diff --git a/hosts/common/default.nix b/hosts/common/default.nix
index 956daa9..d7c6e64 100644
--- a/hosts/common/default.nix
+++ b/hosts/common/default.nix
@@ -80,9 +80,17 @@
   programs.bash = {
     enable = true;
     interactiveShellInit = ''
-      if [[ $- == *i* ]] && [[ -z "''${M3_SHELL_TO_NU:-}" ]]; then
-        export M3_SHELL_TO_NU=1
-        exec ${pkgs.nushell}/bin/nu --login
+      # Interactive bash -> nushell, unless started deliberately from
+      # nu/bash (parent check — an exported env marker would leak into
+      # zellij/zed/herdr children). Non-interactive bash (ssh command
+      # exec, Mosh app bootstrap) stays bash.
+      if [[ $- == *i* ]]; then
+        parent=""
+        [[ -r /proc/$PPID/comm ]] && IFS= read -r parent < /proc/$PPID/comm
+        if [[ "$parent" != "nu" && "$parent" != "bash" ]]; then
+          exec ${pkgs.nushell}/bin/nu --login
+        fi
+        unset parent
       fi
     '';
   };