Reset the protocol version before each startup attempt

bellows/ezsp/__init__.py

@@ -144,7 +144,10 @@ async def _startup_reset(self) -> None:
 
     async def startup_reset(self) -> None:
         for attempt in range(RESET_ATTEMPTS):
-            self._protocol = v4.EZSPv4(self.handle_callback, self._gw)
+            # Start every attempt from a consistent v4 state. A failed attempt may
+            # already have switched to the stick's protocol version; keeping that
+            # version with a v4 protocol object makes `version()` skip the switch.
+            self._switch_protocol_version(v4.EZSPv4.VERSION)
 
             try:
                 await self._startup_reset()

tests/test_ezsp.py

@@ -18,6 +18,7 @@
     InvalidTxPower,
 )
 from bellows.ezsp import EZSP, EZSP_LATEST, xncp
+from bellows.ezsp.v4 import EZSPv4
 from bellows.ezsp.v9.commands import GetTokenDataRsp
 import bellows.types as t
 
@@ -341,6 +342,32 @@ async def startup_reset_mock():
     assert disconnect_mock.call_count == 0
 
 
+@patch.object(EZSP, "disconnect", new_callable=AsyncMock)
+async def test_ezsp_connect_retry_resets_protocol_version(disconnect_mock):
+    """A retry after a failure that already switched protocols starts from v4."""
+    call_count = 0
+    seen = []
+
+    async def startup_reset_mock():
+        nonlocal call_count
+        call_count += 1
+        seen.append((ezsp.ezsp_version, type(ezsp._protocol)))
+        if call_count == 1:
+            # The first attempt negotiates v12, then fails (e.g. a slow `zigbeed` reset)
+            ezsp._switch_protocol_version(12)
+            raise RuntimeError("Startup failed after the version switch")
+
+    with patch("bellows.uart.connect"):
+        ezsp = make_ezsp(version=4)
+
+        with patch.object(ezsp, "_startup_reset", side_effect=startup_reset_mock):
+            await ezsp.connect()
+
+    assert call_count == 2
+    assert seen[1] == (4, EZSPv4)
+    assert disconnect_mock.call_count == 0
+
+
 async def test_ezsp_newer_version(ezsp_f):
     """Test newer version of ezsp."""
     with patch.object(