[ld2420] Address review findings

Clear cmd_active_ when the blocking engine exhausts retries so loop()
does not stay skipped forever, send config mode exit blind before
abandoning a startup sequence so the module resumes streaming, and
repeat the first frame in the delayed boot fixture so the initial
state swallow cannot make the test flaky.

esphome/components/ld2420/ld2420.cpp

@@ -308,6 +308,7 @@ bool LD2420Component::startup_ack_check_() {
     this->send_startup_cmd_();
     return false;
   }
+  this->abort_startup_cmd_();
   if (this->startup_sequence_retries_ < STARTUP_SEQUENCE_MAX_RETRIES) {
     this->startup_sequence_retries_++;
     ESP_LOGW(TAG, "Module setup attempt %u failed; retrying", this->startup_sequence_retries_);
@@ -323,6 +324,19 @@ bool LD2420Component::startup_ack_check_() {
   return false;
 }
 
+void LD2420Component::abort_startup_cmd_() {
+  // If the module already acknowledged config mode it stops streaming until
+  // config mode is exited, so send the exit command blind before abandoning
+  // the sequence; otherwise the stream never resumes and neither passive
+  // parsing nor the next listen phase would ever see data.
+  if (this->startup_state_ == StartupState::STARTUP_STATE_ENTER_CONFIG) {
+    return;  // Config mode was never acknowledged; the module is still streaming
+  }
+  CmdFrameT frame;
+  this->build_config_mode_frame_(frame, false);
+  this->write_cmd_frame_(frame);
+}
+
 void LD2420Component::loop_startup_() {
   switch (this->startup_state_) {
     case StartupState::STARTUP_STATE_LISTEN: {
@@ -875,6 +889,9 @@ int LD2420Component::send_cmd_from_array(CmdFrameT frame) {
       this->handle_cmd_error(this->cmd_reply_.error);
     }
   }
+  // On ack the reply parser already cleared this; clear it here as well so an
+  // exhausted retry loop cannot leave loop() skipping all processing forever.
+  this->cmd_active_ = false;
   return error;
 }
 

esphome/components/ld2420/ld2420.h

@@ -172,6 +172,7 @@ class LD2420Component final : public Component, public uart::UARTDevice {
   void loop_startup_();
   void start_startup_cmd_(StartupState state);
   void send_startup_cmd_();
+  void abort_startup_cmd_();
   bool startup_ack_check_();
   void drain_rx_();
   void write_cmd_frame_(const CmdFrameT &frame);

tests/integration/fixtures/uart_mock_ld2420_delayed_boot.yaml

@@ -45,10 +45,29 @@ uart_mock:
           0xF8, 0xF7, 0xF6, 0xF5,
         ]
 
-    # Post-setup frame (t=3300ms): distance=50 proves streaming still works
-    # after the setup handshake. Delay=1300ms keeps >1000ms publish throttle
-    # gap from the first frame.
-    - delay: 1300ms
+    # Repeat frame (t=3100ms): distance=100 again. If the API client happens
+    # to subscribe after the first frame, the first published state is
+    # swallowed as the entity's initial state; repeating the value makes the
+    # test's first collected state deterministic. Delay=1100ms keeps >1000ms
+    # publish throttle gap from the first frame.
+    - delay: 1100ms
+      inject_rx:
+        [
+          0xF4, 0xF3, 0xF2, 0xF1,
+          0x23, 0x00,
+          0x01,
+          0x64, 0x00,
+          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+          0xF8, 0xF7, 0xF6, 0xF5,
+        ]
+
+    # Post-setup frame (t=4200ms): distance=50 proves streaming still works
+    # after the setup handshake. Delay=1100ms keeps >1000ms publish throttle
+    # gap from the repeat frame.
+    - delay: 1100ms
       inject_rx:
         [
           0xF4, 0xF3, 0xF2, 0xF1,