name the build artifact with its architecture

Rename the CI binary and its artifact to zampler-amd64, and make the
Dockerfile arch-agnostic via ARG TARGETARCH / COPY zampler-$TARGETARCH.
Keeps the pipeline single-arch for now but makes adding an arm64 leg a
smaller change later.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.dockerignore

@@ -1,3 +1,3 @@
-# Build context only needs the prebuilt ./zampler binary and the Dockerfile.
+# Build context only needs the prebuilt zampler-<arch> binary and the Dockerfile.
 *
-!zampler
+!zampler-*

.gitea/workflows/build.yml

@@ -6,7 +6,7 @@ on:
   workflow_dispatch:
 
 jobs:
-  build-and-push:
+  build-binary:
     runs-on: ubuntu-latest
     container:
       image: golang:1.26-alpine
@@ -14,7 +14,7 @@ jobs:
       CGO_ENABLED: "0"
     steps:
       - name: Install toolchain deps
-        run: apk add --no-cache nodejs npm docker-cli git tar
+        run: apk add --no-cache nodejs npm git tar
 
       - uses: actions/checkout@v4
 
@@ -43,7 +43,34 @@ jobs:
           npx vite build --outDir ../internal/server/static --emptyOutDir
 
       - name: Build binary
-        run: go build -ldflags="-s -w" -o zampler .
+        run: go build -ldflags="-s -w" -o zampler-amd64 .
+
+      - name: Upload binary artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: zampler-amd64
+          path: zampler-amd64
+          if-no-files-found: error
+          retention-days: 1
+
+  build-image:
+    runs-on: ubuntu-latest
+    needs: build-binary
+    container:
+      image: docker:cli
+    steps:
+      - name: Install action deps
+        run: apk add --no-cache nodejs
+
+      - uses: actions/checkout@v4
+
+      - name: Download binary artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: zampler-amd64
+
+      - name: Restore executable bit
+        run: chmod +x zampler-amd64
 
       - name: Log in to the container registry
         env:
@@ -61,5 +88,5 @@ jobs:
       - name: Build and push "latest"
         run: |
           IMAGE="code.aneur.in/${{ gitea.repository }}:latest"
-          docker build -t "$IMAGE" .
+          docker build --build-arg TARGETARCH=amd64 -t "$IMAGE" .
           docker push "$IMAGE"

Dockerfile

@@ -1,12 +1,16 @@
 # The zampler binary is built in CI (.gitea/workflows/build.yml) so the compile
 # can use a persistent Go module + build cache. This image is just the runtime
-# wrapper around the prebuilt static binary.
+# wrapper around the prebuilt static binary. The build context must contain a
+# zampler-<arch> binary; TARGETARCH is set automatically by BuildKit (or pass
+# --build-arg TARGETARCH=... on a legacy builder).
 #
-# For a local build: `go build -o zampler .` first, then `docker build .`.
+# For a local build:
+#   go build -o zampler-$(go env GOARCH) . && docker build .
 
 FROM alpine:3.24
 
-COPY zampler /usr/local/bin/zampler
+ARG TARGETARCH
+COPY zampler-$TARGETARCH /usr/local/bin/zampler
 
 ENTRYPOINT ["zampler"]
 CMD ["-s", "/db/zampler.sqlite3", "/data"]