A group of adjacent tool calls was identified by its first call, and the
list is keyed by that identity. But a run can gain members at *either*
end -- a new call arriving beside it, or a page of history arriving in
front of it -- so its first member is not a name, it is a description
that changes. Every time it changed, the row was a different row as far
as the list was concerned: the anchor went with it, and the transcript
stepped under whoever was reading.
Each call now carries the run it belongs to, decided once when it is
folded in and never recomputed, and the row keys on that. A lone call
that gains a neighbour becomes a group *without* changing identity,
which the old key got wrong in the other direction too -- one row was
replaced by another rather than updated.
`joinPages` hands the arriving older calls the name of the run they are
joining, rather than renaming that run after them. The obvious way round
is the wrong one: the newer half is the part already on screen, so
naming the joined run after the older half renames the row the reader is
looking at, which is the whole failure this is meant to remove.
Checked against the same twelve-`/tools 8` rig, whose page boundary falls
inside the second group: every group still reads eight, so the grouping
is unchanged -- what changed is that none of their identities move.
Toward the standing rule for this screen, which is that it may only move
when the reader is at the newest end and something new arrives.
iris
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