When configuration has conditional dependencies, make the system fail fast only for cases that break invariants (correctness/safety), but allow secure graceful degradation for “optional feature” toggles when prerequisites may be missing. Apply this rule: 1) Enforce bidirectional relationships in schema - If the meaning of one field depends on another (e.g., `auth_type`), use JSON Schema conditionals so invalid combinations are rejected rather than silently ignored. - Prefer `allOf` with focused `if`/`then` blocks to avoid partial validation gaps. Example (JSON Schema conditional enforcement): ```json { "allOf": [ { "if": {"properties": {"auth_type": {"const": "per_user_headers"}}, "required": ["auth_type"]}, "then": {"required": ["per_user_header_keys"]} } ] } ``` 2) Don’t turn “safe no-ops” into hard failures - For runtime-dependent options (e.g., requires object storage), if the runtime behavior is explicitly safe (e.g., “drop content, never leak”), keep schema validation non-fatal. - Implement a one-time warning and fall back to the secure default instead of failing startup/validation. Decision heuristic: - If misconfiguration could lead to incorrect/unsafe behavior → enforce in schema (fail validation). - If misconfiguration only disables functionality and the system guarantees secure fallback → allow it, warn, and degrade gracefully.