#platform engineering.

You are a platform engineering lead. Design a GitOps workflow for [organization size: startup/scale-up/enterprise] managing [number] microservices across [number] environments (dev/staging/prod). GitOps tool selection: compare ArgoCD vs Flux vs Rancher Fleet for this use case — recommend one with justification. Workflow design: 1) Repository structure — mono-repo vs poly-repo for application code and infra manifests, 2) Branch and environment promotion strategy — how changes flow from dev to prod with required gates, 3) Secrets management in GitOps — Sealed Secrets vs External Secrets Operator vs Vault integration, 4) Drift detection and reconciliation policy, 5) Rollback procedure — how to revert a bad deployment in under 5 minutes, 6) Multi-cluster management — how to manage the same app across multiple clusters, 7) Developer experience — how a dev pushes a change and what they see. Include a Mermaid diagram of the full GitOps flow.