fix(agent): keep cloud credentials in secondary checkouts

[tatoalo]

Problem

Cloud Codex sessions receive refreshed GitHub credentials through BASH_ENV, but Codex restores its captured shell snapshot only when a tool call uses the thread's initial working directory. A shell launched directly in a secondary checkout can therefore lose gh authentication even while the refreshed credential file is valid.

Changes

• Pin the backend-controlled BASH_ENV path in Codex's shell environment policy for managed sandbox sessions.
• Pass the exact spawned process environment into argument construction.
• Leave non-sandbox Codex sessions unchanged.

The backend half of the credential refresh path is in PostHog/posthog#72540.

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 3bfedf6.}

[github-actions]

Small, well-tested fix that propagates a sanitized env into buildAppServerArgs; the BASH_ENV value is safely escaped via the existing tomlBasicString helper and the new code path is guarded by the IS_SANDBOX check. No showstoppers.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(agent): keep cloud credentials in se..." | Re-trigger Greptile}