fix(affiliate): exact partner-fee math via getPartnerFeeUsd across stats, swaps, and payouts

[kaladinlight]

Description

Consolidates the partner-fee-share calculation onto a single exact helper, getPartnerFeeUsd, and removes getPartnerFeeRate.

The old pattern feeUsd × getPartnerFeeRate(...) multiplies by a lossy float rate (e.g. 50/60 → 0.8333…4), which reintroduces binary-float artifacts (e.g. "0.050000000000000004"). getPartnerFeeUsd multiplies before dividing (feeUsd × partnerBps ÷ verifiedBps, capped at the fee), so the result is exact.

Applied across all three consumers:

• getAffiliateSwaps — per-swap partnerFeeUsd (a full-precision string, so the artifact was directly visible in the response)
• getAffiliateStats — aggregate totals accumulated in BigNumber, so they reconcile exactly with the sum of the per-swap rows
• affiliate-payouts script (aggregateByPartner) — pays the partner share via the same helper; the partnerBpsUnset bucket now gates on partnerBps directly. Payout amounts are unchanged (they floor to 6 dp), so there it's precision-hygiene, not a value change.

With all three on getPartnerFeeUsd, getPartnerFeeRate has no remaining callers and is deleted.

Follow-up to #50 (partner revenue breakout) — the get-stats/get-swaps precision changes were split out of that PR so the fee-precision work reviews as one holistic unit.

Testing

• yarn build — all 6 packages build
• swap-service — affiliate tests pass (8/8)
• yarn affiliate-payouts:test — 25/25 pass

🤖 Generated with Claude Code

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 1d1bde1d-30ee-4736-86db-64e89c8151db

📥 Commits

Reviewing files that changed from the base of the PR and between f252430 and 4c6eb59.

📒 Files selected for processing (6)

• apps/swap-service/src/affiliate/affiliate.service.ts
• apps/swap-service/src/swaps/utils.ts
• scripts/affiliate-payouts/affiliate-payouts.test.ts
• scripts/affiliate-payouts/affiliate-payouts.ts
• scripts/affiliate-payouts/types.ts
• scripts/affiliate-payouts/utils.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/partner-fee-precision

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