Derive Qwen3-TTS codec conv encoder from config instead of hardcoding widths

src/mobius/_configs/_base.py

@@ -1125,6 +1125,14 @@ def from_transformers(cls, config, parent_config=None) -> ArchitectureConfig:
                 max_position_embeddings=getattr(ec, "max_position_embeddings", 8000),
                 num_quantizers=getattr(ec, "num_quantizers", 32),
                 num_semantic_quantizers=getattr(ec, "num_semantic_quantizers", 1),
+                audio_channels=getattr(ec, "audio_channels", 1),
+                num_filters=getattr(ec, "num_filters", 64),
+                num_residual_layers=getattr(ec, "num_residual_layers", 1),
+                kernel_size=getattr(ec, "kernel_size", 7),
+                last_kernel_size=getattr(ec, "last_kernel_size", 3),
+                residual_kernel_size=getattr(ec, "residual_kernel_size", 3),
+                compress=getattr(ec, "compress", 2),
+                upsampling_ratios=list(getattr(ec, "upsampling_ratios", [8, 6, 5, 4])),
             )
 
         # Model dtype

src/mobius/_configs/_base_test.py

@@ -79,3 +79,108 @@ def test_list_intermediate_size_collapses_to_first_element():
     out = ArchitectureConfig.from_transformers(cfg)
     assert out.intermediate_size == 8192
     assert isinstance(out.intermediate_size, int)
+
+
+def _codec_hf_config(**encoder_overrides):
+    """A Qwen3-TTS-Tokenizer-style HF config with nested encoder/decoder."""
+    encoder = {
+        "codebook_dim": 256,
+        "codebook_size": 2048,
+        "hidden_size": 512,
+        "intermediate_size": 2048,
+        "num_hidden_layers": 8,
+        "num_attention_heads": 8,
+        "num_key_value_heads": 8,
+        "head_dim": 64,
+        "num_quantizers": 32,
+        "num_semantic_quantizers": 1,
+        "audio_channels": 1,
+        "num_filters": 64,
+        "num_residual_layers": 1,
+        "kernel_size": 7,
+        "last_kernel_size": 3,
+        "residual_kernel_size": 3,
+        "compress": 2,
+        "upsampling_ratios": [8, 6, 5, 4],
+    }
+    encoder.update(encoder_overrides)
+    return _FakeHFConfig(
+        model_type="qwen3_tts_tokenizer_12hz",
+        hidden_size=512,
+        num_attention_heads=8,
+        num_hidden_layers=8,
+        vocab_size=2048,
+        decoder_config={"hidden_size": 512, "codebook_dim": 512},
+        encoder_config=encoder,
+    )
+
+
+def test_codec_encoder_conv_fields_extracted_from_nested_config():
+    """Nested ``encoder_config`` values drive the derived conv stack.
+
+    These fields are read with ``getattr`` off a nested config, so a wrong
+    key or default would silently fall back to the checkpoint defaults and
+    build the wrong architecture.
+    """
+    out = ArchitectureConfig.from_transformers(_codec_hf_config())
+
+    enc = out.codec_encoder
+    assert enc is not None
+    assert enc.audio_channels == 1
+    assert enc.num_filters == 64
+    assert enc.num_residual_layers == 1
+    assert enc.kernel_size == 7
+    assert enc.last_kernel_size == 3
+    assert enc.residual_kernel_size == 3
+    assert enc.compress == 2
+    assert enc.upsampling_ratios == [8, 6, 5, 4]
+
+
+def test_codec_encoder_conv_fields_honor_non_default_values():
+    """Non-default nested values must survive extraction unchanged."""
+    out = ArchitectureConfig.from_transformers(
+        _codec_hf_config(
+            hidden_size=64,
+            audio_channels=2,
+            num_filters=8,
+            num_residual_layers=3,
+            kernel_size=5,
+            last_kernel_size=1,
+            residual_kernel_size=7,
+            compress=4,
+            upsampling_ratios=[4, 2],
+        )
+    )
+
+    enc = out.codec_encoder
+    assert enc is not None
+    assert enc.hidden_size == 64
+    assert enc.audio_channels == 2
+    assert enc.num_filters == 8
+    assert enc.num_residual_layers == 3
+    assert enc.kernel_size == 5
+    assert enc.last_kernel_size == 1
+    assert enc.residual_kernel_size == 7
+    assert enc.compress == 4
+    assert enc.upsampling_ratios == [4, 2]
+
+
+def test_codec_encoder_conv_fields_fall_back_to_checkpoint_defaults():
+    """A config omitting the conv fields still yields the real architecture."""
+    out = ArchitectureConfig.from_transformers(
+        _FakeHFConfig(
+            model_type="qwen3_tts_tokenizer_12hz",
+            hidden_size=512,
+            num_attention_heads=8,
+            num_hidden_layers=8,
+            vocab_size=2048,
+            decoder_config={"hidden_size": 512},
+            encoder_config={"hidden_size": 512},
+        )
+    )
+
+    enc = out.codec_encoder
+    assert enc is not None
+    assert enc.num_filters == 64
+    assert enc.upsampling_ratios == [8, 6, 5, 4]
+    assert enc.num_residual_layers == 1

src/mobius/_configs/_sub_configs.py

@@ -148,6 +148,18 @@ class CodecEncoderConfig:
     max_position_embeddings: int = 8000
     num_quantizers: int = 32
     num_semantic_quantizers: int = 1
+    # Mimi convolutional encoder shape (HF ``MimiConfig`` defaults). The conv
+    # stack is derived from these: 1 leading conv, then per upsampling ratio
+    # ``num_residual_layers`` residual blocks + ELU + a strided conv that
+    # doubles the channel count, then a trailing ELU + conv to ``hidden_size``.
+    audio_channels: int = 1
+    num_filters: int = 64
+    num_residual_layers: int = 1
+    kernel_size: int = 7
+    last_kernel_size: int = 3
+    residual_kernel_size: int = 3
+    compress: int = 2
+    upsampling_ratios: list[int] = dataclasses.field(default_factory=lambda: [8, 6, 5, 4])
 
 
 @dataclasses.dataclass