Whether an enforcing agent_response policy is attached (TTFT disclaimer)

Whether an ENFORCING agent_response policy is in effect for an assistant + channel.

Drives the dashboard's TTFT-disclaimer surfacing: when blocking_response_policy is true, an attached mode=enforce agent_response policy gates the reply against a verdict before the user sees it (a visible first-token delay on the always-gate path), so the author should see the disclaimer copy. v3 is transport-independent — the signal is enforce vs monitor, not a channel-resolved mode; channel is echoed for the caller only.