`@assistant-ui/store`'s index-keyed child-scope lookup (`tapClientLookup`)
throws — rather than returning undefined — when a subscriber reads an index
the message/parts list no longer has. During high-frequency store replacement
(switching sessions mid-stream, gateway reconnect replay) a subscriber from
the previous, longer list is still in React's notification queue and reads one
slot past the new, shorter array before it can unmount. The throw
(`Index N out of bounds (length: N)`, the classic index === length off-by-one)
unwinds all the way to the root error boundary and blanks the entire window,
even though the store self-heals on the very next consistent snapshot.
Wrap each virtualized message group in a tiny boundary that swallows ONLY this
transient lookup race and auto-recovers when the message signature changes
(the existing list-mutation key). Any other error re-throws to the root
boundary, so genuine bugs still surface.
Upstream-tracked and unresolved: assistant-ui/assistant-ui#4051, #3652.
Co-authored-by: mollusk <mollusk@users.noreply.github.com>
d221e369b8