Run parallel Claude sessions

Each cvm open only annotates its child process — shells stay independent.

1. Create one environment per context (client-acme, client-globex, …).
2. Launch separately:

   cvm open client-acme
   # other tab / pane
   cvm open client-globex

3. Or background them:

   cvm open client-acme &
   cvm open client-globex &

Parent shell activation (if any) is untouched. Use a statusline badge on CVM_ENV so each session shows which env it belongs to — see the statusline guide.