Function default_respond_policy 

pub fn default_respond_policy(
    ctx: &IdentityRequestContext<'_>,
) -> RespondDecision

The default respond policy: answer every request that reached the policy.

Includes our full source key unless the request was authenticated to us (an authenticated pairwise request implies the sender already holds our key). The blind-unicast-over-channel case, where a channel-authenticated sender may still lack our key, is a known edge a custom policy can override.