fix(street-level): review follow-ups — shares judged against the last draw; refused pictures stay refused

From the maintainer review of #1134 (approve with follow-ups):
- lineCoverage: a share is judged against the cap the tile was last drawn
  with, not against later shares that redrew nothing, so small increases
  add up (a retained tile stayed at 100 points after its share grew to
  116). A rebuild's measuring pass no longer counts as a draw.
- photoViewer: a picture refused for its size (bytes, streamed bytes or
  decoded side) is marked `tooLarge`, and the viewer never loads that file
  again by any path; the flat fallback had retried an oversized SD file
  through an <img>, which has no size limit.
- Regressions for both: cumulative share growth below the threshold, and a
  refused SD panorama that is not fetched again as a flat photo.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/lineCoverage.test.mjs

@@ -433,3 +433,43 @@ test('a selected line outside the cap does not make its tile redraw on every set
   for (let i = 0; i < 3; i++) coverage.recolorSequence('short', true);
   assert.equal(after.added, 0);
 });
+
+test('small share increases add up: a retained tile redraws once its share has grown past the threshold since its last draw', async (t) => {
+  const tuning = {
+    ...TUNING,
+    maxTiles: 1,
+    maxSequences: 900,
+    maxPoints: 100,
+    keepOrder: true,
+  };
+  const { state, coverage } = setup(t, {
+    tuning,
+    decoded: (centre, tile) => ({
+      sequences: Array.from({ length: 30 }, (_, i) =>
+        pointsLine(`l${i}`, 4, tile, centre),
+      ),
+      overview: [],
+    }),
+  });
+  coverage.refresh();
+  assert.ok(
+    await until(
+      () => state.coverage.tiles.size === 1 && !state.coverage.pending.size,
+    ),
+  );
+  const [tile] = state.coverage.tiles.values();
+  assert.equal(tile.pointsDrawn, 100);
+  const settle = async () => {
+    coverage.refresh();
+    await until(() => !state.coverage.pending.size);
+    await new Promise((resolve) => setTimeout(resolve, 10));
+  };
+  // +8%: under the threshold, nothing is redrawn.
+  tuning.maxPoints = 108;
+  await settle();
+  assert.equal(tile.pointsDrawn, 100);
+  // +8% again: +16% since the tile was last drawn, so it is redrawn.
+  tuning.maxPoints = 116;
+  await settle();
+  assert.equal(tile.pointsDrawn, 116, 'the grown share is drawn');
+});