BigSimmo · BigSimmo · Aug 8, 2026 · Aug 8, 2026 · Aug 8, 2026 · Aug 8, 2026
@@ -328,7 +328,7 @@ One shared composer (`master-search-header.tsx`) serves every mode. Placement:
 - **Information (detail) pages**: catalogue/record routes under each mode (`/services/[slug]`, `/forms/[slug]`, `/medications/[slug]`, `/specifiers/[slug]`, `/formulation/[slug]`, `/factsheets/[slug]`, `/dsm/diagnoses/[slug]`, …). Route detection: `src/lib/information-pages.ts` (`isInformationPage`). Shared outer chrome: `src/components/information-page-shell.tsx` (`InformationPageShell`, breadcrumbs, optional footer). Specifier/formulation mode shells re-export that primitive. Intentional opt-outs: document viewer, therapy-compass CSS workspace, differentials presentation workflow.
 - **Result and detail views**: fixed bottom dock on phone (compact variant on submitted searches), sticky top from `sm` up.
 - **Results routing**: standalone routes own their submitted searches via `?q=…&run=1` (`/services` → `ServicesNavigatorPage`, `/forms` → `FormsSearchResultsPage`, `/differentials` → `DifferentialsHome` results view, `/formulation` → local mechanism results, `/favourites` filters the command library in place). Answer, Documents, and Prescribing submitted searches render inside `ClinicalDashboard` — intentional, since they need retrieval/answer state. Bare `/?mode=<id>` always renders the shared home with that mode preselected; only a submitted deep link (`q` plus `run=1`) resolves to the mode's own search surface (proxy early-redirect still covers favourites/differentials/specifiers for those submitted aliases).
-- **Intentionally composer-free routes**: `/differentials/presentations/*` (comparison workflow owns its chrome), `/documents/[id]` viewer (has its own in-document ask composer), `/documents/source/*` (document flow owns mobile chrome). Do not re-flag these in search-consistency audits.
+- **Intentionally composer-free routes**: `/differentials/presentations/*` and `/differentials/compare` (comparison workflow owns its chrome), `/documents/[id]` viewer (has its own in-document ask composer), `/documents/source/*` (document flow owns mobile chrome). Do not re-flag these in search-consistency audits.
 - **Shared secondary navigation**: `src/components/secondary-navigation.tsx` (`SecondaryNavigation`, route/section/action items, roving tablist, fragment section tracking) and `src/components/page-secondary-navigation.tsx` (`PageSecondaryNavigation`, per-route selection of mode destinations vs. "On this page" section anchors). Mode destinations come from `src/lib/mode-secondary-navigation.ts` (`modeSecondaryNavigationRegistry`, no "Home" item). `GlobalSearchShell` renders it in normal flow at the top of `#main-content` for its owned namespaced modes; it self-suppresses on clean mode homes, locally-owned detail routes (medications, factsheets, differentials diagnoses) and Therapy Compass, and Specifiers/Formulation keep their existing local `Subnav` (so the shared mode bar is skipped for those two modes to avoid a duplicate row).
 - **Local filter fields** (sidebar "Search chats", document drawer "Find a document"/"Find a source PDF") are scoped filters, not global search; they share the `fieldControlWithIcon`/`fieldIcon` primitives.
 - **Wiring conventions** for buttons and route navigation (and the gates that enforce them — the dead-button ESLint rule and the orphan-route reachability test) live in `docs/wiring-conventions.md`.

@@ -327,12 +327,12 @@ product exclusions; the only route-only disposition is the documented legacy doc
 redirect. Shared shell/component roots carry their own explicit `shared-shell` disposition.
 
 Registered public components: 53
-Declared product roots: 58
+Declared product roots: 59
 Roots with a literal `.ckb-v2` opt-in: 1
-Roots inheriting `.ckb-v2` from the global `<html>`: 57
+Roots inheriting `.ckb-v2` from the global `<html>`: 58
 Production surfaces observed under v2: 14/14
 Dynamic `ckb-v2` constructions: 0
-Declared production page routes: 50/50
+Declared production page routes: 51/51
 
 Source observation and contract declaration are independent. A literal `ckb-v2` on the global `<html>` makes every production surface inherit v2, but it does not approve that adoption.
 The Proof column summarizes each surface's dark, forced-colours, 320px, print and browser declarations; exact statuses and evidence paths live in the manifest.
@@ -342,7 +342,7 @@ Observed v2 under a compatibility declaration fails closed. A declared v2 shell
 | ---------------------------------- | --------------- | -----: | ----: | -------------- | -------------------------- | -------------- | -------------- |
 | `root-shell-and-settings`          | shared-shell    |      3 |     6 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
 | `catalogues-forms-and-info`        | owned           |     13 |    13 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
-| `differentials`                    | owned           |      5 |     5 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
+| `differentials`                    | owned           |      6 |     6 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
 | `formulation`                      | owned           |      5 |     5 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
 | `specifiers`                       | owned           |      5 |     5 | v2             | v2 (inherited-global-root) | passed         | not-committed  |
 | `therapy-compass`                  | owned           |      9 |    10 | v2             | v2 (inherited-global-root) | passed         | not-committed  |

@@ -168,6 +168,7 @@
       "id": "differentials",
       "disposition": "owned",
       "routes": [
+        "src/app/(search-app)/differentials/compare/page.tsx",
         "src/app/(search-app)/differentials/diagnoses/[slug]/page.tsx",
         "src/app/(search-app)/differentials/diagnoses/page.tsx",
         "src/app/(search-app)/differentials/page.tsx",

@@ -2205,6 +2205,7 @@
       "disposition": "owned",
       "documentedDisposition": null,
       "routes": [
+        "src/app/(search-app)/differentials/compare/page.tsx",
         "src/app/(search-app)/differentials/diagnoses/[slug]/page.tsx",
         "src/app/(search-app)/differentials/diagnoses/page.tsx",
         "src/app/(search-app)/differentials/page.tsx",
@@ -2249,6 +2250,16 @@
       "permittedComponentFamilies": ["controls", "feedback", "layout", "source"],
       "sanctionedSpecialPatterns": ["Differential"],
       "roots": [
+        {
+          "file": "src/app/(search-app)/differentials/compare/page.tsx",
+          "exists": true,
+          "imports": [],
+          "importedFamilies": [],
+          "literalCkbV2": false,
+          "dynamicCkbV2": false,
+          "v2MountMode": "inherited-global-root",
+          "sanctionedPatternsPresent": ["Differential"]
+        },
         {
           "file": "src/app/(search-app)/differentials/diagnoses/[slug]/page.tsx",
           "exists": true,
@@ -3182,6 +3193,7 @@
   "routeCoverage": {
     "discovered": [
       "src/app/(search-app)/calculators/page.tsx",
+      "src/app/(search-app)/differentials/compare/page.tsx",
       "src/app/(search-app)/differentials/diagnoses/[slug]/page.tsx",
       "src/app/(search-app)/differentials/diagnoses/page.tsx",
       "src/app/(search-app)/differentials/page.tsx",
@@ -3234,6 +3246,7 @@
     ],
     "declared": [
       "src/app/(search-app)/calculators/page.tsx",
+      "src/app/(search-app)/differentials/compare/page.tsx",
       "src/app/(search-app)/differentials/diagnoses/[slug]/page.tsx",
       "src/app/(search-app)/differentials/diagnoses/page.tsx",
       "src/app/(search-app)/differentials/page.tsx",
@@ -3290,7 +3303,7 @@
   },
   "adoption": {
     "literalCkbV2RootCount": 1,
-    "inheritedCkbV2RootCount": 57,
+    "inheritedCkbV2RootCount": 58,
     "dynamicCkbV2RootCount": 0,
     "v2MountedSurfaceCount": 14,
     "declaredV2SurfaceCount": 14
@@ -3299,8 +3312,8 @@
     "registeredComponentCount": 53,
     "previewCount": 53,
     "productImportedComponentCount": 31,
-    "rootCount": 58,
-    "productionRouteCount": 50,
-    "nextUiEntryCount": 102
+    "rootCount": 59,
+    "productionRouteCount": 51,
+    "nextUiEntryCount": 103
   }
 }
@@ -7,6 +7,7 @@ This file is generated by `npm run docs:update` (or `npm run sitemap:update` dir
 - `/` - Main Clinical KB shell. Source: `src/app/(search-app)/page.tsx`.
 - `/calculators` - Route discovered from app directory Source: `src/app/(search-app)/calculators/page.tsx`.
 - `/differentials` - Differentials home and search surface. Source: `src/app/(search-app)/differentials/page.tsx`.
+- `/differentials/compare` - Compare entry: same-presentation selections redirect into a catalogue workflow; cross-presentation selections render an ad-hoc comparison. Source: `src/app/(search-app)/differentials/compare/page.tsx`.
 - `/differentials/diagnoses` - Diagnosis stream. Source: `src/app/(search-app)/differentials/diagnoses/page.tsx`.
 - `/differentials/presentations` - Presentation catalogue stream. Source: `src/app/(search-app)/differentials/presentations/page.tsx`.
 - `/differentials/presentations/[slug]` - Presentation comparison workflow. Source: `src/app/(search-app)/differentials/presentations/[slug]/page.tsx`.
@@ -1101,7 +1102,6 @@ This file is generated by `npm run docs:update` (or `npm run sitemap:update` dir
 ## Redirects
 
 - `/applications` - Redirects to `/tools`. Source: `src/app/applications/route.ts`.
-- `/differentials/compare` - Redirects to `/differentials/presentations/[workflow-slug]`. Source: `src/app/(search-app)/differentials/compare/route.ts`.
 - `/documents/source` - Redirects to `/documents/[id]`. Source: `src/app/(search-app)/documents/source/page.tsx`.
 - `/mockups/favourites-hub` - Redirects to `/favourites`. Source: `src/app/mockups/favourites-hub/page.tsx`.
 - `/mockups/medication-prescribing` - Redirects to `/medications/acamprosate`. Source: `src/app/mockups/medication-prescribing/page.tsx`.

@@ -38,11 +38,10 @@ type SiteMapData = {
   nonRoutedMockupArtifacts: string[];
 };
 
-const productRouteHandlerPaths = new Set(["/applications", "/differentials/compare"]);
+const productRouteHandlerPaths = new Set(["/applications"]);
 
 const documentedRedirectTargets: Record<string, string> = {
   "/applications": "/tools",
-  "/differentials/compare": "/differentials/presentations/[workflow-slug]",
   // The source page redirects a valid id to the canonical `/documents/[id]` viewer
   // (page.tsx line 20) and only falls back to `/documents/search` for an invalid id
   // (line 14). Pin the canonical target here so the generated map does not report the
@@ -54,11 +53,12 @@ const routeDescriptions: Record<string, string> = {
   "/": "Main Clinical KB shell.",
   "/applications": "Legacy application launcher redirect to Tools.",
   "/differentials": "Differentials home and search surface.",
+  "/differentials/compare":
+    "Compare entry: same-presentation selections redirect into a catalogue workflow; cross-presentation selections render an ad-hoc comparison.",
   "/differentials/diagnoses": "Diagnosis stream.",
   "/differentials/diagnoses/[slug]": "Differential diagnosis detail.",
   "/differentials/presentations": "Presentation catalogue stream.",
   "/differentials/presentations/[slug]": "Presentation comparison workflow.",
-  "/differentials/compare": "Compare entry redirect into a presentation workflow.",
   "/dsm": "DSM-5 Diagnosis home.",
   "/dsm/search": "DSM diagnosis search and catalogue browser.",
   "/dsm/compare": "DSM diagnosis comparison.",

@@ -0,0 +1,49 @@
+import type { Metadata } from "next";
+import { redirect } from "next/navigation";
+
+import { DifferentialPresentationWorkflowPage } from "@/components/differentials/differential-presentation-workflow-page";
+import { resolveDifferentialCompareHandoff } from "@/lib/differentials";
+
+export const metadata: Metadata = {
+  title: "Compare differentials | Clinical KB",
+  description: "Compare selected differential diagnoses side by side with safety and bedside context.",
+};
+
+type DifferentialCompareRouteProps = {
+  searchParams?: Promise<{ query?: string | string[]; q?: string | string[]; ids?: string | string[] }>;
+};
+
+function firstSearchParam(value?: string | string[]) {
+  return Array.isArray(value) ? value[0] : value;
+}
+
+/**
+ * Compare entry page.
+ *
+ * Same-presentation selections (and bare/unknown ids) redirect into a catalogue
+ * presentation workflow. Cross-presentation selections render an ad-hoc compare
+ * view here so every valid id is preserved. A competing `route.ts` at this path
+ * is invalid in the App Router — handoff lives in the page instead.
+ */
+export default async function DifferentialCompareRoute({ searchParams }: DifferentialCompareRouteProps) {
+  const resolvedSearchParams = searchParams ? await searchParams : {};
+  const query = firstSearchParam(resolvedSearchParams.query ?? resolvedSearchParams.q)?.trim() ?? "";
+  const selectedIds = (firstSearchParam(resolvedSearchParams.ids) ?? "")
+    .split(",")
+    .map((value) => value.trim())
+    .filter(Boolean);
+
+  const handoff = resolveDifferentialCompareHandoff(selectedIds, query);
+  if (handoff.kind === "presentation") {
+    redirect(handoff.href);
+  }
+
+  return (
+    <DifferentialPresentationWorkflowPage
+      query={query}
+      presentationSlug={handoff.selection.workflow.id}
+      selectedIds={handoff.selection.diagnosisIds}
+      workflow={handoff.selection.workflow}
+    />
+  );
+}
@@ -36,7 +36,12 @@ import { useResultSort } from "@/components/use-result-sort";
 import { Chip as DesignChip } from "@/components/ui/chip";
 import { cn } from "@/components/ui-primitives";
 import { appModeHomeHref } from "@/lib/app-modes";
-import { differentialRouteWithQuery, differentialSelectedCompareHref } from "@/lib/differentials-navigation";
+import {
+  differentialIdsFromSearchParams,
+  differentialRouteWithQuery,
+  differentialSelectedCompareHref,
+  syncDifferentialSelectionIdsToUrl,
+} from "@/lib/differentials-navigation";
 import { differentialsMobileCompareAddonSlotId } from "@/lib/mode-home-composer";
 import {
   composeDifferentialSearchResults,
@@ -819,6 +824,12 @@ function SearchResultsView({
   const filterPanelId = useId();
   const [filterOpen, setFilterOpen] = useState(false);
   const [selectedIds, setSelectedIds] = useState<Set<string>>(() => new Set());
+  // Capture cold-load URL ids in state so a loading catalogue cannot wipe `ids`
+  // via replaceState before the first result set hydrates selection.
+  const [initialUrlIds] = useState(() =>
+    typeof window === "undefined" ? [] : differentialIdsFromSearchParams(window.location.search),
+  );
+  const [urlHydrationPending, setUrlHydrationPending] = useState(() => initialUrlIds.length > 0);
   // Selection, filter, and sort follow the ranked result set: seed the top two
   // for comparison and drop stale ids whenever a new query changes the results
   // (render-time sync, matching the repo's set-state-in-render pattern).
@@ -827,14 +838,16 @@ function SearchResultsView({
   if (lastResultSignature !== resultSignature) {
     setLastResultSignature(resultSignature);
     setKindFilter("all");
-    setSelectedIds(
-      new Set(
-        results
-          .filter((result) => result.kind === "diagnosis")
-          .slice(0, 2)
-          .map((result) => result.id),
-      ),
-    );
+    const diagnosisIds = results.filter((result) => result.kind === "diagnosis").map((result) => result.id);
+    const diagnosisIdSet = new Set(diagnosisIds);
+    // First result set may hydrate shareable URL ids; later query changes always
+    // re-seed so a new scope never silently inherits the previous ticks.
+    const urlIds = urlHydrationPending ? initialUrlIds.filter((id) => diagnosisIdSet.has(id)) : [];
+    const nextIds = lastResultSignature === "" && urlIds.length > 0 ? urlIds : diagnosisIds.slice(0, 2);
+    if (urlHydrationPending && lastResultSignature === "" && resultSignature !== "") {
+      setUrlHydrationPending(false);
+    }
+    setSelectedIds(new Set(nextIds));
   }
 
   const presentationCount = results.filter((result) => result.kind === "presentation").length;
@@ -861,6 +874,16 @@ function SearchResultsView({
     [results, selectedIds],
   );
   const selectedCount = comparisonIds.size;
+  const comparisonIdsKey = Array.from(comparisonIds).join(",");
+
+  // Publish selection into the URL so ModeNav Compare can forward the same ids.
+  // Defer while the catalogue is still loading so a cold submitted-search load
+  // does not delete bookmarked `ids` before matches arrive for hydration.
+  useEffect(() => {
+    if (typeof window === "undefined") return;
+    if (catalog.status === "loading") return;
+    syncDifferentialSelectionIdsToUrl(comparisonIdsKey ? comparisonIdsKey.split(",") : []);
+  }, [catalog.status, comparisonIdsKey]);
   // Catalogue results follow composer edits live, but document evidence only
   // updates on an executed source search — treat evidence fetched for a
   // different query as pending so the two panels never claim to be in sync.