Initial add backend stuff

appenv/appenv.go

@@ -0,0 +1,17 @@
+// Package appenv exposes the deployment environment that is baked into the
+// binary at compile time. The concrete value of Environment is selected by a
+// build tag (see env_development.go / env_staging.go / env_production.go), so it
+// can never be misconfigured or missing at startup. The bundler propagates it
+// into the JS bundle via the esbuild `__ENV_TYPE__` define.
+//
+// This is the framework half of what used to live in each app's
+// internal/constants: the app keeps its concrete constants (cookie names,
+// password rules, ...) and reads the environment from here.
+package appenv
+
+// The environment type names. Compared against Environment to branch behaviour.
+const (
+	EnvTypeDevelopment = "development"
+	EnvTypeStaging     = "staging"
+	EnvTypeProduction  = "production"
+)