fix(protocol): retain completed DTLS handshakes

smartthings_local/protocol/dtls_handshake.py

@@ -34,14 +34,16 @@ def _drive_dtls_handshake(
     bounded only by its deadline, while the diagnostic probe retains its
     explicit retry budget.
 
-    Return ``True`` only when the handshake completes before the deadline.
-    TLS and socket failures are left to the caller to classify.
+    Return ``True`` once OpenSSL reports the handshake complete. The deadline
+    prevents another setup, retry, or network-wait iteration; it does not tear
+    down a session that completed while ``do_handshake()`` was running. TLS and
+    socket failures are left to the caller to classify.
     """
     retransmits = 0
     while time.monotonic() < deadline:
         try:
             connection.do_handshake()
-            return time.monotonic() < deadline
+            return True
         except SSL.WantReadError:
             pass
 

smartthings_local/protocol/dtls_session.py

@@ -322,13 +322,15 @@ class DtlsCoapSession:
         timeout: float | None = None,
         cancel: ConnectCancellation | None = None,
     ):
-        """Perform a cancellable DTLS handshake within a monotonic deadline.
+        """Perform a cancellable DTLS handshake using a monotonic deadline.
 
         ``timeout`` overrides ``HANDSHAKE_TIMEOUT_S`` for this call. OpenSSL
         owns DTLS retransmission timing while every receive is capped by the
         remaining budget, so wall-clock adjustments cannot change the bound.
-        A ``ConnectCancellation`` wakes the network wait immediately and does
-        not alter an already established session.
+        Once OpenSSL reports completion, that completed session is retained
+        even if the call returns just after the deadline. A
+        ``ConnectCancellation`` wakes the network wait immediately and does not
+        alter an already established session.
         """
         handshake_timeout = _validate_handshake_timeout(
             timeout, self.HANDSHAKE_TIMEOUT_S)