synth-diagnostic: just run tests, no service management

- run-tests.sh: no systemctl start/stop, just runs test-unit.py
- synth-diagnostic.service: removed Before=, keeps After=prometheus-exporter
  (no deadlock risk since run-tests.sh doesn't start services)
- justfile deploy: stop pipeline -> restart prometheus -> start
  synth-diagnostic -> restart pipeline

Pipeline starts independently at boot (no After=synth-diagnostic).
Diagnostic provides visibility at boot without blocking startup.

justfile

@@ -107,7 +107,8 @@ deploy:
         echo '{{BOARD_PASS}}' | sudo -S systemctl stop midi-bridge pd-synth-onboard led-matrix-viz && \
         echo '{{BOARD_PASS}}' | sudo -S systemctl restart prometheus-exporter && \
         echo '{{BOARD_PASS}}' | sudo -S systemctl start synth-diagnostic && \
-        echo '[OK] Deployed + restarted'"
+        echo '{{BOARD_PASS}}' | sudo -S systemctl restart midi-bridge pd-synth-onboard led-matrix-viz && \
+        echo '[OK] Deployed'"
 
 # Start synth (onboard audio)
 synth-onboard:

scripts/run-tests.sh

@@ -1,25 +1,18 @@
 #!/bin/bash
-# run-tests.sh — start services, run tests, clean up on failure
+# run-tests.sh — run synth pipeline diagnostics
 set -euo pipefail
 
 BOARD="${BOARD_HOST:-192.168.9.167}"
 cd /home/arduino/uno-q-audio-synth
 
-echo "[diag] Starting pipeline services for diagnostics..."
-sudo systemctl start midi-bridge pd-synth-onboard led-matrix-viz
-
-echo "[diag] Waiting 3s for services to settle..."
-sleep 3
-
 echo "[diag] Running synth pipeline diagnostics against $BOARD..."
 python3 scripts/test-unit.py "$BOARD"
 exit_code=$?
 
 if [ $exit_code -eq 0 ]; then
-    echo "[diag] All tests PASSED — pipeline healthy, leaving services running"
+    echo "[diag] All tests PASSED"
 else
-    echo "[diag] Tests FAILED (exit $exit_code) — stopping pipeline services"
-    sudo systemctl stop midi-bridge pd-synth-onboard led-matrix-viz
+    echo "[diag] Tests FAILED (exit $exit_code)"
 fi
 
 exit $exit_code

system/synth-diagnostic.service

@@ -2,7 +2,6 @@
 Description=Synth pipeline diagnostic — runs unit tests at boot
 DefaultDependencies=no
 After=multi-user.target prometheus-exporter.service
-Before=midi-bridge.service pd-synth-onboard.service led-matrix-viz.service
 
 [Service]
 Type=oneshot
@@ -10,9 +9,6 @@ ExecStart=/home/arduino/uno-q-audio-synth/scripts/run-tests.sh
 StandardOutput=journal
 StandardError=journal
 RemainAfterExit=yes
-
-# Don't let failures cascade — critical for headless boot
-# On failure: services won't start, board stays SSH-accessible
 FailureAction=none
 
 [Install]