Repair ana-docker database backups and bound CI build caches

configs/buildkit/ana-docker/prune.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+# Bound regenerable cache on ana-docker's named CI builders. BuildKit protects
+# in-use references. Stopped builders cannot grow and are left stopped.
+set -euo pipefail
+failed=0
+for builder in buildx_buildkit_worldtree-builder0 buildx_buildkit_skaldsong-builder0 buildx_buildkit_soong-builder0; do
+  if ! state=$(docker inspect --format '{{.State.Running}}' "$builder" 2>/dev/null); then
+    echo "$builder: absent, skipped"
+    continue
+  fi
+  if [ "$state" != true ]; then
+    echo "$builder: stopped, skipped"
+    continue
+  fi
+  echo "$builder: reclaim unused cache toward 10 GiB budget"
+  if ! docker exec "$builder" buildctl prune --all --keep-storage 10240 | tail -1; then
+    echo "$builder: cache pruning failed" >&2
+    failed=1
+  fi
+done
+exit "$failed"