- Add key `(contourGeom.value)` to `{#each}` block (svelte/require-each-key)
- Run Prettier on four new files (quantile.svelte, volcano.svelte,
  weather.svelte, contour.test.svelte.ts)

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

- Remove spurious "and" in fill="value" description
- Fix "four interpolation strategies" to list all four (add `none`)
- Fix broken Example link to point to /examples/contour/volcano
- Replace mismatched live example in explicit-thresholds section with
  one that actually demonstrates an explicit thresholds array
- Fix "Pass a function to thresholds" inaccuracy in quantile section
  (the example passes a precomputed array, not a function)
- Fix wrong band-count comment (7 → produces 9 bands, not 10)
- Reword quantile section intro for clarity

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

Replace the manual floor/accumulate loop with d3-array's range(), which
handles floating-point precision correctly and is more idiomatic. Also
simplify the control flow: resolve the interval case with an early return
rather than converting to an intermediate floor/range object.

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

…contours

Previously the fill channel was always registered with scalar field values,
which polluted the shared color scale domain even when fill/stroke were
plain CSS colors. This corrupted type/domain inference for sibling marks
(e.g. categorical color encodings gained unexpected numeric entries).

Now scalar values are only registered when fill="value" or stroke="value"
is active (markUsesColorScale). The three modes are handled separately:

- Dense grid / sampler: fill channel omitted entirely when not coloring by value
- Scatter: fill channel is always registered (it's the delivery mechanism for
  scalar values into computeContours via scaledData[].resolved.fill), but
  passes { value, scale: false } when color scale registration is not needed

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

When `value` is omitted and `fill` or `stroke` is a data accessor
(field name string or function) rather than a CSS color, it is
automatically promoted to the `value` channel and replaced with the
`"value"` keyword — matching Observable Plot's behaviour.

Examples:
  <Contour data={pts} x="x" y="y" fill="temp" />
  -- equivalent to: value="temp" fill="value"

  <Contour data={pts} x="x" y="y" stroke={(d) => d.temp} />
  -- equivalent to: value={(d) => d.temp} stroke="value"

Detection uses the existing isColorOrNull helper (d3-color backed) plus
explicit checks for SVG/SveltePlot constants ("none", "value",
"inherit") that d3-color does not recognise as CSS colors. CSS color
strings (named colors, hex, functional notation) and the "value" /
"none" keywords are never promoted.

Throws when both fill and stroke are accessors (ambiguous).

Adds 4 unit tests covering: field-name promotion, function promotion,
no promotion when value is explicit, no promotion for CSS color strings.

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

Both marks now read from getPlotDefaults().contour / .raster at
component initialisation, so project-wide defaults (e.g. blur,
pixelSize, interpolate, smooth) can be set with setPlotDefaults():

  setPlotDefaults({ contour: { blur: 1, pixelSize: 3 } });
  setPlotDefaults({ raster: { pixelSize: 2, imageRendering: 'pixelated' } });

PlotDefaults.contour and .raster were already declared in the type
system; this adds the missing runtime wiring following the same
DEFAULTS pattern used by Dot, Link, Sphere, and other marks.

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

Adds a new example plot derived from the existing interpolated raster
example, using the CA55 aeromagnetic survey dataset. The contour mark
overlays the interpolated field with Dot markers at the original
measurement positions, demonstrating scatter-to-contour interpolation
with the fill shorthand (fill="MAG_IGRF90" auto-promotes to value).

Also removes accidental debug console.log calls left in Contour.svelte.

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