diff --git a/src/tui/tui-client.ts b/src/tui/tui-client.ts
index be1728ed..9683f3b1 100644
--- a/src/tui/tui-client.ts
+++ b/src/tui/tui-client.ts
@@ -1004,6 +1004,13 @@ export class TuiClient {
       // It is already the right size (see presizeWindow), so `latest` changes
       // nothing on arrival and costs no repaint — it matters only if the
       // terminal is resized while sitting in that session.
+      //
+      // ⚠️ The separator MUST be an escaped `\;`. A bare `;` is a command
+      // separator to tmux's own parser, so it ends the `bind-key` and RUNS
+      // what follows immediately: the binding kept only `switch-client`, and
+      // every session got `window-size latest` executed on it at attach time.
+      // That is what left sessions on `latest` after a detach, since the
+      // snapshot was then taken from already-corrupted state.
       await this.exec('tmux', [
         '-L',
         this.socket,
@@ -1014,7 +1021,7 @@ export class TuiClient {
         'switch-client',
         '-t',
         target,
-        ';',
+        '\\;',
         'set-window-option',
         '-t',
         target,
diff --git a/test/tui/tui-client.test.ts b/test/tui/tui-client.test.ts
index 439814c2..907858d5 100644
--- a/test/tui/tui-client.test.ts
+++ b/test/tui/tui-client.test.ts
@@ -602,6 +602,32 @@ describe('attach window sizing', () => {
   });
 });
 
+describe('TuiClient.bindSwitchKey', () => {
+  it('escapes the command separator, or tmux runs the second command instead of binding it', () => {
+    // ⚠️ A bare `;` argument is a command separator to tmux's OWN parser: it
+    // ends the bind-key and executes what follows immediately. That bound only
+    // `switch-client` and ran `window-size latest` against every session at
+    // attach time, which is why sessions were left on `latest` after a detach —
+    // the sizing snapshot was taken from already-corrupted state. Verified
+    // against real tmux both ways before this test was written.
+    const calls: string[][] = [];
+    const exec: TuiExecFile = async (_file, args) => {
+      calls.push([...args]);
+      return { stdout: '', stderr: '' };
+    };
+    const client = new TuiClient({ baseUrl: BASE_URL, socket: 'codeman-beta', exec });
+    return client.bindSwitchKey('M-2', 'codeman-aaaa1111').then(() => {
+      const bind = calls.find((args) => args.includes('bind-key'));
+      expect(bind).toBeDefined();
+      expect(bind).toContain('\\;');
+      expect(bind).not.toContain(';');
+      // Both commands have to be in the ONE binding.
+      expect(bind?.join(' ')).toContain('switch-client -t codeman-aaaa1111');
+      expect(bind?.join(' ')).toContain('window-size latest');
+    });
+  });
+});
+
 describe('parsePrefixBinding', () => {
   const REAL = [
     'bind-key    -T prefix d       detach-client',