writing-golisted

# Go Development Use only for Go modules. Follow the module's target Go version. ## Read First Read [principles.md](references/principles.md) before writing, changing, or reviewing Go code. Read conditional references only when the change touches that area. ## Conditional References - [patterns.md](references/patterns.md) — package layout, interfaces, errors, HTTP/service boundaries, concurrency, comments. - [testing.md](references/testing.md) — adding or reshaping Go tests. - [cli.md](references/cli.md) — writing or changing Go CLIs. ## Version-Gated APIs - Confirm `go.mod`, `toolchain`, CI, and nearby code before using version-specific APIs. - Go 1.25+: use `sync.WaitGroup.Go` when no error propagation is needed. - Use existing `errgroup` for goroutine errors or shared cancellation; add it only when the dependency is justified. - Go 1.25+: use `testing/synctest` for deterministic concurrent tests when available. - Go 1.25+: prefer stdlib `crypto/hpke` and `testing/cryptotest` over third-party code when they fit. - Treat `encoding/json/v2` as experimental unless the project opts into `GOEXPERIMENT=jsonv2`. - Go 1.26+: use `new(expr)` only when clearer than a local variable, composite literal, or address expression. - Go 1.26+: keep recursive type constraints in generic libraries; keep business logic concrete. ## Verification Run the project-configured build, tests, lint, vet, and formatting checks. Add race or concurrency-specific checks when the change touches goro