Fix: stop flagging 1D dashed rules as grid backgrounds (#615)

codex-grid-background treated any 2D px background-size as a grid, so a single hairline tiled as a dash or rail false-positived. A finding now requires two hairline gradients plus a px tile.

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
+// the file. A single hairline is a line, divider, or rail, not a grid, even
-// match the page-level HTML check's existing behavior.
+// 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) {
-    if ((hairlineCount >= 2 && hasPxCell) || hasPxPairCell) {
       return [{
         index: blk.index,
-        snippet: hairlineCount >= 2
+        snippet: 'two-axis grid-line gradient background',
-          ? 'two-axis grid-line gradient background'
-          : 'px-tiled hairline line-field 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
+// the file. A single hairline is a line, divider, or rail, not a grid, even
-// match the page-level HTML check's existing behavior.
+// 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) {
-    if ((hairlineCount >= 2 && hasPxCell) || hasPxPairCell) {
       return [{
         index: blk.index,
-        snippet: hairlineCount >= 2
+        snippet: 'two-axis grid-line gradient background',
-          ? 'two-axis grid-line gradient background'
-          : 'px-tiled hairline line-field background',
       }];
     }
   }

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(grids(css)).toHaveLength(0);
-    expect(f).toHaveLength(1);
-    expect(f[0].snippet).toContain('line-field');
   });
 
   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),