fix(samples): the watcher told you to do something you cannot do

The watcher's not-answering message said 'load the responder once, in SC:
"sample_watch.scd".load'. Checked that against the live rig and it is not
possible here. sclang runs headless under parvagues-sc.service, so there is no
post window to type into; its stdin is /dev/null, so nothing can be piped in;
and neither sclang nor the ParVagues boot exposes any endpoint that interprets
code over OSC. There is no way in.

Which means a rig booted before start_and_midi.scd learned to source the
responder will never answer /pv/ping, no matter how long the watcher waits —
exactly the case right now, sclang having come up 2026-08-13 14:20 against a
boot script that only grew the source line at 2026-08-14 11:07.

So the message now names the real remedy and its real price: a restart of
parvagues-sc, which stops the sound, and therefore belongs between tracks and
never mid-set. A wrong instruction is worse than a blunt one — it sends you
hunting for a window that does not exist.

rose (46 files) and love_parade (5) are still sitting unloaded and unshadowed,
waiting for that restart.

tools/sample-watcher.py

@@ -195,10 +195,18 @@ def main():
         if pong is None:
             sys.exit(
                 "SuperCollider is not answering /pv/ping.\n"
-                "Load the responder once (it survives until sclang restarts):\n"
-                '  in SC:  "/home/pln/Work/Sound/Tidal/sample_watch.scd".load\n'
-                "It is also sourced from start_and_midi.scd, so a normal boot "
-                "arms it automatically.")
+                "\n"
+                "The responder is armed AT BOOT, from start_and_midi.scd. There\n"
+                "is no way to arm it in a rig that is already running: sclang\n"
+                "runs headless under systemd with stdin on /dev/null, so there\n"
+                "is no post window to evaluate a line in and no eval-over-OSC\n"
+                "endpoint. A rig booted before the responder existed will never\n"
+                "answer, however long you wait.\n"
+                "\n"
+                "So the fix is a restart, and a restart STOPS THE SOUND:\n"
+                "  systemctl --user restart parvagues-sc\n"
+                "\n"
+                "Do it between tracks, not mid-set.")
         print(f"  SuperCollider answered: {pong[0]} banks registered")
 
     while True: