fix: state and check the 3.12 build floor

scripts/generate_readme.py

@@ -581,7 +581,7 @@ def generate_readme(db: dict, platforms_dir: str) -> str:
             "python scripts/verify.py --platform retroarch --verbose  # emulator ground truth",
             "```",
             "",
-            "Only dependency: Python 3 + `pyyaml`.",
+            "Requires Python 3.12 and `pyyaml`. The one-line installer alone runs on Python 3.8.",
             "",
             "## Documentation site",
             "",

scripts/pipeline.py

@@ -33,6 +33,12 @@ import sys
 import time
 from pathlib import Path
 
+# The build scripts use syntax CPython 3.12 introduced (generate_readme's
+# f-strings, generate_pack's parenthesized context managers). On an older
+# interpreter the run got through the packs and failed hours in, at step 7.
+if sys.version_info < (3, 12):
+    sys.exit(f"pipeline.py needs Python 3.12 or newer, this is {sys.version.split()[0]}")
+
 sys.path.insert(0, str(Path(__file__).parent))
 from common import ArtifactLockBusy, artifact_lock, hold_artifact_lock