Strong Rust. You've shipped Axum or comparable async services to production.
You know what 'static lifetimes mean in practice and you don't fight the borrow checker — you collaborate with it.
Solid React 18 with TypeScript strict. You write hooks idiomatically, you understand provider composition, and you don't reach for a state library when Context is sufficient.
SQL fluency. MySQL specifically is a bonus; experience with sqlx::query!-style compile-time-verified queries is a bonus on top of that.
Comfort owning a wire contract — meaning you treat API_REFERENCE.md as the source of truth and you update it in the same commit as the code change. You understand why this matters across two repos with two CI pipelines.
Production discipline: you write structured logs, you reason about what gets INFO'd vs DEBUG'd, you don't leave panics on hot paths, you don't unwrap() on user input.