When behavior depends on platform features, build features, feature flags, or user-provided configuration, keep it explicitly scoped and validated. Apply this checklist: - **Gate compilation and code paths**: Put platform/build-specific modules behind the correct `#[cfg(...)]` so non-target platforms don’t even compile unix/fs-only imports. - **Use the same predicate for behavior**: Action availability should follow the exact feature-flag + settings predicate used elsewhere (and include a correct fallback flow when disabled). - **Provide deterministic fallbacks**: If a feature like `local_fs` is off, return a safe default (e.g., `None`/empty map) without referencing unavailable functionality. - **Validate at configuration boundaries**: Parse helpers should enforce invariants (e.g., positive numbers) and surface structured errors. - **Centralize config source/precedence**: When using env vars or other configuration channels, document and implement a clear precedence model (and consider refactoring into shared “prepare config” logic). - **Remove or document dead toggles**: Don’t leave production config flags that only exist in tests; either remove them or clearly document which caller toggles them. Example pattern (cfg + validated parsing): ```rust // Build gating: don't compile unix-only code on Windows. #[cfg(unix)] mod local_api; // Validation: enforce invariants at parse time. fn parse_positive_usize_query_param(url: &Url, name: &str) -> Result> { let Some(raw) = url.query_pairs().find(|(k, _)| k == name).map(|(_, v)| v) else { return Ok(None); }; let value = raw.parse::()?; ensure!(value > 0, "`{name}` must be greater than 0"); Ok(Some(value)) } ``` These practices prevent cross-platform build breaks, mis-scoped feature behavior, and silent misconfiguration—while keeping configuration-driven behavior predictable and maintainable.