[sx126x][sx127x] Stop reading a radio that fails while sends are held back

Also drop a leftover preamble_detect key from a test case.

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

esphome/components/packet_interface/radio_link.h

@@ -49,9 +49,10 @@ class RadioLink : public RadioLinkBase, public Listener {
     this->radio_->register_listener(this);
     this->disable_loop();
   }
-  // Runs only during a busy period; a busy flag that never clears keeps it running
+  // Runs only during a busy period; a busy flag that never clears keeps it running. A radio that failed meanwhile
+  // is not read again, as reading it may wait on the radio every time
   void loop() override {
-    if (!this->radio_->is_receiving())
+    if (!this->radio_->is_ready() || !this->radio_->is_receiving())
       this->radio_free_();
   }
 

tests/components/packet_interface/radio_link.cpp

@@ -105,6 +105,16 @@ TEST_F(RadioLinkTest, FailedRadioRefusesSends) {
   EXPECT_TRUE(this->radio_.sent.empty());
 }
 
+TEST_F(RadioLinkTest, RadioFailingWhileBusyEndsBusyPeriod) {
+  set_time(START);
+  this->radio_.receiving = true;
+  EXPECT_FALSE(this->send_());
+  EXPECT_TRUE(this->link_.is_in_loop_state());
+  this->radio_.fail();
+  this->link_.loop();
+  EXPECT_TRUE(this->link_.is_idle());
+}
+
 TEST_F(RadioLinkTest, ReceivedPacketCarriesSignal) {
   Packet received;
   PacketMetaData meta;

tests/unit_tests/test_lora_packet_interface.py

@@ -137,7 +137,6 @@ class _FullConfig(dict):
                 "packet_mode": True,
                 "payload_length": 0,
                 "sync_value": [],
-                "preamble_detect": 0,
             },
             {},
             "sync_value",