feat: improve multipart file extension detection

Refactor _get_multipart_ext method to use known suffixes list for more reliable file extension detection. The new implementation handles compound file extensions like '.metadata.json.bak' and '.safetensors' by checking against predefined suffixes in order of length. Falls back to existing logic for unknown file types. This improves accuracy when working with model files that have complex naming conventions.

py/services/model_lifecycle_service.py

@@ -236,10 +236,20 @@ class ModelLifecycleService:
     def _get_multipart_ext(filename: str) -> str:
         """Return the extension for files with compound suffixes."""
 
-        parts = filename.split(".")
-        if len(parts) == 3:
-            return "." + ".".join(parts[-2:])
-        if len(parts) >= 4:
-            return "." + ".".join(parts[-3:])
-        return os.path.splitext(filename)[1]
+        known_suffixes = [
+            ".metadata.json.bak",
+            ".metadata.json",
+            ".safetensors",
+            *PREVIEW_EXTENSIONS,
+        ]
 
+        for suffix in sorted(known_suffixes, key=len, reverse=True):
+            if filename.endswith(suffix):
+                return suffix
+
+        basename = os.path.basename(filename)
+        dot_index = basename.find(".")
+        if dot_index != -1:
+            return basename[dot_index:]
+
+        return os.path.splitext(basename)[1]