Test: pin 1D grid-background pass cases in the fixture suite

The unit suite already covered dashed rules; this adds an isolated HTML fixture so the page-level one-finding cap cannot hide a regression.

Prepared with AI assistance (Cursor agent), directed by @abdulwahabone.

Co-authored-by: Cursor <cursoragent@cursor.com>

cli/engine/detect-antipatterns-browser.js

@@ -1955,20 +1955,19 @@ function scanCssTextForGlow(content) {
   return results;
 }
 
-// Decorative grid or line-field backgrounds drawn with hairline
+// Decorative two-axis grid backgrounds drawn with hairline
 // linear-gradient layers tiled by a fixed pixel cell. Shared by the HTML
 // pattern pass and the regex source engine so standalone CSS, component
 // styles, and inline styles receive the same coverage. Both signals must
 // co-occur in one declaration block; unrelated rules must not add up across
-// the file. Returns [{ index, snippet }], capped at one finding per source to
-// match the page-level HTML check's existing behavior.
+// the file. A single hairline is a line, divider, or rail, not a grid, even
+// when tiled by a 2D px cell. Returns [{ index, snippet }], capped at one
+// finding per source to match the page-level HTML check's existing behavior.
 function scanCssTextForGridBackground(content) {
   const hairlineRe = /\b\d{1,3}px\s*,\s*transparent\s+\d{1,3}px/gi;
   const invertedHairlineRe = /transparent\s+calc\(100%\s*-\s*\d{1,3}px\)/gi;
   const sizeDeclPxRe = /background-size\s*:[^;{}"']*\b\d{1,3}px\b/i;
-  const sizeDeclPxPairRe = /background-size\s*:[^;{}"']*\b\d{1,3}px\s+\d{1,3}px/i;
   const shorthandPxAnyRe = /\/\s*\d{1,3}px\b/;
-  const shorthandPxPairRe = /\/\s*\d{1,3}px\s+\d{1,3}px/;
   const bgDeclRe = /\bbackground(?:-image)?\s*:\s*([^;{}"']*)/gi;
   const blockRe = /\{([^{}]*)\}|style\s*=\s*"([^"]*)"|style\s*=\s*'([^']*)'/gi;
   let blk;
@@ -1985,13 +1984,10 @@ function scanCssTextForGridBackground(content) {
     }
     if (hairlineCount === 0) continue;
     const hasPxCell = sizeDeclPxRe.test(block) || shorthandPxAnyRe.test(bgJoined);
-    const hasPxPairCell = sizeDeclPxPairRe.test(block) || shorthandPxPairRe.test(bgJoined);
-    if ((hairlineCount >= 2 && hasPxCell) || hasPxPairCell) {
+    if (hairlineCount >= 2 && hasPxCell) {
       return [{
         index: blk.index,
-        snippet: hairlineCount >= 2
-          ? 'two-axis grid-line gradient background'
-          : 'px-tiled hairline line-field background',
+        snippet: 'two-axis grid-line gradient background',
       }];
     }
   }

cli/engine/rules/checks.mjs

@@ -721,20 +721,19 @@ function scanCssTextForGlow(content) {
   return results;
 }
 
-// Decorative grid or line-field backgrounds drawn with hairline
+// Decorative two-axis grid backgrounds drawn with hairline
 // linear-gradient layers tiled by a fixed pixel cell. Shared by the HTML
 // pattern pass and the regex source engine so standalone CSS, component
 // styles, and inline styles receive the same coverage. Both signals must
 // co-occur in one declaration block; unrelated rules must not add up across
-// the file. Returns [{ index, snippet }], capped at one finding per source to
-// match the page-level HTML check's existing behavior.
+// the file. A single hairline is a line, divider, or rail, not a grid, even
+// when tiled by a 2D px cell. Returns [{ index, snippet }], capped at one
+// finding per source to match the page-level HTML check's existing behavior.
 function scanCssTextForGridBackground(content) {
   const hairlineRe = /\b\d{1,3}px\s*,\s*transparent\s+\d{1,3}px/gi;
   const invertedHairlineRe = /transparent\s+calc\(100%\s*-\s*\d{1,3}px\)/gi;
   const sizeDeclPxRe = /background-size\s*:[^;{}"']*\b\d{1,3}px\b/i;
-  const sizeDeclPxPairRe = /background-size\s*:[^;{}"']*\b\d{1,3}px\s+\d{1,3}px/i;
   const shorthandPxAnyRe = /\/\s*\d{1,3}px\b/;
-  const shorthandPxPairRe = /\/\s*\d{1,3}px\s+\d{1,3}px/;
   const bgDeclRe = /\bbackground(?:-image)?\s*:\s*([^;{}"']*)/gi;
   const blockRe = /\{([^{}]*)\}|style\s*=\s*"([^"]*)"|style\s*=\s*'([^']*)'/gi;
   let blk;
@@ -751,13 +750,10 @@ function scanCssTextForGridBackground(content) {
     }
     if (hairlineCount === 0) continue;
     const hasPxCell = sizeDeclPxRe.test(block) || shorthandPxAnyRe.test(bgJoined);
-    const hasPxPairCell = sizeDeclPxPairRe.test(block) || shorthandPxPairRe.test(bgJoined);
-    if ((hairlineCount >= 2 && hasPxCell) || hasPxPairCell) {
+    if (hairlineCount >= 2 && hasPxCell) {
       return [{
         index: blk.index,
-        snippet: hairlineCount >= 2
-          ? 'two-axis grid-line gradient background'
-          : 'px-tiled hairline line-field background',
+        snippet: 'two-axis grid-line gradient background',
       }];
     }
   }

tests/detect-antipatterns-fixtures.test.mjs

@@ -1278,6 +1278,14 @@ describe('detectHtml — generated-UI tells', () => {
     }
   });
 
+  it('codex-grid-background: 1D dashed rules and px-pair line-fields stay legal', async () => {
+    const f = await detectHtml(path.join(FIXTURES, 'codex-grid-1d-pass.html'));
+    assert.equal(
+      f.filter(r => r.antipattern === 'codex-grid-background').length, 0,
+      `1D tiled hairlines must not flag, got: ${f.filter(r => r.antipattern === 'codex-grid-background').map(r => r.snippet).join('; ')}`,
+    );
+  });
+
   it('gemini-tells: both flag cases surface by default and pass cases stay legal', async () => {
     const findings = await detectHtml(path.join(FIXTURES, 'gemini-tells.html'));
     // Two flag cases: a CSS img:hover{transform} rule and a Tailwind hover:scale on <img>.

tests/detect-antipatterns.test.js

@@ -1806,11 +1806,9 @@ describe('codex-grid-background variants', () => {
     expect(grids(css)).toHaveLength(1);
   });
 
-  test('flags single-axis hairline tiled by a px pair cell', () => {
+  test('keeps single-axis hairline tiled by a px pair cell legal', () => {
     const css = `body { background: linear-gradient(90deg, rgba(23,25,24,.035) 1px, transparent 1px) 0 0 / 40px 40px, #f4f1ea; }`;
-    const f = grids(css);
-    expect(f).toHaveLength(1);
-    expect(f[0].snippet).toContain('line-field');
+    expect(grids(css)).toHaveLength(0);
   });
 
   test('keeps percent-tiled single hairlines (data-viz track rules) legal', () => {
@@ -1818,6 +1816,36 @@ describe('codex-grid-background variants', () => {
     expect(grids(css)).toHaveLength(0);
   });
 
+  test('keeps 1D dashed dot rules legal', () => {
+    const css = `.dot-rule {
+      height: 5px;
+      background-image: linear-gradient(90deg, rgba(255,255,255,.75) 5px, transparent 5px);
+      background-size: 10px 5px;
+      background-repeat: repeat-x;
+    }`;
+    expect(grids(css)).toHaveLength(0);
+  });
+
+  test('keeps 1D progress rails with dash-period px pair tiles legal', () => {
+    const css = `.progress-rail {
+      background-image: linear-gradient(90deg, #eee 1px, transparent 1px);
+      background-size: 8px 4px;
+      background-repeat: repeat-x;
+    }`;
+    expect(grids(css)).toHaveLength(0);
+  });
+
+  test('regex source engine keeps 1D dot rules legal', () => {
+    const css = `.dot-rule {
+      height: 5px;
+      background-image: linear-gradient(90deg, rgba(255,255,255,.75) 5px, transparent 5px);
+      background-size: 10px 5px;
+      background-repeat: repeat-x;
+    }`;
+    const findings = detectText(css, 'dot-rule.css');
+    expect(findings.filter(f => f.antipattern === 'codex-grid-background')).toHaveLength(0);
+  });
+
   test('classic two-axis background-size form still flags', () => {
     const css = `.hero { background-image:
       linear-gradient(#eee 1px, transparent 1px),

tests/fixtures/antipatterns/codex-grid-1d-pass.html

@@ -0,0 +1,21 @@
+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8" />
+  <title>codex-grid-background 1D pass cases</title>
+  <style>
+    body { font-family: system-ui, sans-serif; margin: 0; color: #1a1a1a; background: #fff; }
+    .dot-rule { height: 5px; background-image: linear-gradient(90deg, rgba(255,255,255,.75) 5px, transparent 5px); background-size: 10px 5px; background-repeat: repeat-x; }
+    .progress-rail { height: 4px; background-image: linear-gradient(90deg, #eee 1px, transparent 1px); background-size: 8px 4px; background-repeat: repeat-x; }
+    .line-field { height: 80px; background: linear-gradient(90deg, rgba(23,25,24,.035) 1px, transparent 1px) 0 0 / 40px 40px, #f4f1ea; }
+  </style>
+</head>
+<body>
+  <h2>Dotted horizontal rule</h2>
+  <div class="dot-rule"></div>
+  <h2>Progress rail</h2>
+  <div class="progress-rail"></div>
+  <h2>Single-axis px-pair line field</h2>
+  <div class="line-field"></div>
+</body>
+</html>