Fix: Double symlink issue doesn't throw an error

### Bug Summary

When a person links their app in the `harperdb-config.yaml` and also run `harper run .` inside their app. The app does not update and errors out

### Reproduction Repository (if applicable)

https://github.com/BboyAkers/harper-invoice-app/

### Steps to Reproduce

1. Clone the app
2. Run `npm install` inside the app
3. Open `harperdb-config.yaml` and add the app at the bottom
5. Run `npm run dev` inside your app
6. The app errors out and doesn't run in `localhost:9926`

### Expected Behavior

1. Clone the app
2. Run `npm install` inside the app
3. Open `harperdb-config.yaml` and add the app at the bottom
5. Run `npm run dev` inside your app
6. Harper should throw an error

### Actual Behavior

1. Clone the app
2. Run `npm install` inside the app
3. Open `harperdb-config.yaml` and add the app at the bottom
5. Run `npm run dev` inside your app
6. Harper runs and the app errors out

### Platform

_No response_

### Console Errors

_No response_

### Screenshots or Videos

_No response_

### Additional Context

_No response_

### Are you planning to fix this issue?

Maybe, depending on complexity

### First-time contributor support

- [ ] I'm new to contributing and would appreciate guidance on the process
- [ ] I'd like help understanding the project structure
- [ ] I need assistance with setting up the development environment
- [ ] I'm comfortable contributing, but new to this project specifically

Reproduce the problem using the linked harper-invoice-app: install dependencies, add the app to harperdb-config.yaml, and run npm run dev or harper run . from the app. Trace the app-linking and symlink handling involved in that flow; done means Harper throws a clear error instead of starting while the app fails at localhost:9926.

Written by the indexing model from the issue text.