[Python] How to structure a Serverless Framework project with a root serverless.yml and...

I'm working on a Python project using FastAPI, AWS Lambda, and API Gateway. I'm organizing my project with a root serverless.yml and separate serverless.yml files inside each function's folder.

When I try to deploy, I get the following error:

Cannot resolve '${file(./service/../serverless.yml)}' variable at 'functions.0'. No value is available for this variable, and no default value was provided. Please check your variable definitions or provide a default value
​

root/
│
├── serverless.yml # root
├── service/
│ └── post_event/
│ ├── serverless.yml # function-level
│ └── main.py


In the root serverless.yml, I tried referencing the function-specific config like this:

functions:
- ${file(./service/post_event/serverless.yml)}`


In service/post_event/serverless.yml, I defined the function like so:

postEvent:
name: ${self:service}-${opt:stage, selfrovider.stage}-postEvent
handler: service.post_event.main.handler
module: service/publish_event`


I expected this structure to work by allowing each function to have its own serverless.yml and keeping the root file cleaner, but deployment fails with the error above.

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