DASP: drop the P-ION resend overrides, use standard 512-byte packets

The save and file-open requests used their own fixed resend intervals
(5 s / 15 s) and the hello asked for 256-byte packets. Ontrol's Sedona
Java stack does neither and works with the P-ION: the standard backoff
(1, 2, 4, 8 s) sends a busy device a few copies with the same seqNum,
which its receive window drops. Both are removed.

Also fixes a race in SendWindow.send(): the packet entered the window
before its payload and sent_time were set, so housekeeping could resend
it with an empty payload, and the device would then drop the real one
as a duplicate.

Tested on a P-ION at 192.168.1.252, App > Get with File: save 3.2 s
(2 resends), app.sab + kits.scode in 11.3 s with 500-byte chunks
(was 14.6 s at 256), device stayed up, files identical to a 256-byte
backup.

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

dasp.py

@@ -456,7 +456,7 @@ def _to_ack_more(seq_more, max_bytes):
 
 class _Packet:
     __slots__ = ("seq_num", "payload", "acked", "enqueued_time",
-                 "sent_time", "send_attempts", "send_retry", "next")
+                 "sent_time", "send_attempts", "next")
 
     def __init__(self):
         self.seq_num = 0
@@ -465,7 +465,6 @@ class _Packet:
         self.enqueued_time = 0.0
         self.sent_time = 0.0
         self.send_attempts = 1
-        self.send_retry = None      # seconds; None = the window's own interval
         self.next = None
 
 
@@ -507,17 +506,17 @@ class SendWindow:
             self._tail = None
             self._cond.notify_all()
 
-    def send(self, payload, send_retry=None):
+    def send(self, payload):
         p = _Packet()
-        p.send_retry = send_retry
         p.enqueued_time = _ticks()
+        p.payload = payload
         with self._cond:
             p.seq_num = self._seq_num & 0xFFFF
             self._seq_num = (self._seq_num + 1) & 0xFFFF
 
+        # sent_time is stamped inside the lock: send_retries() must not see the
+        # packet in the window as never sent and resend it before its first send.
         self._enqueue(p)
-        p.payload = payload
-        p.sent_time = _ticks()
         self._session._send_raw(self._to_msg(p))
 
     def _enqueue(self, p):
@@ -531,6 +530,7 @@ class SendWindow:
             else:
                 self._tail.next = p
                 self._tail = p
+            p.sent_time = _ticks()
             self._size += 1
             self._cond.notify_all()
 
@@ -620,15 +620,9 @@ class SendWindow:
             p = self._head
             while p is not None:
                 if not p.acked:
-                    if p.send_retry is not None:
-                        # A request the device is slow to take -- a P-ION saving its
-                        # app, opening a file -- is resent at its own steady interval:
-                        # the 1 s default resends it while the device is still busy.
-                        interval = p.send_retry
-                    else:
-                        backoff_shift = min(p.send_attempts - 1, 32)
-                        interval = min(self.send_retry * (1 << backoff_shift),
-                                       self.max_retry_backoff)
+                    backoff_shift = min(p.send_attempts - 1, 32)
+                    interval = min(self.send_retry * (1 << backoff_shift),
+                                   self.max_retry_backoff)
                     if now - p.sent_time >= interval:
                         self._resend(p)
                     oldest = max(oldest, now - p.enqueued_time)
@@ -784,11 +778,10 @@ class DaspSession:
 
     # ── Send / Receive ──────────────────────────────────────────
 
-    def send(self, payload, send_retry=None):
-        """Queues a datagram. send_retry (seconds) overrides the resend interval."""
+    def send(self, payload):
         if self.is_closed:
             raise DaspException(f"Session closed: {self.close_cause}")
-        self.send_window.send(payload, send_retry)
+        self.send_window.send(payload)
 
     def receive(self, timeout=1.0):
         if self.is_closed: