[sx126x][sx127x] Fixes from code review

- Warn when a send goes ahead over a busy period at its limit, as that
  means a stuck busy indication or a jammed channel
- Log an empty packet at verbose level, and say why it counts as sent
- Name the radio id if code generation cannot find its configuration

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

esphome/components/packet_interface/radio_link.cpp

@@ -21,11 +21,17 @@ bool RadioLinkBase::may_send_(bool busy) {
   if (!this->listen_before_talk_.may_send(busy, now))
     return false;
   if (busy) {
-    ESP_LOGD(TAG, "Radio busy for %" PRIu32 "ms, sending anyway", this->listen_before_talk_.busy_for(now));
+    // The limit is longer than any packet takes, so the radio's busy indication is stuck or the channel is jammed
+    ESP_LOGW(TAG, "Radio busy for %" PRIu32 "ms, sending anyway", this->listen_before_talk_.busy_for(now));
   }
   return true;
 }
 
+bool RadioLinkBase::skip_empty_() const {
+  ESP_LOGV(TAG, "Empty packet not sent");
+  return true;
+}
+
 void RadioLinkBase::radio_free_() {
   this->listen_before_talk_.end_busy();
   this->disable_loop();

esphome/components/packet_interface/radio_link.h

@@ -18,6 +18,8 @@ class RadioLinkBase : public PacketInterface {
   bool check_size_(size_t size) const;
   /// False if sending must wait, as the radio is busy; starts loop() to watch the radio.
   bool may_send_(bool busy);
+  /// Returns true for an empty packet, which the radios cannot send, so there is nothing to retry.
+  bool skip_empty_() const;
   /// Ends the busy period when loop() finds the radio free.
   void radio_free_();
   void receive_(const std::vector<uint8_t> &packet, float rssi, float snr);
@@ -56,7 +58,7 @@ class RadioLink : public RadioLinkBase, public Listener {
       return false;
     size_t size = data.size();
     if (size == 0)
-      return true;
+      return this->skip_empty_();
     if (!this->check_size_(size) || !this->may_send_(this->radio_->is_receiving()))
       return false;
     if (data.is_contiguous()) {

esphome/components/packet_interface/radio_link.py

@@ -7,7 +7,7 @@ import esphome.codegen as cg
 from esphome.components.const import CONF_MAX_PACKET_SIZE
 import esphome.config_validation as cv
 from esphome.const import CONF_ID
-from esphome.core import CORE
+from esphome.core import CORE, EsphomeError
 from esphome.cpp_generator import MockObjClass
 import esphome.final_validate as fv
 from esphome.types import ConfigType
@@ -126,8 +126,13 @@ async def new_radio_link(
     radio = await cg.get_variable(config[radio_id_key])
     var = await new_packet_interface(config, radio, config[CONF_MAX_PACKET_SIZE])
     radio_config = next(
-        conf
-        for conf in CORE.config[radio_domain]
-        if conf[CONF_ID] == config[radio_id_key]
+        (
+            conf
+            for conf in CORE.config[radio_domain]
+            if conf[CONF_ID] == config[radio_id_key]
+        ),
+        None,
     )
+    if radio_config is None:
+        raise EsphomeError(f"No {radio_domain} radio with id '{config[radio_id_key]}'")
     cg.add(var.set_max_busy(max_busy_ms(radio_config, config[CONF_MAX_PACKET_SIZE])))

tests/components/packet_interface/radio_link.cpp

@@ -91,6 +91,12 @@ TEST_F(RadioLinkTest, BusyFlagThatNeverClearsIsSentOver) {
   EXPECT_EQ(this->radio_.sent[0], (Packet{1, 2, 3}));
 }
 
+TEST_F(RadioLinkTest, EmptyPacketCountsAsSentWithoutTransmitting) {
+  static const Packet EMPTY;
+  EXPECT_TRUE(this->link_.send_to_interface(PacketBuffer(EMPTY), {}));
+  EXPECT_TRUE(this->radio_.sent.empty());
+}
+
 TEST_F(RadioLinkTest, ReceivedPacketCarriesSignal) {
   Packet received;
   PacketMetaData meta;