diff --git a/Dockerfile b/Dockerfile
index 5106843..b654200 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,12 +1,22 @@
 FROM golang:1.26-alpine AS build
 WORKDIR /src
-COPY go.* ./
+
+# Keep dependency resolution deterministic. Do NOT run `go mod tidy` before
+# source files are present: it can remove required modules because no packages
+# are visible yet.
+COPY go.mod go.sum ./
 RUN go mod download
-RUN go mod tidy
+
 COPY cmd ./cmd
 COPY internal ./internal
-RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" -o /out/neuralhunt ./cmd/server
-RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" -o /out/neuralhunt-client ./cmd/client
+
+# Fail early with a useful message if a repository/.dockerignore rule ever
+# drops the application's internal data package from the build context.
+RUN test -f /src/internal/data/store.go \
+ && test -f /src/internal/data/schema.sql
+
+RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" -o /out/neuralhunt ./cmd/server \
+ && CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" -o /out/neuralhunt-client ./cmd/client
 
 FROM alpine:3.24
 RUN adduser -D -H app && mkdir -p /data /app && chown -R app:app /data /app