Color.Transparent`.
* `EventObservers` + `WatchBlockAndReport`: wrap the `StateFlow`
lookups in `remember(note)` so each recomposition of the same note
doesn't re-resolve `note.flow().…stateFlow` (and, in
`WatchBlockAndReport`, hit the synchronized LRU lookup) on every
pass. Affects observeNote / Replies / Reactions / Zaps / Reposts /
Ots / Edits and the per-item hidden-flow check.
* `produceCachedState` / `produceCachedStateAsync`: short-circuit on
cache hits. The previous `produceState` body always launched a
coroutine even when the LRU already had the value; this is the
common path for BechLink previews and draft notes during scroll.
Now we read the cache synchronously inside `remember`, and only
launch a `LaunchedEffect` for the actual miss.
No behavior change.
Claude
18c1ab2ece