test: Deterministic test-data factories & seeders

[joelpeace48-cell]

Background & current state

Tests hand-build fixtures inconsistently across the backend/frontend suites, causing duplication and brittle setups. There are no shared factories/seeders.

Goal

Provide deterministic test-data factories + seed scripts for campaigns, participants, API keys, and on-chain fixtures.

Technical design

• Factory helpers (e.g., makeCampaign(overrides), makeParticipant(...)) producing valid, deterministic objects; seed scripts to populate a DB/local devnet (NEW-090) for E2E.
• Shared between backend + frontend where sensible; deterministic via seeded RNG.

Edge cases

• Determinism (seeded RNG) for reproducible tests.
• Keeping factories in sync with schema changes.
• Realistic edge fixtures (windows, caps, allowlists).

Task breakdown

• Factory helpers + seeded RNG.
• Seed scripts for DB + local devnet.
• Refactor a sample suite onto factories.

Acceptance criteria

• Tests use shared factories; seeding is reproducible across runs.

Testing & verification

• Refactor a representative suite; assert determinism.

Out of scope

• Full test rewrite.

Dependencies / related

• Supports all test epics; uses NEW-090.

Difficulty: easy · Effort: S–M · dx