[Launch blocker] Nix installer policy: auto-install vs guided setup

[linear-code]

Classification

Pre-launch decision

Context

Juan ( as well. as Cooper's non-technical friend had issues with the auto install)

Desired outcome

Users who don't have nix installed should be told they need to install it and be pointed to two options (determinate & official nixos) w/ jhigh-level instructions

Acceptance criteria

• @farhankhalaf fill later

Source

Juan sourced: local audit file /Users/farhankhalaf/Downloads/2026-05-09_nixmac-review.md, section Onboarding issues.