fix(model): honor Muse embedding sharing contract

Signed-off-by: yaoyu-33 <yaoyu.094@gmail.com>

Author: yaoyu-33

src/megatron/bridge/models/muse_glimmer/muse_glimmer_bridge.py

@@ -245,7 +245,7 @@ def hf_config_to_model_config(self, hf_config: PretrainedConfig) -> MuseGlimmerM
             should_pad_vocab=False,
             seq_length=int(text_config.max_position_embeddings),
             parallel_output=True,
-            share_embeddings_and_output_weights=bool(text_config.tie_word_embeddings),
+            share_embeddings_and_output_weights=bool(hf_config.tie_word_embeddings),
             hybrid_layer_pattern="*" * int(text_config.num_hidden_layers),
             position_embedding_type="rope",
             rotary_percent=1.0,

tests/unit_tests/models/muse_glimmer/test_muse_glimmer.py

@@ -85,6 +85,7 @@ def _tiny_hf_config() -> MuseGlimmerConfig:
         projector_hidden_size=32,
         projector_hidden_act="gelu",
         architectures=["MuseGlimmerForConditionalGeneration"],
+        tie_word_embeddings=False,
         torch_dtype=torch.bfloat16,
     )
 
@@ -124,6 +125,17 @@ def test_config_conversion_uses_model_config_path_only() -> None:
     assert model_config.vision_config.spatial_merge_size == 2
 
 
+def test_config_conversion_uses_top_level_embedding_sharing_contract() -> None:
+    """The VLM config, not its nested text config, owns HF weight tying."""
+    hf_config = _tiny_hf_config()
+    hf_config.tie_word_embeddings = True
+    hf_config.text_config.tie_word_embeddings = False
+
+    model_config = MuseGlimmerBridge().hf_config_to_model_config(hf_config)
+
+    assert model_config.share_embeddings_and_output_weights is True
+
+
 def test_vision_config_contributes_to_runtime_flops() -> None:
     model_config = MuseGlimmerBridge().hf_config_to_model_config(_tiny_hf_config())
     cfg = SimpleNamespace(model=model_config)