diff --git a/src/cli.ts b/src/cli.ts
index 2e32b75..a3e04a1 100755
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -359,9 +359,15 @@ program
 
 program
   .command("shell")
-  .argument("<branch>", "branch name")
-  .description("Open a shell in the VM at the session's worktree")
-  .action(async (branch: string) => {
+  .argument("[branch]", "branch name (omit for a plain VM shell)")
+  .description("Open a shell in the VM (at the session's worktree if branch given)")
+  .action(async (branch?: string) => {
+    if (!branch) {
+      await vm.ensure()
+      await vm.shell()
+      return
+    }
+
     const root = await git.repoRoot()
     const session = await state.getSession(root, branch)
     if (!session) {