fix: live-API corrections — music result shapes, mesh format honesty, mesh conversion

Round 2 from live smokes on netherstorm (2026-07-14):

- ACE-Step result blob is an ARRAY of objects and carries RAW control
  characters inside string values (literal newlines) — strict JSON
  rejected it. parseMusicResult sanitizes control chars (only legal
  inside string values in the double-encoded blob) and accepts array or
  object shapes. Regression test uses the live payload shape.
- Hunyuan3D GenerationRequest has NO output-format field (the documented
  type param is fiction) — it always returns GLB. Results are now
  labelled by sniffed magic bytes, never by the requested format.
- NEW meshgen.Converter/ConverterProvider optional surface + llamaswap
  impl over the mediautils shim POST /v1/convert_mesh — the STL hop for
  the printer pipeline.

Co-Authored-By: Claude Fable 5 <[email protected]>

provider/llamaswap/music_embed_test.go

@@ -12,6 +12,7 @@ import (
 
 	"gitea.stevedudenhoeffer.com/steve/majordomo/embeddings"
 	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/meshgen"
 	"gitea.stevedudenhoeffer.com/steve/majordomo/musicgen"
 )
 
@@ -293,3 +294,75 @@ func TestMusicGenerateRejectsHostileFileURL(t *testing.T) {
 		t.Fatal("dot-dot result file URL accepted")
 	}
 }
+
+func TestParseMusicResultLiveShapes(t *testing.T) {
+	// Live ACE-Step (2026-07-14): result is an ARRAY and carries raw
+	// control characters inside string values.
+	arrayWithCtrl := "[{\"file\": \"/v1/audio?path=x.mp3\", \"prompt\": \"line1\nline2\"}]"
+	res, ok := parseMusicResult(arrayWithCtrl)
+	if !ok || res.File != "/v1/audio?path=x.mp3" {
+		t.Fatalf("array+ctrl: ok=%v res=%+v", ok, res)
+	}
+	// Docs shape (bare object) still parses.
+	res, ok = parseMusicResult(`{"file": "/v1/audio?path=y.mp3"}`)
+	if !ok || res.File != "/v1/audio?path=y.mp3" {
+		t.Fatalf("object: ok=%v res=%+v", ok, res)
+	}
+	if _, ok := parseMusicResult("not json"); ok {
+		t.Fatal("garbage parsed")
+	}
+}
+
+func TestMeshResultSniffsActualFormat(t *testing.T) {
+	// Live Hunyuan3D always returns GLB regardless of the requested
+	// format — the result must be labelled by its magic bytes.
+	glb := append([]byte("glTF"), []byte("\x02\x00\x00\x00rest")...)
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/octet-stream")
+		_, _ = w.Write(glb)
+	}))
+	defer srv.Close()
+
+	p := New(WithBaseURL(srv.URL), WithHTTPClient(srv.Client()))
+	mm, _ := p.MeshModel("image3d-hunyuan21")
+	res, err := mm.Generate(context.Background(),
+		meshgen.Request{Image: meshgen.Image{Data: []byte{1}}, Format: "stl"})
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if res.Mesh.Format != "glb" || res.Mesh.MIME != "model/gltf-binary" {
+		t.Fatalf("mesh labelled %s/%s, want glb (sniffed)", res.Mesh.Format, res.Mesh.MIME)
+	}
+}
+
+func TestMeshConverter(t *testing.T) {
+	stl := []byte("solid m\nendsolid m\n")
+	var gotTarget, gotPath string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		if err := r.ParseMultipartForm(1 << 20); err != nil {
+			t.Errorf("multipart: %v", err)
+		}
+		gotTarget = r.FormValue("target")
+		w.Header().Set("Content-Type", "model/stl")
+		_, _ = w.Write(stl)
+	}))
+	defer srv.Close()
+
+	p := New(WithBaseURL(srv.URL), WithHTTPClient(srv.Client()))
+	mc, err := p.MeshConverter("mediautils")
+	if err != nil {
+		t.Fatalf("MeshConverter: %v", err)
+	}
+	res, err := mc.Convert(context.Background(),
+		meshgen.Mesh{Data: []byte("glTFxxxx"), Format: "glb"}, "stl")
+	if err != nil {
+		t.Fatalf("Convert: %v", err)
+	}
+	if gotPath != "/upstream/mediautils/v1/convert_mesh" || gotTarget != "stl" {
+		t.Errorf("path/target = %q/%q", gotPath, gotTarget)
+	}
+	if res.Mesh.Format != "stl" {
+		t.Errorf("format = %q", res.Mesh.Format)
+	}
+}