paint-app: serve the app from the plotter server and retire Electron

.github/workflows/plotter-server-image.yml

@@ -0,0 +1,85 @@
+name: plotter server image
+
+# Publishes the plotter backend container to GHCR.
+#
+# Tags are prefixed `plotter-server-` so image releases don't collide with the
+# Python package's versioning elsewhere in this repo. Push
+# `plotter-server-v1.0.0` to cut a release; pushes to main refresh `edge` so
+# there's always something current to pull onto the Pi.
+on:
+  push:
+    branches: [main]
+    tags: ["plotter-server-v*"]
+    paths:
+      - "paint-app/server/**"
+      - ".github/workflows/plotter-server-image.yml"
+  pull_request:
+    paths:
+      - "paint-app/server/**"
+      - ".github/workflows/plotter-server-image.yml"
+  workflow_dispatch:
+
+env:
+  IMAGE: ghcr.io/${{ github.repository_owner }}/plotter-server
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: paint-app/server
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+          cache-dependency-path: paint-app/server/package-lock.json
+      - run: npm ci
+      - run: npm run lint
+      - run: npm run typecheck
+      - run: npm test
+
+  build:
+    needs: test
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v4
+
+      # The Pi is arm64 and these runners are amd64. Emulation is slow but the
+      # only compile step is `tsc`; the native serialport binding comes down as
+      # a prebuilt arm64 binary rather than being built here.
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+
+      # Skipped on pull_request: forks have no write access, and a PR should
+      # verify the image builds without publishing it.
+      - if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.IMAGE }}
+          tags: |
+            type=match,pattern=plotter-server-v(.*),group=1
+            type=raw,value=edge,enable={{is_default_branch}}
+            type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/plotter-server-v') }}
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: paint-app/server
+          platforms: linux/arm64
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

paint-app/README.md

@@ -118,6 +118,18 @@ strokes drawn while connected get plotted.
   (clipped to the page rectangle and translated to machine origin), with a
   pause + audio chime + on-screen prompt between layers so you can swap pens.
 
+## Network backend (`server/`)
+
+Web Serial means the browser has to be on the machine holding the USB cable —
+one laptop, tethered, for the whole print. [`server/`](server/README.md) is a
+Node backend that owns the port instead, so the plotter can live on a Raspberry
+Pi and be driven from anywhere on the network.
+
+It is not wired into this app yet. The client still talks Web Serial and is
+unchanged; swapping it over is a follow-up. See
+[`server/README.md`](server/README.md) for the protocol and the deployment
+notes.
+
 ## Hardware notes
 
 See [`experiments/README.md`](experiments/README.md) for the CH340 driver

paint-app/server/.dockerignore

@@ -0,0 +1,6 @@
+node_modules
+dist
+*.log
+.DS_Store
+README.md
+docker-compose.example.yml

paint-app/server/.gitignore

@@ -0,0 +1,3 @@
+node_modules
+dist
+*.log

paint-app/server/Dockerfile

@@ -0,0 +1,50 @@
+# Debian, not Alpine, on purpose.
+#
+# `serialport` is a native addon. Its prebuilt binaries are glibc; on musl there
+# is no prebuild, so `npm ci` falls back to compiling from source and the image
+# needs a whole toolchain — under QEMU that turns a 30-second build into a very
+# long one, for a runtime that then behaves subtly differently. bookworm-slim is
+# a few MB larger and just works.
+FROM node:22-bookworm-slim AS build
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci
+COPY tsconfig.json tsconfig.build.json ./
+COPY src ./src
+RUN npm run build
+
+# Reinstall with dev dependencies pruned. `npm ci --omit=dev` from scratch is
+# what gets the right prebuild for the target arch into the runtime layer.
+FROM node:22-bookworm-slim AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev
+
+FROM node:22-bookworm-slim
+WORKDIR /app
+ENV NODE_ENV=production
+
+# `SerialPort.list()` shells out to `udevadm` on Linux to read the USB
+# descriptors it ranks ports by. Without it enumeration fails outright with
+# "spawn udevadm ENOENT" — the server starts fine and then has no ports to
+# offer, which is a confusing way to find out.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends udev \
+  && rm -rf /var/lib/apt/lists/*
+
+COPY --from=deps /app/node_modules ./node_modules
+COPY --from=build /app/dist ./dist
+COPY package.json ./
+
+# The node user needs to be in the group that owns the tty device, or opening
+# it fails with EACCES. On Raspberry Pi OS that group is `dialout` (GID 20).
+# Compose passes the real GID via `group_add:` — see docker-compose.example.yml.
+USER node
+
+EXPOSE 8080
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
+  CMD node -e "fetch('http://127.0.0.1:'+(process.env.PORT||8080)+'/api/health').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"
+
+CMD ["node", "dist/index.js"]