test(ui): explore branch as workspace context

components/reasoning-workspace.jsx

@@ -521,6 +521,7 @@ export default function ReasoningWorkspace({
   onAnswerSubmit,
   lastSubmittedAnswer,
   onRestart,
+  branchContext,
 }) {
   const [investigationHistory, setInvestigationHistory] = useState([]);
   const turnCounter = useRef(0);
@@ -823,6 +824,21 @@ export default function ReasoningWorkspace({
             <div className="grid grid-cols-1 gap-6 lg:grid-cols-3">
               {/* ── Left lane: active conversation & notebook ───────── */}
               <div className="space-y-6 lg:col-span-2">
+                {/* Active branch context (experiment RTO.25D) */}
+                {branchContext && hasGraph && (
+                  <div className="rounded-lg border border-blue-200/60 bg-blue-50/40 px-5 py-4">
+                    <h2 className="mb-1 text-[11px] font-semibold tracking-widest uppercase text-gray-500">
+                      Current branch
+                    </h2>
+                    <p className="text-base font-medium leading-tight text-gray-900">{branchContext.label}</p>
+                    {branchContext.origin && (
+                      <p className="mt-2 text-sm leading-relaxed text-gray-600">
+                        Trying to understand: {branchContext.origin}
+                      </p>
+                    )}
+                  </div>
+                )}
+
                 {/* ── Open questions (case workspace) — no ranking bias ── */}
                 {(() => {
                   const openNodes = graph.nodes.filter(
@@ -1104,9 +1120,9 @@ export default function ReasoningWorkspace({
                 {hasCurrentSummaryCondition && (
                   <>
                     <CurrentUnderstandingCard currentSummary={graph?.currentSummary || result?.updatedSituationGraph?.currentSummary} plainLanguage={propUnderstanding || null} />
-                    {/* ── Experiment 12: progress panel A / B / C toggle (temporary experimental UI) ── */}
+                    {/* ── Experiment 12: progress panel A / B / C toggle (temporary experimental UI) — de-emphasised by branch-as-context experiment RTO.25D */}
                     {hasGraph && (
-                      <div className="space-y-2">
+                      <div className="hidden space-y-2">
                         <div className="flex items-center gap-2" role="radiogroup" aria-label="Progress panel variant">
                           <button
                             role="radio"