Document Buildx builder lifecycle

docs/deployment-and-usage.md

@@ -259,6 +259,28 @@ Generated protobuf Python bindings are committed in each consumer with the
 exact `archive-control-proto` tag/commit recorded. Release order is proto,
 control consumer, client consumer, E2E, then image publication.
 
+### Reproducible multi-platform Buildx lifecycle
+
+The named Buildx builders are local acceleration/cache only; they are not a
+deployment dependency and can be removed after publication. To create a fresh
+builder, verify its platforms, publish a release, and remove it afterwards:
+
+```bash
+docker buildx create --name archive-control-release --driver docker-container --use
+docker buildx inspect --bootstrap
+docker buildx build --platform linux/amd64,linux/arm64 \
+  --tag sodium/archive-clients:vX.Y.Z --push .
+docker buildx rm archive-control-release
+```
+
+`docker buildx inspect` must list both `linux/amd64` and `linux/arm64` before
+publishing. If the host has no arm64 emulation, install/configure it according
+to the host Docker distribution before the build; do not publish a partial
+single-platform tag. Retain the pushed manifest digest in the release notes
+and deploy the immutable tag or digest. The optional `archive-control-qemu`
+builder follows the same lifecycle when it is used for an emulation smoke
+build.
+
 ## Operator usage
 
 1. Prepare local qB, sync, state, backup, config, and secret mounts with the