fix: replace fragile ssh archive one-liners with tools/archive-images.sh

The inline find -exec broke through the double shell hop (the remote
shell consumed the ; separator). The script pipes its payload to remote
bash via stdin, tolerates zero matches, and fails loudly on missing
directories or failed moves.

tools/archive-images.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+# Archive old build images on the fileserver before publishing new ones.
+#
+# Usage: tools/archive-images.sh <ssh-target> <images-dir> <archive-dir> <pattern>...
+#
+# Zero matching files is fine (nothing to archive yet); a missing directory
+# or a failed move aborts non-zero so CI stops before publishing.
+# The remote half is piped to `bash -s` over stdin so there is no nested
+# shell quoting to get wrong.
+
+set -euo pipefail
+
+die() { echo "error: $*" >&2; exit 1; }
+
+(( $# >= 4 )) || die "usage: $0 <ssh-target> <images-dir> <archive-dir> <pattern>..."
+
+target=$1 images_dir=$2 archive_dir=$3
+shift 3
+patterns=("$@")
+
+for v in "$images_dir" "$archive_dir" "${patterns[@]}"; do
+	case $v in
+		*[\ space\'\"]*) die "unsafe argument (whitespace/quotes): $v" ;;
+	esac
+done
+
+echo "Archiving previous images on $target:"
+printf '  pattern: %s\n' "${patterns[@]}"
+
+# Assignments prefixed to `bash -s` are parsed by the remote shell as
+# environment variables for the script below; the quoted heredoc marker
+# keeps every byte of the payload literal until bash executes it.
+ssh "$target" "IMAGES_DIR=$images_dir ARCHIVE_DIR=$archive_dir bash -s" <<'REMOTE'
+set -euo pipefail
+shopt -s nullglob
+
+if [ ! -d "$IMAGES_DIR" ]; then
+	echo "error: images dir not found: $IMAGES_DIR" >&2
+	exit 1
+fi
+if [ ! -d "$ARCHIVE_DIR" ]; then
+	echo "error: archive dir not found: $ARCHIVE_DIR" >&2
+	exit 1
+fi
+
+moved=0
+for pat in "${PATTERNS[@]}"; do
+	for f in "$IMAGES_DIR"/$pat; do
+		echo "  archiving $(basename "$f")"
+		mv "$f" "$ARCHIVE_DIR/"
+		moved=$((moved + 1))
+	done
+done
+
+echo "Archived $moved file(s)."
+REMOTE