Record verified production baseline and reuse Go module cache

build/Dockerfile

@@ -1,10 +1,10 @@
 FROM docker.io/library/golang:1.25.14-bookworm@sha256:c268a04d59aea0b180ed9946a658cfab9e7b3391dc90eed6e4969ccff98c851f AS build
 ENV GOTOOLCHAIN=local CGO_ENABLED=0
 WORKDIR /src
-COPY src/go.mod ./
+COPY src/go.* ./
 RUN --mount=type=cache,target=/go/pkg/mod go mod download
 COPY src/ ./
-RUN --mount=type=cache,target=/root/.cache/go-build \
+RUN --mount=type=cache,target=/root/.cache/go-build --mount=type=cache,target=/go/pkg/mod \
     test -z "$(gofmt -l .)" \
     && go test ./... \
     && go vet ./... \