Type Alias FlexibleVersionThreshold

Maps API keys to their header version requirements.

• Request header v0-v1: non-flexible (API key, version, correlation ID, client ID)
• Request header v2: flexible (adds tagged fields, KIP-482)
• Response header v0: non-flexible
• Response header v1: flexible (adds tagged fields)

The threshold version is the API version at which the API transitions from non-flexible to flexible headers. null means the API always uses non-flexible headers.