Mirrors --add - removes AMOUNT (default: all) of a building from the
copied spec. Used this to check whether BHP's HWP is still worth
running after its price drop (still +19.8k-28.4k/day marginal,
nowhere near a teardown call) without hand-writing two spec files.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>