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The passage around this formula

The shape of the exposure is simple enough to write down. Let n be the number of side-effecting tool calls in a session, p the probability that any one call’s response is lost after the server has already executed it, and i the fraction of those calls actually covered by a working, executor-enforced idempotency key. Then the expected count of uncontrolled duplicate side effects across the session is approximately $\mathbb{E}[\text{duplicates}] \;\approx\; n \cdot p \cdot (1 - i)$. The only term a protocol upgrade could move is i ; n and p are properties of the workload and the network. Today, for most deployments, i is close to zero, because nothing in the base protocol gives a server a caller-supplied key to deduplicate against.

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