Regime-Conditioned Commodity Exposure: A Chain-of-Events Method for Anticipating Climatic and Biological Shocks to Brazilian Exports

We describe a reproducible method for anticipating the economic consequences of exogenous shocks — climatic, and by extension biological — on a country's commodity exports, using Brazil as the testbed. The core object is an event-conditioned exposure map: for a shock localized in space and time, we intersect its geography with a defensible, lens-structured trade-exposure layer (Genoma, derived from MDIC/Comex primary data) to identify which commodities and which subnational units carry the loss — often the opposite of what national export-share statistics suggest. We formalize the "export-share illusion", give the estimator, and present a validated case: an extratropical cyclone over Rio Grande do Sul in August 2026, where the method identified rice as the exposed commodity (RS = 96.2% of national rice exports) about one month before a mainstream report of a 22% producer-price rise. We generalize the engine into a hazard ladder (acute weather, seasonal regime, exotic tail, biological) and argue that the same exposure engine, fed a biological hazard, is closed by metagenomic pathogen surveillance. We are explicit about the method's boundaries: exposure is not realized loss, single-case validation is not a track record, and several loss layers remain gated behind data access. Working paper (draft) — RR Magma / Genoma de Mercado.