fix: stabilize runtime follow-up regressions

tests/plugins/uce_demo_smoke.py

@@ -0,0 +1,37 @@
+from pathlib import Path
+
+# The demo pages are not regression suites, but every one of them must at
+# least compile and render: a preprocessor or runtime change that breaks a
+# demo page (e.g. literal text that looks like an entry point) should fail CI.
+
+ERROR_MARKERS = [
+	"uce compile error",
+	"fatal signal during request",
+	"uncaught exception during request",
+]
+
+
+def _repo_root():
+	return Path(__file__).resolve().parents[2]
+
+
+def _make_demo_case(page_path):
+	def run(context):
+		response = context.expect_status(page_path, 200)
+		body_lower = response.text.lower()
+		for marker in ERROR_MARKERS:
+			if marker in body_lower:
+				raise Exception("response body contained error marker %r for %s" % (marker, page_path))
+		return "HTTP 200 without error markers for %s" % page_path
+
+	return run
+
+
+def register(registry):
+	demo_dir = _repo_root() / "site" / "demo"
+	for path in sorted(demo_dir.glob("*.uce")):
+		registry.case(
+			"demo page " + path.name,
+			_make_demo_case("/demo/" + path.name),
+			tags=["http", "smoke", "uce", "demo", "public"],
+		)