diff --git a/rootfs/home/developer/.bash_aliases b/rootfs/home/developer/.bash_aliases
index 0a6da46..ca9e902 100644
--- a/rootfs/home/developer/.bash_aliases
+++ b/rootfs/home/developer/.bash_aliases
@@ -76,7 +76,10 @@ fi
 
 # ── Prompt: show [opencode-devbox] tag so it's obvious you're in the container
 # Preserves the default Debian PS1 logic but prefixes with a container marker.
-if [ -n "${PS1:-}" ] && [ -z "${DEVBOX_PS1_SET:-}" ]; then
+# We check for the literal '[devbox]' substring in PS1 rather than relying on
+# an exported guard variable — otherwise `exec bash` inherits the guard but
+# gets a fresh (prefix-less) PS1 from .bashrc, and the prefix would never be
+# re-added in the new shell.
+if [ -n "${PS1:-}" ] && [[ "$PS1" != *"[devbox]"* ]]; then
   PS1='\[\e[38;5;39m\][devbox]\[\e[0m\] '"${PS1}"
-  export DEVBOX_PS1_SET=1
 fi