nvidia: fix shadowed agent usb disconnect + suppress teardown replug prompts

[lee-reinhardt]

Problem

The wrynose BSP rebase re-imported upstream copies of seven initrd-flash.sh helper functions without removing the agent-aware block grafted at the top of the file. Bash keeps the later definition, so the live disconnect_usb_device was the plain sysfs-only copy and _twiddle_via_agent (plus the device-gone idempotency guard) was dead code. Any provision running inside the avocado-vm would hang at the first cable-cycle point with no prompt anywhere, since the authorized=0 toggle is a no-op through vhci_hcd.

Separately, the teardown-prompt fix from #277 (scarthgap) had not been ported, so once the agent path is live again, the releases in get_final_status_t234 and the end-of-script lingering-device deauthorize would each age out the host's 120s replug waiter after flashing already completed.

Change

Commit 1 — remove the duplicates. Six of the seven pairs are byte-identical modulo whitespace; only disconnect_usb_device differs, by exactly the agent path and the device-gone guard. Keep the agent-aware copy, delete the shadowing re-imports. Pure deletion, −202 lines.

Commit 2 — port the relevant half of #277:

• disconnect_usb_device gains an optional no-prompt mode (threaded through unmount_and_release): teardown/cleanup releases never engage the agent, keeping only the free sysfs toggle. Applied to get_final_status_t234's release and the end-of-script deauthorize.
• _twiddle_via_agent prints ACTION NEEDED: unplug and replug the device's USB cable to continue provisioning to stderr before blocking, so CLI-driven provisions surface the prompt in the terminal instead of stalling silently.
• The reuse-cycle mode from nvidia: suppress redundant usb twiddle prompts in initrd-flash #277 is intentionally not ported: the back-to-back double disconnect in generate_flash_package that required it does not exist in the wrynose flow.

With AVOCADO_AGENT_SOCK unset (bare Linux / CI), every call site behaves exactly as before in all modes.

Validation

• bash -n clean; no duplicate function definitions remain (verified by scan).
• 13-case stub harness (real _twiddle_via_agent / disconnect_usb_device / unmount_and_release extracted from this file, fake agent on a real AF_UNIX socket): mode threading, device-gone idempotency, prompt emission, and no-agent parity all pass.
• Hardware bench on a Jetson Orin Nano is pending a wrynose Orin runtime build; the equivalent scarthgap change was validated end-to-end on real hardware in nvidia: suppress redundant usb twiddle prompts in initrd-flash #277.