Function set_pane_env 

pub fn set_pane_env(args: &mut [String], block_id: &str)

Name the pane in launch’s SetEnv too (AGENTMUX_BLOCKID), so a host that accepts it (AcceptEnv AGENTMUX_*) lets the pane’s stats badge find its shell there (PaneProcs). Dropped quietly by any other host, like the rest of that SetEnv. A block id is AgentMux’s own UUID; anything with another character is left out rather than quoted.