Function planCascadeTree

planCascadeTree(
    params: {
        availableNodeIds: string[];
        capacityOf?: (nodeId: string) => number;
        fanout: number;
        originId: string;
        viewerCount: number;
        viewersPerNode: number;
    },
): CascadePlan
Compute a balanced cascade fan-out tree that distributes a room's media to a large viewer population across many SFU nodes.

Starting from the origin, nodes are drawn from availableNodeIds and attached tier by tier, each parent taking up to fanout children, until the current tier can seat viewerCount viewers (at viewersPerNode each) or the node pool is exhausted. Leaf nodes are then filled with viewer slots up to their per-node capacity. This shallow, wide tree keeps forwarding hops low while scaling to very large audiences (for example a live stream to 1M viewers).
Parameters
- params: {
      availableNodeIds: string[];
      capacityOf?: (nodeId: string) => number;
      fanout: number;
      originId: string;
      viewerCount: number;
      viewersPerNode: number;
  }
  Planning inputs.
  - availableNodeIds: string[]
    Candidate node ids to draw from (the origin is excluded automatically).
  - OptionalcapacityOf?: (nodeId: string) => number
    Optional per-node capacity lookup overriding viewersPerNode for leaf seating.
  - fanout: number
    Maximum children per node; must be >= 1.
  - originId: string
    Identifier of the origin node (tree root).
  - viewerCount: number
    Total number of viewers to seat.
  - viewersPerNode: number
    Default viewer capacity per node (and the origin's assumed capacity); must be >= 1.
Returns CascadePlan
The computed CascadePlan, including any unmetViewers shortfall.
Throws
InvalidArgumentError when fanout < 1 or viewersPerNode < 1.
Example
```
const plan = planCascadeTree({
  originId: 'origin',
  viewerCount: 1_000_000,
  fanout: 8,
  viewersPerNode: 1000,
  availableNodeIds: relayIds,
})
console.log(plan.tiers, plan.servedViewers, plan.unmetViewers)
```
- Defined in packages/sfu/src/CascadeTree.ts:99