Flag inset stripes written with the two-length box-shadow form

box-shadow takes <length>{2,4}: only the two offsets are required, so
`inset 4px 0 red` is valid and paints the same single-edge stripe as
`inset 4px 0 0 red`. The scan demanded a third length, so the short form was
silently missed.

Blur and spread now default to 0 when omitted, which is exactly the stripe shape
the rule looks for. The neutral-color and blur/spread exclusions still hold:
`inset 4px 0 #000` and `inset 4px 0 5px var(--brand-accent)` both pass. Fixture
covers both orders of the short form plus those two exclusions, and fails against
the previous regex.

Third false negative found in this rule (after trailing `inset` and literal
neutral colors), all from the same cause: the scan was written against one
spelling of the syntax rather than the grammar.

Prepared with AI assistance under maintainer direction.

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

tests/detect-antipatterns-fixtures.test.mjs

@@ -33,6 +33,9 @@ describe('detectText - Astro structural CSS fixtures', () => {
     'Trailing Inset Edge',
     'Trailing Inset Token Edge',
     'Inset Named Token Edge',
+    // Only the two offsets are required; blur/spread default to 0.
+    'Two Length Edge',
+    'Two Length Trailing Inset Edge',
   ];
   const SHOULD_PASS = [
     'Neutral Shadow Token',
@@ -56,6 +59,9 @@ describe('detectText - Astro structural CSS fixtures', () => {
     'Commented Out Edge',
     // Trailing `inset` still respects the neutral-color exemption.
     'Trailing Inset Neutral Edge',
+    // The short form still respects the neutral and blur exclusions.
+    'Two Length Neutral Edge',
+    'Two Length Blurred Edge',
   ];
 
   it('Astro style blocks flag unresolved chromatic inset stripes only', () => {

tests/fixtures/antipatterns/astro-inset-shadow-stripe.astro

@@ -17,6 +17,8 @@ const title = 'Astro inset shadow stripe regression';
     <article data-case="Trailing Inset Edge"><h3>Trailing Inset Edge</h3></article>
     <article data-case="Trailing Inset Token Edge"><h3>Trailing Inset Token Edge</h3></article>
     <article data-case="Inset Named Token Edge"><h3>Inset Named Token Edge</h3></article>
+    <article data-case="Two Length Edge"><h3>Two Length Edge</h3></article>
+    <article data-case="Two Length Trailing Inset Edge"><h3>Two Length Trailing Inset Edge</h3></article>
   </section>
   <section aria-labelledby="should-pass">
     <h2 id="should-pass">Should pass</h2>
@@ -35,6 +37,8 @@ const title = 'Astro inset shadow stripe regression';
     <article data-case="Shorthand Neutral Hex Edge"><h3>Shorthand Neutral Hex Edge</h3></article>
     <article data-case="Commented Out Edge"><h3>Commented Out Edge</h3></article>
     <article data-case="Trailing Inset Neutral Edge"><h3>Trailing Inset Neutral Edge</h3></article>
+    <article data-case="Two Length Neutral Edge"><h3>Two Length Neutral Edge</h3></article>
+    <article data-case="Two Length Blurred Edge"><h3>Two Length Blurred Edge</h3></article>
   </section>
 </main>
 
@@ -71,6 +75,13 @@ const title = 'Astro inset shadow stripe regression';
   [data-case="Inset Named Token Edge"] { box-shadow: inset 4px 0 0 var(--inset-accent); }
   [data-case="Trailing Inset Neutral Edge"] { box-shadow: 4px 0 0 #000 inset; }
 
+  /* box-shadow takes <length>{2,4}: blur and spread are optional and default to
+     0, so these paint the same stripe as the four-length forms above. */
+  [data-case="Two Length Edge"] { box-shadow: inset 4px 0 var(--brand-accent); }
+  [data-case="Two Length Trailing Inset Edge"] { box-shadow: 0 5px #6366f1 inset; }
+  [data-case="Two Length Neutral Edge"] { box-shadow: inset 4px 0 #000; }
+  [data-case="Two Length Blurred Edge"] { box-shadow: inset 4px 0 5px var(--brand-accent); }
+
   /* Commented-out rules are not live CSS.
   [data-case="Commented Out Edge"] { box-shadow: inset 4px 0 0 var(--brand-accent); }
   */