test(e2e): compare help popover stays within the mobile viewport

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/superpowers/plans/2026-07-22-info-popover.md

@@ -0,0 +1,739 @@
+# Info Popover Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Replace the two broken metric-help affordances (the off-viewport `MetricTooltip` bubble and the native-`title` compare `?` help) with one `@floating-ui/react`-backed `InfoPopover` that stays on-screen in any viewport and shows a custom (non-native) tooltip on desktop.
+
+**Architecture:** One shared engine (`InfoPopover`) owns all Floating UI positioning and interactions. Two existing components become thin adapters over it: `MetricTooltip` keeps its public API (so ~24 detail-page call sites are untouched), and `RowLabel` in `sectionShared.tsx` swaps its native-`title` span for `InfoPopover` (so ~14 compare `tip=` call sites are untouched).
+
+**Tech Stack:** Next.js 16, React 19, TypeScript, `@floating-ui/react`, CSS Modules, Jest + jsdom + Testing Library, Playwright (e2e).
+
+## Global Constraints
+
+- All work happens in `nextjs-app/` unless a path says otherwise. Commands below assume the working directory is `nextjs-app/`.
+- Path alias: `@/` → `nextjs-app/` root (jest `moduleNameMapper` and tsconfig).
+- Jest test locations: files under `__tests__/**` or named `*.test.tsx`. Env is `jest-environment-jsdom`.
+- Trigger glyph is the circled **?** everywhere (replaces ⓘ on detail pages).
+- Trigger is a real `<button>` with a min 24px tap target (WCAG 2.5.8) and an accessible name.
+- `InfoPopover` renders `null` when it has no `plain` content (preserves current `MetricTooltip` behaviour).
+- Positioning/interaction is delegated to Floating UI — do not hand-roll positioning, outside-click, or Escape handling.
+- Run `npx tsc --noEmit` and `npx jest` green before every commit that changes code.
+- Never push to `main`; this plan's branch is `feat/info-popover-tooltip`.
+
+---
+
+### Task 1: Add the `@floating-ui/react` dependency
+
+**Files:**
+- Modify: `nextjs-app/package.json` (dependencies)
+- Modify: `nextjs-app/package-lock.json` (generated)
+
+**Interfaces:**
+- Consumes: nothing.
+- Produces: `@floating-ui/react` importable — the hooks `useFloating`, `autoUpdate`, `offset`, `flip`, `shift`, `arrow`, `useHover`, `useFocus`, `useClick`, `useDismiss`, `useRole`, `useInteractions`, and the component `FloatingPortal`, `FloatingArrow`.
+
+- [ ] **Step 1: Install the package**
+
+Run:
+```bash
+npm install @floating-ui/react@^0.27.0
+```
+Expected: `package.json` gains `"@floating-ui/react": "^0.27.0"` under `dependencies`; `package-lock.json` updates; exit 0.
+
+- [ ] **Step 2: Verify it resolves**
+
+Run:
+```bash
+node -e "const f=require('@floating-ui/react'); console.log(typeof f.useFloating, typeof f.FloatingPortal, typeof f.useInteractions)"
+```
+Expected: `function function function`
+
+- [ ] **Step 3: Typecheck still passes**
+
+Run:
+```bash
+npx tsc --noEmit
+```
+Expected: no output (exit 0).
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add package.json package-lock.json
+git commit -m "build(deps): add @floating-ui/react for the info popover"
+```
+
+---
+
+### Task 2: Build `InfoPopover` (the shared engine) with unit tests
+
+**Files:**
+- Create: `nextjs-app/components/InfoPopover.tsx`
+- Create: `nextjs-app/components/InfoPopover.module.css`
+- Test: `nextjs-app/__tests__/components/InfoPopover.test.tsx`
+
+**Interfaces:**
+- Consumes: `@floating-ui/react` (Task 1).
+- Produces:
+  ```ts
+  export interface InfoPopoverProps {
+    label?: string;    // bold heading
+    plain?: string;    // body text (primary explanation)
+    detail?: string;   // muted supplementary line
+    ariaLabel?: string; // accessible name for the trigger button
+  }
+  export function InfoPopover(props: InfoPopoverProps): JSX.Element | null;
+  ```
+  Behaviour: renders `null` if `plain` is falsy. Otherwise renders a `<button>`
+  (the circled `?`) with `aria-label={ariaLabel ?? 'More information'}` and
+  `aria-expanded`. When open, a portalled `role="tooltip"` container shows
+  `label` (if any), `plain`, and `detail` (if any). Opens on hover (100ms
+  open / 0ms close) and focus on desktop, on click for touch; closes on
+  outside-press and Escape.
+
+- [ ] **Step 1: Write the failing test**
+
+Create `nextjs-app/__tests__/components/InfoPopover.test.tsx`:
+```tsx
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { InfoPopover } from '@/components/InfoPopover';
+
+describe('InfoPopover', () => {
+  it('renders nothing when there is no plain content', () => {
+    const { container } = render(<InfoPopover label="X" />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it('renders a labelled, collapsed trigger button', () => {
+    render(<InfoPopover plain="what it means" ariaLabel="Reading score" />);
+    const btn = screen.getByRole('button', { name: 'Reading score' });
+    expect(btn).toHaveAttribute('aria-expanded', 'false');
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('opens on click and shows label, plain and detail', async () => {
+    const user = userEvent.setup();
+    render(
+      <InfoPopover
+        label="Reading, Writing & Maths"
+        plain="% reaching the expected standard"
+        detail="National average ~60%"
+        ariaLabel="RWM"
+      />,
+    );
+    await user.click(screen.getByRole('button', { name: 'RWM' }));
+    const tip = await screen.findByRole('tooltip');
+    expect(tip).toHaveTextContent('Reading, Writing & Maths');
+    expect(tip).toHaveTextContent('% reaching the expected standard');
+    expect(tip).toHaveTextContent('National average ~60%');
+    expect(screen.getByRole('button', { name: 'RWM' })).toHaveAttribute(
+      'aria-expanded',
+      'true',
+    );
+  });
+
+  it('closes again on a second click', async () => {
+    const user = userEvent.setup();
+    render(<InfoPopover plain="body" ariaLabel="Info" />);
+    const btn = screen.getByRole('button', { name: 'Info' });
+    await user.click(btn);
+    expect(await screen.findByRole('tooltip')).toBeInTheDocument();
+    await user.click(btn);
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('closes on Escape', async () => {
+    const user = userEvent.setup();
+    render(<InfoPopover plain="body" ariaLabel="Info" />);
+    await user.click(screen.getByRole('button', { name: 'Info' }));
+    expect(await screen.findByRole('tooltip')).toBeInTheDocument();
+    await user.keyboard('{Escape}');
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('defaults the accessible name when no ariaLabel is given', () => {
+    render(<InfoPopover plain="body" />);
+    expect(
+      screen.getByRole('button', { name: 'More information' }),
+    ).toBeInTheDocument();
+  });
+});
+```
+
+- [ ] **Step 2: Run the test to verify it fails**
+
+Run:
+```bash
+npx jest __tests__/components/InfoPopover.test.tsx
+```
+Expected: FAIL — `Cannot find module '@/components/InfoPopover'`.
+
+- [ ] **Step 3: Write the component**
+
+Create `nextjs-app/components/InfoPopover.tsx`:
+```tsx
+'use client';
+
+import { useRef, useState } from 'react';
+import {
+  useFloating,
+  autoUpdate,
+  offset,
+  flip,
+  shift,
+  arrow,
+  useHover,
+  useFocus,
+  useClick,
+  useDismiss,
+  useRole,
+  useInteractions,
+  FloatingPortal,
+  FloatingArrow,
+} from '@floating-ui/react';
+import styles from './InfoPopover.module.css';
+
+export interface InfoPopoverProps {
+  label?: string;
+  plain?: string;
+  detail?: string;
+  ariaLabel?: string;
+}
+
+export function InfoPopover({ label, plain, detail, ariaLabel }: InfoPopoverProps) {
+  const [open, setOpen] = useState(false);
+  const arrowRef = useRef<SVGSVGElement>(null);
+
+  const { refs, floatingStyles, context } = useFloating({
+    open,
+    onOpenChange: setOpen,
+    placement: 'top',
+    whileElementsMounted: autoUpdate,
+    middleware: [
+      offset(8),
+      flip({ fallbackAxisSideDirection: 'start' }),
+      shift({ padding: 8 }),
+      arrow({ element: arrowRef, padding: 8 }),
+    ],
+  });
+
+  // Hover (desktop) with a short open delay, keyboard focus, tap (touch),
+  // outside-press + Escape to dismiss. Floating UI disables hover on touch,
+  // so tap and hover never double-fire.
+  const hover = useHover(context, { delay: { open: 100, close: 0 } });
+  const focus = useFocus(context);
+  const click = useClick(context);
+  const dismiss = useDismiss(context);
+  const role = useRole(context, { role: 'tooltip' });
+  const { getReferenceProps, getFloatingProps } = useInteractions([
+    hover,
+    focus,
+    click,
+    dismiss,
+    role,
+  ]);
+
+  if (!plain) return null;
+
+  return (
+    <>
+      <button
+        type="button"
+        ref={refs.setReference}
+        className={styles.icon}
+        aria-label={ariaLabel ?? 'More information'}
+        aria-expanded={open}
+        {...getReferenceProps()}
+      >
+        ?
+      </button>
+      {open && (
+        <FloatingPortal>
+          <div
+            ref={refs.setFloating}
+            className={styles.tooltip}
+            style={floatingStyles}
+            {...getFloatingProps()}
+          >
+            <FloatingArrow ref={arrowRef} context={context} className={styles.arrow} />
+            {label && <span className={styles.label}>{label}</span>}
+            <span className={styles.plain}>{plain}</span>
+            {detail && <span className={styles.detail}>{detail}</span>}
+          </div>
+        </FloatingPortal>
+      )}
+    </>
+  );
+}
+```
+
+- [ ] **Step 4: Write the styles**
+
+Create `nextjs-app/components/InfoPopover.module.css`:
+```css
+.icon {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 24px;
+  min-height: 24px;
+  margin: -6px 0;
+  padding: 0;
+  border: none;
+  background: none;
+  /* font-size:0 hides the button's own "?" text node; the ::before glyph
+     below carries the visible circled "?" at its own explicit size. */
+  font-size: 0;
+  color: var(--text-muted, #8a7a72);
+  cursor: help;
+  line-height: 1;
+  user-select: none;
+  transition: color 0.15s ease;
+}
+
+/* The visible affordance: a small circled "?" centred in the 24px target. */
+.icon::before {
+  content: '?';
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 15px;
+  height: 15px;
+  border-radius: 50%;
+  border: 1px solid currentColor;
+  font-size: 0.65rem;
+}
+
+.icon:hover,
+.icon[aria-expanded='true'],
+.icon:focus-visible {
+  color: var(--accent-coral-dark, #b04a2e);
+}
+
+.tooltip {
+  z-index: 9999;
+  width: max-content;
+  max-width: min(260px, calc(100vw - 24px));
+  background: var(--bg-primary, #faf7f2);
+  border: 1px solid var(--border-color, #e8ddd4);
+  border-radius: 10px;
+  box-shadow: 0 4px 16px rgba(44, 36, 32, 0.15);
+  padding: 0.6rem 0.75rem;
+  display: flex;
+  flex-direction: column;
+  gap: 0.3rem;
+}
+
+.arrow {
+  fill: var(--bg-primary, #faf7f2);
+  stroke: var(--border-color, #e8ddd4);
+  stroke-width: 1px;
+}
+
+.label {
+  font-weight: 600;
+  font-size: 0.75rem;
+  color: var(--text-primary, #2c2420);
+}
+
+.plain {
+  font-size: 0.75rem;
+  color: var(--text-secondary, #5a4a44);
+  line-height: 1.4;
+}
+
+.detail {
+  font-size: 0.7rem;
+  color: var(--text-muted, #8a7a72);
+  line-height: 1.4;
+  margin-top: 0.1rem;
+}
+```
+
+- [ ] **Step 5: Run the tests to verify they pass**
+
+Run:
+```bash
+npx jest __tests__/components/InfoPopover.test.tsx
+```
+Expected: PASS (6 tests).
+
+- [ ] **Step 6: Typecheck**
+
+Run:
+```bash
+npx tsc --noEmit
+```
+Expected: no output (exit 0).
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add components/InfoPopover.tsx components/InfoPopover.module.css __tests__/components/InfoPopover.test.tsx
+git commit -m "feat(ui): add InfoPopover — viewport-aware metric help via Floating UI"
+```
+
+---
+
+### Task 3: Reduce `MetricTooltip` to a thin adapter over `InfoPopover`
+
+**Files:**
+- Modify: `nextjs-app/components/MetricTooltip.tsx` (full rewrite of body)
+- Delete: `nextjs-app/components/MetricTooltip.module.css`
+- Test: `nextjs-app/__tests__/components/MetricTooltip.test.tsx` (create)
+
+**Interfaces:**
+- Consumes: `InfoPopover` (Task 2), `METRIC_EXPLANATIONS` from `@/lib/metrics`.
+- Produces: `MetricTooltip` with unchanged public props
+  `{ metricKey?: string; label?: string; plain?: string; detail?: string }`.
+  Resolves `metricKey` → `METRIC_EXPLANATIONS[metricKey]`, with explicit
+  `label`/`plain`/`detail` props overriding the looked-up values. Passes the
+  resolved label as `InfoPopover`'s `ariaLabel`.
+
+- [ ] **Step 1: Write the failing test**
+
+Create `nextjs-app/__tests__/components/MetricTooltip.test.tsx`:
+```tsx
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { MetricTooltip } from '@/components/MetricTooltip';
+import { METRIC_EXPLANATIONS } from '@/lib/metrics';
+
+describe('MetricTooltip', () => {
+  it('resolves content from a metricKey', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const exp = METRIC_EXPLANATIONS[key];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} />);
+    await user.click(screen.getByRole('button', { name: exp.label }));
+    const tip = await screen.findByRole('tooltip');
+    expect(tip).toHaveTextContent(exp.plain);
+  });
+
+  it('renders nothing for an unknown metricKey with no explicit content', () => {
+    const { container } = render(<MetricTooltip metricKey="__nope__" />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it('lets explicit props override the looked-up explanation', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} plain="custom text" />);
+    await user.click(screen.getByRole('button'));
+    expect(await screen.findByRole('tooltip')).toHaveTextContent('custom text');
+  });
+});
+```
+
+- [ ] **Step 2: Run the test to verify it fails**
+
+Run:
+```bash
+npx jest __tests__/components/MetricTooltip.test.tsx
+```
+Expected: FAIL — the old `MetricTooltip` renders a `.tooltip` span even when
+collapsed (no `role="tooltip"` gating on open) / different structure, so
+`findByRole('tooltip')` after click and the empty-render assertion diverge from
+the new contract. (If any assertion happens to pass against the old component,
+it still must fail overall before Step 3.)
+
+- [ ] **Step 3: Rewrite the component**
+
+Replace the entire contents of `nextjs-app/components/MetricTooltip.tsx` with:
+```tsx
+'use client';
+
+import { METRIC_EXPLANATIONS } from '@/lib/metrics';
+import { InfoPopover } from './InfoPopover';
+
+interface MetricTooltipProps {
+  metricKey?: string;
+  label?: string;
+  plain?: string;
+  detail?: string;
+}
+
+export function MetricTooltip({ metricKey, label, plain, detail }: MetricTooltipProps) {
+  const explanation = metricKey ? METRIC_EXPLANATIONS[metricKey] : undefined;
+  const resolvedLabel = label ?? explanation?.label;
+  return (
+    <InfoPopover
+      label={resolvedLabel}
+      plain={plain ?? explanation?.plain}
+      detail={detail ?? explanation?.detail}
+      ariaLabel={resolvedLabel ? `What does ${resolvedLabel} mean?` : undefined}
+    />
+  );
+}
+```
+
+- [ ] **Step 4: Delete the now-unused stylesheet**
+
+Run:
+```bash
+git rm components/MetricTooltip.module.css
+```
+Expected: file staged for deletion. (The old component was its only importer;
+`InfoPopover.module.css` supersedes it.)
+
+- [ ] **Step 5: Verify nothing else imports the deleted CSS**
+
+Run:
+```bash
+grep -rn "MetricTooltip.module.css" components app lib || echo "no importers"
+```
+Expected: `no importers`.
+
+- [ ] **Step 6: Run the tests to verify they pass**
+
+Run:
+```bash
+npx jest __tests__/components/MetricTooltip.test.tsx
+```
+Expected: PASS (3 tests).
+
+- [ ] **Step 7: Typecheck**
+
+Run:
+```bash
+npx tsc --noEmit
+```
+Expected: no output (exit 0).
+
+- [ ] **Step 8: Commit**
+
+```bash
+git add components/MetricTooltip.tsx __tests__/components/MetricTooltip.test.tsx
+git commit -m "refactor(ui): MetricTooltip delegates to InfoPopover (circled ? glyph)"
+```
+
+---
+
+### Task 4: Swap the compare `?` help (`RowLabel`) to `InfoPopover`
+
+**Files:**
+- Modify: `nextjs-app/components/compare/sectionShared.tsx` (`RowLabel`)
+- Modify: `nextjs-app/components/compare/compareSections.module.css` (remove `.help`)
+- Test: `nextjs-app/__tests__/components/sectionShared.test.tsx` (create)
+
+**Interfaces:**
+- Consumes: `InfoPopover` (Task 2).
+- Produces: `RowLabel({ children, tip })` renders the label text plus, when
+  `tip` is set, an `InfoPopover` with `plain={tip}`. `ariaLabel` is omitted, so
+  the trigger uses `InfoPopover`'s default accessible name `"More information"`
+  (the row label is arbitrary `ReactNode`, so there is no clean string to derive
+  a per-row name from). `Measure` and all compare `tip=` call sites are
+  unchanged.
+
+- [ ] **Step 1: Write the failing test**
+
+Create `nextjs-app/__tests__/components/sectionShared.test.tsx`:
+```tsx
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { RowLabel } from '@/components/compare/sectionShared';
+
+describe('RowLabel', () => {
+  it('renders its label text', () => {
+    render(<RowLabel>Attainment 8</RowLabel>);
+    expect(screen.getByText('Attainment 8')).toBeInTheDocument();
+  });
+
+  it('shows no help affordance when no tip is given', () => {
+    render(<RowLabel>Attainment 8</RowLabel>);
+    expect(screen.queryByRole('button')).not.toBeInTheDocument();
+  });
+
+  it('opens the tip in a popover on click', async () => {
+    const user = userEvent.setup();
+    render(<RowLabel tip="Average GCSE score across 8 subjects">Attainment 8</RowLabel>);
+    await user.click(screen.getByRole('button'));
+    expect(await screen.findByRole('tooltip')).toHaveTextContent(
+      'Average GCSE score across 8 subjects',
+    );
+  });
+});
+```
+
+- [ ] **Step 2: Run the test to verify it fails**
+
+Run:
+```bash
+npx jest __tests__/components/sectionShared.test.tsx
+```
+Expected: FAIL — the current `RowLabel` renders a `<span title=...>` (not a
+`button`/`role="tooltip"`), so the click test fails.
+
+- [ ] **Step 3: Update `RowLabel`**
+
+In `nextjs-app/components/compare/sectionShared.tsx`, add the import near the
+other imports:
+```tsx
+import { InfoPopover } from '@/components/InfoPopover';
+```
+Then replace the `RowLabel` function:
+```tsx
+export function RowLabel({ children, tip }: { children: ReactNode; tip?: string }) {
+  return (
+    <div className={styles.rowLabel}>
+      {children}
+      {tip && <InfoPopover plain={tip} />}
+    </div>
+  );
+}
+```
+
+- [ ] **Step 4: Remove the dead `.help` style**
+
+In `nextjs-app/components/compare/compareSections.module.css`, delete the entire
+`.help { … }` rule (the `display: inline-flex; width: 15px; … flex: none;`
+block — the circled-`?` styling now lives in `InfoPopover.module.css`).
+
+- [ ] **Step 5: Confirm `.help` is unreferenced**
+
+Run:
+```bash
+grep -rn "styles.help\|\.help\b" components/compare || echo "no references"
+```
+Expected: `no references`.
+
+- [ ] **Step 6: Run the tests to verify they pass**
+
+Run:
+```bash
+npx jest __tests__/components/sectionShared.test.tsx
+```
+Expected: PASS (3 tests).
+
+- [ ] **Step 7: Full unit suite + typecheck**
+
+Run:
+```bash
+npx tsc --noEmit && npx jest
+```
+Expected: typecheck clean; all suites pass (existing + the 3 new suites).
+
+- [ ] **Step 8: Commit**
+
+```bash
+git add components/compare/sectionShared.tsx components/compare/compareSections.module.css __tests__/components/sectionShared.test.tsx
+git commit -m "refactor(compare): row-label help uses InfoPopover, not native title"
+```
+
+---
+
+### Task 5: E2E regression guard — popover stays within the mobile viewport
+
+**Files:**
+- Modify: `nextjs-app/../e2e/tests/journeys.spec.ts` (add one test)
+
+**Interfaces:**
+- Consumes: the running app (staging/local baseURL), the `twoPrimaryUrns`
+  helper already defined in `journeys.spec.ts`.
+- Produces: a Playwright test asserting an opened compare help popover's
+  bounding box is fully within the viewport on a narrow screen.
+
+- [ ] **Step 1: Add the failing-guard test**
+
+Append to `nextjs-app/../e2e/tests/journeys.spec.ts` (i.e. `e2e/tests/journeys.spec.ts`):
+```ts
+test('compare metric-help popover stays within the mobile viewport', async ({ page }) => {
+  await page.setViewportSize({ width: 390, height: 844 });
+  const [urn0, urn1] = await twoPrimaryUrns(page);
+  await page.goto(`/compare?urns=${urn0},${urn1}`);
+
+  await expect(
+    page.getByRole('heading', { name: 'At a glance' }),
+  ).toBeVisible({ timeout: 15_000 });
+
+  // The metric-help triggers are the circled-"?" buttons in the row labels.
+  // "More information" is InfoPopover's default accessible name.
+  const help = page.getByRole('button', { name: 'More information' }).first();
+  await expect(help).toBeVisible({ timeout: 15_000 });
+  await help.click();
+
+  const tip = page.getByRole('tooltip');
+  await expect(tip).toBeVisible();
+
+  // The whole bubble must sit inside the viewport — the original bug pushed it
+  // off the right edge with no way to scroll to it.
+  const box = await tip.boundingBox();
+  const width = page.viewportSize()!.width;
+  expect(box).not.toBeNull();
+  expect(box!.x).toBeGreaterThanOrEqual(0);
+  expect(box!.x + box!.width).toBeLessThanOrEqual(width);
+
+  // And the page must not have gained a horizontal scrollbar from the bubble.
+  const bodyOverflowsX = await page
+    .locator('body')
+    .evaluate((el) => el.scrollWidth > el.clientWidth + 1);
+  expect(bodyOverflowsX).toBe(false);
+});
+```
+
+- [ ] **Step 2: Lint/typecheck the e2e file**
+
+Run (from `e2e/`):
+```bash
+cd ../e2e && npx tsc --noEmit -p . 2>/dev/null || npx tsc --noEmit journeys 2>/dev/null; cd ../nextjs-app
+```
+Expected: no type errors reported for `journeys.spec.ts`. (If the e2e package
+has no standalone tsconfig, this is a no-op; the CI Playwright run type-checks
+on execution.)
+
+- [ ] **Step 3: Note on running e2e**
+
+The e2e journeys run against a deployed environment (staging) in CI, per
+`CLAUDE.md`; they are not run locally here (no local server). This test will
+execute in the staging gate after merge. Do not attempt to start a local server.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add ../e2e/tests/journeys.spec.ts
+git commit -m "test(e2e): compare help popover stays within the mobile viewport"
+```
+
+---
+
+### Task 6: Final verification and PR
+
+**Files:** none (verification + PR).
+
+- [ ] **Step 1: Full typecheck + unit suite**
+
+Run (from `nextjs-app/`):
+```bash
+npx tsc --noEmit && npx jest 2>&1 | tail -8
+```
+Expected: typecheck clean; all suites pass.
+
+- [ ] **Step 2: Production build sanity (catches client/server boundary issues)**
+
+Run:
+```bash
+npx next build 2>&1 | tail -20
+```
+Expected: build completes without errors. (`InfoPopover` is a client
+component — `'use client'` — so this confirms the portal usage compiles.)
+
+- [ ] **Step 3: Confirm no stragglers reference removed APIs**
+
+Run:
+```bash
+grep -rn "MetricTooltip.module.css\|styles.help\|title={tip}" components app || echo "clean"
+```
+Expected: `clean`.
+
+- [ ] **Step 4: Push and open the PR**
+
+```bash
+git push -u origin feat/info-popover-tooltip
+```
+Then open a Gitea PR (base `main`, head `feat/info-popover-tooltip`) via the
+credential-helper + API pattern used in this repo, summarising: the two bugs
+fixed (off-viewport mobile bubble; slow native-`title` desktop hover), the
+unified `InfoPopover` approach, the circled-`?` standardisation, the new
+`@floating-ui/react` dependency, and the mobile-viewport e2e guard.
+```

docs/superpowers/specs/2026-07-22-info-popover-design.md

@@ -0,0 +1,125 @@
+# Info Popover — unified metric-help affordance
+
+**Date:** 2026-07-22
+**Status:** Approved (design)
+
+## Problem
+
+Two different "info affordance" patterns explain metrics across the app, and both are broken:
+
+1. **`MetricTooltip` (ⓘ)** — used on the two detail pages (`SchoolDetailView`,
+   `SecondarySchoolDetailView`). Its bubble is `position: absolute` with a fixed
+   `220px` width and no viewport-collision detection. Near a screen edge on
+   mobile the bubble renders **partly or wholly off-viewport with no way to
+   scroll to it** — effectively unusable. A `left: -12px` mobile hack only
+   shifts the problem, it doesn't solve it.
+
+2. **Compare-section `?` help** — every compare section funnels through
+   `RowLabel` in `components/compare/sectionShared.tsx`, which uses the **native
+   `title=` attribute**. On desktop the native tooltip has a long, unconfigurable
+   hover delay; on touch it barely surfaces at all.
+
+We want a single component that positions itself correctly in any viewport and
+shows a custom (non-native) tooltip on desktop.
+
+## Decisions
+
+- **Positioning: `@floating-ui/react`** (industry standard, ~10KB gzipped, React
+  19 compatible). Chosen over a hand-rolled portal + JS positioning because the
+  current hand-rolled approach is exactly what failed, and Floating UI already
+  solves flip/shift/portal/interactions/ARIA.
+- **Mobile presentation: repositioning popover** (not a bottom-sheet). Same small
+  bubble as desktop; Floating UI's `shift`/`flip` keep it fully on-screen. One
+  presentation to build and maintain, consistent across platforms.
+- **Glyph: standardise on the circled `?`** everywhere (replaces ⓘ on the detail
+  pages). Matches the common "help" convention.
+- **Bundle:** adding `@floating-ui/react` as a runtime dependency is accepted.
+
+## Architecture
+
+One shared engine, two thin adapters — **no call-site churn**.
+
+### `InfoPopover` (new — `components/InfoPopover.tsx`)
+
+Owns all behaviour via `@floating-ui/react`.
+
+- **Trigger:** a real `<button>` (min 24px tap target — WCAG 2.5.8 —
+  keyboard-focusable) showing the circled `?` glyph. Muted colour; hover / focus
+  / open → accent colour.
+- **Positioning middleware:** `offset(6)` + `flip()` + `shift({ padding: 8 })`
+  so the bubble flips above/below and slides sideways to **always stay fully
+  on-screen** (the direct fix for the off-viewport bug). An `arrow()` element
+  tracks the trigger.
+- **Portal:** rendered inside a `FloatingPortal` so it escapes the compare
+  grid's `overflow`/`transform` clipping contexts.
+- **Interactions** (merged via `useInteractions`, one code path for both
+  platforms):
+  - `useHover(context, { delay: { open: 100, close: 0 } })` — short open delay
+    fixes the slow native-`title` hover; Floating UI disables hover on touch
+    devices so it doesn't double-fire with tap.
+  - `useFocus` — keyboard focus reveals it.
+  - `useClick` — tap toggles on touch.
+  - `useDismiss` — outside-press and `Escape` close it (opening another popover
+    closes the first, since the outside-press lands on the new trigger).
+  - `useRole(context, { role: 'tooltip' })` — ARIA wiring.
+- **Content:** optional `label` (bold), `plain` (body), `detail` (muted) — same
+  content shape as today.
+
+**Props:**
+
+```ts
+interface InfoPopoverProps {
+  label?: string;   // bold heading
+  plain?: string;   // body text (the primary explanation)
+  detail?: string;  // muted supplementary line
+  /** Accessible name for the trigger button, e.g. the metric label. */
+  ariaLabel?: string;
+}
+```
+
+Renders `null` when there is no `plain` content (mirrors current
+`MetricTooltip` behaviour).
+
+### Adapter 1 — `MetricTooltip` (public API unchanged)
+
+Keeps its existing props (`metricKey`, `label`, `plain`, `detail`), still
+resolves `metricKey` → `METRIC_EXPLANATIONS`, and renders `InfoPopover` with the
+resolved content. **All ~24 detail-page call sites are untouched.** The
+hand-rolled positioning/dismiss `useEffect` and the `.tooltip` absolute-position
+CSS (including the `left: -12px` mobile hack) are deleted.
+
+### Adapter 2 — `RowLabel` (in `sectionShared.tsx`)
+
+Replaces the native-`title` `?` span with `InfoPopover`, passing the `tip`
+string as `plain` and the row label as `ariaLabel`. **All ~14 compare `tip=`
+call sites are untouched** (they pass through `Measure` → `RowLabel`).
+
+## Removed / replaced
+
+- `MetricTooltip`'s hand-rolled open/dismiss `useEffect`.
+- `MetricTooltip.module.css` `.tooltip` absolute positioning + arrow + the
+  `@media (max-width: 640px)` `left: -12px` hack (superseded by Floating UI).
+- Native `title=` on the compare `?` help span.
+
+## Testing
+
+1. **Unit (jest + jsdom)** — `InfoPopover`:
+   - trigger button renders with the correct `aria-label` and `aria-expanded`;
+   - click opens and closes it;
+   - `label` / `plain` / `detail` render when open;
+   - `Escape` closes it.
+   Positioning (flip/shift) is Floating UI's own tested concern, not re-tested
+   here.
+
+2. **E2E (Playwright, mobile viewport)** — the regression guard for the reported
+   bug. On a narrow viewport, open a help popover near the **right edge** of a
+   compare section and assert its bounding box is fully within the viewport
+   (`rect.right <= innerWidth && rect.left >= 0`). This is the check that would
+   have caught the original overflow. Satisfies the CLAUDE.md rule to extend
+   `e2e/` when user-facing behaviour changes.
+
+## Out of scope
+
+- Other `title=` usages (button/link hints, empty-state props) — these are not
+  metric explainers and keep native `title`.
+- No bottom-sheet / alternate mobile presentation.

e2e/tests/journeys.spec.ts

@@ -478,3 +478,36 @@ test('rankings stay populated after picking a specific year', async ({ page }) =
   await expect(rows.first()).toBeVisible({ timeout: 15_000 });
   expect(await rows.count()).toBeGreaterThan(5);
 });
+
+test('compare metric-help popover stays within the mobile viewport', async ({ page }) => {
+  await page.setViewportSize({ width: 390, height: 844 });
+  const [urn0, urn1] = await twoPrimaryUrns(page);
+  await page.goto(`/compare?urns=${urn0},${urn1}`);
+
+  await expect(
+    page.getByRole('heading', { name: 'At a glance' }),
+  ).toBeVisible({ timeout: 15_000 });
+
+  // The metric-help triggers are the circled-"?" buttons in the row labels.
+  // "More information" is InfoPopover's default accessible name.
+  const help = page.getByRole('button', { name: 'More information' }).first();
+  await expect(help).toBeVisible({ timeout: 15_000 });
+  await help.click();
+
+  const tip = page.getByRole('tooltip');
+  await expect(tip).toBeVisible();
+
+  // The whole bubble must sit inside the viewport — the original bug pushed it
+  // off the right edge with no way to scroll to it.
+  const box = await tip.boundingBox();
+  const width = page.viewportSize()!.width;
+  expect(box).not.toBeNull();
+  expect(box!.x).toBeGreaterThanOrEqual(0);
+  expect(box!.x + box!.width).toBeLessThanOrEqual(width);
+
+  // And the page must not have gained a horizontal scrollbar from the bubble.
+  const bodyOverflowsX = await page
+    .locator('body')
+    .evaluate((el) => el.scrollWidth > el.clientWidth + 1);
+  expect(bodyOverflowsX).toBe(false);
+});

nextjs-app/__tests__/components/InfoPopover.test.tsx

@@ -0,0 +1,64 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { InfoPopover } from '@/components/InfoPopover';
+
+describe('InfoPopover', () => {
+  it('renders nothing when there is no plain content', () => {
+    const { container } = render(<InfoPopover label="X" />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it('renders a labelled, collapsed trigger button', () => {
+    render(<InfoPopover plain="what it means" ariaLabel="Reading score" />);
+    const btn = screen.getByRole('button', { name: 'Reading score' });
+    expect(btn).toHaveAttribute('aria-expanded', 'false');
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('opens on click and shows label, plain and detail', async () => {
+    const user = userEvent.setup();
+    render(
+      <InfoPopover
+        label="Reading, Writing & Maths"
+        plain="% reaching the expected standard"
+        detail="National average ~60%"
+        ariaLabel="RWM"
+      />,
+    );
+    await user.click(screen.getByRole('button', { name: 'RWM' }));
+    const tip = await screen.findByRole('tooltip');
+    expect(tip).toHaveTextContent('Reading, Writing & Maths');
+    expect(tip).toHaveTextContent('% reaching the expected standard');
+    expect(tip).toHaveTextContent('National average ~60%');
+    expect(screen.getByRole('button', { name: 'RWM' })).toHaveAttribute(
+      'aria-expanded',
+      'true',
+    );
+  });
+
+  it('closes again on a second click', async () => {
+    const user = userEvent.setup();
+    render(<InfoPopover plain="body" ariaLabel="Info" />);
+    const btn = screen.getByRole('button', { name: 'Info' });
+    await user.click(btn);
+    expect(await screen.findByRole('tooltip')).toBeInTheDocument();
+    await user.click(btn);
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('closes on Escape', async () => {
+    const user = userEvent.setup();
+    render(<InfoPopover plain="body" ariaLabel="Info" />);
+    await user.click(screen.getByRole('button', { name: 'Info' }));
+    expect(await screen.findByRole('tooltip')).toBeInTheDocument();
+    await user.keyboard('{Escape}');
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+  });
+
+  it('defaults the accessible name when no ariaLabel is given', () => {
+    render(<InfoPopover plain="body" />);
+    expect(
+      screen.getByRole('button', { name: 'More information' }),
+    ).toBeInTheDocument();
+  });
+});

nextjs-app/__tests__/components/MetricTooltip.test.tsx

@@ -0,0 +1,32 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { MetricTooltip } from '@/components/MetricTooltip';
+import { METRIC_EXPLANATIONS } from '@/lib/metrics';
+
+describe('MetricTooltip', () => {
+  it('resolves content from a metricKey', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const exp = METRIC_EXPLANATIONS[key];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} />);
+    // Collapsed by default — the popover content is not in the DOM until opened
+    // (the old component left an always-present role="tooltip" span behind).
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+    await user.click(screen.getByRole('button', { name: `What does ${exp.label} mean?` }));
+    const tip = await screen.findByRole('tooltip');
+    expect(tip).toHaveTextContent(exp.plain);
+  });
+
+  it('renders nothing for an unknown metricKey with no explicit content', () => {
+    const { container } = render(<MetricTooltip metricKey="__nope__" />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it('lets explicit props override the looked-up explanation', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} plain="custom text" />);
+    await user.click(screen.getByRole('button'));
+    expect(await screen.findByRole('tooltip')).toHaveTextContent('custom text');
+  });
+});

nextjs-app/__tests__/components/sectionShared.test.tsx

@@ -0,0 +1,24 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { RowLabel } from '@/components/compare/sectionShared';
+
+describe('RowLabel', () => {
+  it('renders its label text', () => {
+    render(<RowLabel>Attainment 8</RowLabel>);
+    expect(screen.getByText('Attainment 8')).toBeInTheDocument();
+  });
+
+  it('shows no help affordance when no tip is given', () => {
+    render(<RowLabel>Attainment 8</RowLabel>);
+    expect(screen.queryByRole('button')).not.toBeInTheDocument();
+  });
+
+  it('opens the tip in a popover on click', async () => {
+    const user = userEvent.setup();
+    render(<RowLabel tip="Average GCSE score across 8 subjects">Attainment 8</RowLabel>);
+    await user.click(screen.getByRole('button'));
+    expect(await screen.findByRole('tooltip')).toHaveTextContent(
+      'Average GCSE score across 8 subjects',
+    );
+  });
+});

nextjs-app/app/layout.tsx

@@ -85,6 +85,14 @@ export default function RootLayout({
           data-performance="true"
           strategy="afterInteractive"
         />
+        {/* Heatmap / session recorder — same data-domains guard so staging
+            (same image, different host) never feeds the heatmap. */}
+        <Script
+          src="https://analytics.schoolcompare.co.uk/recorder.js"
+          data-website-id="d7fb0c95-bb6c-4336-8209-bd10077e50dd"
+          data-domains="schoolcompare.co.uk,www.schoolcompare.co.uk"
+          strategy="afterInteractive"
+        />
       </head>
       <body className={`${dmSans.variable} ${playfairDisplay.variable}`}>
         <div className="noise-overlay" />

nextjs-app/components/InfoPopover.module.css

@@ -0,0 +1,77 @@
+.icon {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 24px;
+  min-height: 24px;
+  margin: -6px 0;
+  padding: 0;
+  border: none;
+  background: none;
+  /* font-size:0 hides the button's own "?" text node; the ::before glyph
+     below carries the visible circled "?" at its own explicit size. */
+  font-size: 0;
+  color: var(--text-muted, #8a7a72);
+  cursor: help;
+  line-height: 1;
+  user-select: none;
+  transition: color 0.15s ease;
+}
+
+/* The visible affordance: a small circled "?" centred in the 24px target. */
+.icon::before {
+  content: '?';
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 15px;
+  height: 15px;
+  border-radius: 50%;
+  border: 1px solid currentColor;
+  font-size: 0.65rem;
+}
+
+.icon:hover,
+.icon[aria-expanded='true'],
+.icon:focus-visible {
+  color: var(--accent-coral-dark, #b04a2e);
+}
+
+.tooltip {
+  z-index: 9999;
+  width: max-content;
+  max-width: min(260px, calc(100vw - 24px));
+  background: var(--bg-primary, #faf7f2);
+  border: 1px solid var(--border-color, #e8ddd4);
+  border-radius: 10px;
+  box-shadow: 0 4px 16px rgba(44, 36, 32, 0.15);
+  padding: 0.6rem 0.75rem;
+  display: flex;
+  flex-direction: column;
+  gap: 0.3rem;
+}
+
+.arrow {
+  fill: var(--bg-primary, #faf7f2);
+  stroke: var(--border-color, #e8ddd4);
+  stroke-width: 1px;
+}
+
+.label {
+  font-weight: 600;
+  font-size: 0.75rem;
+  color: var(--text-primary, #2c2420);
+}
+
+.plain {
+  font-size: 0.75rem;
+  color: var(--text-secondary, #5a4a44);
+  line-height: 1.4;
+}
+
+.detail {
+  font-size: 0.7rem;
+  color: var(--text-muted, #8a7a72);
+  line-height: 1.4;
+  margin-top: 0.1rem;
+}

nextjs-app/components/InfoPopover.tsx

@@ -0,0 +1,93 @@
+'use client';
+
+import { useRef, useState } from 'react';
+import {
+  useFloating,
+  autoUpdate,
+  offset,
+  flip,
+  shift,
+  arrow,
+  useHover,
+  useFocus,
+  useClick,
+  useDismiss,
+  useRole,
+  useInteractions,
+  FloatingPortal,
+  FloatingArrow,
+} from '@floating-ui/react';
+import styles from './InfoPopover.module.css';
+
+export interface InfoPopoverProps {
+  label?: string;
+  plain?: string;
+  detail?: string;
+  ariaLabel?: string;
+}
+
+export function InfoPopover({ label, plain, detail, ariaLabel }: InfoPopoverProps) {
+  const [open, setOpen] = useState(false);
+  const arrowRef = useRef<SVGSVGElement>(null);
+
+  const { refs, floatingStyles, context } = useFloating({
+    open,
+    onOpenChange: setOpen,
+    placement: 'top',
+    whileElementsMounted: autoUpdate,
+    middleware: [
+      offset(8),
+      flip({ fallbackAxisSideDirection: 'start' }),
+      shift({ padding: 8 }),
+      arrow({ element: arrowRef, padding: 8 }),
+    ],
+  });
+
+  // Hover (desktop) with a short open delay, keyboard focus, tap (touch),
+  // outside-press + Escape to dismiss. Floating UI disables hover on touch,
+  // so tap and hover never double-fire.
+  const hover = useHover(context, { delay: { open: 100, close: 0 } });
+  const focus = useFocus(context);
+  const click = useClick(context);
+  const dismiss = useDismiss(context);
+  const role = useRole(context, { role: 'tooltip' });
+  const { getReferenceProps, getFloatingProps } = useInteractions([
+    hover,
+    focus,
+    click,
+    dismiss,
+    role,
+  ]);
+
+  if (!plain) return null;
+
+  return (
+    <>
+      <button
+        type="button"
+        ref={refs.setReference}
+        className={styles.icon}
+        aria-label={ariaLabel ?? 'More information'}
+        aria-expanded={open}
+        {...getReferenceProps()}
+      >
+        ?
+      </button>
+      {open && (
+        <FloatingPortal>
+          <div
+            ref={refs.setFloating}
+            className={styles.tooltip}
+            style={floatingStyles}
+            {...getFloatingProps()}
+          >
+            <FloatingArrow ref={arrowRef} context={context} className={styles.arrow} />
+            {label && <span className={styles.label}>{label}</span>}
+            <span className={styles.plain}>{plain}</span>
+            {detail && <span className={styles.detail}>{detail}</span>}
+          </div>
+        </FloatingPortal>
+      )}
+    </>
+  );
+}

nextjs-app/components/MetricTooltip.module.css

@@ -1,114 +0,0 @@
-.wrapper {
-  position: relative;
-  display: inline-flex;
-  align-items: center;
-  margin-left: 0.3em;
-}
-
-.icon {
-  /* A real button: 24px tap target (WCAG 2.5.8) drawn as the small glyph. */
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  min-width: 24px;
-  min-height: 24px;
-  margin: -6px 0;
-  padding: 0;
-  border: none;
-  background: none;
-  font-size: 0.9em;
-  color: var(--text-muted, #8a7a72);
-  cursor: help;
-  line-height: 1;
-  user-select: none;
-  transition: color 0.15s ease;
-}
-
-.wrapper:hover .icon,
-.icon[aria-expanded="true"] {
-  color: var(--accent-coral-dark, #b04a2e);
-}
-
-.tooltip {
-  visibility: hidden;
-  opacity: 0;
-  position: absolute;
-  bottom: calc(100% + 6px);
-  left: 50%;
-  transform: translateX(-50%);
-  z-index: 9999;
-  width: 220px;
-  background: var(--bg-primary, #faf7f2);
-  border: 1px solid var(--border-color, #e8ddd4);
-  border-radius: 10px;
-  box-shadow: 0 4px 16px rgba(44, 36, 32, 0.15);
-  padding: 0.6rem 0.75rem;
-  display: flex;
-  flex-direction: column;
-  gap: 0.3rem;
-  pointer-events: none;
-  transition: opacity 0.15s ease, visibility 0.15s ease;
-}
-
-/* Reveal on hover (desktop), keyboard focus, or explicit tap/click toggle. */
-.wrapper:hover .tooltip,
-.wrapper:focus-within .tooltip,
-.tooltipOpen {
-  visibility: visible;
-  opacity: 1;
-}
-
-.tooltipOpen {
-  pointer-events: auto;
-}
-
-/* Small arrow pointing down */
-.tooltip::after {
-  content: '';
-  position: absolute;
-  top: 100%;
-  left: 50%;
-  transform: translateX(-50%);
-  border: 5px solid transparent;
-  border-top-color: var(--border-color, #e8ddd4);
-}
-
-.tooltipLabel {
-  font-weight: 600;
-  font-size: 0.75rem;
-  color: var(--text-primary, #2c2420);
-}
-
-.tooltipPlain {
-  font-size: 0.75rem;
-  color: var(--text-secondary, #5a4a44);
-  line-height: 1.4;
-}
-
-.tooltipDetail {
-  font-size: 0.7rem;
-  color: var(--text-muted, #8a7a72);
-  line-height: 1.4;
-  margin-top: 0.1rem;
-}
-
-@media (max-width: 480px) {
-  .tooltip {
-    width: 180px;
-  }
-}
-
-/* Anchor the bubble to open rightward on phones — icons follow their labels,
-   which start at the left edge, so centring pushed the bubble off-screen. */
-@media (max-width: 640px) {
-  .tooltip {
-    left: -12px;
-    right: auto;
-    transform: none;
-  }
-
-  .tooltip::after {
-    left: 16px;
-    transform: none;
-  }
-}

nextjs-app/components/MetricTooltip.tsx

@@ -1,8 +1,7 @@
 'use client';
 
-import { useEffect, useRef, useState } from 'react';
 import { METRIC_EXPLANATIONS } from '@/lib/metrics';
-import styles from './MetricTooltip.module.css';
+import { InfoPopover } from './InfoPopover';
 
 interface MetricTooltipProps {
   metricKey?: string;
@@ -13,51 +12,13 @@ interface MetricTooltipProps {
 
 export function MetricTooltip({ metricKey, label, plain, detail }: MetricTooltipProps) {
   const explanation = metricKey ? METRIC_EXPLANATIONS[metricKey] : undefined;
-  const tooltipLabel = label ?? explanation?.label;
-  const tooltipPlain = plain ?? explanation?.plain;
-  const tooltipDetail = detail ?? explanation?.detail;
-
-  // Tap/click/keyboard toggle so the definition is reachable on touch devices
-  // and by keyboard, not just mouse hover (hover still works on desktop).
-  const [open, setOpen] = useState(false);
-  const wrapperRef = useRef<HTMLSpanElement>(null);
-
-  useEffect(() => {
-    if (!open) return;
-    const dismiss = (e: Event) => {
-      if (wrapperRef.current && e.target instanceof Node && !wrapperRef.current.contains(e.target)) {
-        setOpen(false);
-      }
-    };
-    const onKey = (e: KeyboardEvent) => {
-      if (e.key === 'Escape') setOpen(false);
-    };
-    document.addEventListener('click', dismiss);
-    document.addEventListener('keydown', onKey);
-    return () => {
-      document.removeEventListener('click', dismiss);
-      document.removeEventListener('keydown', onKey);
-    };
-  }, [open]);
-
-  if (!tooltipPlain) return null;
-
+  const resolvedLabel = label ?? explanation?.label;
   return (
-    <span className={styles.wrapper} ref={wrapperRef}>
-      <button
-        type="button"
-        className={styles.icon}
-        aria-expanded={open}
-        aria-label={`What does ${tooltipLabel ?? 'this metric'} mean?`}
-        onClick={() => setOpen((o) => !o)}
-      >
-        ⓘ
-      </button>
-      <span className={`${styles.tooltip}${open ? ` ${styles.tooltipOpen}` : ''}`} role="tooltip">
-        {tooltipLabel && <span className={styles.tooltipLabel}>{tooltipLabel}</span>}
-        <span className={styles.tooltipPlain}>{tooltipPlain}</span>
-        {tooltipDetail && <span className={styles.tooltipDetail}>{tooltipDetail}</span>}
-      </span>
-    </span>
+    <InfoPopover
+      label={resolvedLabel}
+      plain={plain ?? explanation?.plain}
+      detail={detail ?? explanation?.detail}
+      ariaLabel={resolvedLabel ? `What does ${resolvedLabel} mean?` : undefined}
+    />
   );
 }

nextjs-app/components/SchoolDetailView.module.css

@@ -855,7 +855,10 @@
 /* Charts Section */
 .chartContainer {
     width: 100%;
-    height: 280px;
+    /* Taller on desktop so the trend lines have vertical room to separate
+       and read clearly. Mobile overrides this to height:auto below (the
+       max-width:768px query), so this only affects desktop. */
+    height: 380px;
     position: relative;
 }
 

nextjs-app/components/SecondarySchoolDetailView.module.css

@@ -490,7 +490,10 @@
 /* ── Charts & Map ────────────────────────────────────── */
 .chartContainer {
     width: 100%;
-    height: 280px;
+    /* Taller on desktop so the trend lines have vertical room to separate
+       and read clearly. Mobile overrides this to height:auto below (the
+       max-width:768px query), so this only affects desktop. */
+    height: 380px;
     position: relative;
 }
 

nextjs-app/components/compare/compareSections.module.css

@@ -132,20 +132,6 @@
   color: var(--text-secondary);
 }
 
-.help {
-  display: inline-flex;
-  width: 15px;
-  height: 15px;
-  border-radius: 50%;
-  border: 1px solid var(--text-muted);
-  color: var(--text-muted);
-  font-size: 0.65rem;
-  align-items: center;
-  justify-content: center;
-  cursor: help;
-  flex: none;
-}
-
 .badge {
   display: inline-block;
   font-weight: 700;

nextjs-app/components/compare/sectionShared.tsx

@@ -11,6 +11,7 @@ import type { CSSProperties, ReactNode } from 'react';
 
 import type { School } from '@/lib/types';
 import { CHART_COLORS, CHART_TEXT_COLORS, shortName } from '@/lib/utils';
+import { InfoPopover } from '@/components/InfoPopover';
 import styles from './compareSections.module.css';
 
 export function Section({
@@ -52,11 +53,7 @@ export function RowLabel({ children, tip }: { children: ReactNode; tip?: string
   return (
     <div className={styles.rowLabel}>
       {children}
-      {tip && (
-        <span className={styles.help} title={tip} aria-label={tip}>
-          ?
-        </span>
-      )}
+      {tip && <InfoPopover plain={tip} />}
     </div>
   );
 }

nextjs-app/package-lock.json

@@ -8,6 +8,7 @@
       "name": "nextjs-app",
       "version": "0.1.0",
       "dependencies": {
+        "@floating-ui/react": "^0.27.20",
         "@types/node": "^25.2.0",
         "@types/react": "^19.2.10",
         "@types/react-dom": "^19.2.3",
@@ -832,6 +833,59 @@
         "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
       }
     },
+    "node_modules/@floating-ui/core": {
+      "version": "1.8.0",
+      "resolved": "https://registry.npmjs.org/@floating-ui/core/-/core-1.8.0.tgz",
+      "integrity": "sha512-0CIZ5itps/8x7BG8dEIhs53BvCUH2PCoogtakwRTut+Arm58sJooJ0AuZhLw2HJYIR5cMLNPBSS728sPho2khQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@floating-ui/utils": "^0.2.12"
+      }
+    },
+    "node_modules/@floating-ui/dom": {
+      "version": "1.8.0",
+      "resolved": "https://registry.npmjs.org/@floating-ui/dom/-/dom-1.8.0.tgz",
+      "integrity": "sha512-yXSrzeHZBTZadLOlfyhCkJHNeLJnHRnRInwdZ40L7ZiaAtrBwoYlsDrX3v5zB1Utk7CLfzcOVnVVWoXEky7Ceg==",
+      "license": "MIT",
+      "dependencies": {
+        "@floating-ui/core": "^1.8.0",
+        "@floating-ui/utils": "^0.2.12"
+      }
+    },
+    "node_modules/@floating-ui/react": {
+      "version": "0.27.20",
+      "resolved": "https://registry.npmjs.org/@floating-ui/react/-/react-0.27.20.tgz",
+      "integrity": "sha512-CMqMy7OaXl9W0eq1Uy7L7i2Y/anPvHmFmESd2CEw0t5YvZhcVCeo4MBevAmswRllX7Y2dEidA4ozGPunLSTQpw==",
+      "license": "MIT",
+      "dependencies": {
+        "@floating-ui/react-dom": "^2.1.9",
+        "@floating-ui/utils": "^0.2.12",
+        "tabbable": "^6.0.0"
+      },
+      "peerDependencies": {
+        "react": ">=17.0.0",
+        "react-dom": ">=17.0.0"
+      }
+    },
+    "node_modules/@floating-ui/react-dom": {
+      "version": "2.1.9",
+      "resolved": "https://registry.npmjs.org/@floating-ui/react-dom/-/react-dom-2.1.9.tgz",
+      "integrity": "sha512-JDjEFGCpImxDCA7JJKviA0M9+RtmJdj0m/NVU5IMgBK+AmZouAQQ7/+2GLH0GXXY0YMw9oXPB8hKdbPYg5QLYg==",
+      "license": "MIT",
+      "dependencies": {
+        "@floating-ui/dom": "^1.8.0"
+      },
+      "peerDependencies": {
+        "react": ">=16.8.0",
+        "react-dom": ">=16.8.0"
+      }
+    },
+    "node_modules/@floating-ui/utils": {
+      "version": "0.2.12",
+      "resolved": "https://registry.npmjs.org/@floating-ui/utils/-/utils-0.2.12.tgz",
+      "integrity": "sha512-HpCo8tmWzLVad5s2d19EhAz5zqrrQ6s69qd6moPMQvkOuSwDT1YgRfWSVuc4ennqrgv3OHppiOGMQ7oC13yIww==",
+      "license": "MIT"
+    },
     "node_modules/@humanfs/core": {
       "version": "0.19.1",
       "resolved": "https://registry.npmjs.org/@humanfs/core/-/core-0.19.1.tgz",
@@ -9136,6 +9190,12 @@
         "url": "https://opencollective.com/synckit"
       }
     },
+    "node_modules/tabbable": {
+      "version": "6.5.0",
+      "resolved": "https://registry.npmjs.org/tabbable/-/tabbable-6.5.0.tgz",
+      "integrity": "sha512-wieBHXygIm7OyQOu5hQlkk62/WyCFYGlWg7L6/ZCUZwx0o398Zkn4pVmMyfYhfMG8kGrj/Krt8eIk6UKC6VzwA==",
+      "license": "MIT"
+    },
     "node_modules/test-exclude": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/test-exclude/-/test-exclude-6.0.0.tgz",

nextjs-app/package.json

@@ -13,6 +13,7 @@
     "test:coverage": "jest --coverage"
   },
   "dependencies": {
+    "@floating-ui/react": "^0.27.20",
     "@types/node": "^25.2.0",
     "@types/react": "^19.2.10",
     "@types/react-dom": "^19.2.3",