Incoming request-like object containing Node headers.
Resolved B2 config, or null only when the primary key header pair
is absent or incomplete.
This compatibility export always parses request headers through the shared
header credential provider; it does not consult the selected HTTP credential
mode. Hosted deployments should prefer server or principal credential
modes in the request pipeline when B2 keys must not be supplied directly by
MCP clients.
Extract B2 credential configuration from HTTP headers.