CngxMatTabAggregatorContent

Structural slot directive marking the aggregator-descriptor template for [cngxMatTabs]. Discovered via contentChild on the directive; when bound, the projector renders an embedded view of this template into the SR-only descriptor span instead of writing the aggregator's announcement() string verbatim.

Pure marker - zero logic. Holds only a typed TemplateRef reference. Mirrors the family-standard slot pattern (CngxStepBadge, CngxTabErrorBadge, CngxTabOverflowItem).

Material owns the tab-button chrome; the cngx descriptor span is the only consumer-visible decoration seam, so this slot directive lands with one in-package consumer (the package-private aggregator-decoration projector).

<mat-tab-group cngxMatTabs>
  <ng-template
    cngxMatTabAggregatorContent
    let-count="count"
    let-label="label"
  >
    {{ label }}: {{ count }} validation issue(s)
  </ng-template>
  <mat-tab label="Profile" cngxMatTabError="profile">…</mat-tab>
</mat-tab-group>