build_request inserts header params first, then default_headers, then
credential headers — HeaderMap::insert replaces, so a declared
in: header parameter whose name matched a default or credential header
silently never delivered the peer's value upstream.
check_header_param_collisions runs at import (the assembly's
HttpServiceConfig is visible there): Authorization on an authed
namespace is rejected outright, a default_headers name match (compared
case-insensitively) fails import naming both keys, and an ApiKey
header_name match fails naming the credential header. Per the task's
decision note: the import-time surface does see the adapter's config,
so the loud point stays at import rather than first-call warn-once.
Tests: Authorization+Bearer, X-Tenant/x-tenant case-insensitive
default_headers, x-api-key/X-API-Key, and the no-collision clean path.
glm-5.3-flash
903a91f1d2