feat(confidence-engine): v0.54b integrate Investigation Overview UI seam + bounded scroll cleanup

- Wire transient overview state from ScenarioForm to ReasoningWorkspace
- Inline rendering of investigation overview below milestone invitation
- Remove obsolete scrollIntoView after overview request (scrolled away from rendered content)
- All four overview props consumed in ReasoningWorkspace render path
- Targeted Vitest: 9/9 PASS (tests/ui/investigation-overview-ui.test.jsx)
- Production build: compiles successfully

components/scenario-form.jsx

@@ -285,6 +285,10 @@ export default function ScenarioForm() {
   const [mockScenario, setMockScenario] = useState("");
   const [hideFacilitatorOnLanding, setHideFacilitatorOnLanding] = useState(false);
 
+  /* ── v0.54b — investigation overview transient state ────── */
+  const [overviewState, setOverviewState] = useState(null);
+  const [overviewLoading, setOverviewLoading] = useState(false);
+
   /* ── in-flight gate for episode reconsideration on Done ──── */
   const doneInProgressRef = useRef(false);
 
@@ -413,6 +417,36 @@ export default function ScenarioForm() {
     }
   }
 
+  /**
+   * v0.54b — request investigation overview via the established POST /api/cases/overview seam.
+   * Transient state only: never persists to SituationGraph or currentUnderstanding.
+   */
+  async function handleRequestOverview() {
+    if (overviewLoading || !result?.situationGraph) return;
+
+    setOverviewLoading(true);
+    setOverviewState(null); // clear any previous overview before new request
+
+    try {
+      const res = await fetch("/api/cases/overview", {
+        method: "POST",
+        headers: { "content-type": "application/json" },
+        body: JSON.stringify({
+          situationGraph: result.situationGraph,
+          findings,
+          plausibleInterpretations: (result.situationGraph?.reconstruction || {}).plausibleInterpretations ?? [],
+        }),
+      }).then((r) => r.json());
+
+      if (res?.success && res?.understanding != null) {
+        setOverviewState(res);
+      }
+      // On failure: do not clear existing CU, do not block further attempts
+    } finally {
+      setOverviewLoading(false);
+    }
+  }
+
   function appendFocusedContribution(contribution) {
     // Derive a single stored contribution object and use it for BOTH
     // contribution storage AND Finding derivation so the same identity
@@ -813,6 +847,11 @@ export default function ScenarioForm() {
                 updateStatus={updateStatus}
                 cuSynthesisLoading={cuSynthesisLoading}
                 currentUnderstanding={currentUnderstanding}
+                /* ── v0.54b — investigation overview transient state ─── */
+                overviewState={overviewState}
+                setOverviewState={setOverviewState}
+                overviewLoading={overviewLoading}
+                handleRequestOverview={handleRequestOverview}
                 result={{
                   ...(result || {}),
                   situationGraph: updateResult?.updatedSituationGraph ?? result?.situationGraph,