bedrock.guardrail was only attached on the Converse route (guardrailConfig in the
body). Claude on Bedrock goes through the AnthropicBedrock SDK, i.e. InvokeModel,
whose body has no guardrailConfig, so the default Claude route ran with no guardrail
at all (#52179; live-verified by JiaDe-Wu: the blocked word came back through Hermes).
Bedrock reads the guardrail for InvokeModel from X-Amzn-Bedrock-GuardrailIdentifier /
-GuardrailVersion / -Trace headers. Attach them as default_headers in
build_anthropic_bedrock_client so every AnthropicBedrock client Hermes builds
(primary init, /model switch, fallback, per-request rebuild, auxiliary) enforces the
same guardrail, with prompt caching / thinking / 1M context kept (the reason Claude is
not routed through Converse).
InvokeModel blocks do NOT change stop_reason (stays end_turn) and return the guardrail's
canned text as an ordinary assistant reply, flagged only by
amazon-bedrock-guardrailAction=INTERVENED in the body (SDK: response.model_extra).
AnthropicTransport.response_finish_reason maps that to content_filter so the loop runs
its refusal handling instead of reasoning over the canned text; _derive_finish_reason
uses it for the anthropic_messages branch.
Mantle (openai.gpt-5.x) is documented by AWS as not supporting Guardrails on the
Responses endpoint; the docs now say so instead of promising "all model invocations".
Header mechanism proposed in #52312 by @JoaoMarcos44 (stale base, 7-file conflict,
detection keyed on a Converse-only stopReason); reimplemented on current main.
Live probe (local sink, SigV4 fake creds): before, no X-Amzn-Bedrock-* header on the
InvokeModel request; after, headers present, SigV4 intact, INTERVENED → content_filter.
Teknium