fix OSC 52 not working in multiplexer

closes: https://github.com/wez/wezterm/issues/764

docs/changelog.md

@@ -30,6 +30,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Fixed: Windows: pane could linger after the process has died, closing only when a new pane/tab event occurs
 * Fixed: Windows: first character after `wezterm ssh` keyboard authention was swallowed [#771](https://github.com/wez/wezterm/issues/771)
 * Fixed: Windows: detect window resizes while authenticating for `wezterm ssh` [#696](https://github.com/wez/wezterm/issues/696)
+* Fixed: OSC 52 clipboard escape didn't work in the initial pane spawned in the multiplexer server [#764](https://github.com/wez/wezterm/issues/764)
 
 ### 20210502-154244-3f7122cb
 

wezterm-mux-server-impl/src/sessionhandler.rs

@@ -158,6 +158,17 @@ pub struct SessionHandler {
 
 impl SessionHandler {
     pub fn new(to_write_tx: PduSender) -> Self {
+        // Fixup the clipboard on the empty initial pane that is
+        // spawned into the mux
+        let mux = Mux::get().unwrap();
+        for pane in mux.iter_panes() {
+            let clip: Arc<dyn Clipboard> = Arc::new(RemoteClipboard {
+                pane_id: pane.pane_id(),
+                sender: to_write_tx.clone(),
+            });
+            pane.set_clipboard(&clip);
+        }
+
         Self {
             to_write_tx,
             per_pane: HashMap::new(),