### Problem to Solve The config crate dependency uses `features = ["yaml-rust2"]` (the dependency name) instead of `features = ["yaml"]` (the feature flag). In config 0.15, the `yaml` feature gates `FileFormat::Yaml` behind `#[cfg(feature = "yaml")]`, so using the wrong feature name means `FileFormat::all()` returns an empty list and `File::with_name("config/default")` can never discover `.yaml` files. The file source silently skips (`.required(false)`), so the bug was invisible while all config came from environment variables. This showed up when switching Helm charts from env vars to ConfigMap-mounted YAML files — pods crashed with `missing configuration field "datalake.database"` because only the password env vars populated a partial config tree. Reproduced both locally and on the GKE sandbox. ### Proposed Solution Change `Cargo.toml` from `features = ["yaml-rust2"]` to `features = ["yaml"]`. The `yaml` feature internally depends on `yaml-rust2`, so the same crate is pulled in, but the `#[cfg(feature = "yaml")]` guards now compile in the YAML format support.