mopac-pdf v0: markdown to beautiful PDFs via digest-pinned typst

Go CLI that turns the markdown currency of this stack (Redmine notes,
Discourse posts, briefing output) into typeset PDFs: two embedded typst
templates (report with title page/TOC/headers, dense brief), front-matter
(title/subtitle/author/date/classification/template), GFM tables, and
bar charts rendered in pure Go (go-chart) from fenced chart data blocks.
Engine is a prebuilt typst 0.15.1 container pinned by digest and run
--network none; PDF bytes to stdout or -o. Exit codes 0/1/2.

All dev in docker (dev.sh/Makefile); unit tests + golden typst fixtures
plus a host-side smoke against the real engine container.

Generated with Crush

Assisted-by: Crush:glm-5.2

vendor/github.com/wcharczuk/go-chart/v2/image_writer.go

@@ -0,0 +1,42 @@
+package chart
+
+import (
+	"bytes"
+	"errors"
+	"image"
+	"image/png"
+)
+
+// RGBACollector is a render target for a chart.
+type RGBACollector interface {
+	SetRGBA(i *image.RGBA)
+}
+
+// ImageWriter is a special type of io.Writer that produces a final image.
+type ImageWriter struct {
+	rgba     *image.RGBA
+	contents *bytes.Buffer
+}
+
+func (ir *ImageWriter) Write(buffer []byte) (int, error) {
+	if ir.contents == nil {
+		ir.contents = bytes.NewBuffer([]byte{})
+	}
+	return ir.contents.Write(buffer)
+}
+
+// SetRGBA sets a raw version of the image.
+func (ir *ImageWriter) SetRGBA(i *image.RGBA) {
+	ir.rgba = i
+}
+
+// Image returns an *image.Image for the result.
+func (ir *ImageWriter) Image() (image.Image, error) {
+	if ir.rgba != nil {
+		return ir.rgba, nil
+	}
+	if ir.contents != nil && ir.contents.Len() > 0 {
+		return png.Decode(ir.contents)
+	}
+	return nil, errors.New("no valid sources for image data, cannot continue")
+}