The install flow previously captured current system DNS servers
verbatim into the backup file. If numa was already installed, current
DNS was 127.0.0.1, so the "backup" recorded 127.0.0.1 as the "original"
— making a subsequent uninstall a no-op self-reference.
Reproduced 2026-04-08 during v0.10.0 brew dogfood: after
`sudo numa uninstall; sudo /opt/homebrew/bin/numa install`,
`sudo numa uninstall` printed `restored DNS for "Wi-Fi" -> 127.0.0.1`
because the brew binary's install step had overwritten the backup with
the already-stub state.
Fix (all three platforms):
- macOS/Windows: if the existing backup already contains at least one
non-loopback/non-stub upstream, preserve it as-is. If writing a fresh
backup, filter loopback/stub addresses first so a capture from
already-numa-managed state isn't self-referential.
- Linux (resolv.conf fallback path): detect numa-managed or all-loopback
resolv.conf content and skip the file copy in that case; preserve an
existing useful backup rather than overwriting it. systemd-resolved
path is unaffected (uses a drop-in, no backup file).
Adds three unit tests for the predicates: macOS HashMap detection,
Windows interface filter, and resolv.conf parsing (real upstream,
self-referential, numa-marker, systemd stub, mixed).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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