Fix theta breaks with negative angles causing partial-arc regression

ax.set_xticks() with negative radian values silently extends xlim below 0,
converting a full circle into a partial arc.  When start is chosen so that
the first few months map to negative radians (e.g. start = -π/2), the theta
labels passed to set_xticks triggered this matplotlib behaviour.

Normalise all break positions into [0, 2π] for full-circle plots before they
are stored in panel_params.x.breaks so that set_xticks never receives a
negative value.  Partial-arc plots are unaffected (their breaks are always
within [arc_lo, arc_hi] which is already in [0, 2π]).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: iangow

plotnine/coords/coord_radial.py

@@ -160,6 +160,12 @@ def setup_panel_params(self, scale_x: scale, scale_y: scale) -> panel_view:
                 keep = [arc_lo <= r <= arc_hi for r in radian_pos]
                 radian_pos = [r for r, k in zip(radian_pos, keep) if k]
                 theta_labels = [l for l, k in zip(theta_labels, keep) if k]
+            else:
+                # Full circle: ax.set_xticks with negative values silently extends
+                # xlim below 0, turning the full circle into a partial arc.  Wrap
+                # all break positions into [0, 2π] to avoid this.
+                tau = 2.0 * np.pi
+                radian_pos = [r % tau for r in radian_pos]
             x_updates["breaks"] = radian_pos
             x_updates["labels"] = theta_labels