feat(ui): draw pane frames, page keys and a scroll thumb

tests/test_header.py

@@ -86,6 +86,22 @@ def test_the_font_still_spells_soma_the_way_the_original_logo_did() -> None:
     )
 
 
+@pytest.mark.parametrize("slug", sorted(PROVIDERS))
+def test_the_caption_block_starts_on_one_column(slug: str) -> None:
+    """Art rows are right-trimmed; a row ending in a blank cell must not pull
+    its caption a column to the left."""
+    provider = PROVIDERS[slug]
+    captions = provider.hero_lines
+    offset = max(0, (len(provider.hero) - len(captions)) // 2)
+    lines = render_header(200, height=len(provider.hero), provider=provider)
+    lines = lines[offset : offset + len(captions)]
+    columns = {
+        line.index(caption)
+        for line, caption in zip(lines, captions, strict=True)
+    }
+    assert len(columns) == 1, (slug, columns)
+
+
 def test_every_catalogue_has_a_three_row_wordmark() -> None:
     for slug, provider in PROVIDERS.items():
         assert len(provider.hero) == 3, slug