fix(10.1): CR-01 answer a value that does not fit its column with a 422

lagoon.Fill now returns a *lagoon.FillTypeError naming the key when a
requested value cannot be stored in its column (a fraction, exponent or
overflow for an integer field, or a value of the wrong type). The admin
save path maps it to a validation_failed 422 on that field instead of a
500 CapabilityError; genuine capability failures keep the 500.

modules/cabana/crud.go

@@ -325,6 +325,12 @@ func (s CRUDService) save(ctx context.Context, cc *CompiledController, id any, i
 		}
 		projected := projectOperation(cc, in.Body, op)
 		if err := lagoon.Fill(target, fillAllowed(cc, target, op), projected, false); err != nil {
+			// A value that does not fit its column is the admin's input,
+			// not a missing capability: answer it on the field.
+			var typed *lagoon.FillTypeError
+			if errors.As(err, &typed) {
+				return &ValidationError{Details: fillTypeDetails(typed.Key)}
+			}
 			return &CapabilityError{ControllerID: controllerID(cc)}
 		}
 		if hook, ok := target.(lagoon.HasBeforeValidate); ok && hook != nil {
@@ -737,6 +743,12 @@ func valuesForRules(model any, rules map[string]string) map[string]any {
 	return out
 }
 
+// fillTypeDetails is the 422 detail for a value lagoon.Fill could not store
+// in its column. Writable fill keys equal their form field names.
+func fillTypeDetails(key string) map[string]any {
+	return map[string]any{key: []string{"The " + key + " field has an invalid value."}}
+}
+
 func validationDetails(msgs map[string][]string) map[string]any {
 	out := make(map[string]any, len(msgs))
 	for key, messages := range msgs {