GeezerVison

fred-review did not finish; see https://github.com/feldera/feldera/actions/runs/42325328478

What I ran

Findings

• bug (high): The new NoIntegralOrDifferentiatorVisitor breaks every NOW() query that still has a DBSPNowOperator → D pair. CI will go red.
• missing (medium), gate "tests for changed behaviour": The compiler commit changes the generated circuit but adds no Java tests. Tests should cover these rewrites:
  • PullFilterVisitor folding a filter into an incremental constant.
  • RemoveIAfterD turning I(incremental constant) into a plain constant.
  • CSE keeping a ConstantOperator and an IncrementalConstantOperator with the same rows distinct.
  • PropagateEmptySources/RemoveConstantFilters producing an empty incremental constant.
  • A JSON round trip of the new operator (fromJson).
• pitfall (medium), checkpoint compatibility: Existing pipelines compiled with the old ConstantGenerator+Differentiator pair will get new persistent IDs on upgrade. Everything downstream of a constant will then be treated as new and bootstrapped again. Please confirm that this is acceptable. If it is, note it in the PR description or release notes.
• missing (medium), Rust test gap: No DBSP test covers a nested (recursive) scope, where clock_end resets emitted once per parent step and fixedpoint depends on it. No test covers bootstrapping a modified circuit either, which is what is_deterministic_source is for.