chore: clean diagnostics and prepare for designer structural refactor (stub legacy useActiveStudy)

src/app/(dashboard)/experiments/[id]/designer/page.tsx

@@ -1,5 +1,5 @@
 import { notFound } from "next/navigation";
-import { BlockDesigner } from "~/components/experiments/designer/BlockDesigner";
+import { DesignerShell } from "~/components/experiments/designer/DesignerShell";
 import type { ExperimentStep } from "~/lib/experiment-designer/types";
 import { api } from "~/trpc/server";
 
@@ -44,7 +44,7 @@ export default async function ExperimentDesignerPage({
         : undefined;
 
     return (
-      <BlockDesigner
+      <DesignerShell
         experimentId={experiment.id}
         initialDesign={initialDesign}
       />

src/app/(dashboard)/layout.tsx

@@ -35,8 +35,12 @@ export default async function DashboardLayout({
   const cookieStore = await cookies();
   const defaultOpen = cookieStore.get("sidebar_state")?.value === "true";
 
+  // Pre-seed selected study from cookie (SSR) to avoid client flash
+  const selectedStudyCookie =
+    cookieStore.get("hristudio_selected_study")?.value ?? null;
+
   return (
-    <StudyProvider>
+    <StudyProvider initialStudyId={selectedStudyCookie}>
       <BreadcrumbProvider>
         <SidebarProvider defaultOpen={defaultOpen}>
           <AppSidebar userRole={userRole} />

src/app/(dashboard)/studies/[id]/participants/page.tsx

@@ -4,19 +4,21 @@ import { useParams } from "next/navigation";
 import { Suspense, useEffect } from "react";
 import { ParticipantsTable } from "~/components/participants/ParticipantsTable";
 import { ManagementPageLayout } from "~/components/ui/page-layout";
-import { useActiveStudy } from "~/hooks/useActiveStudy";
+import { useStudyContext } from "~/lib/study-context";
+import { useSelectedStudyDetails } from "~/hooks/useSelectedStudyDetails";
 
 export default function StudyParticipantsPage() {
   const params = useParams();
   const studyId: string = typeof params.id === "string" ? params.id : "";
-  const { setActiveStudy, activeStudy } = useActiveStudy();
+  const { setSelectedStudyId, selectedStudyId } = useStudyContext();
+  const { study } = useSelectedStudyDetails();
 
-  // Set the active study if it doesn't match the current route
+  // Sync selected study (unified study-context)
   useEffect(() => {
-    if (studyId && activeStudy?.id !== studyId) {
-      setActiveStudy(studyId);
+    if (studyId && selectedStudyId !== studyId) {
+      setSelectedStudyId(studyId);
     }
-  }, [studyId, activeStudy?.id, setActiveStudy]);
+  }, [studyId, selectedStudyId, setSelectedStudyId]);
 
   return (
     <ManagementPageLayout
@@ -25,7 +27,7 @@ export default function StudyParticipantsPage() {
       breadcrumb={[
         { label: "Dashboard", href: "/dashboard" },
         { label: "Studies", href: "/studies" },
-        { label: activeStudy?.title ?? "Study", href: `/studies/${studyId}` },
+        { label: study?.name ?? "Study", href: `/studies/${studyId}` },
         { label: "Participants" },
       ]}
       createButton={{

src/app/(dashboard)/studies/[id]/trials/page.tsx

@@ -4,19 +4,21 @@ import { useParams } from "next/navigation";
 import { Suspense, useEffect } from "react";
 import { TrialsTable } from "~/components/trials/TrialsTable";
 import { ManagementPageLayout } from "~/components/ui/page-layout";
-import { useActiveStudy } from "~/hooks/useActiveStudy";
+import { useStudyContext } from "~/lib/study-context";
+import { useSelectedStudyDetails } from "~/hooks/useSelectedStudyDetails";
 
 export default function StudyTrialsPage() {
   const params = useParams();
   const studyId: string = typeof params.id === "string" ? params.id : "";
-  const { setActiveStudy, activeStudy } = useActiveStudy();
+  const { setSelectedStudyId, selectedStudyId } = useStudyContext();
+  const { study } = useSelectedStudyDetails();
 
   // Set the active study if it doesn't match the current route
   useEffect(() => {
-    if (studyId && activeStudy?.id !== studyId) {
-      setActiveStudy(studyId);
+    if (studyId && selectedStudyId !== studyId) {
+      setSelectedStudyId(studyId);
     }
-  }, [studyId, activeStudy?.id, setActiveStudy]);
+  }, [studyId, selectedStudyId, setSelectedStudyId]);
 
   return (
     <ManagementPageLayout
@@ -25,7 +27,7 @@ export default function StudyTrialsPage() {
       breadcrumb={[
         { label: "Dashboard", href: "/dashboard" },
         { label: "Studies", href: "/studies" },
-        { label: activeStudy?.title ?? "Study", href: `/studies/${studyId}` },
+        { label: study?.name ?? "Study", href: `/studies/${studyId}` },
         { label: "Trials" },
       ]}
       createButton={{