diff --git a/.project-docs/30-worklog/tasks/20260815-go-mod-download-timeout-5b8e2c.md b/.project-docs/30-worklog/tasks/20260815-go-mod-download-timeout-5b8e2c.md
new file mode 100644
index 0000000..8a88c42
--- /dev/null
+++ b/.project-docs/30-worklog/tasks/20260815-go-mod-download-timeout-5b8e2c.md
@@ -0,0 +1,54 @@
+# Task: Diagnose Go module download timeout during Docker build
+
+## Identity
+
+- Task ID: 20260815-go-mod-download-timeout-5b8e2c
+- Mode: Feature
+- Branch: main
+- Worktree: D:\Datas\OthersProjects\NianAIGC
+- Base commit: 9f40162c6be33797792a447fbda3843faf4621e5
+- Owner: codex
+- Status: Ready for Integration
+
+## Scope
+
+- Diagnose the Jenkins Docker build failure at `backend/Dockerfile:20` without changing application or deployment code.
+- Verify whether `github.com/jackc/pgpassfile@v1.0.0` is invalid or whether the failure is limited to dependency-network access.
+- Identify the repository-supported build path for China-hosted CI and provide a target-environment verification command.
+- Make the standard Go Docker build use a China-reachable, integrity-checked module source by default while allowing CI to override it.
+
+## Intent And Constraints
+
+- Treat the supplied Jenkins log as the production-environment failure artifact and keep confirmed repository facts separate from target-network assumptions.
+- Keep the implementation surgical: change only the standard Go Docker build configuration and its task record; Jenkins configuration is outside this repository.
+- Do not weaken module integrity checks (`go.sum`/`GOSUMDB`) to work around a transport timeout.
+
+## Outcome
+
+- The failure occurs before compilation while the standard `backend/Dockerfile` runs `go mod download`; its build stage has no `GOPROXY` override and therefore attempted `https://proxy.golang.org`.
+- The failing module is a valid indirect dependency of `github.com/jackc/pgx/v5@v5.5.5`, and both its module and checksum entries are present.
+- A cold download of the failing module and then the complete module set succeeded through `https://goproxy.cn,direct`; the individual fetch completed in 0.18 seconds and the complete set in 1 second in the diagnostic environment.
+- The repository already supplies `backend/Dockerfile.alpine` as the recommended China-CI build. It uses the Aliyun Alpine package mirror, `GOPROXY=https://goproxy.cn,direct`, and `GOSUMDB=sum.golang.google.cn`.
+- Updated the standard `backend/Dockerfile` to use the same integrity-checked Go module endpoints by default and expose `GOPROXY`/`GOSUMDB` as build arguments for internal or global proxy overrides.
+- No application, deployment manifest, dependency, checksum, or CI file was changed.
+
+## Verification
+
+- Confirmed that the supplied `Dockerfile:20` location matches `backend/Dockerfile` and that `backend/Dockerfile.alpine` places its module download at line 17.
+- Ran a fresh-cache `go mod download -x github.com/jackc/pgpassfile@v1.0.0` through `goproxy.cn`: exit 0.
+- Ran a fresh-cache full `go mod download` through `goproxy.cn`: exit 0.
+- Confirmed with `go mod graph` that `pgx/v5@v5.5.5` depends on `pgpassfile@v1.0.0`.
+- Static Dockerfile contract check passed: both proxy arguments and their environment bindings precede `RUN go mod download`.
+- `go test ./...` passed for all 19 Go packages, and `go vet ./...` passed.
+- Re-ran a fresh-cache full module download using the new defaults: exit 0.
+- Ran `go mod verify`: all downloaded modules verified.
+- Could not run a full Docker image build because the local Docker Desktop Linux daemon is unavailable; the Jenkins-node rerun remains the authoritative end-to-end check.
+
+## Follow-ups
+
+- Re-run the existing standard Docker build on the Jenkins agent; `backend/Dockerfile.alpine` remains the more self-contained fallback when Alpine package downloads also need an Aliyun mirror.
+- If that command still times out, test HTTPS egress/DNS from the Jenkins Docker build network to `mirrors.aliyun.com`, `goproxy.cn`, and `sum.golang.google.cn`, or use the organization's internal Go module proxy.
+
+## Promotion Candidates
+
+- None recorded.
diff --git a/backend/Dockerfile b/backend/Dockerfile
index caac47e..628b92d 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -6,6 +6,7 @@
 #   docker build -f backend/Dockerfile \
 #     --build-arg GOLANG_IMAGE=<working-mirror>/golang:1.21-alpine \
 #     --build-arg RUNTIME_IMAGE=<working-mirror>/alpine:3.20 \
+#     --build-arg GOPROXY=https://<internal-go-proxy>,direct \
 #     -t REGISTRY/PROJECT/zhinian-go-api:TAG backend/
 #
 # If no mirror can serve the golang image at all, use backend/Dockerfile.runtime
@@ -15,7 +16,12 @@ ARG RUNTIME_IMAGE=alpine:3.20
 
 FROM ${GOLANG_IMAGE} AS build
 WORKDIR /src
-ENV CGO_ENABLED=0 GOOS=linux
+ARG GOPROXY=https://goproxy.cn,direct
+ARG GOSUMDB=sum.golang.google.cn
+ENV CGO_ENABLED=0 \
+    GOOS=linux \
+    GOPROXY=${GOPROXY} \
+    GOSUMDB=${GOSUMDB}
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .