bug: gossip inserts in `MessagePool::add()` use `TrustPolicy::Trusted` instead of `TrustPolicy::Untrusted`

[akaladarshi]

Summary

The MessagePool::add() method, which is used to insert messages received via gossip,
currently calls add_to_pool with TrustPolicy::Trusted. This bypasses the stricter
untrusted caps and gap rules that are intended for externally sourced traffic.

Details

File: src/message_pool/msgpool/msg_pool.rs

Messages received over gossipsub come from untrusted external peers. Using
TrustPolicy::Trusted for these inserts means:

• The per-actor pending message limit of MAX_ACTOR_PENDING_MESSAGES (1000) applies
  instead of the tighter MAX_UNTRUSTED_ACTOR_PENDING_MESSAGES (10).
• Gap/strictness rules intended for untrusted sources (StrictnessPolicy::Strict) may
  not be enforced correctly.

Suggested Fix

pub fn add(&self, msg: SignedMessage) -> Result<(), Error> {
    self.add_to_pool(msg, false, TrustPolicy::Untrusted)?;
    Ok(())
}

References

• Identified in PR #7033: refactor: msg pool to make more structured part 3 #7033 (comment)

Note:

It's not actually a bug because TrustPolicy here merely tells us how many messages are allowed in the pending store nothing else, but opening this so we discuss changing things around because current naming creates confusion.