nika:chart is the data twin of nika:image_fx:
pure compute plus one permit-gated write — no network, no clock, no
provider. Rows and a semantic spec compile to an SVG that is
byte-identical forever for identical inputs, and the artifact’s sha256
joins the run’s hash-chained trace. Your cost report draws its own
receipts.
The 30-second chart
role="img" +
aria-label, a <title> node) and carries its own recipe in a
<metadata> block — the chart explains itself with no sidecar.
The five types (closed · v1)
x / y / y_lo / y_hi / y2 / color are field names into your
rows. title, width, height are optional.
Semantics drive the rendering
semantics: maps each field to what it means — the type picks the
formatting and the palette, so the chart is right by construction:
Rows in, artifact out
data accepts inline rows (an array of flat string/number objects) or
{ path: "rows.json" } to read a JSON file — the natural pair with an
upstream task that produced it. out must end in .svg (the
attestation surface); parents are created; the write is fs-permit
gated like every artifact.
The Vega-Lite sibling
out/spend.vl.json next to the SVG — a real Vega-Lite spec
($schema · data · encoding · mark) for any downstream tool that
speaks it. The SVG stays the canonical, hash-verified artifact; the
sibling is a projection.
Determinism is the contract
Same rows, same spec, same bytes — proven across architectures (wasm32 ≡ aarch64 in the engine’s own parity suite). That makes charts evidence: the sha256 in the task output is the same one the trace chain records,nika trace verify walks it, and a regenerated chart
that stops matching is a tamper signal, not a formatting quirk.
Pair it with the flight recorder: draw your run costs from
.nika/traces/ data, and the report about your runs is itself a
receipt in one.