Fix _meta parameter passing in TextResourceContents and BlobResourceContents

Use the field name 'meta' instead of the alias '_meta' when constructing
Pydantic model instances. The alias is only used for JSON serialization.

This fixes a bug where passing **{'_meta': meta} would cause Pydantic
validation errors since '_meta' is an alias, not a field name.

Author: claude

src/mcp/server/lowlevel/server.py

@@ -325,7 +325,7 @@ def create_content(data: str | bytes, mime_type: str | None, meta: dict[str, Any
                                 uri=req.params.uri,
                                 text=data,
                                 mimeType=mime_type or "text/plain",
-                                **{"_meta": meta} if meta is not None else {},
+                                meta=meta,
                             )
                         case bytes() as data:  # pragma: no cover
                             import base64
@@ -334,7 +334,7 @@ def create_content(data: str | bytes, mime_type: str | None, meta: dict[str, Any
                                 uri=req.params.uri,
                                 blob=base64.b64encode(data).decode(),
                                 mimeType=mime_type or "application/octet-stream",
-                                **{"_meta": meta} if meta is not None else {},
+                                meta=meta,
                             )
 
                 match result: