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]>

meshgen/meshgen.go

@@ -150,3 +150,23 @@ type Provider interface {
 	// backend verbatim; no catalog validation).
 	MeshModel(id string, opts ...ModelOption) (Model, error)
 }
+
+// Converter re-encodes a mesh between containers (GLB/STL/OBJ). A separate
+// optional surface because conversion typically runs on a DIFFERENT backend
+// than generation (the reference host converts on its mediautils shim —
+// Hunyuan3D's live server always emits GLB regardless of the requested
+// format).
+type Converter interface {
+	// Convert returns the mesh re-encoded in the given format.
+	Convert(ctx context.Context, mesh Mesh, format string) (*Result, error)
+}
+
+// ConverterProvider mints Converters bound to one backend.
+type ConverterProvider interface {
+	// Name is the registry identifier for the provider.
+	Name() string
+
+	// MeshConverter returns a Converter bound to the given id (passed
+	// through to the backend verbatim; no catalog validation).
+	MeshConverter(id string) (Converter, error)
+}

provider/llamaswap/mesh.go

@@ -42,7 +42,11 @@ type meshModel struct {
 
 // hunyuanGenerateRequest is the Hunyuan3D api_server /generate shape.
 // Optional fields are pointers/omitempty so unset values fall back to the
-// server's defaults (mirrors the sd-server wire structs).
+// server's defaults (mirrors the sd-server wire structs). Type is sent for
+// forward-compat but the LIVE server's GenerationRequest has no such field
+// and always returns GLB (verified 2026-07-14) — the response format is
+// therefore SNIFFED, and non-GLB output is the caller's conversion problem
+// (meshgen.Converter / the mediautils shim).
 type hunyuanGenerateRequest struct {
 	Image             string   `json:"image"`
 	Type              string   `json:"type,omitempty"`
@@ -123,7 +127,24 @@ func (m *meshModel) Generate(ctx context.Context, req meshgen.Request, opts ...m
 		return nil, &llm.APIError{Provider: m.p.name, Model: m.id,
 			Message: "mesh response is JSON, not mesh bytes: " + truncateForError(raw)}
 	}
-	return &meshgen.Result{Mesh: meshgen.Mesh{Data: raw, Format: format, MIME: mimeType}}, nil
+	// Label the result by what the bytes ARE, not what was requested: the
+	// live server ignores the format field entirely.
+	actualFormat, actualMIME := sniffMeshFormat(raw, format, mimeType)
+	return &meshgen.Result{Mesh: meshgen.Mesh{Data: raw, Format: actualFormat, MIME: actualMIME}}, nil
+}
+
+// sniffMeshFormat identifies the mesh container from magic bytes, falling
+// back to the requested format only when the bytes are ambiguous (binary
+// STL has no magic).
+func sniffMeshFormat(raw []byte, requested, requestedMIME string) (string, string) {
+	switch {
+	case len(raw) >= 4 && string(raw[:4]) == "glTF":
+		return "glb", meshFormats["glb"]
+	case len(raw) >= 6 && strings.EqualFold(string(raw[:6]), "solid "):
+		return "stl", meshFormats["stl"]
+	default:
+		return requested, requestedMIME
+	}
 }
 
 // truncateForError bounds a payload quoted into an error message.

provider/llamaswap/mesh_convert.go

@@ -0,0 +1,64 @@
+// mesh_convert.go implements meshgen.ConverterProvider against the
+// mediautils shim's POST /v1/convert_mesh (multipart file + target),
+// reached through the /upstream passthrough (ADR-0020). Exists because
+// Hunyuan3D's api_server always returns GLB — STL for the printer
+// pipeline is produced by this conversion hop.
+package llamaswap
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
+	"gitea.stevedudenhoeffer.com/steve/majordomo/meshgen"
+)
+
+// MeshConverter implements meshgen.ConverterProvider.
+func (p *Provider) MeshConverter(id string) (meshgen.Converter, error) {
+	if err := p.requireBaseURL(); err != nil {
+		return nil, err
+	}
+	return &meshConverter{p: p, id: id}, nil
+}
+
+type meshConverter struct {
+	p  *Provider
+	id string
+}
+
+// Convert implements meshgen.Converter.
+func (m *meshConverter) Convert(ctx context.Context, mesh meshgen.Mesh, format string) (*meshgen.Result, error) {
+	if len(mesh.Data) == 0 {
+		return nil, fmt.Errorf("%w: mesh conversion requires mesh bytes", llm.ErrUnsupported)
+	}
+	format = strings.ToLower(strings.TrimSpace(format))
+	mimeType, ok := meshFormats[format]
+	if !ok {
+		return nil, fmt.Errorf("%w: unsupported mesh format %q (want glb, stl, or obj)", llm.ErrUnsupported, format)
+	}
+	path, err := upstreamPath(m.id, "/v1/convert_mesh")
+	if err != nil {
+		return nil, err
+	}
+	filename := "mesh." + mesh.Format
+	if mesh.Format == "" {
+		filename = "mesh"
+	}
+	body, contentType, err := buildMultipart("build mesh-convert form",
+		filePart{field: "file", filename: filename, data: mesh.Data},
+		[]formField{{"target", format, true}})
+	if err != nil {
+		return nil, err
+	}
+	raw, _, err := m.p.doRaw(ctx, http.MethodPost, path, m.id, contentType, body, maxMeshResponseBytes)
+	if err != nil {
+		return nil, err
+	}
+	if len(raw) == 0 {
+		return nil, &llm.APIError{Provider: m.p.name, Model: m.id, Message: "mesh conversion returned no data"}
+	}
+	actualFormat, actualMIME := sniffMeshFormat(raw, format, mimeType)
+	return &meshgen.Result{Mesh: meshgen.Mesh{Data: raw, Format: actualFormat, MIME: actualMIME}}, nil
+}

provider/llamaswap/music.go

@@ -72,6 +72,36 @@ type queryItem struct {
 	Result string `json:"result"`
 }
 
+// musicResult is the useful subset of ACE-Step's double-encoded result
+// blob.
+type musicResult struct {
+	File string `json:"file"`
+}
+
+// parseMusicResult decodes the `result` string, tolerating two live-API
+// quirks (observed 2026-07-14): the payload is an ARRAY of result objects
+// (not a bare object), and string values can contain RAW control
+// characters (a literal newline in timing fields) that strict JSON
+// rejects. Control chars can only legally sit inside string values in the
+// double-encoded blob, so replacing them with spaces preserves structure.
+func parseMusicResult(blob string) (musicResult, bool) {
+	sanitized := strings.Map(func(r rune) rune {
+		if r < 0x20 {
+			return ' '
+		}
+		return r
+	}, blob)
+	var arr []musicResult
+	if err := json.Unmarshal([]byte(sanitized), &arr); err == nil && len(arr) > 0 {
+		return arr[0], true
+	}
+	var one musicResult
+	if err := json.Unmarshal([]byte(sanitized), &one); err == nil {
+		return one, true
+	}
+	return musicResult{}, false
+}
+
 // musicFormatMIME resolves the clip MIME from the response Content-Type
 // or the requested format, reusing speechMIME's table (one format->MIME
 // map for the whole provider). wav32 is ACE-Step-specific: normalize it
@@ -232,10 +262,8 @@ func findQueryItem(raw json.RawMessage, taskID string) (*queryItem, error) {
 
 // fetchResult downloads the finished clip named by the job's result blob.
 func (m *musicModel) fetchResult(ctx context.Context, format string, item *queryItem) (*musicgen.Result, error) {
-	var result struct {
+	result, ok := parseMusicResult(item.Result)
-		File string `json:"file"`
+	if !ok || result.File == "" {
-	}
-	if err := json.Unmarshal([]byte(item.Result), &result); err != nil || result.File == "" {
 		return nil, &llm.APIError{Provider: m.p.name, Model: m.id,
 			Message: "music result blob missing file URL: " + truncateForError([]byte(item.Result))}
 	}

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)
+	}
+}