Original Research Lead hypothesis. Mechanism: a sharp daily price drop can come from two different kinds of selling, and open interest tells them apart. If OI falls hard on the down day, longs were closing or being liquidated. That selling is forced and price-insensitive, it is finished once the deleveraging ends, and it leaves a liquidity-provision rebound (the Nagel 2012 'evaporating liquidity' reversal, here identified directly from positioning data rather than from BTC return z-scores). If OI rises on the down day, new shorts opened into the drop. That is discretionary, information-bearing selling, and the drift continues (the OI-confirmed continuation literature). This hypothesis trades the CONTRAST between the two arms on the same date, so the market-wide post-crash beta that sank the three recent OKX down-shock books cancels inside the spread. The 2026-10-18 analyst note on OkxStressDayResidualReversalBtcHedged asked for exactly this: 'positioning/liquidation data that marks forced selling directly'. Difference from BybitOiFlushDownShockAbsorptionPanel (in pipeline): that design is long-only and uses Bybit OI. This one is a dollar-neutral long/short spread whose short arm is defined by OI BUILD, uses the deepest derivatives venue's OI (Binance USD-M) as the signal, and executes on OKX swaps. PRE-STUDY (Research Lead, fixed rule, OKX SPOT daily closes as the price proxy and Binance metrics end-of-day OI, 19 names, 2022-01 to 2026-10). Down-shock z<=-1.0 vs own 30-day vol; flush = OI log-change z<=-1.5 vs its own 30-day std; build = OI change >=0. Results: 120 dates had both arms. The same-date long-flush minus short-build 3-day spread averages +1.38% gross (date-clustered t 2.11). By year: 2022 +3.73%, 2023 +0.37%, 2024 -0.18%, 2025 +1.89%, 2026 YTD -0.96%. A stricter shock (z<=-1.5) gave 60 dates, +2.06%, t 1.97, with all five years positive. The short arm was measured separately on these names (lesson L230): down-shock days with rising OI had a mean 3-day forward return of -0.63% (484 events), against an unconditional -0.28% and +0.78% for the deep-flush long arm. The long arm on its own is weak once clustered by date (+0.17%, t 0.2). The edge is in the spread, not in buying the dip, which is why the design is market-neutral. The incremental value of the OI signal (lesson L217) is pre-registered against the price-only comparator: the same down-shock names unconditioned on OI average -0.34% over 3 days. Event count (lesson L237): every leg has OKX bars and Binance OI from 2021-12, so the overlap is about 4.8 years with roughly 120 qualifying event dates (about 25 a year). Execution: 24/7 venue, so per the capability registry the 'next-day open' entry is a market order at the signal day's close (next_bar_open_fill -> use_equivalent). Binance OI is read point-in-time with supp_as_of / supp_window; the value used is the last 5-minute metrics row KNOWN at the daily close (metrics rows are stamped at the window start, so a row is available one period later).