diff --git a/.gitattributes b/.gitattributes
index 18454b2..91648a9 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,5 +1,5 @@
-# The artwork under docs/art/ is generated, and a gate compares the committed
-# bytes to a fresh render. Normalizing line endings per platform would make that
-# comparison depend on who checked the repository out.
+# The art under docs/art/ is generated. render_repo_art.py writes LF on every
+# platform, so pin the checkout to LF as well and each file's byte count and
+# SHA-256 stay the same whoever cloned the repository.
 docs/art/*.svg text eol=lf
 docs/art/*.json text eol=lf
diff --git a/tests/test_repo_art.py b/tests/test_repo_art.py
index 2b1e63f..d8e0360 100644
--- a/tests/test_repo_art.py
+++ b/tests/test_repo_art.py
@@ -25,6 +25,7 @@
     "art.every_illustration_is_shown",
     "art.tagline_stays_inside_its_rule",
     "art.outcome_fits_its_box",
+    "art.the_gate_can_fail",
 )
 
 DRAWINGS = (
diff --git a/tools/check_repo_art.py b/tools/check_repo_art.py
index 3d70deb..1cd4559 100644
--- a/tools/check_repo_art.py
+++ b/tools/check_repo_art.py
@@ -130,8 +130,12 @@ def check_note_survives_the_wrapper(_unused: list[Path]) -> list[str]:
     """Card notes wrap to three lines and the wrapper drops the rest, so an
     edited sentence can lose its ending in the drawing while reading fine
     in the spec."""
+    return _notes_the_wrapper_cuts(_loaded())
+
+
+def _notes_the_wrapper_cuts(specs: list[dict]) -> list[str]:
     bad = []
-    for spec in _loaded():
+    for spec in specs:
         for flow in spec.get("flows", []):
             for stage in flow["stages"]:
                 drawn = " ".join(FLOW._wrap(stage["note"]))
@@ -167,8 +171,12 @@ def check_every_illustration_is_shown(_unused: list[Path]) -> list[str]:
 def check_tagline_stays_inside_its_rule(_unused: list[Path]) -> list[str]:
     """The tagline is one unwrapped line under a rule that ends at x=700. Past
     that it runs on toward the aperture and nothing about the render fails."""
+    return _taglines_that_overrun(_loaded())
+
+
+def _taglines_that_overrun(specs: list[dict]) -> list[str]:
     bad = []
-    for spec in _loaded():
+    for spec in specs:
         tagline = spec["header"]["tagline"]
         if len(tagline) > TAGLINE_BUDGET:
             bad.append(f"{len(tagline)} characters runs past the rule: {tagline!r}")
@@ -185,8 +193,12 @@ def _outcome_budgets(count: int) -> tuple[int, int]:
 def check_outcome_fits_its_box(_unused: list[Path]) -> list[str]:
     """An outcome box is one unwrapped label over one unwrapped note, and
     neither is clipped, so an over-long note runs into the next box."""
+    return _outcomes_that_overflow(_loaded())
+
+
+def _outcomes_that_overflow(specs: list[dict]) -> list[str]:
     bad = []
-    for spec in _loaded():
+    for spec in specs:
         for flow in spec.get("flows", []):
             label_budget, note_budget = _outcome_budgets(len(flow["outcomes"]))
             for item in flow["outcomes"]:
@@ -198,6 +210,28 @@ def check_outcome_fits_its_box(_unused: list[Path]) -> list[str]:
     return bad
 
 
+# A spec built to break all three geometry budgets at once. Every other check
+# here reports clean, which says it ran and not that it works.
+CONTROL = [{
+    "header": {"tagline": "x" * (TAGLINE_BUDGET + 1)},
+    "flows": [{
+        "stages": [{"title": "CARD", "note": "word " * 60}],
+        "outcomes": [{"label": "OK", "note": "x" * 200},
+                     {"label": "y" * 200, "note": "short"}],
+    }],
+}]
+
+
+def check_the_gate_can_fail(_unused: list[Path]) -> list[str]:
+    """Feed the three geometry checks input they have to reject."""
+    return [f"the gate missed {what}" for caught, what in (
+        (len(_notes_the_wrapper_cuts(CONTROL)) == 1, "a truncated note"),
+        (len(_taglines_that_overrun(CONTROL)) == 1, "a tagline past its rule"),
+        (len(_outcomes_that_overflow(CONTROL)) == 2,
+         "an over-wide label and an over-long note"),
+    ) if not caught]
+
+
 CHECKS = [
     ("spec.present", check_spec_present),
     ("art.matches_spec", check_artwork_matches_spec),
@@ -211,6 +245,7 @@ def check_outcome_fits_its_box(_unused: list[Path]) -> list[str]:
     ("art.every_illustration_is_shown", check_every_illustration_is_shown),
     ("art.tagline_stays_inside_its_rule", check_tagline_stays_inside_its_rule),
     ("art.outcome_fits_its_box", check_outcome_fits_its_box),
+    ("art.the_gate_can_fail", check_the_gate_can_fail),
 ]