How to merge a mapping into template

,
1

I have just combined several automations into one:

- alias: "Handle Color Cards"
  id: handle_colorcards
  mode: single
  max_exceeded: silent
  variables:
    # Map tag ID to content
    tags:
      f36a212d-5d8a-4d0e-8f96-xxxxxxxxxxx:
        alias: red
        service: light.turn_on
        data:
          hs_color:
            - 0
            - 100
          transition: 1
      2841c96f-aff7-4905-8ec0-xxxxxxxxxxx:
        alias: orange
        service: light.turn_on
        data:
          hs_color:
            - 30
            - 100
          transition: 1
      3c92bafa-205f-461c-a45e-xxxxxxxxxxx:
        alias: yellow
        service: light.turn_on
        data:
          hs_color:
            - 60
            - 100
          transition: 1
      [... more variables...]
  trigger:
    platform: event
    event_type: tag_scanned
  condition:
    - "{{ trigger.event.data.tag_id in tags }}"
  action:
    - variables:
        tag_service: "{{tags[trigger.event.data.tag_id].service }}"
        tag_data: "{{tags[trigger.event.data.tag_id].data }}"
    - service: "{{ tag_service }}"
      target:
        entity_id: light.hue_2_light
      data: "{{ tag_data }}"        <------ THIS IS THE ISSUE

I wonder how to further reduce the code by setting the transition centrally in the service data of the action block.

I have tried several approaches:

data: >
  "{{ tag_data }}"
  transition: 1

...

data: "{{ tag_data }}"
  transition: 1

...

but they all give one of these errors:

Error rendering data template: Result is not a Dictionary

OR

expected a dictionary for dictionary value @ data['action'][0]['variables']. Got None extra keys not allowed @ data['action'][0]['tag_data']. Got None extra keys not allowed @ data['action'][0]['tag_service']. Got None.

How do I combine / merge / join / mix a template with a mapping?
All help appreciated in advance