integ: RemoteEnd half-close through master's Transport::shutdown(how)

W's f43fba88 added RemoteEnd::shutdown_write; the trait on master has
shutdown(how) instead (SHUT_WR and SHUT_RDWR end the sends).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_1896c5b302a54696aaa92c5f4047f20b

crates/gex-kernel/src/net.rs

@@ -349,9 +349,13 @@ impl Transport for RemoteEnd {
     fn close(&self) {
         (self.remote.close)(self.id);
     }
-    /// The global kernel's shutdown is SHUT_WR's: the far end reads to its end.
-    fn shutdown_write(&self) {
-        (self.remote.shutdown)(self.id);
+    /// The global kernel's shutdown is SHUT_WR's: the far end reads to its
+    /// end. SHUT_RD only changes this end, which the far end is not told.
+    fn shutdown(&self, how: u64) -> Result<(), Errno> {
+        if how == 1 || how == 2 {
+            (self.remote.shutdown)(self.id);
+        }
+        Ok(())
     }
 }