Handle registry read and environment-write failures in setup's existing
post-install outcome handler. Keep installation separate from environment
persistence, as the missing-shell-config fallback already does.
Print session-local PowerShell assignments and profile instructions when
registry persistence is unavailable. Preserve the original diagnostic and
leave environment conflicts and other failures fatal. Do not attempt to
replace an unreadable persisted PATH or elevate to another Windows user.
Apply the behavior in both CLI versions, with regression tests for read and
write failures and literal quoting of ASCII and typographic apostrophes.
Closespnpm/pnpm#17167.