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

internal/chart/chart_test.go

@@ -0,0 +1,52 @@
+package chart
+
+import (
+	"bytes"
+	"image"
+	_ "image/png"
+	"testing"
+
+	"ukrrs.com/mopac/pdf/internal/markdown"
+)
+
+func TestBarPNG(t *testing.T) {
+	c := &markdown.Chart{
+		Type:   "bar",
+		Title:  "Revenue",
+		Unit:   "$K",
+		Labels: []string{"Q1", "Q2", "Q3"},
+		Values: []float64{10, 20, 15},
+	}
+	png, err := Bar(c)
+	if err != nil {
+		t.Fatalf("render: %v", err)
+	}
+	if !bytes.HasPrefix(png, []byte{0x89, 'P', 'N', 'G'}) {
+		t.Fatalf("not a PNG: % x", png[:4])
+	}
+	img, _, err := image.Decode(bytes.NewReader(png))
+	if err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	b := img.Bounds()
+	if b.Dx() < 300 || b.Dy() < 200 {
+		t.Fatalf("unexpected dimensions %dx%d", b.Dx(), b.Dy())
+	}
+}
+
+func TestBarRejectsUnknownType(t *testing.T) {
+	c := &markdown.Chart{Type: "pie", Labels: []string{"a"}, Values: []float64{1}}
+	if _, err := Bar(c); err == nil {
+		t.Fatal("pie must be rejected in v0")
+	}
+}
+
+func TestBarRejectsEmpty(t *testing.T) {
+	if _, err := Bar(nil); err == nil {
+		t.Fatal("nil chart must be rejected")
+	}
+	c := &markdown.Chart{Type: "bar"}
+	if _, err := Bar(c); err == nil {
+		t.Fatal("chart without data must be rejected")
+	}
+}