envconfig

Closes #130 Summary Adds built-in support for the Docker/Kubernetes secrets convention. When an environment variable is unset or empty, envconfig also looks for a companion variable with a suffix (e.g. ). If set, that value is treated as a filesystem path; the file contents are read and used as the configuration value after trailing newlines are trimmed. Non-empty environment variables take precedence over Missing/unreadable files return an error is satisfied when the value comes from a file treats known companions as allowed Existing / API is unchanged (always-on, no new options) This differs from #210, which only exposes a custom hook for applications to implement themselves. Built-in support matches the convention used by Postgres, Redis, and similar images and what was requested in #130. Example Test plan [x] Unit tests with temp files covering: basic read and trailing newline trim env takes precedence over empty env falls back to required field via missing file error alt () name with default when neither env nor file is set allows [x] Full suite:

Summary Map env values are split on every , so entries like failed with . Use so only the first colon separates key and value. Test plan [x] [x] full package tests

Summary Small documentation cleanups: Setter interface comment: "types can" → "types that can" usage template test comment: "lieteral" → "literal" Test plan [x]