Docker PoC for batteries

eg4battery/Dockerfile

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+# eg4-battery daemon — containerized.
+#
+# Build:   docker build -t eg4-battery .
+# Run:     see docker-compose.yml for device passthrough + config mount
+#
+# Design notes:
+#   - Same Python source (bin/eg4-battery) used in both systemd and Docker
+#     deployments. PEP-723 inline deps are ignored when run with `python` directly,
+#     so they're harmless. Container deps come from requirements.txt.
+#   - Config is mounted at /config/eg4-battery.yaml (read-only). MQTT
+#     credentials can be overridden via env vars (see env-override block in
+#     bin/eg4-battery's main()), making them suitable for Docker secrets or
+#     HA-addon options translation.
+#   - Logs go to stdout (Python logging defaults work — `docker logs` captures).
+
+FROM python:3.11-slim AS base
+
+# pyserial wants the native serial-port permissions to "just work" inside
+# the container; we hand the device through via docker-compose `devices:`.
+# No extra system packages needed.
+
+WORKDIR /app
+
+# --- Python deps --------------------------------------------------------
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# --- daemon source ------------------------------------------------------
+COPY bin/eg4-battery /app/eg4-battery
+RUN chmod +x /app/eg4-battery
+
+# --- runtime ------------------------------------------------------------
+# Config volume mount expected at /config (read-only); see compose file.
+VOLUME ["/config"]
+
+# Run as the daemon's main entrypoint. We exec via `python` so the PEP-723
+# shebang isn't invoked (uv isn't in this image).
+ENTRYPOINT ["python", "/app/eg4-battery", "-C", "/config/eg4-battery.yaml"]