The four §6-VERBOSE-only backend boundaries (request.ingress, llm.call.start,
llm.call.response, sse.first_byte) called _emit with no tier_gate, so they
over-emitted at DEFAULT tier — 4 extra events/request vs the middleware family,
breaking the §7 tier budget and cross-backend apples-to-apples parity. Gate
them with tier_gate=_VERBOSE_TIERS, matching emit.ts:58-63 and the agno
_BOUNDARY_TIER. langgraph-fastapi received the identical change (the two LGP
files differ only by docstring/plan-unit/_SLUG). Adds default-suppressed +
verbose-emits red-green coverage; updates the pre-existing first_byte
correlation test to drive at VERBOSE tier (the boundary is VERBOSE-only).