diff --git a/Dockerfile b/Dockerfile
index fa1460b..04e60ea 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,22 @@
+# Lint stage — fast feedback on formatting and lint issues.
+# The golangci-lint image bundles Go, gcc and make, so it can run go vet on
+# the CGO sqlite package and golangci-lint without extra installs.
+# golangci/golangci-lint:v2.7.2 (Go 1.25.5), 2026-09-21
+FROM golangci/golangci-lint@sha256:5d6d5c70a61f1356adfd9dd6316ce286799fefc9d743421356ff1b00842368ba AS lint
+
+WORKDIR /src
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+RUN make fmt-check
+RUN make lint
+
 # Build stage
-FROM golang:1.24-bookworm AS builder
+# golang:1.24-bookworm, 2026-09-21
+FROM golang@sha256:1a6d4452c65dea36aac2e2d606b01b4a029ec90cc1ae53890540ce6173ea77ac AS builder
 
 # Install build dependencies (zstd for archive, gcc for CGO/sqlite3)
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -10,12 +27,19 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /src
 
+# Force BuildKit to run the lint stage before compiling or testing.
+COPY --from=lint /src/go.sum /dev/null
+
 # Copy everything
 COPY . .
 
 # Vendor dependencies (must be after copying source)
 RUN go mod download && go mod vendor
 
+# Run the test suite in the build stage: -race needs cgo and the C compiler
+# installed above. The suite is offline (the live-feed test is opt-in).
+RUN make test
+
 # Build the binary with CGO enabled (required for sqlite3)
 RUN CGO_ENABLED=1 GOOS=linux go build -o /routewatch ./cmd/routewatch
 
@@ -26,7 +50,8 @@ RUN tar --zstd -cf /routewatch-source.tar.zst \
     .
 
 # Runtime stage
-FROM debian:bookworm-slim
+# debian:bookworm-slim, 2026-09-21
+FROM debian@sha256:3783cc01769c7b2b1b83a5c5ad96c815348e28ed7da68e2e3687004faa906251
 
 # Install runtime dependencies
 # - ca-certificates: for HTTPS connections