[Python] avoid building .egg-info files in read-only docker mount for local dependencies (uv...

I'm trying to use uv sync from within docker with this command:

Dockerfile

RUN --mount=type=cache,target=/root/.cache/uv \
--mount=type=bind,source=uv.lock,target=uv.lock \
--mount=type=bind,source=pyproject.toml,target=pyproject.toml \
--mount=type=bind,source=packages,target=/app/packages \
uv sync --package ftp-mock --locked --no-editable


However this wants to create .egg files which fails because I mounted the packages folder as read only (and I want to keep it this way). This is my current project layout:

.
├── packages
│ ├── ftp-mock
│ │ ├── config
│ │ │ ├── config_dev.json
│ │ │ └── ftp_mock_config.py
│ │ ├── Dockerfile
│ │ ├── ftp_mock.py
│ │ └── pyproject.toml
│ ├── http-mock
│ │ ├── config
│ │ │ ├── config_dev.json
│ │ │ └── http_mock_config.py
│ │ ├── Dockerfile
│ │ ├── pyproject.toml
│ │ ├── http_mock.py
│ │ └── templates
│ │ └── index.html
│ ├── local-shared
│ │ ├── __init__.py
│ │ ├── pyproject.toml
│ │ ├── mymodule.py
│ ├── main-app
│ │ ├── config
│ │ │ ├── config_dev.json
│ │ │ └── main_app_config.py
│ │ ├── Dockerfile
│ │ ├── pyproject.toml
│ │ └── main_app.py
│ └── __init__.py


...

As you can see I'm only trying to build the workspace-member ftp-mock which in turn requires local-shared. Now uv sync tries to install local-shared which creates the .egg-info file (or rather it tries and fails because it only has read access to the mount). How can I avoid polluting my the directory with the egg file (or any new files for that matter) so that docker stops complaining?

Here's the exact error from docker:

> [builder 4/6] RUN --mount=type=cache,target=/root/.cache/uv --mount=type=bind,source=uv.lock,target=uv.lock --mount=type=bind,source=pyproject.toml,target=pyproject.toml --mount=type=bind,source=packages,target=/app/packages uv sync --project ftp-mock --package -ftp-mock --no-install-project --locked --no-editable:
0.382 Using CPython 3.11.12 interpreter at: /usr/local/bin/python3
0.382 Creating virtual environment at: .venv
0.384 Resolved 15 packages in 1ms
0.385 Building local-shared @ file:///app/packages/local-shared
0.588 Downloading pydantic-core (1.9MiB)
0.660 Building pyftpdlib==2.0.1
0.693 Downloading pydantic-core
3.815 × Failed to build `local-shared @ file:///app/packages/local-shared`
3.815 ├─▶ The build backend returned an error
3.815 ╰─▶ Call to `setuptools.build_meta.build_wheel` failed (exit status: 1)
3.815
3.815 [stdout]
3.815 running egg_info
3.815 creating local_shared.egg-info
3.815
3.815 [stderr]
3.815 error: could not create 'local_shared.egg-info': Read-only file system
3.815
3.815 hint: This usually indicates a problem with the package or the build
3.815 environment.
3.815 help: `local-shared` was included because `ftp-mock` (v0.1.0) depends
3.815 on `local-shared`
------
Dockerfile:10
--------------------
9 | # # Uses a cache to speed up the build. To clear the cache run docker with the --no-cache flag
10 | >>> RUN --mount=type=cache,target=/root/.cache/uv \
11 | >>> --mount=type=bind,source=uv.lock,target=uv.lock \
12 | >>> --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
13 | >>> --mount=type=bind,source=packages,target=/app/packages \
14 | >>> uv sync --project ftp-mock --package ftp-mock --no-install-project --locked --no-editable
15 |
--------------------
ERROR: failed to solve: process "/bin/sh -c uv sync --project ftp-mock --package ftp-mock --no-install-project --locked --no-editable" did not complete successfully: exit code: 1

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