Keep poster graphics and text inside the poster

The diagonal stripe graphic started left of the paper and long titles
or unbreakable words (repository and file names) overflowed the sides
and bottom. Posters are now clipped to the paper, and text is fitted:
the largest size at which it wraps within the width, line limit and
remaining height; words too wide even at the smallest size are
shortened individually with an ellipsis so the rest of the text stays.

webtest/labels.test.mjs

@@ -109,3 +109,20 @@ test('hazard tape crosses each wall corner to corner, readable from outside', ()
   }
   assert.equal(tapeQuads({ x: 0, y: 0, w: 2, h: 2, height: 30 }, 6).length, 0, 'too narrow for tape');
 });
+
+import { fitText } from '../web/labels.js';
+
+test('poster text shrinks and wraps until it fits inside the box', () => {
+  const measure = (text, size) => text.length * size * .6; // monospace-ish stand-in for canvas
+  const short = fitText(measure, 'SHIP SMALL', 200, 120, 34, 12, 3);
+  assert.equal(short.size, 34);
+  const long = fitText(measure, 'WELCOME TO AN EXTREMELY LONG REPOSITORY NAME THAT GOES ON', 200, 120, 34, 12, 3);
+  assert.ok(long.lines.length <= 3 && long.lines.length * long.size * 1.08 <= 120);
+  for (const fit of [short, long]) for (const line of fit.lines) assert.ok(measure(line, fit.size) <= 200, line);
+  const word = fitText(measure, 'supercalifragilistic_expialidocious_really_long_filename.go', 200, 120, 34, 12, 3);
+  assert.ok(word.lines.every(line => measure(line, word.size) <= 200) && word.lines[0].endsWith('…'), 'unbreakable words are truncated');
+  const mixed = fitText(measure, 'WELCOME TO PROMETHEUS-OPERATOR-HELM-CHARTS-MONOREPO', 200, 120, 34, 12, 3);
+  assert.ok(mixed.lines[0].startsWith('WELCOME TO') && mixed.lines.every(line => measure(line, mixed.size) <= 200), `keeps the short words: ${mixed.lines}`);
+  const crowded = fitText(measure, 'one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen', 60, 30, 20, 12, 3);
+  assert.ok(crowded.lines.length * 12 * 1.08 <= 30 && crowded.lines.every(line => measure(line, 12) <= 60 + 1e-9), `crowded: ${crowded.lines}`);
+});