vellumplot 0.8.0

• Flow maps: mark_flow_map(). A one-to-many flow map on a vgraph() plot:
  a single root fans out to every destination along smooth, merging branches
  whose width tracks the flow volume (the Minard / migration-map idiom).
  type = "spiral" (default) builds an angle-restricted spiral tree from the
  \pkg{edgebundle} package; type = "steiner" builds an approximate Steiner tree
  (additionally needs \pkg{interp}). Edge weight drives the flow, which is
  mapped onto width_range. Needs the suggested \pkg{edgebundle} package.

• Edge bundling: mark_edge_bundle(). A drop-in alternative to mark_edges()
  that routes a graph's edges as bundled curves instead of straight lines, so a
  dense node-link hairball collapses into a few legible trunks. type selects the
  algorithm ("force", "divided", "stub", "path", "hammer", "mingle")
  and params passes tuning through to the \pkg{edgebundle} package, which
  computes the geometry; vellumplot draws the returned paths with the usual edge
  aesthetics (faint by default so overlapping trunks read as density). Needs the
  suggested \pkg{edgebundle} package (>= 1.0.0).

• Chord diagrams: vchord(). Wraps a weighted flow (a from/to/value
  list or a square flow matrix) onto a circle -- one arc per node, one ribbon per
  flow through the centre. Directed: each node's arc splits into an outgoing then
  an incoming block, so a -> b and b -> a are distinct ribbons and self-flows
  loop within a node's sector. direction shows a ribbon's direction by fading
  it from source to target ("gradient", default), stopping it short of the
  target ("gap"), or "both". sort, gap, and link_color echo
  vsankey(); mark_chord() is the exported layer.

• Removed the unused max_overlaps argument from mark_text(),
  mark_label(), and mark_node_text(). It was reserved for a never-implemented
  overlap cap and did nothing; drop it from any call.

• More robust handling of degenerate and extreme inputs. A single distinct
  value on an axis under coord_fixed() / coord_sf() no longer collapses the
  panel to nothing; a map centred on a pole no longer gets a runaway aspect
  ratio; a circle-pack of collinear equal-value leaves no longer produces NaN
  coordinates; and a pathologically deep hierarchy or dendrogram aborts with a
  clear "too deep" message instead of overflowing the call stack.

• mark_line(window = ) requires a positive integer k. A zero, negative,
  or fractional window size now errors clearly instead of silently producing a
  wrong (or empty) result.

• A computed-constant if_false in condition() is carried into the
  interaction model. A negative literal (e.g. -0.5) or a computed constant
  (e.g. grey(0.5)) was previously dropped; only genuine per-row column
  references are now excluded (and carried per element instead).

• A faceted layer whose own data lacks the facet variable still draws on every
  panel, but a genuine evaluation error there is no longer silently swallowed
  into that fallback.

• mark_point(auto = TRUE) no longer datashades under a warped coordinate
  system. Under coord_polar() / coord_trans() the >50000-row datashade
  fallback — which bins in linear data space — would rasterise into the wrong
  place; it is now skipped and the vector path draws, matching the documented
  behaviour and the other auto marks (line/step/segment/edges).

• A sankey column with too many nodes errors clearly. When a column has more
  nodes than its inter-node gaps can fit, the node/ribbon heights previously went
  negative and spilled outside the panel; vsankey() / mark_sankey() now abort
  with a message pointing at node_gap.

• Aggregating stats drop missing summaries consistently, with a warning. For
  a value-summarising bar (mark_bar(y = , fun = ) and friends), a category
  whose summary is NA (an empty group, or a summary of data containing NA
  when the function does not remove it) is now dropped with a warning on both
  the grouped and ungrouped paths, which previously treated NA differently. A
  layer mapping both color and fill also keeps both aligned after
  aggregation (fill could previously be left at the wrong length).

• Clearer errors for malformed scale bounds. scale_x_continuous(),
  scale_y_continuous(), scale_size(), scale_size_area(), scale_alpha(),
  scale_edge_width(), and scale_edge_alpha() now reject a limits (or output
  range) that is not a length-2 vector — and, for the size/alpha/edge scales, a
  non-numeric one — with a clear message, instead of failing later with a cryptic
  low-level error (e.g. 'length = 2' in coercion to 'logical(1)'). scale_size_area()
  also validates max_size.

• add_marginal() rejects a non-numeric mapping. A factor x/y previously
  slipped through and the marginal was computed over the integer level codes
  rather than the data; it now errors clearly, as a character column already did.

• Stricter validation of interactivity and layout arguments.
  select_point()/select_interval() reject a non-logical toggle/empty (it
  was silently coerced to FALSE); vgraph() validates width/height like
  vsankey()/vhierarchy(); and area() rejects a non-numeric or non-integer
  cell index instead of aborting with an opaque "missing value where TRUE/FALSE
  needed".

• mark_text() honours hjust/vjust passed as a variable. They were only
  read as constant params, so a value routed through a variable (as
  vdendrogram() does per direction) silently fell back to centred, letting leaf
  labels run over the edges. .emit_text() now reads them value-first, like
  angle. vdendrogram() leaf labels also get a larger default gap.

• Dendrograms and unrooted trees. vgraph() now accepts a base
  hclust/dendrogram and gains a height-aware "dendrogram" layout plus an
  "unrooted" layout (via graphlayouts::layout_as_tree_unrooted(), needs
  graphlayouts >= 1.2.5). mark_edges(routing = "elbow") gained elbow_at /
  elbow_axis so the elbow can be the dendrogram bracket (corner at the
  parent's level) rather than only the midpoint S-bend. vdendrogram() is a
  one-line preset: bracket edges, leaf labels, direction, and k to cut the
  tree and colour clusters. Also fixes mark_node_text(label = ) so an explicit
  label mapping overrides the default vertex name (it was previously ignored).

• vhierarchy() respects scale_fill_*(). By default nodes are still
  coloured by their depth-1 branch and lightened with depth, but the branch is
  now an ordinary discrete fill scale, so scale_fill_manual() /
  scale_fill_discrete() recolour the branches and a lighten argument controls
  the depth fade (0 = flat colour per branch). Mapping fill to a node column
  instead colours every node by that variable (discrete or continuous, with the
  matching scale_fill_*()), with no depth fade.