Router liveliness tokens aren't properly cleaned up on link disconnects

[Evanev7]

Describe the bug

two zenoh routers do not unregister each others liveliness tokens.

i traced this to zenoh::net::routing::hat::router::token::Hat::unregister_node_tokens - it successfully receives unregister_node_tokens(<expired ZID>), but self.net() has already had the graph pruned, and so remove_link doesn't find any zid's to unpropagate tokens.

i'm going to look into a patch now, i'll update this issue if i find the route cause.

To reproduce

running the following script on two devices connected by a thunderbolt 5 cable (one macos, one linux if that's relevant)

use zenoh::{Result, Wait};

#[tokio::main]
async fn main() -> Result<()> {
    let mut cfg = zenoh::Config::default();
    cfg.insert_json5("mode", "\"router\"")?;
    cfg.insert_json5("listen/endpoints", &format!("[\"tcp/[::]:44444\"]"))?;
    cfg.insert_json5(
        "connect/endpoints",
        "[
            \"tcp/fe80::<device A LLA>%iface:44444\",
            \"tcp/fe80::<device B LLA>%iface:44444\"
        ]",
    )?;
    let session = zenoh::open(cfg).wait()?;
    let _tok = session
        .liveliness()
        .declare_token(session.zid().to_string())
        .wait()?;
    session
        .liveliness()
        .declare_subscriber("*")
        .history(true)
        .callback(|sample| println!("{}: {}", sample.kind(), sample.key_expr()))
        .background()
        .wait()?;

    // wait until ctrl c
    tokio::signal::ctrl_c().await?;
    Ok(())
}

produces on A

PUT: <zid A>
PUT: <zid B>
...ctrl c on B...
DELETE: <zid B>

as expected, however when pulling the cable,

PUT: <zid A>
PUT: <zid B>
...cable pulled...

no such DELETE is ever propagated.

System info

• Platform: NixOS 25.5, macOS 26.3
• CPU: AMD AI 9 HX 370, Apple M4
• zenoh commit 77507c1, latest main at time of writing
• also seen on release v1.9.0

[Evanev7]

traced to zenoh::net::routing::dispatcher::face::Face::send_close - each call to
hats[region].unregister_face_subscribers(ctx.reborrow())
hats[region].unregister_face_queryables(ctx.reborrow())
hats[region].unregister_face_tokens(ctx.reborrow())
prunes the graph - meaning only subscribers are pruned correctly. i'll open a pr with a bad fix for now and can work out the details later.

[Evanev7]

got a fix! cleaning it up a bit now