Senior Full-Stack Engineer for Finance/GHG Calculations

Seeking a senior full-stack engineer to work on an existing codebase with a strict test gate. The role focuses on backend development for finance and GHG calculations behind a decision engine, with a plain JavaScript front end and Docker support. You should be comfortable improving and maintaining an established system, writing reliable code, and collaborating closely with the founder. Strong numeracy and attention to detail are essential; UI flair is less important. The platform. Node.js/Express API, PostgreSQL, plain JavaScript front end (no framework), Docker, deployed on Render and an Azure VM. Five modules take a water system from engineering inputs to an investment decision (NPV, benefit-cost ratio, IRR, GHG). The repository carries specifications, decision registers, a test harness and an operating guide; every change goes through a pull request and the harness must stay green. Work, in milestones (fixed price each, paid on acceptance): WO-1, first milestone and trial (4 days, due 26 September). Evaluate the bankability gates on the served financial values instead of a secondary cost basis; remove a deprecated composite gate; make the reference case reproduce its published results. Acceptance: harness green, ten reference values match. WO-2, external access (about 3 days). Named-user accounts for a client evaluation on the hosted demo, with access logging. WO-P, PDF export (1–2 days). Integrate an Investment Decision Memo I have already built: HTML template, data-binding module, sample data and a field-by-field mapping table are supplied; the work is serving it from the API and adding the export action. WO-S, API completions (3–4 days). Expose values the platform already holds (system definitions, a sensitivity block, provenance fields) and fix a few label inconsistencies. WO-3, pilot readiness (about 7 days). A client can create, save and run its own asset end to end; multi-asset persistence; climate inputs from an extended data pack. How we work. I direct daily and answer within hours (Sydney time; overlap with Gulf hours useful). Scope is frozen per milestone; changes go into the next one. Acceptance means the pull request merges with the test harness green and, for anything printed, the mapping table reconciled. Later milestones are awarded on the strength of the first. To apply: two or three sentences on a comparable Node/PostgreSQL system you maintained, your availability from 22 September, and your price for milestone 1.