normalizers: Updated error handling within the JSON helper function.

internal/normalizers/common/json.go

@@ -42,6 +42,10 @@ func DecodeJSONPayload[T any](in event.Event) (T, error) {
 // label should be short and specific, e.g. "openweather observation".
 // outSchema should be the canonical schema constant.
 // build should contain ONLY provider/domain mapping logic.
+//
+// Error policy:
+//   - NormalizeJSON wraps ALL failures with consistent context: "<label> normalize: <stage>: ..."
+//   - build() should return specific errors without repeating the label prefix.
 func NormalizeJSON[T any, P any](
 	in event.Event,
 	label string,
@@ -55,8 +59,7 @@ func NormalizeJSON[T any, P any](
 
 	payload, effectiveAt, err := build(parsed)
 	if err != nil {
-		// build() should already include provider-specific context where appropriate.
-		return nil, err
+		return nil, fmt.Errorf("%s normalize: build: %w", label, err)
 	}
 
 	out, err := Finalize(in, outSchema, payload, effectiveAt)