diff --git a/Cargo.toml b/Cargo.toml
index b833138d..8ca676b3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -42,7 +42,9 @@ firecracker_client = { version = "1.15.1", path = "thirdparty/firecracker-client
 envd = { version = "0.1.0", path = "thirdparty/envd" }
 custom_extension_client = { version = "0.1.0", path = "src/custom_extension_api/generated" }
 tokio = { version = "1", features = ["full"] }
-reqwest = { version = "0.13", features = ["json", "stream"] }
+# `socks` lets dependency downloads honour socks5:// values in the standard
+# proxy environment variables; without it reqwest silently ignores them.
+reqwest = { version = "0.13", features = ["json", "stream", "socks"] }
 opendal = { version = "0.55.0", features = ["services-s3"] }
 object-store-operator = { path = "crates/object-store-operator" }
 hyper = { version = "1", features = ["full"] }
diff --git a/Makefile b/Makefile
index 116b30c0..92ee8c34 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,23 @@ K8S_GATEWAY_IMAGE ?= agentenv-gateway:latest
 K8S_SCHEDULER_IMAGE ?= agentenv-scheduler:latest
 K3S_CTR ?= sudo k3s ctr
 
+# Optional build-time proxy for the image builds. The `--setup-only` layer of
+# Dockerfile.agentenv downloads regctl, firecracker, the kernel, the overlaybd
+# package and the ghcr.io tools image, which is the slowest part of a cold
+# build behind a restricted network. Export HTTPS_PROXY (socks5:// is
+# supported) before `make k8s-build` and it is forwarded to every stage.
+HTTP_PROXY ?= $(http_proxy)
+HTTPS_PROXY ?= $(https_proxy)
+ALL_PROXY ?= $(all_proxy)
+NO_PROXY ?= $(no_proxy)
+# Both cases are passed because Go and Rust HTTP clients differ in which
+# spelling they look up.
+DOCKER_PROXY_ARGS := \
+	$(if $(HTTP_PROXY),--build-arg HTTP_PROXY="$(HTTP_PROXY)" --build-arg http_proxy="$(HTTP_PROXY)",) \
+	$(if $(HTTPS_PROXY),--build-arg HTTPS_PROXY="$(HTTPS_PROXY)" --build-arg https_proxy="$(HTTPS_PROXY)",) \
+	$(if $(ALL_PROXY),--build-arg ALL_PROXY="$(ALL_PROXY)" --build-arg all_proxy="$(ALL_PROXY)",) \
+	$(if $(NO_PROXY),--build-arg NO_PROXY="$(NO_PROXY)" --build-arg no_proxy="$(NO_PROXY)",)
+
 # aenv home path.
 AENV_HOME_PATH ?= /var/lib/aenv
 export AENV_HOME_PATH
@@ -234,9 +251,9 @@ deploy-ps:
 	$(DOCKER_COMPOSE) -f $(DEPLOY_COMPOSE_FILE) ps
 
 k8s-build:
-	$(DOCKER) build $(if $(APT_MIRROR_BASE),--build-arg APT_MIRROR_BASE="$(APT_MIRROR_BASE)",) -f deploy/docker/Dockerfile.agentenv -t $(K8S_RUNTIME_IMAGE) .
-	$(DOCKER) build -f deploy/docker/Dockerfile.gateway -t $(K8S_GATEWAY_IMAGE) .
-	$(DOCKER) build -f deploy/docker/Dockerfile.scheduler -t $(K8S_SCHEDULER_IMAGE) .
+	$(DOCKER) build $(if $(APT_MIRROR_BASE),--build-arg APT_MIRROR_BASE="$(APT_MIRROR_BASE)",) $(DOCKER_PROXY_ARGS) -f deploy/docker/Dockerfile.agentenv -t $(K8S_RUNTIME_IMAGE) .
+	$(DOCKER) build $(DOCKER_PROXY_ARGS) -f deploy/docker/Dockerfile.gateway -t $(K8S_GATEWAY_IMAGE) .
+	$(DOCKER) build $(DOCKER_PROXY_ARGS) -f deploy/docker/Dockerfile.scheduler -t $(K8S_SCHEDULER_IMAGE) .
 
 k8s-redeploy:
 	$(KUBECTL) rollout restart deploy/agentenv-gateway -n $(K8S_NAMESPACE)
diff --git a/deploy/docker-compose.yml b/deploy/docker-compose.yml
index f87621ef..a7e50702 100644
--- a/deploy/docker-compose.yml
+++ b/deploy/docker-compose.yml
@@ -84,6 +84,12 @@ services:
       dockerfile: deploy/docker/Dockerfile.agentenv
       args:
         APT_MIRROR_BASE: ${APT_MIRROR_BASE:-}
+        # Forwarded from the caller's shell so the `--setup-only` dependency
+        # downloads can use a proxy; empty values are ignored by BuildKit.
+        HTTP_PROXY: ${HTTP_PROXY:-${http_proxy:-}}
+        HTTPS_PROXY: ${HTTPS_PROXY:-${https_proxy:-}}
+        ALL_PROXY: ${ALL_PROXY:-${all_proxy:-}}
+        NO_PROXY: ${NO_PROXY:-${no_proxy:-}}
     container_name: agentenv-a
     environment:
       <<: *agentenv-environment
diff --git a/deploy/docker/Dockerfile.agentenv b/deploy/docker/Dockerfile.agentenv
index e6128cfa..f32d7092 100644
--- a/deploy/docker/Dockerfile.agentenv
+++ b/deploy/docker/Dockerfile.agentenv
@@ -1,7 +1,13 @@
 # syntax=docker/dockerfile:1.7
 
 FROM rust:1-bookworm AS chef
-
+# HTTP_PROXY/HTTPS_PROXY/ALL_PROXY/NO_PROXY are predefined BuildKit build args:
+# passing them with `--build-arg` makes them available to every stage's `RUN`
+# without an `ARG` declaration, and keeps them out of the image environment,
+# `docker history`, and the layer cache key. `make k8s-build` forwards whatever
+# is exported in the caller's shell. Declaring them here instead would scope
+# them to this stage only, leaving the `--setup-only` dependency downloads in
+# `deps-stage` on a direct connection.
 WORKDIR /build
 ENV CARGO_TARGET_DIR=/build/target
 ENV RUSTUP_TOOLCHAIN=${RUST_VERSION}