restore-volumes: add /slowdisk absolute floor gate for static offload

Skip static-file offload when projected /slowdisk free space after restore
would fall below SLOWDISK_FLOOR_GB (default 150 GB); warn after extract if
the floor is breached. Restore never aborts — falls back to primary extract.

Co-authored-by: Cursor <cursoragent@cursor.com>

restore-volumes.sh

@@ -20,6 +20,7 @@ set -- "${_pos[@]}"
 [ -f "$dir/.env" ] && source "$dir/.env"
 SLOWDISK="${SLOWDISK:-}"
 [ "$no_slowdisk_flag" = 1 ] && SLOWDISK=False
+SLOWDISK_FLOOR_GB="${SLOWDISK_FLOOR_GB:-150}"
 
 remote_source="$2"
 if [[ -n "$remote_source" ]] && is_local_backup_url "$remote_source"; then
@@ -46,15 +47,71 @@ fi
 # GATED on SLOWDISK (see top): offload runs only when SLOWDISK is the Python-templated boolean
 # "True" (set in the host .env on dedicated-extra-disk hosts) and the --no-slowdisk flag was
 # not passed. Case matters — the value comes through as capitalized "True"/"False". Safe
-# fallbacks (normal extract): SLOWDISK not True, /slowdisk missing, no manifest, no static paths.
+# fallbacks (normal extract): SLOWDISK not True, /slowdisk missing, no manifest, no static paths,
+# or slowdisk free space below SLOWDISK_FLOOR_GB after projected static payload.
+slowdisk_free_gb() {
+    local free
+    free=$(df -BG /slowdisk 2>/dev/null | awk 'NR==2 {gsub(/G/,"",$4); print $4}')
+    [ -n "$free" ] && [[ "$free" =~ ^[0-9]+$ ]] || return 1
+    echo "$free"
+}
+
+# Best cheap size signal for incoming static payload: backup archive bytes (local stat or
+# remote Content-Length). Archive is compressed (.tar.zst); treat size as a LOWER bound and
+# assume ~2x when estimating uncompressed footprint on /slowdisk.
+backup_archive_bytes() {
+    local newest_file=$1
+    if [[ -n "$remote_source" ]]; then
+        local cached="$backup_dir/$(basename "$newest_file")"
+        if [[ -f "$cached" && ! -e "${cached}.aria2" ]]; then
+            stat -c%s "$cached" 2>/dev/null && return 0
+        fi
+        curl --ipv4 -fsSI "${remote_source}${newest_file}" 2>/dev/null \
+            | awk -F': ' 'tolower($1)=="content-length" {gsub(/\r/,"",$2); print $2; exit}'
+    else
+        stat -c%s "$newest_file" 2>/dev/null
+    fi
+}
+
+# Pre-extract floor gate: return 0 if offload may proceed, 1 to fall back to primary extract.
+slowdisk_floor_allows_offload() {
+    local newest_file=$1 archive_bytes need_gb free_gb floor_gb
+    floor_gb="${SLOWDISK_FLOOR_GB:-150}"
+    free_gb=$(slowdisk_free_gb) || return 0
+    archive_bytes=$(backup_archive_bytes "$newest_file")
+    if [[ -z "$archive_bytes" || ! "$archive_bytes" =~ ^[0-9]+$ ]]; then
+        return 0
+    fi
+    # ~2x uncompressed factor (archive is compressed zstd tar)
+    need_gb=$(( (archive_bytes * 2 + 1024*1024*1024 - 1) / (1024*1024*1024) ))
+    if (( free_gb - need_gb < floor_gb )); then
+        echo "slowdisk floor gate: skipping offload (free ${free_gb} GB, projected need ${need_gb} GB, floor ${floor_gb} GB) — extracting to primary"
+        return 1
+    fi
+    return 0
+}
+
+warn_slowdisk_floor_breach() {
+    local free_gb floor_gb
+    floor_gb="${SLOWDISK_FLOOR_GB:-150}"
+    free_gb=$(slowdisk_free_gb) || return 0
+    if (( free_gb < floor_gb )); then
+        echo "WARNING: slowdisk floor breach after static offload (free ${free_gb} GB < floor ${floor_gb} GB) — OS headroom compromised"
+    fi
+}
+
 prep_static_offload() {
-    local key=$1 meta=$2 data_dir=$3 rel target
+    local key=$1 meta=$2 data_dir=$3 newest_file=$4 rel target
     case "$SLOWDISK" in
         True|true) ;;  # offload enabled (Python "True"; also accept manual lowercase "true")
         *) echo "  static offload disabled (SLOWDISK=$SLOWDISK) — normal extract"; return 0 ;;
     esac
     [ -d /slowdisk ] || { echo "  /slowdisk absent — no static offload"; return 0; }
     [ -f "$meta" ]   || { echo "  no manifest ($meta) — no static offload"; return 0; }
+    if ! slowdisk_floor_allows_offload "$newest_file"; then
+        return 0
+    fi
+    static_offload_used=1
     # manifest data lines (after the 3-line header) are "<size>  <relpath>"
     while IFS= read -r rel; do
         [ -z "$rel" ] && continue
@@ -89,6 +146,7 @@ while IFS= read -r key; do
     fi
     meta_file="${newest_file%.tar.zst}.txt"
     echo "=== restoring rpc_$key  <-  $newest_file ==="
+    static_offload_used=0
 
     # 1) wipe live data AND any /slowdisk static targets for this key (no leak on re-restore)
     delete_slowdisk_targets_for_key "$key"
@@ -108,7 +166,7 @@ while IFS= read -r key; do
     if [[ "$1" == *reth* ]]; then
 	echo "  reth node: static-file symlink offload disabled (reth broke whole-dir symlinks)"
     elif [ -n "$local_meta" ]; then
-	prep_static_offload "$key" "$local_meta" "$data_dir"
+	prep_static_offload "$key" "$local_meta" "$data_dir" "$newest_file"
     fi
 
     # 3) extract THROUGH the pre-created symlinks (keep them, don't clobber)
@@ -138,6 +196,9 @@ while IFS= read -r key; do
 		exit 1
 	    fi
     fi
+    if [ "$static_offload_used" = 1 ]; then
+	warn_slowdisk_floor_breach
+    fi
     echo "Backup '$newest_file' restored"
 done <<< "$keys"