/** Media progress and capture freshness are independent of DOM painting and inventory SSE. */
export class PreviewLiveness {
 private lastFrame:number|null=null;
 private sourceSeen=Number.NEGATIVE_INFINITY;
 private staleSince:number|null=null;
 constructor(private connectedAt:number){}
 connected(now:number){this.connectedAt=now;}
 frame(now:number){this.lastFrame=now;}
 source(fresh:boolean,now:number){
  this.sourceSeen=now;
  this.staleSince=fresh?null:this.staleSince??now;
 }
 state(now:number):'live'|'waiting'|'delayed'|'source-stalled'|'peer-stalled'{
  if(this.staleSince!==null&&now-this.sourceSeen<3000){
   return now-this.staleSince>=12000?'source-stalled':'delayed';
  }
  const elapsed=now-(this.lastFrame??this.connectedAt);
  if(elapsed>8000)return 'peer-stalled';
  if(this.lastFrame===null)return 'waiting';
  return elapsed>2000?'delayed':'live';
 }
}