joinPages healed a tool call split across a page boundary but not a
message split across one, so a long reply came back as two rows with a
paragraph break through the middle of a sentence -- visible on any
session whose replies are longer than an eighty-event page.
Same cause, same cure, and the rule was already written down one member
of the set: `foldEvent` never leaves two assistant messages adjacent
inside a page, since deltas accumulate into the message before them, so
two meeting at a join are always halves of one reply.
The newer half keeps its identity for the reason adoptRun gives -- it is
the row already on screen. It grows by what the older half brings, which
is safe at this join and nowhere else: the join is at the oldest end of
what is loaded, so the growth extends off the top, away from the row the
list anchors to.
iris
ad791a0d84