Fallback when zsh shell snapshots time out

[saud-oai]

Summary

• retry zsh shell snapshot capture without sourcing .zshrc when the full snapshot command times out
• preserve the existing failure path for non-timeout errors
• add regression coverage with a fake zsh that blocks on the initial rc-sourcing capture and succeeds only for the fallback script

Motivation

Shell snapshot capture intentionally sources .zshrc to preserve interactive command state. A slow or blocking .zshrc currently causes snapshot creation to time out entirely, leaving subsequent shell execution without a usable snapshot. This fallback preserves a login-shell baseline when interactive rc capture cannot complete, while retaining a warning for visibility.

Validation

Passed:

• just fmt
• CARGO_NET_GIT_FETCH_WITH_CLI=true CARGO_HTTP_TIMEOUT=600 CARGO_HTTP_LOW_SPEED_LIMIT=1 just test -p codex-core -E 'test(timed_out_zsh_user_rc_uses_login_shell_fallback_snapshot)' --status-level fail --final-status-level fail --failure-output final (includes bench-smoke)
• CARGO_NET_GIT_FETCH_WITH_CLI=true CARGO_HTTP_TIMEOUT=600 CARGO_HTTP_LOW_SPEED_LIMIT=1 just fix -p codex-core

Attempted:

• CARGO_NET_GIT_FETCH_WITH_CLI=true CARGO_HTTP_TIMEOUT=600 CARGO_HTTP_LOW_SPEED_LIMIT=1 just test -p codex-core --status-level fail --final-status-level fail --failure-output final
  • 2507 tests passed and 47 failed in local integration/harness paths unrelated to this change, primarily missing expected helper binaries such as codex / test_stdio_server and approval-sandbox environment expectations.

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