feat(ernie): register ERNIE_SPEC for native dispatch

ErnieImageTransformer2DModel has no from_single_file; selecting an
Ernie finetune in the UNET dropdown previously crashed with
"is not a valid JSON file" from from_pretrained.

Probe of jibMixErnie_v20.safetensors: 409/409 keys overlap with the
model state dict after stripping model.diffusion_model., zero missing
or unexpected. Spec is the minimum TransformerSpec(cls=...).

pipelines/ernie/__init__.py

@@ -0,0 +1,29 @@
+"""ERNIE-Image pipeline package.
+
+Exports :data:`ERNIE_SPEC` for use by :mod:`pipelines.model_ernie` together
+with :mod:`pipelines.native_transformer`. The spec captures the
+ERNIE-Image-specific knobs that differ from the native-loader defaults:
+
+- No converter is needed: community Ernie trainer dumps use BFL-style keys
+  (``model.diffusion_model.``-prefixed) whose names match diffusers'
+  ``ErnieImageTransformer2DModel.state_dict()`` verbatim after prefix strip.
+  Probed against ``jibMixErnie_v20.safetensors`` (the upstream community
+  finetune): 409/409 keys overlap with zero missing or unexpected.
+- No siblings; no forbidden markers; default prefixes
+  (``model.diffusion_model.``, ``diffusion_model.``, ``net.``) cover every
+  exporter seen in the wild.
+
+Before this spec, selecting an Ernie finetune via the UNET dropdown crashed
+in :func:`diffusers.loaders.ModelMixin.from_pretrained` with a misleading
+``OSError: ... is not a valid JSON file`` because
+``ErnieImageTransformer2DModel`` lacks ``from_single_file`` support and the
+fallback path treats the safetensors as a directory looking for
+``config.json``.
+"""
+
+import diffusers
+
+from pipelines.native_transformer import TransformerSpec
+
+
+ERNIE_SPEC = TransformerSpec(cls=diffusers.ErnieImageTransformer2DModel)

pipelines/model_ernie.py

@@ -14,10 +14,12 @@ def load_ernie_image(checkpoint_info, diffusers_load_config=None):
     load_args, _quant_args = model_quant.get_dit_args(diffusers_load_config, allow_quant=False)
     log.debug(f'Load model: type=ERNIE-Image repo="{repo_id}" offload={shared.opts.diffusers_offload_mode} dtype={devices.dtype} args={load_args} pe={shared.opts.model_ernie_enable_pe}')
 
+    from pipelines.ernie import ERNIE_SPEC
     transformer = generic.load_transformer(
         repo_id,
         cls_name=diffusers.ErnieImageTransformer2DModel,
         load_config=diffusers_load_config,
+        native_spec=ERNIE_SPEC,
     )
     text_encoder = generic.load_text_encoder(
         repo_id,