## Summary
- route macOS through the OpenShell 0.0.37 standalone gateway path
without calling the removed `openshell gateway start` command
- use the VM driver on Darwin (`OPENSHELL_DRIVERS=vm`) while keeping
Linux on the Docker driver path
- repair platform-specific helper installs: Linux requires
`openshell-gateway` + `openshell-sandbox`; macOS arm64 requires
`openshell-gateway` + `openshell-driver-vm`
- add focused installer/onboard tests for platform helper requirements,
Darwin gateway env, and Linux-only `/proc` env verification

## Scope
This is the limited macOS 0.0.37 compatibility path only. It
intentionally leaves the broader legacy-upgrade cleanup and survivor e2e
work out of this PR.

## Validation
- `npm run build:cli`
- `npm run typecheck:cli`
- `npx vitest run test/install-openshell-version-check.test.ts
test/onboard.test.ts --testTimeout 60000`
- `bash -n scripts/install-openshell.sh`
- `git diff --check`
- local macOS/Colima smoke: temp `openshell-driver-vm` from OpenShell
v0.0.37 + `openshell-gateway` with `OPENSHELL_DRIVERS=vm` listened on
`127.0.0.1:18080`

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Installer now validates required driver binaries per OS/arch and
installs macOS ARM64 gateway + VM driver (including sudo flow).
* **Bug Fixes**
* Missing-driver detection and reinstall prompts fixed for macOS;
installer chooses OS/arch-specific release assets and rejects
unsupported macOS x86_64.
* **Tests**
* Added/updated tests and stubs for macOS ARM64 driver presence, asset
selection, and platform-specific runtime behavior.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/NVIDIA/NemoClaw/pull/3391)
<!-- end of auto-generated comment: release notes by coderabbit.ai -->