feat(confidence-engine): persist canonical investigation state

components/scenario-form.jsx

@@ -313,6 +313,33 @@ export default function ScenarioForm() {
     }
   }, []);
 
+  /* ── Canonical autosave — persist whenever state changes (Phase 2) ── */
+
+  useEffect(() => {
+    if (typeof window === "undefined") return;
+    // Guard: no valid investigation yet → skip autosave during idle/start flows.
+    // Also prevents overwriting an existing saved investigation with the initial
+    // empty state of a fresh ScenarioForm instance (hydration race guard).
+    if (!result?.situationGraph) return;
+
+    void saveInvestigation({
+      scenario,
+      situationGraph: result.situationGraph,
+      selectedQuestion: result.selectedQuestion,
+      summary: currentUnderstanding,
+      updatedAt: new Date().toISOString(),
+      focusedContributions,
+      findings,
+    });
+  }, [
+    scenario,
+    result?.situationGraph,
+    result?.selectedQuestion,
+    currentUnderstanding,
+    focusedContributions,
+    findings,
+  ]);
+
   /* Restore facilitator dismiss preference (Experiment 05) ─── */
   useEffect(() => {
     if (typeof window === "undefined") return;