fix: children($var) domain compilation and resolver support

- Add children branch in convertDomain() alongside descendants —
  children() now correctly maps to parentVar: '$parent'
  instead of falling through to the default branch which reversed
  the parentVar/selector mapping.
- SelectorDomainResolver now handles parentVar domains with no
  CSS selector filter (children domain collects all registered
  subject IDs, then filters by parent via ancestor index).
- All 1072 tests pass across 14 packages.

packages/imhotep-dsl/src/compiler.ts

@@ -938,7 +938,7 @@ function convertDomain(domain: DslDomainRef): DomainRef {
 
   // Descendant domains use the first argument as parent and second as filter:
   // descendants($card, '.title') => parentVar: '$card', selector: '.title'
-  if (domain.kind === 'descendants') {
+  if (domain.kind === 'descendants' || domain.kind === 'children') {
     const parentVar = selectorFromVar ?? domain.selector
     const selector = extraArgFromVar ?? (domain as any).extraArg
     return {

packages/imhotep-playwright/src/extraction.ts

@@ -1021,26 +1021,38 @@ export class SelectorDomainResolver implements DomainResolver {
     })
   }
 
+  private allRegisteredSubjectIds(): number[] {
+    const seen = new Set<number>()
+    for (const d of this.domains.values()) {
+      for (const id of d.subjectIds) {
+        seen.add(id)
+      }
+    }
+    return Array.from(seen)
+  }
+
   resolve(domain: DomainRef, env?: BindingEnv): DomainValue | undefined {
     if (domain.parentVar) {
       if (!env || !this.ancestorIndex) return undefined
       const parentId = env.lookup(domain.parentVar)
       if (parentId === undefined) return undefined
-      const selector = domain.selector ?? domain.domain
-      const globalDomain = this.domains.get(selector)
-      if (!globalDomain) return undefined
+      const selector = domain.selector
+      const candidateIds = selector
+        ? this.domains.get(selector)?.subjectIds
+        : this.allRegisteredSubjectIds()
+      if (!candidateIds || candidateIds.length === 0) return undefined
       const filtered: number[] = []
-      for (const id of globalDomain.subjectIds) {
+      for (const id of candidateIds) {
         const ancestors = this.ancestorIndex.get(id)
         if (ancestors?.has(parentId)) {
           filtered.push(id)
         }
       }
-      const key = `descendants_p${parentId}_${selector}`
+      const key = `descendants_p${parentId}_${selector ?? '*'}`
       return {
         domainId: `dom_${key}`,
         subjectIds: new Uint32Array(filtered),
-        provenance: `descendants(parentId=${parentId}, ${selector})`,
+        provenance: `descendants(parentId=${parentId}, ${selector ?? '*'})`,
         closed: true,
       }
     }