fix(autoroute): never prune SC->hardware links when Ardour is absent

The PRUNE ran unconditionally every 2s. With Ardour closed it deleted
SuperCollider's ONLY output links, and a linkless pipewire-jack client
self-drives its data loop into a 100%-CPU error spin at RT priority.
Hours of that starved the SOF DSP's IPC until the firmware wedged
(IPC timeout -110) and every sink vanished (2026-09-07). 'SC must
never reach hardware' is Ardour-session policy, not idle-laptop policy:
routing and pruning now both require Tidal tracks in the graph.

tools/tidal-ardour-autoroute.sh

@@ -58,6 +58,16 @@ reconcile() {
     # ADD: the control surface feed (no-op until Ardour registers the port)
     link "$CTRL_SRC" "$CTRL_IN"
 
+    # No Ardour tracks in the graph = not a performance. Route nothing, and
+    # above all PRUNE nothing: SC's default sink links are then its ONLY
+    # links, and a linkless pipewire-jack client self-drives its data loop
+    # into a 100%-CPU error spin at RT priority. Hours of that starved the
+    # SOF DSP's IPC until the firmware wedged and every sink vanished
+    # (2026-09-07). "SC must never reach hardware" is Ardour-session policy,
+    # not idle-laptop policy.
+    tracks="$(tidal_track_numbers)"
+    [ -n "$tracks" ] || return 0
+
     # ADD: orbit pair -> matching Tidal track
     while read -r nn; do
         [ -n "${nn:-}" ] || continue
@@ -65,9 +75,10 @@ reconcile() {
         l=$((2 * k - 1)); r=$((2 * k))
         link "$SC:out_$l" "ardour:Tidal $nn/audio_in 1"
         link "$SC:out_$r" "ardour:Tidal $nn/audio_in 2"
-    done < <(tidal_track_numbers)
+    done <<< "$tracks"
 
-    # PRUNE: SuperCollider must never reach hardware playback directly
+    # PRUNE: while Ardour is up, SuperCollider must never reach hardware
+    # playback directly — monitoring is via Ardour Master.
     while IFS=$'\t' read -r src dst; do
         [ -n "${src:-}" ] && [ -n "${dst:-}" ] && pw-link -d "$src" "$dst" 2>/dev/null
     done < <(sc_hw_playback_links)