/container-layer

name: container-layer
description: >-
  Authors and caches a personalized container environment from a Dockerfile-
  like spec, as a single layer or as a composition of independently cached
  layers. Use when the user mentions "container layer", "Containerfile",
  "custom container", "cache my installs", "composable layers", "uv shim",
  or wants package installations, skills and environment config to survive
  an ephemeral session. Also for snapshotting, restoring or rebuilding that
  environment, and for capturing ad-hoc installs into a reproducible spec.
metadata:
  version: 0.4.0

Container Layer

Build a reproducible, cached environment overlay for ephemeral containers using a Dockerfile-like spec.

When NOT to use this skill

This authors and caches a layer spec. It is not a Docker troubleshooting tool.

| Situation | Use | |---|---| | A build is slow or failing | read the build log; this skill will not help | | Managing a running container | docker/podman directly | | Session boot sequence and hooks | the workspace's own boot docs |

The tell is tense: this skill is for the environment you want next session, not the container you are fighting now.

Concept

The container resets every session, but your environment shouldn't. This skill: 1. Parses a `Containerfile` (Dockerfile subset) that declares your environment 2. Caches the built result as a tarball in GitHub Releases 3. Restores from cache on subsequent boots (single fetch vs. N installs) 4. Provides a `uv` shim that captures ad-hoc installs back into the Containerfile

Supported Containerfile Instructions

# Environment variables
ENV KEY=value

# Shell commands (including package installs)
RUN apt-get install -y foo        # system packages
RUN uv pip install pandas numpy   # Python packages (preferred)
RUN pip install requests          # also works

# Fetch files from URLs or GitHub
FETCH https://example.com/file.tar.gz /dest/path
FETCH github:user/repo /dest/path              # latest tarball
FETCH github:user/repo@ref /dest/path          # specific ref

# Set working directory for subsequent RUN commands
WORKDIR /some/path

# Declare paths to include in the cached layer snapshot
# (auto-detected for FETCH destinations and pip/uv installs)
SNAPSHOT /additional/path/to/capture

# Ignored (Dockerfile compat, no-op here):
# FROM, EXPOSE, CMD, ENTRYPOINT, LABEL, ARG, VOLUME, USER, SHELL

Usage

Single layer — build / restore

from scripts.containerfile import ContainerLayer

layer = ContainerLayer(
    containerfile_path="/path/to/Containerfile",
    cache_repo="oaustegard/claude-container-layers",  # GitHub repo for release assets
    gh_token="...",
)

# Try cache first, fall back to full build
layer.restore_or_build()

Or via CLI:

python -m scripts.cli restore /path/to/Containerfile --repo user/cache-repo

Multi-layer composition (v0.2.0+)

Decompose a heavy environment into named layers, each cached independently. Compose them in order on session start so most-changed bits don't invalidate stable bits.

from scripts.containerfile import compose

compose(
    containerfile_paths=[
        "layers/Containerfile",            # name='base'  (always-on)
        "layers/Containerfile.scientific", # name='scientific'
        "layers/Containerfile.mojo",       # name='mojo'
    ],
    cache_repo="user/cache-repo",
)

Each layer gets its own cache release tag `layer-<name>-<hash>` so retention policies (keep last N) and cache invalidation operate per-name.

Default layer names are derived from the Containerfile path:

• `Containerfile` → `base`
• `Containerfile.scientific` → `scientific`
• `layers/Containerfile.X` → `X`

CLI equivalent:

python -m scripts.cli compose \
    layers/Containerfile \
    layers/Containerfile.scientific \
    layers/Containerfile.mojo \
    --repo user/cache-repo

Per-layer name override

If filename doesn't derive cleanly, pass `--name NAME:PATH` per layer:

python -m scripts.cli compose \
    --name base:weird-named-file.txt \
    --name mojo:other-file.txt \
    weird-named-file.txt other-file.txt

Single-layer naming (back-compat)

`build` / `restore` / `hash` / `inspect` accept `--name`:

python -m scripts.cli restore Containerfile.mojo --name mojo
# Cache tag becomes 'layer-mojo-<hash>' instead of 'layer-<hash>'.
# Omit --name to keep the old back-compat tag for existing callers.

The uv Shim

After building, install the shim to capture future installs:

source /path/to/container-layer/scripts/uv_shim.sh /path/to/Containerfile

Now `uv pip install foo` both installs the package AND appends `RUN uv pip install foo` to your Containerfile.

Rebuilding the Cache

After modifying the Containerfile:

layer.build_and_push()  # Execute, snapshot, upload

Architecture

Read `scripts/containerfile.py` for the parser/executor and `scripts/layer_cache.py` for the GitHub Releases caching logic. The cache key is a SHA-256 of the Containerfile contents — any change triggers a rebuild.

Configuration

The skill expects these environment variables (or pass as constructor args):

• `GH_TOKEN` — GitHub token with `repo` scope (for releases)
• Cache repo can be any repo the token has write access to

Workflow Integration

This skill is designed to be invoked from a boot script. Example Containerfile:

# Skills
FETCH github:oaustegard/claude-skills /mnt/skills/user

# Python environment
RUN uv pip install --system pandas numpy requests

# Path config
RUN echo '/mnt/skills/user/remembering' > /usr/local/lib/python3.12/dist-packages/muninn-remembering.pth

# Custom setup
ENV MY_VAR=hello
WORKDIR /home/claude