[0xQuerencia]

Verified data-integrity defect

Referral fulfillment currently marks a referral rewarded_at before separately invoking adjust_user_pixels. If the wallet transaction fails, the referral remains claimed and can never earn the promised pixels on retry. Similarly, separate milestone count and credit operations can race when several referred projects are approved concurrently.

Fix

• Migration 0236 adds settle_referral_reward_atomic: validates the reward, serializes per-referrer payout/milestones with a user-row lock, marks the individual referral and credits the wallet and any applicable milestone in one PostgreSQL transaction.
• Dashboard approves/pays via the atomic RPC, and only sends notices after successful settlement.
• PostgreSQL integration tests cover duplicate claims, concurrent milestones, and deliberately failed wallet writes which must roll back both the referral flag and balance change.
• No change to referral eligibility, rate tiers, or milestone amounts.

Do not deploy without migration 0236. Keep open until CI, code review, and database checks are green. Production was not modified by creating this PR.

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