fix: keep zero-offset glow findings when the surface is unreadable

The browser glow adapter abstained from the whole element when
resolveBackgroundInfo reported an unreadable surface, which also dropped
zero-offset chromatic halo findings that do not depend on the background
at all. It now skips only the gradient hunt past the unreadable layer and
scores the halo tell against a null surface, matching what the static
loop already did. Fixture cases pin both sides: the halo over a url()
image ancestor flags in both engines, and an offset chromatic shadow on
the same unknown surface stays abstained.

Also hardens the currentcolor background substitution with the
parseColorResolved fallback used by the text-color path, and adds fixture
coverage proving tokenized currentcolor surfaces already resolve through
the static cascade (flag when knowable, abstain when the token is
undefined).

Addresses Cursor Bugbot review findings on PR #541.

AI-assisted-by: Claude Code

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

cli/engine/detect-antipatterns-browser.js

@@ -2976,7 +2976,12 @@ function resolveBackgroundInfo(el, win, customPropMap) {
     // verbatim, and without this substitution the layer would read as
     // unparseable and force a needless abstention.
     if ((!bg || bg.a < 0.1) && /^currentcolor$/i.test(String(style.backgroundColor || '').trim())) {
-      bg = parseRgb(style.color) || parseAnyColor(style.color);
+      // The static cascade resolves var() text tokens before checks run, so
+      // style.color is normally already an rgb string here; parseColorResolved
+      // is defense in depth for any future caller that passes a live
+      // customPropMap (it matches the text-color path in checkElementColors
+      // and reduces to parseAnyColor when the map is null or absent).
+      bg = parseRgb(style.color) || parseColorResolved(style.color, customPropMap);
     }
 
     if (bg && bg.a > 0.1) {
@@ -3805,12 +3810,14 @@ function checkElementGlowDOM(el) {
   // Use parent's background — glow radiates outward, so the surrounding context matters
   // If resolveBackground returns null (gradient), try to infer from the gradient colors
   const parentBgInfo = resolveBackgroundInfo(el.parentElement || el);
-  // Unknown surface (an unreadable layer on the way up): abstain. The
-  // gradient hunt below would walk PAST that layer and score the glow
-  // against a background the visitor never sees.
-  if (parentBgInfo.unresolved) return [];
+  // Unknown surface (an unreadable layer on the way up): skip only the
+  // gradient hunt below, which would walk PAST that layer and score the
+  // glow against a background the visitor never sees. checkGlow still runs
+  // with a null surface: the zero-offset chromatic halo tell holds on ANY
+  // background, and the static loop already passes the unresolved walk's
+  // null color straight through (detect-html.mjs uses resolveBackground).
   let parentBg = parentBgInfo.color;
-  if (!parentBg) {
+  if (!parentBg && !parentBgInfo.unresolved) {
     // Gradient background — sample its colors to determine if it's dark
     let cur = el.parentElement;
     while (cur && cur.nodeType === 1) {

cli/engine/rules/checks.mjs

@@ -1742,7 +1742,12 @@ function resolveBackgroundInfo(el, win, customPropMap) {
     // verbatim, and without this substitution the layer would read as
     // unparseable and force a needless abstention.
     if ((!bg || bg.a < 0.1) && /^currentcolor$/i.test(String(style.backgroundColor || '').trim())) {
-      bg = parseRgb(style.color) || parseAnyColor(style.color);
+      // The static cascade resolves var() text tokens before checks run, so
+      // style.color is normally already an rgb string here; parseColorResolved
+      // is defense in depth for any future caller that passes a live
+      // customPropMap (it matches the text-color path in checkElementColors
+      // and reduces to parseAnyColor when the map is null or absent).
+      bg = parseRgb(style.color) || parseColorResolved(style.color, customPropMap);
     }
 
     if (bg && bg.a > 0.1) {
@@ -2571,12 +2576,14 @@ function checkElementGlowDOM(el) {
   // Use parent's background — glow radiates outward, so the surrounding context matters
   // If resolveBackground returns null (gradient), try to infer from the gradient colors
   const parentBgInfo = resolveBackgroundInfo(el.parentElement || el);
-  // Unknown surface (an unreadable layer on the way up): abstain. The
-  // gradient hunt below would walk PAST that layer and score the glow
-  // against a background the visitor never sees.
-  if (parentBgInfo.unresolved) return [];
+  // Unknown surface (an unreadable layer on the way up): skip only the
+  // gradient hunt below, which would walk PAST that layer and score the
+  // glow against a background the visitor never sees. checkGlow still runs
+  // with a null surface: the zero-offset chromatic halo tell holds on ANY
+  // background, and the static loop already passes the unresolved walk's
+  // null color straight through (detect-html.mjs uses resolveBackground).
   let parentBg = parentBgInfo.color;
-  if (!parentBg) {
+  if (!parentBg && !parentBgInfo.unresolved) {
     // Gradient background — sample its colors to determine if it's dark
     let cur = el.parentElement;
     while (cur && cur.nodeType === 1) {