internal/rosa: register custom artifacts

This also encodes extra information for iana-etc.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/etc.go

@@ -86,8 +86,27 @@ nobody:x:65534:
 // Kind returns the hardcoded [pkg.Kind] value.
 func (cureEtc) Kind() pkg.Kind { return kindEtc }
 
-// Params is a noop.
-func (cureEtc) Params(*pkg.IContext) {}
+// Params writes whether iana-etc is populated.
+func (a cureEtc) Params(ctx *pkg.IContext) {
+	if a.iana != nil {
+		ctx.WriteUint32(1)
+	} else {
+		ctx.WriteUint32(0)
+	}
+}
+
+func init() {
+	pkg.Register(kindEtc, func(r *pkg.IRReader) pkg.Artifact {
+		a := cureEtc{}
+		if r.ReadUint32() != 0 {
+			a.iana = r.Next()
+		}
+		if _, ok := r.Finalise(); ok {
+			panic(pkg.ErrUnexpectedChecksum)
+		}
+		return a
+	})
+}
 
 // IsExclusive returns false: Cure performs a few trivial filesystem writes.
 func (cureEtc) IsExclusive() bool { return false }