Custom app installed via `pip install -e` is missing the `sites/assets/<app>` symlink that `bench get-app` creates

[oysi2025]

Context

When packaging custom Frappe apps in a Docker image, bench get-app is awkward to use because it requires network access at build time and isn't idempotent for purely local code. The natural alternative — and what every "custom app in Docker" tutorial converges on — is:

COPY apps/oysi_compliance /home/frappe/frappe-bench/apps/oysi_compliance
RUN /home/frappe/frappe-bench/env/bin/pip install -e /home/frappe/frappe-bench/apps/oysi_compliance

This installs the Python package correctly. The app is importable, hooks fire, DocTypes get created on bench migrate, and bench list-apps shows it.

But the sites/assets/<app> symlink is silently missing, and the asset pipeline relies on it for serving static files (<app>/<app>/public/). bench get-app creates this symlink as part of its install flow; pip install -e does not.

Symptom

Custom JS/CSS bundles in <app>/<app>/public/css/... and <app>/<app>/public/js/... return 404 from the frontend. From the user's perspective the app is "installed" — only the assets are silently broken.

Reproduction

1. Base image: frappe/erpnext:v16
2. Add a custom app via COPY + pip install -e (as above), with a <app>/<app>/public/css/<app>.bundle.css referenced via app_include_css hook.
3. Build and start the bench, run bench migrate, request the desk in a browser.
4. Network tab shows 404 for assets/<app>/css/<app>.bundle.css.
5. Inspect: ls -la /home/frappe/frappe-bench/sites/assets/ — missing <app> symlink.
6. Manual fix: ln -s ../../apps/<app>/<app>/public sites/assets/<app>. Assets load immediately.

We hit this with three local custom apps in a row (oysi_compliance, ecommerce_integrations, oysi_branding); each one cost a debug round before the pattern clicked.

Suggested fix

In order of increasing scope:

1. Doc note in the "Custom Apps in Docker" section: explicitly call out that pip install -e skips the asset symlink, and provide the one-line ln -s fix or recommend a wrapper.
2. bench symlink-app-assets <app> subcommand — idempotent, creates the symlink if missing. Easy to drop into a Dockerfile (RUN bench symlink-app-assets oysi_compliance).
3. Refactor bench get-app so the symlink creation lives in its own internal function that can be invoked independently from the network-fetch path.

(2) feels like the sweet spot — small surface, fixes the docker-packaging case cleanly without touching get-app semantics.

Environment

• frappe/erpnext:v16 base image (Frappe 16.13, ERPNext 16.12)
• Three local custom apps installed via COPY + pip install -e
• Symptom and fix verified on production deployment

[kirsysuv]

I use bench get-app when packaging custom Frappe apps in a Docker image, and the sites/assets/ symlink is also missing.
I have to create symlink in running contianers.