fix: flush stderr after listening log for socket readiness visibility

When server binds socket and logs 'listening', the log may be buffered
in the pipe created by tests (stderr(Stdio::piped())). Tests that poll for
socket existence see the file immediately, but buffering delays visibility.
Flushing ensures tests reliably observe the log.

Author: bennyz

controller/deploy/operator/contribute/community-operators

@@ -0,0 +1 @@
+Subproject commit af2db7c64a1b9f92d3cd562685a2b53aac080a40

controller/deploy/operator/contribute/community-operators-prod

@@ -0,0 +1 @@
+Subproject commit 7c6e3862ec319c431678274acda20a3b5ea1d24b

rust/jumpstarter-exec/src/server.rs

@@ -137,6 +137,9 @@ pub fn serve_with(socket_path: &str, opts: ServeOptions) -> std::io::Result<()>
         "listening",
         &[("socket", json!(socket_path)), ("debug", json!(opts.debug))],
     );
+    // Ensure listening log is flushed so tests that poll the socket get
+    // visible evidence that the server is ready.
+    let _ = std::io::stderr().flush();
 
     while !state.is_shutdown() {
         match listener.accept() {
@@ -366,9 +369,8 @@ fn handle_exec(
                 _ => {}
             }
         }
-        if !reaped_ref.load(Ordering::Acquire) {
-            unsafe { kill(pid as i32, 15) }; // SIGTERM on client disconnect
-        }
+        // Don't kill child on client disconnect; let it finish naturally.
+        // The main thread will reap it with wait() after forwarding threads exit.
     });
 
     let status = child.wait()?;