Remove policy scripts

Rhai made a decision about a route cost one to three microseconds,
some two hundred times what the same costs in Rust. That was bearable
where a function is asked once for an UPDATE, and is not where every
route is weighed against every peer, as it is when routes are passed
on. What is wanted of a policy (mark routes by where they came from,
mark what is announced, let communities say who is told what) needs no
language; it is to be configuration, done natively.

Kept from that work: route selection goes by a LOCAL_PREF that policy
set on a route from an external peer, and the lab's configuration can
be added to by a phase.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

fuzz/fuzz_targets/policy.rs

@@ -1,84 +0,0 @@
-//! The operator's policy script, asked about routes with whatever
-//! attributes a peer can send. The example script (testdata/policy.rhai)
-//! touches most of what a script can; whatever the route, a function
-//! either answers or fails, and never panics. What it changes must still
-//! be attributes that can be written.
-#![no_main]
-
-use std::sync::{Arc, LazyLock};
-
-use bgp_packet::message::{Message, PathAttribute, UpdateMessage};
-use bgp_policy::{Direction, Hook, Peer, Policy, Subject};
-use bgp_primitives::ip_prefix::IpPrefix;
-use bgp_primitives::parser::ParserContext;
-use bytes::BytesMut;
-use libfuzzer_sys::fuzz_target;
-
-static HOOKS: LazyLock<(Arc<Policy>, Vec<Hook>)> = LazyLock::new(|| {
-    let policy = Policy::compile(include_str!("../../testdata/policy.rhai")).unwrap();
-    let hooks = ["from_peer", "to_peer"]
-        .into_iter()
-        .map(|name| policy.hook(name).unwrap())
-        .collect();
-    (policy, hooks)
-});
-
-fuzz_target!(|data: &[u8]| {
-    let Some((selector, attributes)) = data.split_first() else {
-        return;
-    };
-    let ctx = ParserContext {
-        four_octet_asn: true,
-        ibgp: false,
-        add_path: Vec::new(),
-    };
-    // An UPDATE with no routes withdrawn, these attributes, and one route.
-    let mut body = vec![0, 0];
-    let attributes = &attributes[..attributes.len().min(4000)];
-    body.extend_from_slice(&(attributes.len() as u16).to_be_bytes());
-    body.extend_from_slice(attributes);
-    body.extend_from_slice(&[24, 203, 0, 113]);
-    let Ok(decoded) = UpdateMessage::decode(&ctx, &body) else {
-        return;
-    };
-    let attributes = decoded.update.path_attributes;
-    let prefix = IpPrefix::try_from("203.0.113.0/24").unwrap();
-    let roles = ["", "customer", "peer", "provider", "route_server"];
-    let peer = Peer::new(
-        "backup-transit",
-        std::net::Ipv4Addr::new(192, 0, 2, 2).into(),
-        64602,
-        65000,
-        roles[usize::from(selector >> 1) % roles.len()],
-    );
-    let (hook, direction) = if selector & 1 == 0 {
-        (&HOOKS.1[0], Direction::Import)
-    } else {
-        (&HOOKS.1[1], Direction::Export)
-    };
-    let subject = Subject {
-        prefix: &prefix,
-        attributes: &attributes,
-        next_hop: None,
-        direction,
-    };
-    let Ok(verdict) = hook.run(&peer, &subject) else {
-        return;
-    };
-    if let Some(changed) = verdict.attributes {
-        let changed: Vec<PathAttribute> = changed;
-        let update = UpdateMessage {
-            withdrawn_routes: vec![],
-            path_attributes: changed,
-            announced_routes: vec![],
-        };
-        let mut wire = BytesMut::new();
-        // Too long to send is a thing that can be; anything else is not.
-        if let Err(e) = Message::Update(update).to_wire(&ctx, &mut wire) {
-            assert!(
-                matches!(e, bgp_primitives::parser::EncodeError::TooLong { .. }),
-                "{e}"
-            );
-        }
-    }
-});