fix: name the python floor in generate_pack

scripts/generate_pack.py

@@ -12,6 +12,13 @@ and 3-tier storage (embedded/external/user_provided).
 
 from __future__ import annotations
 
+import sys
+
+# The README's first command. Under 3.8 it stopped on a SyntaxError that read
+# like a damaged file. The build needs 3.9, as pipeline.py says.
+if sys.version_info < (3, 9):
+    sys.exit(f"generate_pack.py needs Python 3.9 or newer, this is {sys.version.split()[0]}")
+
 from collections.abc import Callable, Iterable, Iterator
 
 from artifacts import _build_timestamp, set_plain_mode
@@ -23,7 +30,6 @@ import json
 import os
 import re
 import shutil
-import sys
 import tempfile
 import zipfile
 from pathlib import Path
@@ -5079,10 +5085,8 @@ def inject_manifest(zip_path: str, manifest: dict) -> None:
             with zipfile.ZipFile(scratch, "a", zipfile.ZIP_DEFLATED) as zf:
                 _write_generated_member(zf, "manifest.json", manifest_json)
         else:
-            with (
-                zipfile.ZipFile(zip_path, "r") as src,
-                zipfile.ZipFile(scratch, "w", zipfile.ZIP_DEFLATED) as dst,
-            ):
+            with zipfile.ZipFile(zip_path, "r") as src, \
+                    zipfile.ZipFile(scratch, "w", zipfile.ZIP_DEFLATED) as dst:
                 for item in src.infolist():
                     if item.filename == "manifest.json":
                         continue

scripts/pipeline.py

@@ -57,8 +57,8 @@ import tempfile
 import time
 from pathlib import Path
 
-# generate_pack's parenthesized context managers do not compile before
-# CPython 3.9, which builds the same database, manifests and packs as 3.12.
+# The build scripts need CPython 3.9, which builds the same database,
+# manifests and packs as 3.12.
 # On an older interpreter the run got through the first steps and failed in
 # the packs, so it stops before step 0. A test compiles every script under
 # this floor.

tests/test_audit_regressions.py

@@ -118,6 +118,24 @@ class ReadmeRegressions(unittest.TestCase):
         self.assertEqual(proc.returncode, 1)
         self.assertIn("needs Python 3.9", proc.stderr)
 
+    def test_the_readme_build_command_names_the_floor(self):
+        """The README's first command is generate_pack.py. Under 3.8 it
+        stopped on a raw SyntaxError at a parenthesized `with`."""
+        import shutil  # noqa: PLC0415
+
+        python38 = shutil.which("python3.8")
+        if python38 is None:
+            if os.environ.get("CI"):
+                self.fail("CI must provide python3.8")
+            self.skipTest("no python3.8 on PATH")
+        proc = subprocess.run(
+            [python38, "-I", "scripts/generate_pack.py", "--help"],
+            cwd=ROOT, capture_output=True, text=True, timeout=60, check=False,
+        )
+        self.assertEqual(proc.returncode, 1)
+        self.assertNotIn("SyntaxError", proc.stderr)
+        self.assertIn("generate_pack.py needs Python 3.9", proc.stderr)
+
     def test_the_floor_interpreter_imports_every_script(self):
         """Every module under scripts/ is loaded by a real interpreter of the
         floor version, as the installer's 3.8 floor is proven by running it.