Real-Postgres round-trips for the external/internal PR-review TaskService
helpers that the existing mock tests can't prove actually persist:
- ingest_external_pr — create-once, head-SHA dedup (unchanged head skips),
and re-review on a new head; internal_pr source wording;
- pr_review_claim / complete_review — the planless, branchless
pending -> in_progress -> completed lifecycle, with re-claim / re-complete
no-ops and the "complete requires in_progress" guard;
- create_supersede_umbrella / find_supersede_umbrella — created on the same
repo (not parented), idempotent lookup, non-review rejection, and the
pr=5-vs-pr=50 exact-marker disambiguation;
- list_external_pr_reviews — source isolation, the data-layer half of the
dispatcher contract (regular tasks never leak into the review queue).
Writes use flush (not commit) so the rollback-per-test fixture keeps each
case isolated from the others against the shared session-scoped test DB.
