Migrating azure-pipelines.yaml to separate repo, but running on code of other repo

Ultimately, I'm trying to do this:

• Move azure-pipelines.yaml and associated templates out of the code repository (code-repo).
• Move them into a separate dedicated repository (pipeline-repo).
• Have the pipeline look at the config for the pipeline in pipeline-repo, but run the pipeline on the code in the code-repo.

I'm referring the following documentation:

• Use other repositories: this one refers to "templates in other repositories," but I'm trying to remove any pipeline configs so the code-repo is just purely application code... and the Dockerfile.
• Define a repositories resource

For testing, I have this simple test.yaml:

# Triggers when PR is created due to branch policies
trigger: none

resources:
  repositories:
  - repository: code-repo
    type: git
    name: code-repo

pool:
  vmImage: 'ubuntu-latest'

stages:
- stage: Testing
  displayName: Test stage
  jobs:
  - job: ParallelA
    steps:
    - bash: echo Hello from parallel job A
      displayName: 'Run a one-line script'

When I create a PR on code-repo, it is triggering the pipeline, which is to say branch policies are configured to refer to that pipeline. I do get the print out the Hello from parallel job A print out.

But I don't see in the run logs it pulling code-repo.

I do see the following, however:

My actual PR pipeline would look something like this:

trigger: none

resources:
  repositories:
  - repository: code-repo
    type: git
    name: code-repo

variables:
- template: templates/variables.yaml

pool:
  vmIMage: $(vmImageName)

stages:
- template: templates/build/buildStage.yaml
...

Testing that, it confirms that it isn't running on the code-repo PR, but the pipeline-repo so everything fails.

So it is unclear to me what I need to do from here to get the pipeline to run on the PR code from code-repo.

Suggestions?