Unable to get the custom extension build_runner dart

Question

I am trying to get the example_model.fti.dart file However, I get only example_model.fti.g.part at the output

I've tried different variations of build_extensions

    .fti.g.part
    .fti.g.dart
    .fti.part
    .fti.dart
    ...

with my build.yaml

builders:
  generators:
    target: ":generators"
    import: "package:generators/generators.dart"
    builder_factories: ["fti"]
    build_extensions: { ".dart": [".fti.dart"] }
    auto_apply: dependents
    build_to: source
    applies_builders: ["source_gen|combining_builder"]
#    runs_before:
#      - source_gen|combining_builder

My worst result is example_model.fti.g.part, and best example_model.g.dart but example_model.g.dart conflicting with json_serializable How I can get example_model.fti.dart