test(cli): forward tests flake when the port is taken after the CLI's port check #4797

User Story

I'm landing the #2912 audit-event follow-ups. #4777 failed Branch Checks because of an unrelated flaky CLI forward test, so the PR needed a rerun before review.

Description

openshell-cli::sandbox_create_lifecycle_integration::sandbox_forward_background_tracks_owned_child_when_pid_discovery_fails failed on x86_64-linux with:

fake forward must bind: Os { code: 98, kind: AddrInUse, message: "Address already in use" }
...
× ssh process started but local forward listener was not reachable
╰─▶ ssh exited with status exit status: 101 before local forward listener opened on 127.0.0.1:39481

#4570 made the forward tests retry on a new port when another process takes theirs, but only when the CLI's pre-check reports "is already in use". The port can also be taken after that check passes and before the fake ssh binds it. The fake then panics with exit status 101, which the retry does not recognize, so the test fails.

Context

• Failing job: https://github.com/NVIDIA/OpenShell/actions/runs/39517397788/job/118952816407
• 8,445 of 8,446 tests passed in that run.
• Real ssh -o ExitOnForwardFailure=yes exits with status 255 when it cannot bind the local forward.

Definition of Done

• Forward tests retry on a new port when the port is taken between the CLI's check and the fake ssh's bind
• The test file passes repeatedly