feat: solver consumes CSS contain:paint for clippedBy diagnostics

- Add Contain=5 to geometry world ClipKind enum (avoids collision with
  topology engine's CONTAIN=3 vs Mask=3)
- Fix CDP isClippingElement() to detect contain:paint (style.contain)
- CDP topology builder sets clipKind=5 for contain:paint, 1 for overflow
- Enrich clippedByPredicate with clipKind metric:
  1=contain:paint, 2=overflow (hidden/scroll/auto)
- Reads world.clipping.clipKind of the reference's clip node

packages/imhotep-cdp/src/topology.ts

@@ -156,6 +156,7 @@ export async function extractTopology(
 
       function isClippingElement(el) {
         const style = window.getComputedStyle(el)
+        if (style.contain && style.contain.includes('paint')) return true
         return style.overflowX === 'hidden' || style.overflowX === 'scroll' || style.overflowX === 'auto' ||
                style.overflowY === 'hidden' || style.overflowY === 'scroll' || style.overflowY === 'auto' ||
                style.clipPath !== 'none'
@@ -252,10 +253,12 @@ export async function extractTopology(
 
         if (isClippingElement(el)) {
           const r = rectFor(el)
+          const style = window.getComputedStyle(el)
+          const isContainPaint = style.contain && style.contain.includes('paint')
           results.clipping.push({
             clipNodeId: results.clipping.length,
             subjectId,
-            clipKind: 1,
+            clipKind: isContainPaint ? 5 : 1,
             clipLeft: r.left,
             clipTop: r.top,
             clipRight: r.right,

packages/imhotep-geometry/src/world.ts

@@ -330,6 +330,7 @@ export const enum ClipKind {
   ClipPath = 2,
   Mask = 3,
   SvgClip = 4,
+  Contain = 5,
 }
 
 export interface Clipping {

packages/imhotep-solver/src/predicates.ts

@@ -687,7 +687,19 @@ export const clippedByPredicate: PredicateEvaluator = {
     // Simplified: check if subject's clipping root is the reference
     const clipRoot = world.topology.clippingRootOf[subjectId - 1] ?? 0;
     const pass = clipRoot === referenceId;
-    return makePredicateResult(pass ? 'true' : 'false', {}, [subjectId, referenceId]);
+    // Determine clip kind from the clipping table entry for the reference.
+    // Encoding: 1=contain:paint, 2=overflow:hidden/scroll/auto
+    const metrics: Record<string, number> = {};
+    if (referenceId !== undefined) {
+      const { clipping } = world;
+      for (let i = 0; i < clipping.subjectId.length; i++) {
+        if (clipping.subjectId[i] === referenceId) {
+          metrics.clipKind = clipping.clipKind[i] === 5 /* Contain */ ? 1 : 2;
+          break;
+        }
+      }
+    }
+    return makePredicateResult(pass ? 'true' : 'false', metrics, [subjectId, referenceId]);
   },
 };