vellumplot 0.6.0

• Sankey styling options. vsankey() / mark_sankey() gain show_values
  (append each node's value to its label), flow_color ("source", "target",
  or "gradient" — a source-to-target colour fade per ribbon), and
  node_width / node_gap to tune the node rectangles.

• Sankey crossing minimisation. vsankey() now orders the nodes within each
  column with the Sugiyama barycenter heuristic to minimise ribbon crossings
  (previously first-appearance order, which left many avoidable crossings). The
  reordering is deterministic and pure R. A related fix stacks each node's ribbon
  slices to meet the node in the same vertical order as the nodes they connect to,
  removing the remaining crossings within a fan of ribbons.

• Sunburst rendering fixes. vsunburst() now colours wedges by their
  top-level branch (each branch a distinct hue, lightened with depth) instead of
  a single colour per ring — sibling branches were previously indistinguishable.
  It also starts the first wedge at twelve o'clock and winds clockwise, matching
  the package's pies/roses (coord_polar) rather than starting at three o'clock
  counter-clockwise.

• Sunburst / radial hierarchies: vsunburst(). A new plot type for
  part-of-whole hierarchies, from a parent list — id, parent (NA at the
  root), and value (leaf values; internal nodes sum their children). Depth maps
  to a ring and each node's angular span is its share of its parent's, drawn as
  one batched sector_grob in an aspect-locked, axis-free square panel (mirroring
  vsankey()/vgraph()). inner_radius opens a central hole (a donut/ring
  sunburst); nodes are coloured by depth. mark_sunburst() is the exported layer.
  See vignette("flows-and-hierarchies").

• Sankey / flow diagrams: vsankey(). A new plot type for layered flows,
  built from a flow list — one row per flow with from, to, and value (the
  ribbon width). Nodes are the union of from/to; a node that is both a source
  and a target makes the diagram multi-stage. vsankey(data, from, to, value)
  returns a ready, axis-free plot (mirroring vgraph()); mark_sankey() is the
  exported layer it adds. The layout is computed R-side (longest-path layering,
  value-proportional node heights and ribbon widths, filled Bézier ribbons) and is
  deterministic. Flows must form a DAG; nodes are coloured from the qualitative
  palette. See vignette("flows-and-hierarchies").

• Uncertainty marks: mark_halfeye() and mark_interval(). ggdist-style
  slab + interval marks for sample/posterior input (many y rows per categorical
  x). mark_halfeye() draws a one-sided density slab with a point-interval at
  its base — the median (or point = "mean"), a thick inner and thin outer
  equal-tailed quantile interval at the .width probabilities (default
  c(0.66, 0.95)); mark_interval() is the point-interval alone. A natural fit
  for visualising posterior draws (e.g. from \pkg{brms}).

• coord_radial() and scale_size_area(). coord_radial() is a fuller
  polar system (ggplot2 3.5's name): besides theta/start/direction it takes
  end to sweep only a partial arc (e.g. start = -pi/2, end = pi/2 for a
  semicircular gauge) and inner_radius for a donut hole; with the defaults
  it matches coord_polar(). scale_size_area() maps a value to the marker's
  area (value 0 → size 0), the perceptually honest default for bubble
  charts, with max_size the size of the largest value.

• Sankey labels stay on-panel. vsankey() now reserves horizontal margin for
  node labels, so the source column's labels (drawn to their left) and the
  terminal column's (drawn to their right) no longer clip at the panel edge.

• Robustness of the new marks. vsunburst()/mark_sunburst() now reject a
  missing or negative leaf value with a clear message (instead of a cryptic
  downstream error), and mark_sunburst() validates inner_radius like
  vsunburst() and coord_radial() do. mark_halfeye()/mark_interval() skip a
  category with fewer than two finite observations (with a warning) rather than
  drawing an empty interval, and reject a width = argument (a likely typo for
  .width) that was previously ignored silently.

• Consistent argument names for the hole radius / ridge height. The
  central-hole fraction is now spelled inner_radius everywhere it appears:
  coord_radial(), vsunburst()/mark_sunburst(), and mark_donut() (was
  hole). mark_ridgeline()'s overlap control is now height (was scale,
  which collided with mark_halfeye(scale=), a different quantity).

• Consistent sketch / blend passthrough. mark_ecdf(), mark_contour(),
  mark_contour_filled(), mark_dotplot(), mark_qq(), and mark_qq_line() now
  accept a per-layer sketch = (their emitters already honoured it), and
  mark_pie() / mark_donut() accept blend =, matching the rest of the mark
  surface.

• Parameterised position adjustments. New position_nudge(),
  position_jitter(), position_dodge(), position_dodge2(), and
  position_jitterdodge() give a mark's position tunable parameters (a bare
  string like "dodge" still works with the defaults). Adds three adjustments:
  nudge (shift every element by a constant in data units), dodge2 (dodge by
  the groups actually present at each x, filling the band with a padding gap —
  so ragged groupings stay centred), and jitterdodge (jitter points within
  their dodged slot). position_jitter(width=, height=, seed=) and
  position_dodge(width=) expose the previously-fixed jitter/dodge extents. A
  plot using the old string positions is unchanged.

• Label repulsion: mark_text(repel = TRUE) / mark_label(repel = TRUE).
  Overlapping text labels are moved apart with a force-directed layout
  (ggrepel-style), each keeping a thin leader line back to its point. Because the
  plot size is fixed on the spec, the repulsion is resolved exactly against the
  true rendered panel — a two-pass compile that reads the panel's device geometry
  from vellum::scene_model(), relaxes the label boxes in pixel space, and maps
  the result back — so it needs no approximation and no vellum change, and is
  deterministic under seed. Tunable via box_padding, point_padding,
  min_segment_length, and seed. Limited to a single cartesian panel for now
  (facets / composition / polar error clearly).

• mark_line(window = ): rolling / cumulative / offset transforms. A line can
  now transform its y per group (over rows ordered by x) before drawing —
  moving mean/sum/median/min/max over a window of k, running
  cumsum/cummean/cummax/cummin, lag/lead shifts, or rank. Pass an op
  name (window = "mean") or a list (window = list(op = "mean", k = 7, align = "right", partial = TRUE)); align is trailing/leading/centred and partial
  fills the edges from the shorter window so the line stays continuous. A plot
  without window is unchanged.

• Diverging colour scales: scale_color_gradient2() / scale_fill_gradient2().
  A three-point ramp (low--mid--high) centred on midpoint (default 0),
  rescaled about the midpoint (scales::rescale_mid) so the neutral colour sits
  on the chosen value and each side spans as far as the data reaches — the correct
  scale for signed / anomaly data. A diverging continuous colorbar also reports
  midpoint + diverging in its colorbar descriptor, so an interactive host can
  centre a value-range filter on the neutral value.

• symlog position transform. scale_x_continuous(trans = "symlog") (and
  y) adds a symmetric-log axis: linear through zero, logarithmic in the tails
  (sign(x) · log10(1 + |x|)), so signed data spanning several orders of magnitude
  — including zero and negatives, which log10 cannot show — reads on one axis.
  Breaks sit at zero and signed powers of ten. The transform name flows into the
  panel scales descriptor like the other transforms.

• New group-region marks: mark_ellipse() and mark_hull(). Both enclose a
  set of (x, y) points in a single region drawn over a scatter — one region per
  group when a color/fill is mapped. mark_ellipse() draws a covariance
  ellipse (type = "t" robust default via \pkg{MASS}, or "norm"/"euclid"),
  following ggplot2's stat_ellipse(); mark_hull() draws the convex hull. Both
  are unfilled boundaries by default (map/set a fill to shade them) and need at
  least 3 points per group. The region's boundary trains the position scales, so
  an ellipse that bulges past the data is not clipped.

• mark_smooth() gains real smoothing methods. Beyond "lm", the smooth
  mark now fits "loess" (local regression, span =), "glm" (with a family
  via method.args, e.g. logistic — the fit and its ribbon are back-transformed
  from the link scale), "gam" (a penalised smooth, default y ~ s(x); needs
  \pkg{mgcv}), and "rq" (quantile regression at a single method.args$tau;
  needs \pkg{quantreg}, line only, no ribbon). The default method = "auto"
  picks loess for small groups (< 1000 points) and gam for large ones, as in
  ggplot2. New formula, span, and method.args arguments; glm/gam bands
  use a normal interval, lm/loess a t-interval. Previously mark_smooth()
  errored on any method other than "lm". \pkg{mgcv} and \pkg{quantreg} are
  Suggests — a gated method errors clearly if its package is absent.

• Data panels are emitted as pannable, gridlines tagged. Cartesian data panels
  (including coord_flip and a linear coord_trans) now push a pannable vellum
  viewport, and gridlines carry role = "grid". This is inert for static rendering
  but lets an interactive host (vellumwidget) pan/zoom a panel's marks while its
  clip + axes stay fixed and hide/redraw gridlines — the groundwork for axis-aware
  zoom. Polar / nonlinear-coord_trans panels stay non-pannable. Requires the
  current development vellum.

• Continuous colorbar filter metadata. A continuous color scale now attaches
  each mark's colour value as filter_value in its element meta, and a colorbar
  descriptor (value domain + orientation) to the gradient-bar grob. Together (via
  vellum::scene_model()) these let a host such as vellumwidget overlay an
  interactive value-range filter on the colorbar. Discrete/binned colour scales are
  unaffected. No change to rendered output.

• Panels now carry a scales descriptor for interactive hosts. Each cartesian
  data panel's viewport gains a meta$scales record — per axis: type
  (continuous / log10 / discrete / binned / date / datetime), transform, the
  data and native domains, tick breaks + labels, and time_unit for date/datetime
  axes. It surfaces via vellum::scene_model()$panels$meta and lets a host (e.g.
  vellumwidget) map device pixels back to data values — so a brush or a reported
  view can be expressed in data coordinates, not just pixels. Requires
  vellum (>= 0.4.0.9000). Internal: trained position scales now also record their
  transform name and, for date/time axes, a time_unit (previously the
  date/datetime nature was lost after training). No change to rendered output.