MMP.19:5.1 - Change the route for an already observed processing case

A routing model gives latency in ticks as Y=2A+U. Route A=1 adds two ticks; residual latency U is 0 or 1 with equal probability. The recorded case used A=1 and had Y=3.

Under the factual equation only U=1 is compatible. Keeping that input and replacing the route by A=0 gives Y_0=1. Drawing a fresh U from the population instead gives mean latency 1/2. That is a new-case mean, not the requested alternative for the observed case.

If the record is noisy, use its likelihood rather than selecting U with certainty. If an exact Y=4 is reported under the unchanged model, neither admitted U is compatible; return the conflict instead of calculating a posterior with zero denominator. Whether the same residual condition would persist under a real route change is a subject premise of this model.