diff --git a/packages/mux/providers/tmux/src/provider.ts b/packages/mux/providers/tmux/src/provider.ts
index 55b2d3d..870404e 100644
--- a/packages/mux/providers/tmux/src/provider.ts
+++ b/packages/mux/providers/tmux/src/provider.ts
@@ -106,9 +106,10 @@ export class TmuxProvider implements MuxProviderV1, WindowCapable, SidebarCapabl
     tmux.setGlobalHook("after-new-window", ensureCmd);
     // client-resized: terminal window changed size — enforce stored width back
     tmux.setGlobalHook("client-resized", clientResizedCmd);
-    // pane-exited: a pane closed — kill orphaned sidebar panes (only pane left in window)
+    // after-kill-pane: a pane was killed — clean up orphaned sidebars and
+    // re-enforce width (pane-exited is not recognised by tmux 3.4+)
     const paneExitedCmd = hookPost("/pane-exited");
-    tmux.setGlobalHook("pane-exited", paneExitedCmd);
+    tmux.setGlobalHook("after-kill-pane", paneExitedCmd);
   }
 
   cleanupHooks(): void {
@@ -118,7 +119,7 @@ export class TmuxProvider implements MuxProviderV1, WindowCapable, SidebarCapabl
     tmux.unsetGlobalHook("after-select-window");
     tmux.unsetGlobalHook("after-new-window");
     tmux.unsetGlobalHook("client-resized");
-    tmux.unsetGlobalHook("pane-exited");
+    tmux.unsetGlobalHook("after-kill-pane");
   }
 
   getAllPaneCounts(): Map<string, number> {
diff --git a/packages/mux/tmux-sdk/src/index.ts b/packages/mux/tmux-sdk/src/index.ts
index 238a50b..d80988e 100644
--- a/packages/mux/tmux-sdk/src/index.ts
+++ b/packages/mux/tmux-sdk/src/index.ts
@@ -102,6 +102,7 @@ export const HOOK_NAMES = [
   "window-layout-changed",
   "after-select-window",
   "after-new-window",
+  "after-kill-pane",
   "after-resize-pane",
   "pane-died",
   "pane-exited",
diff --git a/packages/runtime/src/server/index.ts b/packages/runtime/src/server/index.ts
index 7718c8d..4e01287 100644
--- a/packages/runtime/src/server/index.ts
+++ b/packages/runtime/src/server/index.ts
@@ -2285,13 +2285,15 @@ export function startServer(mux: MuxProvider, extraProviders?: MuxProvider[], wa
         return new Response("ok", { status: 200 });
       }
 
-      // pane-exited hook: a pane closed — kill orphaned sidebar panes
+      // pane-exited hook: a pane closed — kill orphaned sidebar panes and
+      // re-enforce sidebar width (tmux redistributes space when panes close)
       if (req.method === "POST" && url.pathname === "/pane-exited") {
         if (isSidebarVisible()) {
           invalidateSidebarPaneCache();
           for (const { provider } of listSidebarPanesByProvider()) {
             provider.killOrphanedSidebarPanes();
           }
+          scheduleClientResizeSync();
         }
         return new Response("ok", { status: 200 });
       }