qwenpaw env set → subprocess can't see it

Variables added via `env set` mid-session don't appear in
execute_shell_command subprocesses (they only inherit the snapshot
from agent startup). Need `env get KEY` or `--json` flag on `env list`
so scripts can fetch values at runtime without restarting.

Start by locating the implementations or entry points for `env set`, `env list`, and `execute_shell_command`, then trace how environment values are stored and passed to subprocesses. Check the existing command tests, if present; done means a value added with `env set` can be retrieved at runtime through `env get KEY` or `env list --json` without restarting the agent.

Escrito por el modelo de indexación a partir del texto del issue.