qs-stats: single writer, fix @STAT pipe race

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

hosts/FredOS-Mediaserver.nix

@@ -31,28 +31,33 @@
       # one @STAT line per tick (hottest coretemp across both sockets, WAN
       # byte rates from eno1). Everything rides one SSH connection.
       (pkgs.writeShellScriptBin "qs-stats" ''
+        # Single writer: the loop re-emits top's lines itself and injects a
+        # @STAT line at each frame header. top writing the pipe directly in
+        # parallel raced the injected lines (pipe writes aren't line-atomic)
+        # and spliced @STAT mid-frame, where the client parser never saw it.
         C=${pkgs.coreutils}/bin
         export LC_ALL=C
-        ${pkgs.procps}/bin/top -b -d 2 -w 512 &
-        trap 'kill $! 2>/dev/null' EXIT
         prev_rx=""
-        while :; do
+        ${pkgs.procps}/bin/top -b -d 2 -w 512 | while IFS= read -r line; do
-          t=0
+          printf '%s\n' "$line"
-          for h in /sys/class/hwmon/*; do
+          case $line in
-            if [ "$($C/cat "$h/name" 2>/dev/null)" = coretemp ]; then
+            "top - "*)
-              for f in "$h"/temp*_input; do
+              t=0
-                v=$($C/cat "$f" 2>/dev/null || echo 0)
+              for h in /sys/class/hwmon/*; do
-                [ "$v" -gt "$t" ] && t=$v
+                [ "$($C/cat "$h/name" 2>/dev/null)" = coretemp ] || continue
+                for f in "$h"/temp*_input; do
+                  v=$($C/cat "$f" 2>/dev/null || echo 0)
+                  [ "$v" -gt "$t" ] && t=$v
+                done
               done
-            fi
+              read -r rx tx < <(${pkgs.gawk}/bin/awk '$1 == "eno1:" {print $2, $10}' /proc/net/dev)
-          done
+              if [ -n "$prev_rx" ]; then
-          read -r rx tx < <(${pkgs.gawk}/bin/awk '$1 == "eno1:" {print $2, $10}' /proc/net/dev)
+                printf '@STAT temp=%s rxbps=%s txbps=%s\n' "$((t / 1000))" "$(( (rx - prev_rx) / 2 ))" "$(( (tx - prev_tx) / 2 ))"
-          if [ -n "$prev_rx" ]; then
+              fi
-            echo "@STAT temp=$((t / 1000)) rxbps=$(( (rx - prev_rx) / 2 )) txbps=$(( (tx - prev_tx) / 2 ))"
+              prev_rx=$rx
-          fi
+              prev_tx=$tx
-          prev_rx=$rx
+              ;;
-          prev_tx=$tx
+          esac
-          $C/sleep 2
         done
       '')
     ];