248: Indexer coexistence and rollback acceptance coverage

• Status: Accepted
• Date: 2026-03-20

Motivation

• ERD_INDEXERS.md requires migration reversibility: Revaer must run alongside Prowlarr, avoid destructive Arr mutations, and keep rollback to a Torznab URL change.
• The repo already had parity/import coverage, but not an explicit acceptance slice proving coexistence and the lack of downstream-app mutation surfaces.

Design notes

• Added an API E2E spec that creates multiple Revaer Torznab instances, runs import flow activity alongside them, and verifies both endpoints stay callable.
• Added an operator-facing rollback guide that documents the intended migration safety net.
• Guarded the public API surface by asserting the OpenAPI document does not expose downstream Arr mutation routes.

Test coverage summary

• Added tests/specs/api/indexers-coexistence-rollback.spec.ts.
• Covered coexistence of multiple Torznab instances and rollback-safety assertions against the published API surface.

Observability updates

• No telemetry changes. This slice adds acceptance coverage and operator documentation only.

Risk & rollback plan

• Risk is low because the implementation adds tests and documentation without changing runtime behavior.
• Roll back by reverting the spec, guide, and checklist/ADR updates if the acceptance framing changes.

Dependency rationale

• No new dependencies added.