diff --git a/src/components/layout/__tests__/nav-model.test.ts b/src/components/layout/__tests__/nav-model.test.ts
index 0ee21814b..89c8c6c7b 100644
--- a/src/components/layout/__tests__/nav-model.test.ts
+++ b/src/components/layout/__tests__/nav-model.test.ts
@@ -50,9 +50,13 @@ describe("nav-model destination list", () => {
     expect(hrefs).toContain("/vorsorge");
     const vorsorge = NAV_DESTINATIONS.find((d) => d.href === "/vorsorge");
     expect(vorsorge?.tKey).toBe("nav.vorsorge");
-    // Peer to Labs: sits in the clinical spine, before Insights.
-    expect(hrefs.indexOf("/labs")).toBeLessThan(hrefs.indexOf("/vorsorge"));
-    expect(hrefs.indexOf("/vorsorge")).toBeLessThan(hrefs.indexOf("/insights"));
+    // v1.19.1 (S4) — the fixed spine is Medications → Vorsorge → Labs →
+    // Illness → Insights, so Vorsorge sits after Medications and before Labs.
+    expect(hrefs.indexOf("/medications")).toBeLessThan(
+      hrefs.indexOf("/vorsorge"),
+    );
+    expect(hrefs.indexOf("/vorsorge")).toBeLessThan(hrefs.indexOf("/labs"));
+    expect(hrefs.indexOf("/labs")).toBeLessThan(hrefs.indexOf("/insights"));
   });
 
   it("does not list Recovery as a left-nav destination (it is an Insights pill)", () => {
@@ -99,15 +103,17 @@ describe("nav-model utility tail (N-1 — one shared list)", () => {
 });
 
 describe("visibleNavDestinations module gate", () => {
-  it("includes Cycle (between Medications and Insights) only when its module is enabled", () => {
+  it("includes Cycle (between Mood and Medications) only when its module is enabled", () => {
     // v1.18.0 — cycle is `requiresModule: "cycle"` and reads the delegated
     // `cycle` key from the same resolved module map every other gate uses.
+    // v1.19.1 (S4) — cycle sits in the head block, after Mood and before the
+    // fixed Medications → … → Achievements spine.
     const off = visibleNavDestinations({ cycle: false }).map((d) => d.href);
     const on = visibleNavDestinations({ cycle: true }).map((d) => d.href);
     expect(off).not.toContain("/cycle");
     expect(on).toContain("/cycle");
-    expect(on.indexOf("/medications")).toBeLessThan(on.indexOf("/cycle"));
-    expect(on.indexOf("/cycle")).toBeLessThan(on.indexOf("/insights"));
+    expect(on.indexOf("/mood")).toBeLessThan(on.indexOf("/cycle"));
+    expect(on.indexOf("/cycle")).toBeLessThan(on.indexOf("/medications"));
   });
 
   it("drops a module-gated entry (mood / labs / coach / achievements / insights / medications) when its module is disabled", () => {
diff --git a/src/components/layout/__tests__/sidebar-nav.test.tsx b/src/components/layout/__tests__/sidebar-nav.test.tsx
index 14e46af07..049694844 100644
--- a/src/components/layout/__tests__/sidebar-nav.test.tsx
+++ b/src/components/layout/__tests__/sidebar-nav.test.tsx
@@ -109,17 +109,18 @@ describe("<SidebarNav> cycle entry gate (v1.15.0 / v1.18.0 module map)", () => {
     expect(html).not.toContain('href="/cycle"');
   });
 
-  it("places the Cycle entry between Medications and Insights when enabled", () => {
+  it("places the Cycle entry between Mood and Medications when enabled", () => {
     const html = render({ modules: { cycle: true } });
-    const med = html.indexOf('href="/medications"');
+    const mood = html.indexOf('href="/mood"');
     const cycle = html.indexOf('href="/cycle"');
-    const insights = html.indexOf('href="/insights"');
-    expect(med).toBeGreaterThan(-1);
+    const med = html.indexOf('href="/medications"');
+    expect(mood).toBeGreaterThan(-1);
     expect(cycle).toBeGreaterThan(-1);
-    expect(insights).toBeGreaterThan(-1);
-    // Cycle sits after Medications and before Insights in document order.
-    expect(med).toBeLessThan(cycle);
-    expect(cycle).toBeLessThan(insights);
+    expect(med).toBeGreaterThan(-1);
+    // v1.19.1 (S4) — Cycle sits after Mood and before Medications in document
+    // order; Medications opens the fixed clinical/insight spine below it.
+    expect(mood).toBeLessThan(cycle);
+    expect(cycle).toBeLessThan(med);
   });
 });
 
diff --git a/src/components/layout/nav-model.ts b/src/components/layout/nav-model.ts
index c8f083d31..c0c94a18d 100644
--- a/src/components/layout/nav-model.ts
+++ b/src/components/layout/nav-model.ts
@@ -63,6 +63,10 @@ export interface NavDestination {
  * (after Medications) and is filtered out when the account gate is off;
  * the order is otherwise identical for both surfaces.
  */
+// v1.19.1 (S4) — the clinical/insight spine below the dashboard/measurements/
+// mood/cycle head follows one fixed sequence, each entry directly below the
+// previous: Medications → Vorsorge → Labs → Illness → Insights → Coach →
+// Achievements. A disabled module simply drops out; the rest keep this order.
 export const NAV_DESTINATIONS: ReadonlyArray<NavDestination> = [
   { href: "/", tKey: "nav.dashboard", icon: Home, tourId: "nav-dashboard" },
   {
@@ -78,6 +82,13 @@ export const NAV_DESTINATIONS: ReadonlyArray<NavDestination> = [
     tourId: "nav-mood",
     requiresModule: "mood",
   },
+  {
+    href: "/cycle",
+    tKey: "nav.cycle",
+    icon: Droplets,
+    tourId: "nav-cycle",
+    requiresModule: "cycle",
+  },
   {
     href: "/medications",
     tKey: "nav.medications",
@@ -87,12 +98,23 @@ export const NAV_DESTINATIONS: ReadonlyArray<NavDestination> = [
     // module; the nav entry now drops when the account turns the module off.
     requiresModule: "medications",
   },
+  // v1.17.1 — Vorsorge (preventive-care) gets a top-level nav home in the
+  // clinical spine. It is a first-class tracking surface ("wann muss ich was
+  // wo machen"), not pure configuration, so it belongs in the model both bars
+  // render — not buried three taps deep under Settings → Reminders. The
+  // Reminders hub still links to it; this is the direct front door.
   {
-    href: "/cycle",
-    tKey: "nav.cycle",
-    icon: Droplets,
-    tourId: "nav-cycle",
-    requiresModule: "cycle",
+    href: "/vorsorge",
+    tKey: "nav.vorsorge",
+    icon: Stethoscope,
+    tourId: "nav-vorsorge",
+    // v1.18.1 — deliberately NOT module-gated (no `requiresModule`). Unlike
+    // labs / illness / cycle (opt-in clinical-spine verticals born off by
+    // default), preventive-care reminders are a CORE surface available to
+    // every account from birth: a reminder can target core vitals
+    // (weight / BP / pulse) that are never behind a module toggle, and a
+    // free-text "Großes Blutbild" reminder belongs to no module at all.
+    // Gating the entry would orphan reminders the user can still create.
   },
   {
     href: "/labs",
@@ -112,25 +134,6 @@ export const NAV_DESTINATIONS: ReadonlyArray<NavDestination> = [
     tourId: "nav-illness",
     requiresModule: "illness",
   },
-  // v1.17.1 — Vorsorge (preventive-care) gets a top-level nav home in the
-  // clinical spine, peer to Labs and Recovery. It is a first-class tracking
-  // surface ("wann muss ich was wo machen"), not pure configuration, so it
-  // belongs in the model both bars render — not buried three taps deep under
-  // Settings → Reminders. The Reminders hub still links to it; this is the
-  // direct front door so the customer knows where it lives.
-  {
-    href: "/vorsorge",
-    tKey: "nav.vorsorge",
-    icon: Stethoscope,
-    tourId: "nav-vorsorge",
-    // v1.18.1 — deliberately NOT module-gated (no `requiresModule`). Unlike
-    // labs / illness / cycle (opt-in clinical-spine verticals born off by
-    // default), preventive-care reminders are a CORE surface available to
-    // every account from birth: a reminder can target core vitals
-    // (weight / BP / pulse) that are never behind a module toggle, and a
-    // free-text "Großes Blutbild" reminder belongs to no module at all.
-    // Gating the entry would orphan reminders the user can still create.
-  },
   // v1.18.0 — Workouts and Recovery both left the left-nav: each already
   // surfaces as an Insights tab-strip pill (`/insights/workouts` gated on
   // a workout row, `/insights/recovery` always present), so neither is a