Dominoes or weather? Separating self-excitation from latent-regime clustering, in three forms

Clustered crisis events admit two very different explanations. In the dominoes reading each event raises the hazard of the next: self-excitation, endogenous contagion. In the weather reading a slowly varying latent regime makes some periods broadly dangerous: exogenous modulation with no event-to-event causation. The two produce nearly identical clustering, and the policy readings they invite are opposite. This paper races a Hawkes self-excitation arm against a Markov-switching multifractal Cox arm with an exact filter, in three forms, and reports where the race can be decided at all. The central negative is a decidability result: over much of the sample-size and branching-ratio range the two mechanisms are not separable, and a Hawkes fit to a regime-switching truth infers a spurious near-critical branching ratio. On the corpus at hand the mechanism question is undecidable at the available N — which is a finding about what the data can support, and is reported as such rather than resolved by choosing the more interesting arm. Programme context. Fenocrisis is the crisis-entanglement repository of the Feno programme. Its discipline is stated once and applies to every record here: a verdict ships only where a decidability atlas computed on known-truth simulation says the design could have seen the effect; every number regenerates bit-for-bit from a pinned seed; the results ledger is append-only; and nothing forecasts, warns, or ranks — every figure is a retrospective model comparison on public, aggregate data. Part of the Feno program. The source repository is private; the reproduction materials for this record are contained in the record itself.