fix: container now copies managed python into runtime

Author: coretl

.devcontainer/devcontainer.json

@@ -8,8 +8,6 @@
     "remoteEnv": {
         // Allow X11 apps to run inside the container
         "DISPLAY": "${localEnv:DISPLAY}",
-        // We put venv on a different volume to cache so have to copy
-        "UV_LINK_MODE": "copy",
         // Do the equivalent of "activate" the venv so we don't have to "uv run" everything
         "PATH": "/workspaces/${localWorkspaceFolderBasename}/.venv/bin:${containerEnv:PATH}"
     },

template/Dockerfile.jinja

@@ -2,6 +2,12 @@
 # or docker with user namespaces.
 FROM ghcr.io/diamondlightsource/ubuntu-devcontainer:noble AS developer
 
+# We will mount in a cache for uv, so silence warnings about it being on a different volume
+ENV UV_LINK_MODE=copy
+
+# Cache the python download in the same directory as the uv cache
+ENV UV_PYTHON_CACHE_DIR=/root/.cache/uv/python
+
 # Add any system dependencies for the developer/build environment here
 RUN apt-get update && apt-get install -y --no-install-recommends \
     graphviz \
@@ -16,6 +22,9 @@ WORKDIR /app
 COPY . /app
 RUN chmod o+wrX .
 
+# Tell uv sync to install python in a known location so we can copy it out later
+ENV UV_PYTHON_INSTALL_DIR=/python
+
 # Sync the project without its dev dependencies
 RUN --mount=type=cache,target=/root/.cache/uv \
     uv sync --locked --no-editable --no-dev
@@ -50,6 +59,9 @@ FROM ubuntu:noble AS runtime
 #     some-library \
 #     && apt-get dist-clean
 
+# Copy the python installation from the build stage
+COPY --from=build /python /python
+
 # Copy the environment, but not the source code
 COPY --from=build /app/.venv /app/.venv
 ENV PATH=/app/.venv/bin:$PATH