Bundle / foldkit-bundle

The placed parts

Each placement exposes its parts in parent terms:

Part	Type	Built from
`placed.update(parent, message)`	`Option<Update.Return>`: `None` when the Message is not this placement's	`Update.foldChildStep`
`placed.init`	`Update.Step`: writes the child's initial Model and lifts its Commands	`Update.foldChildInit`
`placed.subscriptions`	a Subscriptions record keyed `Name@path/key`	`Subscription.lift` with a gate
`placed.resources`	a Managed Resources record keyed `Name@path/key`	`ManagedResource.lift`
`placed.view(parent, h, viewInputs?)`	`Html`; nothing while the child is absent	`h.submodel`
`placed.viewIn(slot)`	the same view under another slot id, to render one placement in two positions	`h.submodel`
`placed.helpers.name(...input)`	`Update.Step` for a programmatic entry point	`Update.foldChildStep`

Keys are prefixed with the placement, so two placements of one bundle never collide in Subscription.aggregate.