Test class 4: aggregate-invariant tests — verify counts/projections move in a known direction

Tracking issue for Class 4 of the test taxonomy (parent: meta-issue #192).

Shape

Pre/post state: aggregate or projection moves in a known direction (count increments, statistics shift).
Verifier: aggregate query (getProcessInstanceStatistics, getProcessDefinitionStatistics).

Op examples

Status

Lowest priority of the four classes. Useful for completeness; many ops in this class don't have a clean delta (audit log just appends, statistics counts can shift for reasons unrelated to the op under test).

Goal

Decide whether this class is worth implementing. Possible outcomes:

• Implement as a thin generator on top of Class 2/3.
• Mark won't-do; the value is mostly captured by Class 2's per-entity assertions.

Acceptance

• Decision recorded with reasoning.
• If implemented: at least one Class 4 generated test with a delta assertion. If not: this issue closes with the decision documented.

Start by reading the Class 4 shape, operation examples, and the proposed thin-generator relationship to Classes 2/3 in this issue. Decide whether aggregate or projection deltas provide value beyond Class 2 assertions, and record the reasoning. If implementing, add at least one generated test with a delta assertion; otherwise document the decision and close the issue.