Add docker-test skill for running commands in arcticdb Docker container

.claude/skills/docker-test/SKILL.md

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+---
+name: docker-test
+description: Run commands or tests inside the arcticdb Docker container
+argument-hint: "[command]"
+---
+
+Run commands or tests inside the arcticdb Docker container.
+
+The image is a **build environment only** — ArcticDB is not pre-installed. On first use, you need to build it inside the container (e.g. `pip install -ve .`). The repo is bind-mounted at `/workspace`, so build artifacts persist across container restarts.
+
+## Usage
+
+- `/docker-test` — start the container if not running, then open an interactive prompt for what to run
+- `/docker-test pytest python/tests/unit/some_test.py` — run a specific test
+- `/docker-test python -c "import arcticdb"` — run arbitrary command
+- `/docker-test --name mydev pytest ...` — use a named container `arc-dev-mydev` (reusable across sessions)
+- `/docker-test --name mydev` — reconnect to an existing named container
+
+## Instructions
+
+Image name: `arcticdb-env`
+Dockerfile: `docker/Dockerfile`
+
+### 0. Determine the container name
+
+First, check if `$ARGUMENTS` starts with `--name <name>`. If so:
+- Use `arc-dev-<name>` as the container name.
+- Strip `--name <name>` from `$ARGUMENTS` before executing in step 3.
+
+If no `--name` was provided, generate a random name on **first invocation only**:
+```bash
+_ARC_CONTAINER="arc-dev-$(openssl rand -hex 4)"
+```
+
+**Important**: Once determined, reuse the same container name for all subsequent `/docker-test` invocations in this conversation. Do NOT re-derive.
+
+Named containers (`--name`) survive across sessions so the user can reconnect later. Random containers are ephemeral.
+
+### 1. Ensure the image is built
+
+Check if the image exists:
+```bash
+docker image inspect arcticdb-env >/dev/null 2>&1
+```
+
+If it doesn't exist, build it. Use `docker/` as the build context (not `.`) to avoid sending the entire repo tree to the Docker daemon:
+```bash
+docker build -t arcticdb-env docker/
+```
+
+### 2. Ensure the container is running
+
+Check the container state with a single command:
+```bash
+docker inspect --format '{{.State.Status}}' "$_ARC_CONTAINER" 2>/dev/null
+```
+
+- If the command **fails** (container does not exist), create it:
+  ```bash
+  docker run -d --name "$_ARC_CONTAINER" \
+    -v "$(git rev-parse --show-toplevel)":/workspace \
+    -w /workspace \
+    arcticdb-env sleep infinity
+  ```
+
+- If it returns **`exited`** or **`created`**, start it:
+  ```bash
+  docker start "$_ARC_CONTAINER"
+  ```
+
+- If it returns **`running`**, nothing to do.
+
+### 3. Execute the command
+
+Always use `bash -c` to avoid word-splitting issues with paths containing spaces:
+```bash
+docker exec -w /workspace "$_ARC_CONTAINER" bash -c "$ARGUMENTS"
+```
+Escape any inner double quotes in `$ARGUMENTS` appropriately.
+
+If no command was provided, ask the user what they want to run.
+
+### 4. Show results
+
+Display the command output. If the command fails, help debug as usual.
+
+### 5. Cleanup
+
+When the user explicitly asks to clean up, remove the current session's container:
+```bash
+docker rm -f "$_ARC_CONTAINER"
+```
+
+To list all arc-dev containers from this skill:
+```bash
+docker ps -a --filter "name=^arc-dev-" --format "table {{.Names}}\t{{.Status}}"
+```
+
+To prune all **stopped** arc-dev containers (only do this if the user asks):
+```bash
+docker container ls -a --filter "name=^arc-dev-" --filter "status=exited" -q | xargs -r docker rm
+```
+Warn the user before pruning, as this will remove named containers they may want to reuse.