convert: fixes for qwen3next model conversion (#16354)

This change addresses some problems with GGUF conversion including:
 * correctly naming the MoE tensors
 * correctly quantizing the nextn.eh_proj.weight MTP tensor

convert/convert_qwen3next.go

@@ -934,8 +934,11 @@ func safetensorFloat32Data(st safetensor) ([]float32, error) {
 func (q *qwen3NextModel) Tensors(ts []Tensor) []*ggml.Tensor {
 	var out []*ggml.Tensor
 
-	merges := make([]merge, q.NumHiddenLayers*3)
-	for i := range q.NumHiddenLayers {
+	ts = q.renameMTPLayerTensors(ts)
+
+	blockCount := q.NumHiddenLayers + q.NumNextNPredictLayers
+	merges := make([]merge, blockCount*3)
+	for i := range blockCount {
 		merges[i*3+0] = merge{
 			fmt.Sprintf("blk.%d.mlp.experts.*.gate_proj.weight", i),
 			fmt.Sprintf("blk.%d.ffn_gate_exps.weight", i),
@@ -1065,6 +1068,57 @@ func (q *qwen3NextModel) Tensors(ts []Tensor) []*ggml.Tensor {
 	return out
 }
 
+func (q *qwen3NextModel) renameMTPLayerTensors(ts []Tensor) []Tensor {
+	var out []Tensor
+	for i, t := range ts {
+		name, ok := q.mtpLayerTensorName(t.Name())
+		if !ok {
+			continue
+		}
+		if out == nil {
+			out = slices.Clone(ts)
+		}
+		out[i] = &renamedTensor{Tensor: t, name: name}
+	}
+	if out != nil {
+		return out
+	}
+	return ts
+}
+
+func (q *qwen3NextModel) mtpLayerTensorName(name string) (string, bool) {
+	rest := strings.TrimPrefix(name, "mtp.layers.")
+	if rest == name {
+		return "", false
+	}
+	layer, suffix, ok := strings.Cut(rest, ".")
+	if !ok {
+		return "", false
+	}
+	idx, err := strconv.ParseUint(layer, 10, 32)
+	if err != nil {
+		return "", false
+	}
+	return fmt.Sprintf("blk.%d.%s", q.NumHiddenLayers+uint32(idx), suffix), true
+}
+
+type renamedTensor struct {
+	Tensor
+	name string
+}
+
+func (t *renamedTensor) Name() string {
+	return t.name
+}
+
+func (t *renamedTensor) Clone() Tensor {
+	return &renamedTensor{Tensor: t.Tensor.Clone(), name: t.name}
+}
+
+func (t *renamedTensor) SourceDType() string {
+	return sourceDType(t.Tensor)
+}
+
 func (q *qwen3NextModel) appendDirectTensor(out []*ggml.Tensor, t Tensor, name string) []*ggml.Tensor {
 	if qwen3NextShouldShiftNorm(name) {
 		t = t.Clone()
@@ -1093,18 +1147,6 @@ func (q *qwen3NextModel) mtpTensorNames(name string) []string {
 		nextn = 1
 	}
 
-	if rest := strings.TrimPrefix(name, "mtp.layers."); rest != name {
-		layer, suffix, ok := strings.Cut(rest, ".")
-		if !ok {
-			return nil
-		}
-		idx, err := strconv.ParseUint(layer, 10, 32)
-		if err != nil {
-			return nil
-		}
-		return []string{fmt.Sprintf("blk.%d.%s", base+uint32(idx), suffix)}
-	}
-
 	var suffix string
 	switch name {
 	case "mtp.fc.weight":

convert/convert_qwen3next_test.go

@@ -819,6 +819,101 @@ func TestQwen35MoePackedExperts(t *testing.T) {
 	}
 }
 
+func TestQwen35MTPMoePackedExperts(t *testing.T) {
+	m := &qwen3NextModel{
+		qwen3NextTextConfig: qwen3NextTextConfig{
+			NumHiddenLayers:       40,
+			NumNextNPredictLayers: 1,
+		},
+	}
+
+	out := m.Tensors([]Tensor{
+		&fakeTensor{
+			name:  "mtp.layers.0.mlp.experts.gate_up_proj",
+			shape: []uint64{2, 4, 3},
+			data: []float32{
+				0, 1, 2,
+				3, 4, 5,
+				6, 7, 8,
+				9, 10, 11,
+				12, 13, 14,
+				15, 16, 17,
+				18, 19, 20,
+				21, 22, 23,
+			},
+		},
+		&fakeTensor{
+			name:  "mtp.layers.0.mlp.experts.down_proj",
+			shape: []uint64{2, 5, 3},
+			data:  make([]float32, 2*5*3),
+		},
+	})
+
+	byName := map[string]*ggml.Tensor{}
+	for _, tensor := range out {
+		if strings.Contains(tensor.Name, ".mlp.experts.") {
+			t.Fatalf("unexpected raw expert tensor %q", tensor.Name)
+		}
+		byName[tensor.Name] = tensor
+	}
+
+	gate := byName["blk.40.ffn_gate_exps.weight"]
+	if gate == nil {
+		t.Fatalf("missing tensor %q", "blk.40.ffn_gate_exps.weight")
+	}
+	if got, want := gate.Shape, []uint64{2, 2, 3}; !slices.Equal(got, want) {
+		t.Fatalf("unexpected gate shape: got %v want %v", got, want)
+	}
+	if got, want := readTensorData(t, gate), []float32{
+		0, 1, 2, 3, 4, 5,
+		12, 13, 14, 15, 16, 17,
+	}; !slices.Equal(got, want) {
+		t.Fatalf("unexpected gate values: got %v want %v", got, want)
+	}
+
+	if _, ok := byName["blk.40.ffn_up_exps.weight"]; !ok {
+		t.Fatalf("missing tensor %q", "blk.40.ffn_up_exps.weight")
+	}
+	if _, ok := byName["blk.40.ffn_down_exps.weight"]; !ok {
+		t.Fatalf("missing tensor %q", "blk.40.ffn_down_exps.weight")
+	}
+}
+
+func TestQwen35MTPMoePerExpertTensors(t *testing.T) {
+	m := &qwen3NextModel{
+		qwen3NextTextConfig: qwen3NextTextConfig{
+			NumHiddenLayers:       40,
+			NumNextNPredictLayers: 1,
+		},
+	}
+
+	out := m.Tensors([]Tensor{
+		&fakeTensor{
+			name:  "mtp.layers.0.mlp.experts.1.gate_proj.weight",
+			shape: []uint64{2, 2},
+			data:  []float32{10, 11, 12, 13},
+		},
+		&fakeTensor{
+			name:  "mtp.layers.0.mlp.experts.0.gate_proj.weight",
+			shape: []uint64{2, 2},
+			data:  []float32{0, 1, 2, 3},
+		},
+	})
+
+	if len(out) != 1 {
+		t.Fatalf("unexpected output tensor count: got %d want 1", len(out))
+	}
+	if got, want := out[0].Name, "blk.40.ffn_gate_exps.weight"; got != want {
+		t.Fatalf("unexpected tensor name: got %q want %q", got, want)
+	}
+	if got, want := out[0].Shape, []uint64{2, 2, 2}; !slices.Equal(got, want) {
+		t.Fatalf("unexpected tensor shape: got %v want %v", got, want)
+	}
+	if got, want := readTensorData(t, out[0]), []float32{0, 1, 2, 3, 10, 11, 12, 13}; !slices.Equal(got, want) {
+		t.Fatalf("unexpected tensor values: got %v want %v", got, want)
+	}
+}
+
 func TestQwen35SharedExpertGateKeepsMatrixShape(t *testing.T) {
 	m := &qwen3NextModel{}