How I Structured User Data for My AI SaaS

Most developers building their first SaaS make the same mistake I almost made — they reach for sessionStorage because it works in the demo, then discover it breaks the moment a real user opens a second tab. This is the post I wish I'd had before Week 5. The problem with sessionStorage Resume Tailor's pipeline works like this: upload a PDF, paste a job description, get AI-rewritten bullets, download a tailored resume. In the demo, sessionStorage holds everything together — the parsed resume, the analysis, the rewritten bullets. It works perfectly. Until a user refreshes the page. Or opens the app on their phone after signing up on their laptop. Or closes the tab by accident. sessionStorage is scoped to a single browser tab. It doesn't survive a refresh. It doesn't sync across devices. It's fine for prototyping — it's not a database. The fix is obvious in hindsight: persist to Postgres, load from the database on every session. But getting there requires a set of decisions that aren't obv