The branch control on user and consumed-steering bubbles could enable
only when a completed turn ended with no node after the message at all,
so readers saw a permanently unavailable control whose tooltip promised
a state it could not reach. An enabled one would mislead anyway: a fork
at a message seq cuts at the containing turn/end and takes the answer
along, the opposite of the branch-to-re-ask reading a control on one's
own bubble suggests.
MessageItem loses its fork props, PendingSteeringBubble loses the
showBranch special case, and messageBranchSeqs narrows to
assistantBranchSeqs: only a completed turn's transcript tail that is
the turn's own content-text assistant may fork. A steered turn keeps
its fork point under the settled answer, because fork is a log-prefix
cut and the steer is model-visible history the child inherits.
Web aria goldens drop the user-bubble disabled-branch row and its
hidden explanation text; the nested-subagent golden also loses the one
enabled user-tail fork handle, a loss the decision note accepts.
The ui-subagent catalog and read-only composer copy moved from hardcoded
Chinese to the locale-aware `subagent` namespace, so an en-US headless
browser now renders English. The e2e's selectors and goldens still
asserted the old hardcoded Chinese strings, leaving the scenario unable
to find the catalog trigger.
Convert the selectors to the default (en-US) render and re-record the
catalog goldens (ui, tree, nested) in English. The locale-aware parts of
the remaining goldens were already English (recorded under the en-US
default), so sidebar and fork are untouched.
