Codex was the only agent that bind-mounted its host home into the
container via an explicit `Mounts: [{home}/.codex → /root/.codex]`
entry, while every other ACP agent uses `SessionConfig.SessionDirTemplate`
+ `SessionDirTarget`. Move codex onto the same surface so the
host-state isolation work in the next commit covers it uniformly.
This change alone does not stop the host-state leak — the bind mount
still resolves to the host's ~/.codex for now — but it removes the
last agent-specific branch in the runtime config so the docker
container manager can apply one rule for all agents.
José Almeida
7be7aede8b