Move arr tracked-data cache to tmpfs, keep disk copy as persistent backup

Reads/writes now hit tmpfs (ARR_CACHE_DIR) instead of the array disk --
a full rebuild for all three arrs measures ~12s live, so there's no real
cost to losing it on reboot. The existing on-disk file becomes a backup
that arr_cache_write() keeps in sync on every write, and
arr_cache_age_seconds() transparently restores it into tmpfs the moment
it notices tmpfs is missing -- so a cache that was fresh before reboot
reads as fresh after too, closing the cold-start gap without needing a
dedicated restore step anywhere else.

common.sh

@@ -2294,7 +2294,17 @@ declare -gA ARR_API_VERSION=(
     [radarr]="v3"
 )
 
-arr_cache_file() { echo "${DATA_DIR}/${1}_tracked_cache.json"; }
+# tmpfs — primary read/write location. Cleared every reboot; that's fine, a full rebuild for
+# all three arrs measures ~12s live, and arr_cache_age_seconds() transparently restores from
+# the persistent backup below the moment it notices this is missing.
+arr_cache_file() { echo "${ARR_CACHE_DIR}/${1}_tracked_cache.json"; }
+
+# Persistent backup — survives reboot. Kept in sync by arr_cache_write() dual-writing here on
+# every write, so it's never more than one write-cycle stale (2026-07-17). Exists purely so a
+# reboot doesn't leave the tmpfs cache genuinely empty until the next live fetch completes —
+# not a source of truth in its own right, just what tmpfs gets restored from when missing.
+arr_cache_backup_file() { echo "${DATA_DIR}/${1}_tracked_cache.json"; }
+
 arr_rescan_duration_db() { echo "${DATA_DIR}/${1}_rescan_duration.db"; }
 
 # Writes the current library-list JSON + computed total tracked count to arr_type's cache.
@@ -2332,14 +2342,16 @@ arr_cache_write() {
     total=$(echo "$items_json" | jq "$expr" 2>/dev/null)
     [[ -z "$total" || "$total" == "null" ]] && return 1
 
-    local cache_file items_tmp
+    local cache_file backup_file items_tmp
     cache_file=$(arr_cache_file "$arr_type")
+    backup_file=$(arr_cache_backup_file "$arr_type")
     items_tmp=$(mktemp)
     echo "$items_json" > "$items_tmp"
-    mkdir -p "$(dirname "$cache_file")" 2>/dev/null
+    mkdir -p "$(dirname "$cache_file")" "$(dirname "$backup_file")" 2>/dev/null
     jq -c -n --slurpfile items "$items_tmp" --argjson total "$total" --argjson ts "$(date +%s)" \
         '{ts:$ts, totalTracked:$total, items:$items[0]}' > "${cache_file}.tmp" 2>/dev/null \
-        && mv "${cache_file}.tmp" "$cache_file"
+        && mv "${cache_file}.tmp" "$cache_file" \
+        && cp "$cache_file" "$backup_file" 2>/dev/null
     rm -f "$items_tmp"
 }
 
@@ -2353,12 +2365,22 @@ arr_cache_read_raw() {
     jq -c '.items // empty' "$cache_file" 2>/dev/null
 }
 
-# Echoes arr_type's cache age in seconds, or a very large number if no cache exists (so age
-# comparisons naturally treat "no cache" the same as "very stale cache").
+# Echoes arr_type's cache age in seconds, or a very large number if no cache and no backup
+# exist (so age comparisons naturally treat that as "very stale"). Transparently restores the
+# tmpfs cache from its persistent backup first if tmpfs is missing (e.g. right after a reboot)
+# — a cache that was fresh before reboot reads as fresh here too, not as if it never existed.
 arr_cache_age_seconds() {
     local arr_type="$1"
     local cache_file
     cache_file=$(arr_cache_file "$arr_type")
+    if [[ ! -f "$cache_file" ]]; then
+        local backup_file
+        backup_file=$(arr_cache_backup_file "$arr_type")
+        if [[ -f "$backup_file" ]]; then
+            mkdir -p "$(dirname "$cache_file")" 2>/dev/null
+            cp "$backup_file" "$cache_file" 2>/dev/null
+        fi
+    fi
     [[ -f "$cache_file" ]] || { echo 999999999; return; }
     local ts
     ts=$(jq -r '.ts // 0' "$cache_file" 2>/dev/null)

load_config.sh

@@ -136,7 +136,8 @@
     LOG_DIR="/var/log/varaverk"
     VV_CACHE_DIR="/tmp/vv_cache"
     CONF_RAM_CACHE_DIR="/tmp/.cache/vv/d"   # tmpfs — cleared every reboot, repopulated by conf_sync.sh
-    export CONF_DIR LOG_DIR VV_CACHE_DIR CONF_RAM_CACHE_DIR
+    ARR_CACHE_DIR="/tmp/arr_cache"           # tmpfs — cleared every reboot, restored from DATA_DIR backup by arr_cache_age_seconds()
+    export CONF_DIR LOG_DIR VV_CACHE_DIR CONF_RAM_CACHE_DIR ARR_CACHE_DIR
 
 # ━━━ Cleanup ━━━
     unset _conf _host_confs_loaded _adapter LOAD_CONFIG_DIR