In multi-step turns (assistant -> tool_call -> assistant -> tool_call ->
final assistant), only the turn-final assistant bubble was rendering the
'jump to question' navigation button because the gate keyed on
isTurnFinalAssistant. Intermediate assistant bubbles that *do* have a
resolvable question raw-index lost the affordance entirely.
Switch the gate to 'show whenever questionRawIdxByAssistantRawIdx has a
target for this rawIdx', which is the actual precondition for the button
being meaningful. Turn-finality was a proxy for 'has a question target'
that under-covered multi-step turns.
No template/CSS change needed; _questionJumpButtonHtml already handles
the rawIdx-or-undefined contract.
24b175045f
