Backend: add a versioningService compatibility test asserting event-schema version downgrades are rejected

[Baskarayelu]

📋 Description

versioningService.ts labels indexed records by contract/event-schema version. There is no test asserting the service rejects a downgrade — ingesting an event tagged with an older schema version than already recorded for that stream must be refused or explicitly handled, never silently overwriting newer-version data.

Why this matters: version downgrades during a replay or a misconfigured indexer can corrupt newer state with stale schemas. A focused test pins the monotonic-version guarantee.

🎯 Requirements & Context

• Add a jest suite covering: accept a higher/equal version; reject (or quarantine) a lower version for the same stream.
• Assert the recorded version never moves backward.
• Cover the first-seen version (no prior record) accepted.
• Cover mixed-version batches processed in order.

Context & constraints

• TypeScript, jest, better-sqlite3 in-memory. Reuse the version labels in contract.ts types.

🛠️ Suggested Execution

git checkout -b test/versioning-downgrade-reject
npm --prefix backend test -- versioning

• Edge cases: equal version (idempotent accept); downgrade by one; downgrade after several upgrades; unknown stream first-seen.

Example commit message

test(backend): assert versioningService rejects schema-version downgrades

Pins the monotonic-version guarantee so replays cannot overwrite newer state
with older schemas.

✅ Acceptance Criteria & Guidelines

Requirement	Target
Downgrade rejection asserted	Required
Monotonic version invariant	Required
Coverage of versioning logic	≥ 95%
jest + lint clean	Required
Timeframe	96 hours from assignment

💬 Community & Support

Join Discord: https://discord.gg/VpngvTjWa — comment to claim. 🚀

[YfengJ]

Hi maintainers, I would like to apply for this issue if it is still available.

If assigned, I will keep the PR focused on the backend versioningService compatibility tests only: cover first-seen/equal/higher schema versions, reject or quarantine lower-version downgrades for the same stream, assert the stored version never moves backward, and include mixed-version batch coverage using the existing TypeScript/Jest + in-memory sqlite test setup. I will wait for assignment or explicit confirmation before opening a PR.