Each subagent's progress and completion rendered as its own timeline row
on mobile, while web folds a turn's spawns into one "Kicked off N
subagents" row. Use the same spawn-group keys as web's session-logic,
keep the batch anchored where the run launched, derive its lifecycle
from the members, and list the members with their states when the row
is opened.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>