ci: cover the entry points in the runtime contract

.github/workflows/python_runtime_contract.yml

@@ -12,6 +12,10 @@ on:
       # change parses on the oldest supported Python. Lint runs on one, newer
       # version and cannot see this class of break.
       - 'scripts/**'
+      # The entry points are covered by the same suite and are equally able to
+      # break on an older Python
+      - 'vleapp.py'
+      - 'vleappGUI.py'
 
 jobs:
   runtime-contract:

admin/test/scripts/test_entry_points.py

@@ -0,0 +1,49 @@
+"""The command line and GUI entry points must load on every supported Python.
+
+The artifact import test covers scripts/, but the entry points themselves sat
+outside any version-matrixed check, so a change to either could break on the
+oldest supported Python and only surface when a user ran it.
+
+The two are checked differently on purpose. vleapp.py guards its startup with
+'if __name__', so it can be imported outright, which catches import-time errors
+as well as syntax. vleappGUI.py builds its window at module level, so importing
+it would need a display that CI does not have; compiling it still catches the
+syntax-level breakage this is chiefly guarding against, such as an f-string
+that only parses on Python 3.12 (PEP 701).
+"""
+import importlib.util
+import pathlib
+import sys
+import unittest
+
+REPO_ROOT = pathlib.Path(__file__).resolve().parents[3]
+if str(REPO_ROOT) not in sys.path:
+    sys.path.insert(0, str(REPO_ROOT))
+
+CLI_ENTRY_POINT = REPO_ROOT / 'vleapp.py'
+GUI_ENTRY_POINT = REPO_ROOT / 'vleappGUI.py'
+
+
+class TestEntryPoints(unittest.TestCase):
+
+    def test_cli_entry_point_imports(self):
+        """vleapp.py must import, and expose main()."""
+        self.assertTrue(CLI_ENTRY_POINT.is_file(), f'{CLI_ENTRY_POINT} is missing')
+        spec = importlib.util.spec_from_file_location('entry_point_check', CLI_ENTRY_POINT)
+        module = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(module)
+        self.assertTrue(hasattr(module, 'main'), 'vleapp.py no longer exposes main()')
+
+    def test_gui_entry_point_compiles(self):
+        """vleappGUI.py must at least compile; it cannot be imported without a display."""
+        self.assertTrue(GUI_ENTRY_POINT.is_file(), f'{GUI_ENTRY_POINT} is missing')
+        source = GUI_ENTRY_POINT.read_text(encoding='utf-8', errors='replace')
+        try:
+            compile(source, str(GUI_ENTRY_POINT), 'exec')
+        except SyntaxError as error:
+            self.fail(f'vleappGUI.py does not compile on this Python: '
+                      f'line {error.lineno}: {error.msg}')
+
+
+if __name__ == '__main__':
+    unittest.main()