frontend/src/components/Tabs.tsx

@@ -1,3 +1,5 @@
+import type { KeyboardEvent } from 'react';
+
 interface TabItem {
   id: string;
   label: string;
@@ -11,12 +13,22 @@ interface TabsProps {
 }
 
 export function Tabs({ items, activeId, onChange }: TabsProps): JSX.Element {
+  function handleKeyDown(e: KeyboardEvent<HTMLButtonElement>, index: number) {
+    if (e.key === 'ArrowRight') {
+      e.preventDefault();
+      onChange(items[(index + 1) % items.length].id);
+    } else if (e.key === 'ArrowLeft') {
+      e.preventDefault();
+      onChange(items[(index - 1 + items.length) % items.length].id);
+    }
+  }
+
   return (
     <div
       role="tablist"
       className="flex items-end border-b border-hairline gap-xs"
     >
-      {items.map((item) => {
+      {items.map((item, index) => {
         const isActive = item.id === activeId;
         return (
           <button
@@ -27,6 +39,7 @@ export function Tabs({ items, activeId, onChange }: TabsProps): JSX.Element {
             aria-controls={`tabpanel-${item.id}`}
             type="button"
             onClick={() => onChange(item.id)}
+            onKeyDown={(e) => handleKeyDown(e, index)}
             className={`tab-underline${isActive ? ' tab-underline-active' : ''} pb-xs`}
           >
             {item.label}

frontend/src/hooks/useHashTab.ts

@@ -17,7 +17,8 @@ export function useHashTab(defaultId: string): [string, (id: string) => void] {
   }, [defaultId]);
 
   const navigate = useCallback((id: string) => {
-    window.location.hash = id;
+    // replaceState: no history entry (Back button unaffected), no anchor-jump scroll
+    history.replaceState(null, '', '#' + id);
     setActiveId(id);
   }, []);
 

frontend/src/pages/EngagementDetailPage.tsx

@@ -13,6 +13,8 @@ import { BackLink } from '@/components/BackLink';
 import { Tabs } from '@/components/Tabs';
 import { Link } from 'react-router-dom';
 
+type TabId = 'schedule' | 'description' | 'simulations';
+
 export function EngagementDetailPage(): JSX.Element {
   const { id } = useParams<{ id: string }>();
   const numericId = id ? Number(id) : undefined;
@@ -21,7 +23,8 @@ export function EngagementDetailPage(): JSX.Element {
   const detail = useEngagement(numericId);
   const simsQuery = useEngagementSimulations(numericId);
 
-  const [activeTab, setActiveTab] = useHashTab('schedule');
+  const [activeTabRaw, setActiveTab] = useHashTab('schedule');
+  const activeTab = activeTabRaw as TabId;
 
   if (detail.isLoading) return <LoadingState label="Loading engagement…" />;
   if (detail.isError) {

frontend/src/pages/UsersAdminPage.tsx

@@ -248,6 +248,7 @@ export function UsersAdminPage(): JSX.Element {
                       </tr>
                       {resetOpen === u.id ? (
                         <tr className="border-b border-hairline last:border-0 bg-cloud">
+                          {/* Aerated row — inline form needs room; compact-density tradeoff intentional */}
                           <td colSpan={4} className="px-xl py-md">
                             <form
                               onSubmit={(e) => onResetPassword(u, e)}

frontend/tests/components/Tabs.test.tsx

@@ -59,6 +59,20 @@ describe('Tabs', () => {
     expect(simsBtn).toHaveAttribute('aria-controls', 'tabpanel-simulations');
   });
 
+  it('ArrowRight moves focus to the next tab', () => {
+    const onChange = vi.fn();
+    render(<Tabs items={ITEMS} activeId="schedule" onChange={onChange} />);
+    fireEvent.keyDown(screen.getByRole('tab', { name: /Schedule/i }), { key: 'ArrowRight' });
+    expect(onChange).toHaveBeenCalledWith('description');
+  });
+
+  it('ArrowLeft wraps around to the last tab', () => {
+    const onChange = vi.fn();
+    render(<Tabs items={ITEMS} activeId="schedule" onChange={onChange} />);
+    fireEvent.keyDown(screen.getByRole('tab', { name: /Schedule/i }), { key: 'ArrowLeft' });
+    expect(onChange).toHaveBeenCalledWith('simulations');
+  });
+
   it('has no rounded-md, transition-*, or shadow-* on tab buttons (brutalism)', () => {
     render(<Tabs items={ITEMS} activeId="schedule" onChange={vi.fn()} />);
     for (const btn of screen.getAllByRole('tab')) {

frontend/tests/hooks/useHashTab.test.tsx

@@ -22,7 +22,7 @@ describe('useHashTab', () => {
     expect(result.current[0]).toBe('simulations');
   });
 
-  it('navigate() updates activeId and sets location.hash', () => {
+  it('navigate() updates activeId and sets hash via replaceState (no history entry)', () => {
     const { result } = renderHook(() => useHashTab('schedule'));
     act(() => {
       result.current[1]('description');