Say what is written about a world, when asked

Every figure this map shows is a measurement or something derived from one,
and it says which. What it could not do was tell you what a place is — a
radius and an eccentricity do not say that Titan is the only moon with a dense
atmosphere. An About control on a body's panel now fetches the Wikipedia lead,
and it is labelled as what it is: prose from another site, credited and linked
back, below the line where this map's own figures end.

Only on the press. Nothing is fetched while a body loads, and nothing is
fetched twice.

Three things the encyclopedia does that had to be handled, all found by asking
it rather than by guessing:

It redirects, generously — "Proxima Cen b" lands on "Proxima Centauri b" and
"Kepler-22 b" on "Kepler-22b" — so the catalogue's own names can be sent as
they are, with no mapping table to maintain.

It disambiguates. "Titan" is a list of everything called Titan, and so are
"Mercury" and "Io". Wikipedia says so in the response, and this app happens to
know the kind, so a disambiguation is retried as "Titan (moon)". Only in
English: every wiki words its own qualifiers, and inventing a translation of
one would be inventing an article title.

And it rate-limits, which it did to me while I was checking the above. A
refusal to answer is not an empty answer, so the two are separate outcomes:
"Wikipedia has no article on this" is about the world, "Wikipedia could not be
reached" is about this minute — and only the first is remembered, so a second
press is allowed to try again.

The extract is capped and scrollable. A lead can run a dozen lines, and this
panel is anchored to the top of a viewport that may be shorter than the prose.

Verified: build clean, 606/606 unit including twelve for the lookup chain, 16/16
end-to-end including three that stub the encyclopedia — this suite tests the
panel, not Wikipedia — design detector clean, and the real thing exercised by
hand against Earth, Titan and Proxima Cen b at three viewport sizes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

e2e/about.spec.ts

@@ -0,0 +1,62 @@
+import { expect, test } from '@playwright/test';
+
+/** Every request the article service makes, whichever language it is asking in. */
+const isWikipedia = (url: URL): boolean => url.hostname.endsWith('wikipedia.org');
+
+/** The article Wikipedia would send, stubbed: this suite tests the panel, not the encyclopedia. */
+const SUMMARY = {
+  type: 'standard',
+  titles: { normalized: 'Titan (moon)' },
+  extract: 'Titan is the largest moon of Saturn.',
+  content_urls: { desktop: { page: 'https://en.wikipedia.org/wiki/Titan_(moon)' } }
+};
+
+test.describe('About', () => {
+  test('fetches an article only when asked, and says where it came from', async ({ page }) => {
+    let requests = 0;
+    await page.route(isWikipedia, async (route) => {
+      requests++;
+      await route.fulfill({ status: 200, contentType: 'application/json', body: JSON.stringify(SUMMARY) });
+    });
+
+    await page.goto('/body/titan');
+    await expect(page.getByRole('heading', { name: 'Titan' })).toBeVisible({ timeout: 30_000 });
+
+    // Nothing has been fetched yet: the panel is measurements until a reader asks for prose.
+    expect(requests).toBe(0);
+    await expect(page.getByText('Titan is the largest moon')).toHaveCount(0);
+
+    await page.getByRole('button', { name: 'About', exact: true }).click();
+
+    await expect(page.getByText('Titan is the largest moon of Saturn.')).toBeVisible();
+    const credit = page.getByRole('link', { name: /Wikipedia/ });
+    await expect(credit).toHaveAttribute('href', 'https://en.wikipedia.org/wiki/Titan_(moon)');
+    expect(requests).toBeGreaterThan(0);
+  });
+
+  test('says nothing is written rather than leaving the press unanswered', async ({ page }) => {
+    await page.route(isWikipedia, (route) => route.fulfill({ status: 404, body: '{}' }));
+
+    await page.goto('/body/titan');
+    await expect(page.getByRole('heading', { name: 'Titan' })).toBeVisible({ timeout: 30_000 });
+    await page.getByRole('button', { name: 'About', exact: true }).click();
+
+    await expect(page.getByText(/Wikipedia has no article on Titan/)).toBeVisible();
+  });
+
+  test('tells being unable to ask apart from there being no answer, and offers to try again', async ({ page }) => {
+    await page.route(isWikipedia, (route) => route.abort('failed'));
+
+    await page.goto('/body/titan');
+    await expect(page.getByRole('heading', { name: 'Titan' })).toBeVisible({ timeout: 30_000 });
+    await page.getByRole('button', { name: 'About', exact: true }).click();
+    await expect(page.getByText(/could not be reached/)).toBeVisible();
+
+    // And the retry actually retries, rather than reading back a remembered failure.
+    await page.unroute(isWikipedia);
+    await page.route(isWikipedia, (route) => route.fulfill({ status: 200, contentType: 'application/json', body: JSON.stringify(SUMMARY) }));
+    await page.getByRole('button', { name: 'Try again' }).click();
+
+    await expect(page.getByText('Titan is the largest moon of Saturn.')).toBeVisible();
+  });
+});