fix(render): drop y title columns the chrome clamp cut short

src/render/renderer.cpp

@@ -622,11 +622,27 @@ void Renderer::draw_titles(const Plot& plot, const PlotLayout& layout) {
     const Axis& axis = plot.y_axis(i);
     if (axis.label.empty()) continue;
     const Rect& strip = layout.y_title_area;
+    // A column must *fit* before it is staged, and its own cell is what has to fit:
+    // with this basis the cell occupies [pen.x, pen.x + line_h], so the strip's
+    // width -- the one dimension the run never advances along -- is the whole of a
+    // column's cross extent, and nothing else in this path can see it. `walk_text_clipped()`
+    // cuts along the run and would happily stage a column that is wider than the
+    // strip it belongs to, drawing its cells over whatever is beside them.
+    //
+    // The layout clamps the strip against the viewport's chrome allowance (see
+    // `Plot::layout()`), so a viewport narrow enough to spend that allowance on the
+    // tick labels leaves room for fewer columns than there are titled axes, or for
+    // none at all. Columns are laid out left to right, so the ones the clamp cut
+    // short are the trailing ones: keep the leading columns that fit and stage no
+    // more. A dropped title is chrome that had no room, which is the same bargain
+    // the label strip already makes -- never drawn outside its strip, and never
+    // inside `axes`.
+    const f32 x = strip.x + pad + static_cast<f32>(column) * line_h;
+    if (x + line_h > strip.right()) break;
     const f32 budget = strip.h - 2.0f * pad;
     const f32 length = clipped_text_width(axis.label.c_str(), budget, kTextUp);
-    stage_text_clipped({strip.x + pad + static_cast<f32>(column) * line_h,
-                        strip.bottom() - 0.5f * (strip.h - length)},
-                       axis.label.c_str(), budget, kTextUp);
+    stage_text_clipped({x, strip.bottom() - 0.5f * (strip.h - length)}, axis.label.c_str(), budget,
+                       kTextUp);
     ++column;
   }
 }