CML
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    Variable CMCD_HEADER_MAPConst

    CMCD_HEADER_MAP: Record<CmcdRequestKey | "nrr", CmcdHeaderField> = ...

    The map of CMCD keys to their appropriate header shard.

    Note: Event-only keys (e, ts, cen, h) and response-received keys (rc, ttfb, ttlb, url, etc.) are intentionally absent. They are transmitted via the event-mode POST body, not HTTP headers.