This is a two-instrument lead-lag trade on US ETFs (venue USEQ, 1-DAY bars, history from 2006-05-22, 5121 joint sessions in the catalog: GDX.USEQ and GLD.USEQ, both checked). Gold-miner equities are a levered claim on the gold price: rolling 250-day beta of GDX daily log returns on GLD has a median of about 1.79. Equity investors who hold miners are a different clientele from bullion holders, and they absorb commodity-price news slowly. This is the producer-equity version of the documented commodity-to-equity underreaction (Driesprong, Jacobsen & Maat 2008, 'Striking Oil: Another Puzzle?', JFE). On each daily close, compute the 3-session residual gap = beta_250(t-1) * GLD 3-day log return - GDX 3-day log return. Z-score that gap against its own trailing 250-session mean and standard deviation, using only data up to t. If z > +entry_z, miners have lagged what bullion implies: go LONG GDX and SHORT beta x GLD. If z < -entry_z, miners have overshot bullion: go SHORT GDX and LONG beta x GLD. The position is beta-hedged against the gold price, so the P&L is the miner residual alone. Pre-study (point-in-time beta and z, daily closes 2006-2026, forward window starting the next session): with entry_z=1.5, the forward 3-session hedged residual averaged +0.36% after the long signal (284 signal days) and +0.60% after the short signal (273 signal days). With entry_z=2.0 it averaged +0.87% (152 days) and +1.02% (112 days). Over 5 sessions it was +0.58% / +0.74% at z 1.5. The edge decays by 10 sessions on the long side, so the clock is set at the peak (3-5 sessions), following lesson L166. This is not a calendar trigger, not a crypto mechanism, and not a cross-sectional basket: it is a single economically linked pair with a specific information-diffusion cause. It fills under-represented buckets: long-short (15.6% vs a 45%+ target), pairs, USEQ (4.9%), and a non-BTC data estate.