Add offline workflow and coverage tests

scripts/run_coverage.py

@@ -0,0 +1,40 @@
+"""Run pytest under coverage in this environment.
+
+The plain ``coverage run -m pytest`` path reloads NumPy under the current VS Code
+Python startup environment, which breaks pandas/numpy reductions. Import NumPy
+before starting coverage so the measured test run uses one stable NumPy module.
+"""
+
+from __future__ import annotations
+
+import sys
+
+import numpy  # noqa: F401
+import coverage
+import pytest
+
+
+def main(argv: list[str]) -> int:
+    pytest_args = argv or ["tests/", "-v"]
+
+    cov = coverage.Coverage(config_file=True)
+    cov.erase()
+    cov.start()
+    test_status = pytest.main(pytest_args)
+    cov.stop()
+    cov.save()
+
+    if test_status != 0:
+        return int(test_status)
+
+    total = cov.report()
+    print(f"\nCoverage total: {total:.2f}%")
+    fail_under = float(cov.config.fail_under)
+    if total < fail_under:
+        print(f"Coverage failure: total {total:.2f}% is below {fail_under:.2f}%")
+        return 2
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main(sys.argv[1:]))