fix(station-g3): apply FEM PA level at TX start

PA PL1 re-targets the PA's DC-DC supply rail rather than selecting a
logic-level gain, and the serial CLI is serviced on every main-loop pass
regardless of whether a transmit is in flight. A `set radio.fem.txgain`
write could therefore move the rail mid-transmit, while the SX1262 was
still driving the PA at full input power.

Record the requested level in setPAGainEnable() and drive the pin from
setTxModeEnable(), which runs from onBeforeTransmit() ahead of
startTransmit(). The level only matters while transmitting, so deferring
costs nothing.

Document that the pref is saved immediately but applied at the next
transmit, so `get radio.fem.txgain` can lead the hardware until then.

variants/station_g3_esp32/LoRaFEMControl.cpp

@@ -7,7 +7,7 @@ void LoRaFEMControl::init() {
 #ifdef P_PA1_EN
   rtc_gpio_hold_dis((gpio_num_t)P_PA1_EN);
   pinMode(P_PA1_EN, OUTPUT);
-  setPAGainEnable(pa_gain_enabled);
+  applyPAGain();
 #endif
 
 #ifdef P_PRIMARY_LNA_EN
@@ -29,6 +29,10 @@ void LoRaFEMControl::setSleepModeEnable() {
 }
 
 void LoRaFEMControl::setTxModeEnable() {
+  // Latch the requested PA level here, before the SX1262 starts driving the PA. PA PL1
+  // retargets the PA's DC-DC rail, so moving it mid-transmit collapses the supply while
+  // the PA is still driven at full input power.
+  applyPAGain();
 #ifdef P_PRIMARY_LNA_EN
   digitalWrite(P_PRIMARY_LNA_EN, !P_PRIMARY_LNA_EN_ACTIVE);
 #endif
@@ -46,9 +50,15 @@ void LoRaFEMControl::setLNAEnable(bool enabled) {
 }
 
 void LoRaFEMControl::setPAGainEnable(bool enabled) {
+  // Recorded only -- the pin is driven from setTxModeEnable(). The PA level only matters
+  // while transmitting, so deferring costs nothing and keeps the rail change out of an
+  // in-flight transmit (the CLI runs on every main-loop pass, including mid-TX).
   pa_gain_enabled = enabled;
+}
+
+void LoRaFEMControl::applyPAGain() {
 #ifdef P_PA1_EN
-  digitalWrite(P_PA1_EN, enabled ? P_PA1_EN_ACTIVE : !P_PA1_EN_ACTIVE);
+  digitalWrite(P_PA1_EN, pa_gain_enabled ? P_PA1_EN_ACTIVE : !P_PA1_EN_ACTIVE);
 #endif
 }
 

variants/station_g3_esp32/LoRaFEMControl.h

@@ -15,6 +15,8 @@ public:
   bool isPAGainEnabled() const { return pa_gain_enabled; }
 
 private:
+  void applyPAGain();
+
   bool lna_enabled = true;
   bool pa_gain_enabled = false;
 };