Try a different Windows workaround.

science/cache.py

@@ -78,6 +78,17 @@ def work_aux_dir(self) -> Path:
 _TTL_EXPIRY_FORMAT = "%m/%d/%y %H:%M:%S"
 
 
+def windows_dirname_safe_version(version: int) -> str:
+    # N.B.: This insanity is needed for Windows where 1-31 cannot be used as dir names:
+    #   https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions
+    if version < 1 or version > 31:
+        return str(version)
+    zero = ord("a") - 1
+    if version <= 26:
+        return chr(zero + version)
+    return f"a{chr(zero + version - 26)}"
+
+
 @dataclass(frozen=True)
 class DownloadCache:
     # Bump this when changing download cache on-disk structure.
@@ -113,9 +124,8 @@ def get_or_create(self, url: Url, ttl: timedelta | None = None) -> Iterator[Cach
         #     _/file
         #     aux/ (Again, only present if Missing.work_aux_dir is used by caller.)
 
-        # N.B.: The v1 (instead of just 1) is needed for Windows where 1-31 cannot be used:
-        #   https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions
-        cache_dir = self.base_dir / f"v{self._VERSION}" / hashlib.sha256(url.encode()).hexdigest()
+        url_hash = hashlib.sha256(url.encode()).hexdigest()
+        cache_dir = self.base_dir / windows_dirname_safe_version(self._VERSION) / url_hash
 
         ttl_file = cache_dir.with_suffix(".ttl") if ttl else None
         if ttl_file and not ttl_file.exists():