[cikzh]

What & why

Closes

During #4136 the fuzzer hit on a case where P 9 and P 10 were applied. When this happens in Abacus, the user will be presented a warning that this happened and that they should contact Kiesraad. See:

abacus/backend/apportionment/src/seat_assignment/structs.rs

Lines 33 to 35 in 472d08d

	if has_p9 && has_p10 {
	warnings.push(ApportionmentWarning::AbsoluteMajorityAndListExhaustion);
	}

See for more explanation and context: #3219 and #1357

How to test

1. Run the fuzzer, see that it fuzzes
2. Download the artifact: crash-d38c2d9f596d7bbf84f8bff53b25d639b03a986b.zip and run:

cargo fuzz run population_monotonicity artifacts/population_monotonicity/crash-d38c2d9f596d7bbf84f8bff53b25d639b03a986b

See that it doesn't crash. It does crash when running this on main

[praseodym]

I think we also need to check the if the second allocation has P 9 + P 10, not just the first allocation.

And we can check for AbsoluteMajorityAndListExhaustion in alloc.seat_assignment.warnings() instead of using the log.

[jschuurk-kr]

Reviewed code. Performed the steps in "How to test".

[stacktraceghost]

Tested, fuzz artifact works on this branch and not on main. Checked code.