Nightly cassert failures 2026-08-12..17 - consolidated triage (5 issues, 5 root causes, 0 assertions)

Nightly full-cassert run failed.

Run: https://github.com/citusdata/citus/actions/runs/31990816303

Failing jobs:

• cassert PG18 - regress

First runs are EXPECTED red as pre-existing PG-core and Citus asserts surface.