Graceful config validation

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):

{
  "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.