Get with File on P-ION: connect and transfer the way Ontrol's Niagara driver does

A real P-ION (fw 1.32) restarted on every Sox file get. Ontrol's Niagara 4
driver gets app.sab from the same device, so its settings are copied:
- DASP hello asks for 256-byte packets (idealMax/absMax), so file chunks
  are 238 bytes
- the message-length header (0x81) goes to Orion only, decided once the
  platform id is read
- the app is saved on the device before app.sab is read, the save resent
  every 5 s rather than 1 s (a P-ION save takes 2-3+ s)
- the file open is resent every 15 s; DASP gains a per-packet resend
  interval for this

Tested on a P-ION at 192.168.1.252: save 3.2 s, app.sab + kits.scode +
app.sax in 15.8 s, no resends, device stayed up. The unsaved-changes
question became a notice, since the app is now always saved first.

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

app_backup.py

@@ -23,6 +23,7 @@ import zipfile
 
 import app_state
 import sab_app
+import sox
 from ox_widget_properties import IMAGE_EXTENSIONS, ORION_KIT, RION_KIT
 
 APP_SAB = "app.sab"
@@ -159,6 +160,19 @@ def _source_entry(media, source_path):
     return f"{media.bank_folder}/{file_name}"
 
 
+def save_app(client):
+    """Invokes App.save on the device and waits for it to finish.
+
+    Ontrol's Niagara driver does this before every app.sab get, resending the request
+    only every 5 s: a P-ION saving a large app takes seconds, and 1 s resends of the
+    request while it is busy are what knocked it over.
+    """
+    comp = client.cache_get(0) or client.load(0)
+    slots = client.slot_registry.get((comp.kit_id, comp.type_id)) or []
+    slot = next((s for s in slots if s["name"] == "save" and s.get("is_action")), None)
+    client.invoke(0, slot["id"] if slot else 0, send_retry=sox.SAVE_SEND_RETRY)
+
+
 class BackupResult:
     def __init__(self):
         self.path = None
@@ -171,8 +185,9 @@ class BackupResult:
 def get_with_file(client, path, status=None):
     """Reads the app and its media off the device and writes the backup zip to `path`.
 
-    Runs off the main thread; status(text, fraction) reports progress. Returns a
-    BackupResult; a failure to read app.sab or kits.scode raises.
+    The app is saved on the device first, so app.sab holds what is running. Runs off
+    the main thread; status(text, fraction) reports progress. Returns a BackupResult;
+    a failure to save, or to read app.sab or kits.scode, raises.
     """
     def report(text, fraction=None):
         if status:
@@ -190,6 +205,11 @@ def get_with_file(client, path, status=None):
     result = BackupResult()
     entries = []                                    # (zip name, bytes or local path)
 
+    report("Saving the app on the device ...", 0.0)
+    try:
+        save_app(client)
+    except Exception as e:
+        raise RuntimeError(f"Saving the app on the device: {e}") from e
     sab = fetch(APP_SAB, 0.0, 0.15)
     entries.append(("device/" + APP_SAB, sab))
     entries.append(("device/" + KITS_SCODE, fetch(KITS_SCODE, 0.15, 0.35)))