bunpen: --bunpen-drop-shell: specify argv0 more correctly

pkgs/additional/bunpen/main.ha

@@ -13,7 +13,7 @@ fn do_exec(name: str, args: []str) (os::exec::error | void) = {
   {
     let joined = strings::join(" ", args...);
     defer free(joined);
-    log::printfln("exec: {}", joined);
+    log::printfln("exec ({}): {}", name, joined);
   };
 
   let path = args[0];
@@ -50,7 +50,8 @@ export fn main() void = {
   restrict::namespace_restrict(&what);
   restrict::landlock_restrict(&what);
   if (opts.drop_shell) {
-    rtext::check_error("exec /bin/sh", do_exec(name, ["/bin/sh"]));
+    // TODO: respect the user's $SHELL
+    rtext::check_error("exec /bin/sh", do_exec("sh", ["/bin/sh"]));
   } else {
     rtext::check_error("exec <user command>", do_exec(name, opts.cmd));
   };