python: accept free-form custom extension vendors

converters/README.md

@@ -281,7 +281,7 @@ Given the [TPC-DS example](../examples/tpcds_semantic_model.yaml) included in th
 
 To add support for a new vendor:
 
-1. Add the vendor to the `vendors` enum in the [core specification](../core-spec/spec.md) if not already present.
+1. Use a stable `vendor_name` string in each custom extension emitted by the converter.
 2. Define the custom extension schema for the vendor (what vendor-specific metadata fields are supported in the `data` JSON).
 3. Implement the export converter (Ossie → Vendor).
 4. Implement the import converter (Vendor → Ossie).

python/src/ossie/models.py

@@ -35,7 +35,7 @@ class OSIDialect(str, Enum):
 
 
 class OSIVendor(str, Enum):
-    """Vendors with supported custom extensions."""
+    """Well-known vendor names for custom extensions."""
 
     COMMON = "COMMON"
     SNOWFLAKE = "SNOWFLAKE"
@@ -63,7 +63,7 @@ class OSICustomExtension(BaseModel):
 
     model_config = ConfigDict(frozen=True)
 
-    vendor_name: OSIVendor
+    vendor_name: str
     data: str