ci(deploy): 镜像发布 - 原生多架构构建并复用提交镜像与缓存

backend/Dockerfile

@@ -2,18 +2,17 @@
 
 FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS payment-package-build
 
-ARG TARGETOS
-ARG TARGETARCH
 ARG GOPROXY=https://proxy.golang.org,direct
 ENV GOPROXY=$GOPROXY
 
 RUN apk add --no-cache nodejs unzip zip
 
 WORKDIR /src
-COPY backend/go.mod backend/go.sum ./backend/
-RUN --mount=type=cache,target=/go/pkg/mod cd backend && go mod download
+# 插件只下载实际依赖，不为四个小程序预取整个业务后端的模块图。
 COPY backend ./backend
 COPY plugin-packages ./plugin-packages
+ARG TARGETOS
+ARG TARGETARCH
 RUN --mount=type=cache,target=/root/.cache/go-build set -eu; \
     test -n "$TARGETOS"; \
     test -n "$TARGETARCH"; \
@@ -35,18 +34,19 @@ RUN PAYMENT_PLUGIN_SMOKE_TEST=1 \
 FROM golang:1.25-alpine AS backend-build
 
 ARG GOPROXY=https://proxy.golang.org,direct
-ARG BUILD_VERSION
-ARG BUILD_COMMIT=unknown
-ARG BUILD_TIME=unknown
 ENV GOPROXY=$GOPROXY
 
 RUN apk add --no-cache build-base
 
 WORKDIR /src/backend
-COPY VERSION /src/VERSION
 COPY backend/go.mod backend/go.sum ./
-RUN --mount=type=cache,target=/go/pkg/mod go mod download
+# 模块保留在普通镜像层中，供后续编译及跨 Runner 的 GHA 层缓存复用。
+RUN go mod download
 COPY backend ./
+COPY VERSION /src/VERSION
+ARG BUILD_VERSION
+ARG BUILD_COMMIT=unknown
+ARG BUILD_TIME=unknown
 RUN --mount=type=cache,target=/root/.cache/go-build set -eu; \
     version="${BUILD_VERSION:-$(tr -d '\r\n' </src/VERSION)}"; \
     ldflags="-s -w -X infinite-canvas/backend/internal/buildinfo.Version=${version} -X infinite-canvas/backend/internal/buildinfo.Commit=${BUILD_COMMIT} -X infinite-canvas/backend/internal/buildinfo.BuildTime=${BUILD_TIME}"; \