Cap concurrent ssh connections a batch opens at once

Deleting or importing several Claude Code sessions fired one ssh
process per item, all in the same tick. A large enough batch opened
more connections than the remote sshd's default MaxStartups tolerates
before it starts randomly refusing, so some rows failed with
"Connection closed by ... port 2222" -- not a real delete failure,
just too many handshakes landing at once.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server/src/setups.rs

@@ -163,6 +163,13 @@ pub fn tidy(value: &str) -> Option<String> {
 /// Runs a launch to completion and returns its stdout.
 impl Transport {
     pub async fn capture(&self, launch: &Launch) -> Result<String> {
+        // See `CAPTURE_PERMITS`: caps how many of these run their ssh
+        // connection at once, so a batch doesn't open more than the remote
+        // sshd tolerates before it starts dropping them.
+        let _permit = super::session::transport::CAPTURE_PERMITS
+            .acquire()
+            .await
+            .expect("capture semaphore is never closed");
         let child = self.spawn(launch, super::session::transport::Streams::Piped)?;
         let output = child
             .wait_with_output()