fix(markdown): set the correct discriminator in md backend options (#2501)

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>

docling/backend/md_backend.py

@@ -536,6 +536,11 @@ class MarkdownDocumentBackend(DeclarativeDocumentBackend):
     def supported_formats(cls) -> set[InputFormat]:
         return {InputFormat.MD}
 
+    @classmethod
+    @override
+    def get_default_options(cls) -> MarkdownBackendOptions:
+        return MarkdownBackendOptions()
+
     def convert(self) -> DoclingDocument:
         _log.debug("converting Markdown...")
 
@@ -587,17 +592,24 @@ class MarkdownDocumentBackend(DeclarativeDocumentBackend):
                 self._html_blocks = 0
                 # delegate to HTML backend
                 stream = BytesIO(bytes(html_str, encoding="utf-8"))
+                md_options = cast(MarkdownBackendOptions, self.options)
+                html_options = HTMLBackendOptions(
+                    enable_local_fetch=md_options.enable_local_fetch,
+                    enable_remote_fetch=md_options.enable_remote_fetch,
+                    fetch_images=md_options.fetch_images,
+                    source_uri=md_options.source_uri,
+                )
                 in_doc = InputDocument(
                     path_or_stream=stream,
                     format=InputFormat.HTML,
                     backend=html_backend_cls,
                     filename=self.file.name,
-                    backend_options=self.options,
+                    backend_options=html_options,
                 )
                 html_backend_obj = html_backend_cls(
                     in_doc=in_doc,
                     path_or_stream=stream,
-                    options=cast(HTMLBackendOptions, self.options),
+                    options=html_options,
                 )
                 doc = html_backend_obj.convert()
         else:

docling/datamodel/backend_options.py

@@ -44,10 +44,27 @@ class HTMLBackendOptions(BaseBackendOptions):
     )
 
 
-class MarkdownBackendOptions(HTMLBackendOptions):
+class MarkdownBackendOptions(BaseBackendOptions):
     """Options specific to the Markdown backend."""
 
+    kind: Literal["md"] = Field("md", exclude=True, repr=False)
+    fetch_images: bool = Field(
+        False,
+        description=(
+            "Whether the backend should access remote or local resources to parse "
+            "images in the markdown document."
+        ),
+    )
+    source_uri: Optional[Union[AnyUrl, PurePath]] = Field(
+        None,
+        description=(
+            "The URI that originates the markdown document. If provided, the backend "
+            "will use it to resolve relative paths in the markdown document."
+        ),
+    )
+
 
 BackendOptions = Annotated[
-    Union[DeclarativeBackendOptions, HTMLBackendOptions], Field(discriminator="kind")
+    Union[DeclarativeBackendOptions, HTMLBackendOptions, MarkdownBackendOptions],
+    Field(discriminator="kind"),
 ]