Senior Software Engineer, Payroll Engine in United

• Has shipped a system where money is the output: payroll, billing, banking, insurance claims, accounting. You can explain how you kept a ledger correct under concurrency and corrections.

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• Fluent in integer-cents arithmetic, rounding rules, and the difference between a correction and a reversal.

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• Designs state machines and event-sourced or append-only data models; knows why committed records are never edited.

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• PostgreSQL depth: migrations against live data, constraints, transactions, advisory locks or equivalent.

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• Writes tests as part of the change; has built or maintained a replay or golden-file regression suite.

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• Has worked with AI coding agents on real deliverables: writes specs an agent can execute and reviews agent output critically.

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• Comfortable in a monorepo with CI, Docker Compose and GitHub Actions.

• 5+ years building transactional backend systems in Python; Django and PostgreSQL in production.

• Design and build the domain model: pay groups and calendars, earning and deduction codes with limits and ordering, employee tax profiles, year-to-date and quarter-to-date accumulators per EIN.

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• Build the ledger as an append-only record of every committed check and adjustment, the single source for registers, general ledger, year-end and audit.

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• Build the pay-run state machine: draft, preview, calculate, approve, commit; regular and off-cycle runs; manual checks; voids and reversals; retroactive pay.

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• Implement gross-to-net orchestration around the tax adapter: pre-tax and post-tax deductions, imputed income, supplemental wages, garnishment calculation with withholding limits.

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• Build the generic hours-and-earnings import, then the bridge from the portfolio company’s time-and-attendance product that turns locked, approved timecards into earnings lines with rate, pay code, work location and job-cost dimensions.

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• Build and maintain the regression harness: replay the corpus on every change, report variances to the cent, and run every variance to ground.

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• Write Technical Documents from the product manager’s PRDs, direct coding agents against them, and review every agent-authored PR line by line before merge.

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• Keep money as integer cents and committed runs immutable; make every calculation re-runnable from stored inputs and engine version.

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