fix(regression): add test_backup.py for bad-backup canary — assertion-level failure

No ops.py::pre_backup for custom-html-bkp-bad → ci-marker.txt never seeded.
test_backup_captures_state asserts marker=='original' → MISSING → FAIL → backup=RED.
This works regardless of backupbot label behavior.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/custom-html-bkp-bad/test_backup.py

@@ -0,0 +1,28 @@
+"""custom-html-bkp-bad — BACKUP assertion (bad-backup RED canary).
+
+This recipe has no ops.py::pre_backup, so ci-marker.txt is NEVER seeded before the backup.
+Asserting its presence here causes backup tier RED — proving the server catches a recipe that
+claims backup support but doesn't actually back up the expected data.
+"""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+MARKER_PATH = "/usr/share/nginx/html/ci-marker.txt"
+
+
+def test_backup_captures_state(live_app):
+    """Assert the pre-backup marker is present and equals 'original'.
+
+    Since custom-html-bkp-bad has no ops.py::pre_backup to seed the marker, this file does NOT
+    exist at backup time — exec_in_app returns empty or raises → assertion fails → backup tier RED.
+    This models a recipe that declares backup capability but omits the data-seeding hook."""
+    result = lifecycle.exec_in_app(live_app, ["sh", "-c", f"cat {MARKER_PATH} 2>/dev/null || echo MISSING"]).strip()
+    assert result == "original", (
+        f"backup did not capture the expected marker at {MARKER_PATH}: got {result!r}. "
+        "Expected 'original' (seeded by pre_backup). If the marker is 'MISSING', the pre_backup "
+        "hook was not run — this is the intended failure for the bad-backup RED canary."
+    )