fix(tun): preserve shared NIC ownership and failure invariants

Keep mobile address and route claims in dispatcher tables without
applying desktop interface configuration to synthetic TUN names.

Limit the Magic DNS overlap exemption to route claims and remove the
shared route retry that bypassed claim accounting after invalidation.

Invalidate and stop dispatchers on failed mobile TUN replacement or I/O.
Bound TUN writes so stalled devices release pending source updates and
member cleanup instead of retaining an unusable shared dispatcher.

Treat missing Darwin and Windows addresses and routes as successful
deletions while preserving permission and other configuration errors.

Add regressions for claim conflicts, mobile configuration, failed TUN
replacement, stalled writes, and platform deletion error handling.

easytier/src/instance/dns_server/runner.rs

@@ -5,15 +5,7 @@ use std::{net::Ipv4Addr, sync::Arc, time::Duration};
 
 use easytier_core::instance::CorePacketPlane;
 
-use crate::{
-    common::{
-        error::Error as EtError,
-        global_ctx::ArcGlobalCtx,
-        ifcfg::{IfConfiger, IfConfiguerTrait},
-        netns::NetNS,
-    },
-    instance::virtual_nic::NicBackend,
-};
+use crate::{common::global_ctx::ArcGlobalCtx, instance::virtual_nic::NicBackend};
 
 use super::{client_instance::MagicDnsClientInstance, server_instance::MagicDnsServerInstance};
 
@@ -30,8 +22,6 @@ pub struct DnsRunner {
 }
 
 struct MagicDnsFakeIpRouteClaim {
-    tun_dev: Option<String>,
-    net_ns: NetNS,
     fake_ip: Ipv4Addr,
     route_backend: NicBackend,
 }
@@ -44,26 +34,10 @@ impl MagicDnsFakeIpRouteClaim {
             None
         };
 
-        match self
-            .route_backend
+        self.route_backend
             .add_route_with_cost(self.fake_ip, 32, cost)
-            .await
-        {
-            Err(EtError::IOError(err))
-                if err.kind() == std::io::ErrorKind::AlreadyExists && self.tun_dev.is_some() =>
-            {
-                let ifcfg = IfConfiger::default();
-                let _guard = self.net_ns.guard();
-                ifcfg
-                    .remove_ipv4_route(self.tun_dev.as_deref().unwrap(), self.fake_ip, 32)
-                    .await?;
-                self.route_backend
-                    .add_route_with_cost(self.fake_ip, 32, cost)
-                    .await?;
-                Ok(())
-            }
-            result => result.map_err(Into::into),
-        }
+            .await?;
+        Ok(())
     }
 
     async fn remove(&self) {
@@ -119,8 +93,6 @@ impl DnsRunner {
         }
 
         Some(MagicDnsFakeIpRouteClaim {
-            tun_dev: self.tun_dev.clone(),
-            net_ns: self.global_ctx.net_ns.clone(),
             fake_ip: self.fake_ip,
             route_backend: self.shared_route_backend.clone()?,
         })