use Cargo Chef to use pre-built Rust backend container image in local testing

backend/Dockerfile.test-rust

@@ -1,16 +1,31 @@
-# Rust testing environment for CI/CD
-ARG REGISTRY_HOST=localhost
-ARG OWNER_REPO=owner/repo
-FROM ${REGISTRY_HOST}/${OWNER_REPO}/rust:1.75-slim
+# planner: produce recipe.json
+FROM rust:1.89-slim AS planner
+WORKDIR /app
+RUN apt-get update && apt-get install -y --no-install-recommends pkg-config libssl-dev ca-certificates postgresql-client curl && rm -rf /var/lib/apt/lists/*
+RUN cargo install --locked cargo-chef
+COPY . .
+RUN cargo chef prepare --recipe-path recipe.json
 
-# Install additional tools needed for testing
-RUN apt-get update && apt-get install -y \
-    postgresql-client \
-    curl \
-    && rm -rf /var/lib/apt/lists/*
+# deps: compile only external crates
+FROM rust:1.89-slim AS deps
+WORKDIR /app
+RUN apt-get update && apt-get install -y --no-install-recommends pkg-config libssl-dev ca-certificates postgresql-client curl && rm -rf /var/lib/apt/lists/*
+RUN cargo install --locked cargo-chef
+ENV CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse
+COPY --from=planner /app/recipe.json recipe.json
+RUN cargo chef cook --release --recipe-path recipe.json
 
-# Set working directory
+# builder: compile local workspace crates using cached deps
+FROM rust:1.89-slim AS builder
+WORKDIR /app
+COPY --from=deps /usr/local/cargo /usr/local/cargo
+COPY --from=deps /usr/local/rustup /usr/local/rustup
+COPY --from=deps /app/target /app/target
+COPY . .
+RUN cargo build --release --locked
+
+# runtime: minimal test environment
+FROM rust:1.89-slim AS runtime
+RUN apt-get update && apt-get install -y --no-install-recommends postgresql-client curl && rm -rf /var/lib/apt/lists/*
 WORKDIR /workspace/backend
-
-# Keep container running for testing
 CMD ["sleep", "infinity"]

local-test-pod.yaml

@@ -17,7 +17,7 @@ spec:
     - containerPort: 5432
 
   - name: backend
-    image: rust:1.89-slim
+    image: localhost/sharenet-test-rust:latest
     workingDir: /app/backend
     env:
     - name: DATABASE_URL