DRA Sharing Affinity

This KEP proposes an extension to Dynamic Resource Allocation (DRA) that allows the kube-scheduler to handle resources that are conditionally fungible. KEP-5075 (Consumable Capacity) introduced the ability to track numerical capacity (e.g., 16 slots of a NIC) and share devices across multiple claims via allowMultipleAllocations. However, it assumes all claims are fungible—any claim can share the device with any other claim. Real-world hardware is often modal (i.e., once partially allocated, it must operate in a single configuration mode for all of its current consumers): the device requires all subsequent consumers to share a specific configuration. For example: - Multi-pod NIC sharing: A network DRA driver shares a NIC across 16 pods, but all pods must belong to the same subnet. Once the first pod configures the NIC for Subnet A, the remaining 15 slots are restricted to Subnet A. - FPGA bitstream sharing: An FPGA can serve multiple inference pods, but all must use the same bitstream. Once bitstream-ml-v2 is loaded, other pods needing bitstream-crypto-v1 must use a different FPGA. This KEP introduces a sharingAffinity field on ResourceSlice.spec that allows drivers to declare, via CEL expressions, how to extract the affinity keys that constrain sharing from the driver's existing opaque device configuration. sharingAffinity is published as pool-level metadata in dedicated slices within the pool — a slice that carries sharingAffinity does not carry devices, and vice versa — mirroring the established sharedCounters (KEP-4815) pattern. A pool may publish one or more such slices; the scheduler takes the union of their extractors, so the schema declaration stays scoped to the pool even when the pool is chunked across many ResourceSlices. On the claim side, there is no API change — workloads continue to author their driver's opaque config exactly as they do today. Whe