MIDI alarm when the Lighting PC drops out of NA Tracks' session (FX lights)

Tracks sends the FX lighting cues to the Lighting PC through NA Tracks'
network MIDI session. A midi_peer check may now name a "host": the watchdog
reads that Mac's sessions over SSH every 5 s, sending this folder's
coremidi.py over stdin (nothing installed there). Unreachable = no verdict;
the Tracks Mac's own ping check covers that.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

status_panel.py

@@ -133,6 +133,7 @@ class Snapshot:
         self.conns_time = 0.0
         self.vars = {}           # (label, name) -> str or None
         self.midi = {}           # session name -> {"peers": [...]}
+        self.remote_midi = {}    # host -> the same, read on that Mac over SSH (None: unreachable)
         self.midi_time = 0.0
         self.mdns = set()        # Bonjour _apple-midi._udp instance names
         self.mdns_time = 0.0
@@ -400,9 +401,12 @@ def check_disk(chk, snap, ctx):
 
 
 def check_midi_peer(chk, snap, ctx):
-    if not snap.midi_time:
+    # "host": a session on another Mac (e.g. NA Tracks -> Lighting PC, the FX lighting cues),
+    # read over SSH. Unreachable or not read yet = no verdict (that Mac's own ping says if it is down).
+    sessions = snap.remote_midi.get(chk["host"]) if chk.get("host") else (snap.midi if snap.midi_time else None)
+    if sessions is None:
         return [("peer", Result(OK))]
-    sess = snap.midi.get(chk["session"])
+    sess = sessions.get(chk["session"])
     if sess is None:
         return [("peer", Result(ERR, "NO SESSION"))]
     for p in sess["peers"]:
@@ -1135,6 +1139,39 @@ def poll_midi(snap, cfg):
 
 # --- Other machines: SSH checks and fixes ------------------------------------
 
+def remote_midi_hosts(cfg):
+    return sorted({c["host"] for t in cfg["tiles"] for c in t.get("checks", [])
+                   if c["type"] == "midi_peer" and c.get("host")})
+
+
+def remote_midi_script():
+    """Python for /usr/bin/python3 on another Mac: this folder's coremidi.py, then print its sessions.
+    Nothing is installed there; the code goes over stdin each time."""
+    src = open(os.path.join(os.path.dirname(os.path.abspath(__file__)), "coremidi.py"), encoding="utf-8").read()
+    return ("import json\nns = {'__name__': 'spcm'}\nexec(compile(%r, 'coremidi.py', 'exec'), ns)\n"
+            "print('SPMIDI' + json.dumps(ns['sessions']()))\n" % src)
+
+
+def parse_remote_midi(out):
+    for line in (out or "").splitlines():
+        if line.startswith("SPMIDI"):
+            try:
+                return json.loads(line[6:])
+            except ValueError:
+                return None
+    return None
+
+
+def poll_remote_midi(snap, cfg):
+    script = remote_midi_script()
+    for host in remote_midi_hosts(cfg):
+        try:
+            r = subprocess.run(ssh_cmd(cfg, host) + ["/usr/bin/python3", "-"], input=script,
+                               capture_output=True, text=True, timeout=20)
+            snap.remote_midi[host] = parse_remote_midi(r.stdout) if r.returncode == 0 else None
+        except (OSError, subprocess.SubprocessError):
+            snap.remote_midi[host] = None
+
 def ssh_cmd(cfg, host):
     """ssh to a machine in config "hosts", with NA Ingest's status-panel key; one shared connection per host."""
     return ["/usr/bin/ssh", "-i", os.path.expanduser(cfg.get("ssh_key", "~/.ssh/id_status_panel")),
@@ -1477,6 +1514,7 @@ def start_pollers(cfg, snap, stop, data_dir=None):
         Periodic("bonjour", 15.0, lambda: poll_mdns(snap), stop),
         Periodic("http", 5.0, lambda: poll_http(snap, http_checks(cfg)), stop),
         Periodic("remote", 10.0, lambda: poll_remote(snap, cfg), stop),
+        Periodic("remote-midi", 5.0, lambda: poll_remote_midi(snap, cfg), stop),
         Periodic("dante-map", 30.0, lambda: poll_dante_map(snap, cfg, c4, dante_map_path(data_dir)), stop),
     ]
     for t in threads: