fix: games tools write whole files, name options

The games importers wrote through fixed .part names, the new options had
no help text, and romfolders stopped on the first setup the offline cache
lacked. RetroArch's rom folder map is regenerated from its source spec
(path null, as the schema says). The installer's Python 3.8 job imports
the games tests without pyyaml, so the region rules load lazily.

scripts/scraper/game_dat_importer.py

@@ -26,7 +26,6 @@ import gzip
 import io
 import json
 import re
-import shutil
 import sys
 import urllib.request
 import zipfile
@@ -39,6 +38,7 @@ _SCRIPTS_DIR = str(Path(__file__).resolve().parents[1])
 if _SCRIPTS_DIR not in sys.path:
     sys.path.insert(0, _SCRIPTS_DIR)
 
+from artifacts import copy_stream_atomic, write_text_atomic  # noqa: E402
 from common import parse_untrusted_xml  # noqa: E402
 from region import REGIONS, WORLD  # noqa: E402
 from region_audit import NOINTRO  # noqa: E402
@@ -279,9 +279,7 @@ def write_if_changed(path: Path, text: str) -> bool:
     if path.is_file() and path.read_text(encoding="utf-8") == text:
         return False
     path.parent.mkdir(parents=True, exist_ok=True)
-    scratch = path.with_suffix(path.suffix + ".part")
-    scratch.write_text(text, encoding="utf-8")
-    scratch.replace(path)
+    write_text_atomic(str(path), text)
     return True
 
 
@@ -296,15 +294,9 @@ def _download(url: str, destination: Path, headers: dict[str, str] | None = None
     """Stream url to destination and return the response headers kept."""
     destination.parent.mkdir(parents=True, exist_ok=True)
     request = urllib.request.Request(url, headers={"User-Agent": "retrobios", **(headers or {})})
-    scratch = destination.with_suffix(destination.suffix + ".part")
-    try:
-        with urllib.request.urlopen(request, timeout=300) as response, scratch.open("wb") as out:
-            shutil.copyfileobj(response, out)
-            kept = {"content_disposition": response.headers.get("Content-Disposition", "")}
-        scratch.replace(destination)
-    finally:
-        scratch.unlink(missing_ok=True)
-    return kept
+    with urllib.request.urlopen(request, timeout=300) as response:
+        copy_stream_atomic(response, str(destination))
+        return {"content_disposition": response.headers.get("Content-Disposition", "")}
 
 
 def _today() -> str:
@@ -340,7 +332,7 @@ def fetch_nointro(cache_dir: Path, offline: bool, refresh: bool) -> tuple[Path,
         "asset_size": asset["size"],
         "fetched": _today(),
     }
-    meta_path.write_text(json.dumps(meta, indent=1) + "\n", encoding="utf-8")
+    write_text_atomic(str(meta_path), json.dumps(meta, indent=1) + "\n")
     return pack, meta
 
 
@@ -359,7 +351,7 @@ def fetch_redump(code: str, cache_dir: Path, offline: bool, refresh: bool) -> tu
     if not match:
         raise RuntimeError(f"{url} answered without a datfile name")
     meta = {"file": match["file"], "url": url, "fetched": _today()}
-    meta_path.write_text(json.dumps(meta, indent=1) + "\n", encoding="utf-8")
+    write_text_atomic(str(meta_path), json.dumps(meta, indent=1) + "\n")
     return pack, meta
 
 
@@ -459,8 +451,10 @@ def main() -> int:
     parser.add_argument("--refresh", action="store_true", help="ask the servers again")
     parser.add_argument("--floor", action="store_true",
                         help="fail when a system holds fewer games than its stored floor")
-    parser.add_argument("--cache-dir", type=Path, default=CACHE_DIR)
-    parser.add_argument("--output-dir", type=Path, default=OUTPUT_DIR)
+    parser.add_argument("--cache-dir", type=Path, default=CACHE_DIR,
+                        help=f"downloaded packs (default {CACHE_DIR})")
+    parser.add_argument("--output-dir", type=Path, default=OUTPUT_DIR,
+                        help=f"where the catalogs are written (default {OUTPUT_DIR})")
     parser.add_argument("--dry-run", action="store_true", help="print coverage, write nothing")
     args = parser.parse_args()