Harden first-release validation and dependency hygiene

tests/synthetic_docker_e2e.sh

@@ -38,7 +38,12 @@ for _ in $(seq 1 50); do
 done
 rg -qx 'ready' "$work_root/server.log"
 
-docker build -f "$repo_root/docker/Dockerfile" -t panda-rpki:synthetic-e2e "$repo_root"
+image="${PANDA_RPKI_TEST_IMAGE:-panda-rpki:synthetic-e2e}"
+if [[ -z "${PANDA_RPKI_TEST_IMAGE:-}" ]]; then
+    docker build -f "$repo_root/docker/Dockerfile" -t "$image" "$repo_root"
+else
+    docker image inspect "$image" >/dev/null
+fi
 run_validator() {
     local out="$1"
     local mode="$2"
@@ -46,7 +51,7 @@ run_validator() {
         -v "$fixture:/fixture:ro" \
         -v "$work_root/state:/state" \
         -v "$out:/output" \
-        panda-rpki:synthetic-e2e validate \
+        "$image" validate \
         --tal /fixture/tal/custom.tal --ta /fixture/ta/custom-ta.cer \
         --http-root-cert /fixture/certs/rrdp-ca.pem \
         --http-timeout-secs 5 \
@@ -94,7 +99,7 @@ daemon_container="panda-rpki-daemon-$(basename "$work_root")"
 docker run --rm --name "$daemon_container" --network host --read-only --tmpfs /tmp \
     --user "$(id -u):$(id -g)" \
     -v "$fixture:/fixture:ro" -v "$work_root/daemon:/data" \
-    panda-rpki:synthetic-e2e daemon \
+    "$image" daemon \
     --state-root /data --max-runs 3 --interval-secs 2 --retain-runs 3 -- \
     --tal /fixture/tal/custom.tal --ta /fixture/ta/custom-ta.cer \
     --http-root-cert /fixture/certs/rrdp-ca.pem --log-format json \