fix: recover mempool frontend after backend address changes

docker/mempool-frontend/Dockerfile

@@ -1,14 +1,13 @@
 # Archipelago mempool frontend — adds a resilient nginx backend proxy.
 #
-# The only delta vs the upstream image is /patch/entrypoint.sh, which rewrites
-# the generated nginx-mempool.conf to use `resolver` + a variable proxy_pass so
-# the frontend re-resolves the backend (mempool-api) via DNS on every request.
-# Without this, nginx pins the backend IP at startup and serves 502 / "offline"
-# after any backend restart (podman reassigns the IP). See the script header.
-ARG BASE=source.archipelago-foundation.org/lfg2025/mempool-frontend:v3.0.0
+# Keep the upstream startup logic; repair its rendered proxy configuration.
+# Publish this derived image under an Archipelago-specific tag, never the
+# upstream version tag that the registry mirror can overwrite.
+ARG BASE=source.archipelago-foundation.org/lfg2025/mempool-frontend@sha256:d63498a109622475c913db4e3199d893f2440a451450e542923d2e55a38407a0
 FROM ${BASE}
 
 # --chmod keeps the exec bit (build runs as USER 1000, plain COPY lands root:0644
 # → "not executable"). Base USER/ENTRYPOINT/CMD (1000 / /patch/entrypoint.sh /
 # nginx -g "daemon off;") are inherited unchanged.
-COPY --chmod=0755 entrypoint.sh /patch/entrypoint.sh
+RUN cp /patch/entrypoint.sh /patch/upstream-entrypoint.sh
+COPY --chmod=0755 entrypoint.sh start-nginx.sh repair-nginx.sh /patch/