For runtime-modifiable values. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
It was accidentally deleted in the earlier 0022c3d2e (#2143) refactor. Lock it in with a test. Fixes tailscale/corp#2503 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: David Anderson <danderson@tailscale.com>