JsonLogFn typedef

A logging callback invoked by JsonSentinel on every validation failure.

Register an implementation once at app startup via JsonSentinel.configure:

JsonSentinel.configure((message, {error, stackTrace, extras, escalate}) {
  myLogger.warn(message, stackTrace: stackTrace, extras: extras);
});

message is the formatted validation failure report. For JsonSentinel.validate it has the form [Model] JSON validation failed (N errors):\n • …. For JsonSentinel.validateBatch it has the form [Model] JSON batch validation failed (N of M items failed):\n Item I (K errors):\n • ….

error is reserved for potential future exception-based callers; both JsonSentinel.validate and JsonSentinel.validateBatch always pass null. Treat it as always null in current implementations.

stackTrace is a stack trace captured inside JsonSentinel at the point where the failure is detected.

extras carries structured data about the failure. The keys depend on which method fired the callback:

• JsonSentinel.validate: always 'context' (model name) and 'json_preview' (truncated JSON string of the validated map).
• JsonSentinel.validateBatch: always 'context', 'failure_count' (int), 'total_count' (int), and 'item_previews' (List<String> of truncated JSON strings for each failing item, in failureIndices order). Does not include 'json_preview'. Absent when generatePreviews: false.

escalate hints that the failure warrants elevated capture (e.g. a Sentry event rather than a breadcrumb). Nullable so implementations may omit it from their signature; treat null as false.