Fix zmx kill racing tab teardown on Close Tab.

Keep a strong reference through the async kill, snapshot the live tsshd session up front, and wrap `zmx kill --force` in `sh -c` so the probe actually runs.

Author: jvanderen1

rootshell/Features/Multiplexer/MuxSessionDetach.swift

@@ -294,12 +294,17 @@ enum MuxSessionDetach {
             return
         }
 
+        // Snapshot the live transport before clearing bindings / any close
+        // side effects — closeTab may already be removing us from the model.
+        let trzsz = terminal.session as? TrzszSession
+        let connectionConfig = terminal.connectionConfig
+
         // Drop the binding so a concurrent detach/close path cannot double-kill.
         terminal.passthroughMultiplexer = nil
         AgentAttentionCenter.shared.topologyDidChange()
 
         // 1) Live tsshd probe — same connection, no re-auth.
-        if let trzsz = terminal.session as? TrzszSession {
+        if let trzsz {
             do {
                 _ = try await trzsz.runProbeCommand(command)
                 Ghostty.logger.info("zmx kill via tsshd probe succeeded for \(name, privacy: .public)")
@@ -311,7 +316,6 @@ enum MuxSessionDetach {
         }
 
         // 2) Headless SSH fallback (new connection — may prompt the agent).
-        let connectionConfig = terminal.connectionConfig
         if let ssh = connectionConfig.sshConfigForHistory
             ?? connectionConfig.underlyingSSHConfig {
             do {

rootshell/Features/SSH/Config/SSHConfig.swift

@@ -804,11 +804,12 @@ struct SSHConfig: Codable, Hashable {
 
     /// Best-effort destroy for an explicit tab/split close. Names must already
     /// pass ``isEmbeddableZmxSessionName`` (no shell quoting). `--force` kills
-    /// the session even while this client is still attached.
+    /// the session even while this client is still attached. Wrapped in
+    /// `sh -c` so PATH prefix / `&&` work under tsshd `runCommand` and SSH exec.
     static func zmxKillCommandLine(sessionName: String) -> String? {
         guard isEmbeddableZmxSessionName(sessionName) else { return nil }
-        return "\(remoteExecPathPrefix)command -v zmx >/dev/null 2>&1"
-            + " && ZMX_SESSION_PREFIX= zmx kill --force \(sessionName)"
+        return "sh -c '\(remoteExecPathPrefix)command -v zmx >/dev/null 2>&1"
+            + " && ZMX_SESSION_PREFIX= exec zmx kill --force \(sessionName)'"
     }
 
     /// Shared zmx exec command used by all session types.

rootshell/UI/Terminal/TerminalView.swift

@@ -1558,9 +1558,13 @@ extension Ghostty {
             // remote session (`zmx kill`) BEFORE tearing down the client —
             // closing the client alone is zmx’s detach path. Prefer an
             // in-band tsshd probe so agent keys do not need a second approval.
+            //
+            // Strongly capture `self`: closeTab removes the pane from the
+            // model immediately after cleanup returns, and a `[weak self]`
+            // Task would often see nil and skip both kill and teardown —
+            // leaving the zmx session alive (looks like detach).
             if reason == .userClose, MuxSessionDetach.hasZmxSessionToDestroy(on: self) {
-                Task { @MainActor [weak self] in
-                    guard let self else { return }
+                Task { @MainActor in
                     await MuxSessionDetach.destroyZmxSessionIfNeeded(on: self)
                     self.completeCleanupAfterSessionStop(reason: reason)
                 }