The radio's noise: the GNSS receiver costs 8 dB; a setting pauses it (#20)

Debug Builds: `lora noise test` changes one thing at a time, Sweeps the
band, and reports the floor under each condition; it runs on the device
by itself, since one condition pauses Wi-Fi (not saved, so a restart
brings it back). Result, at 125 kHz: -117 dBm with the antenna switched
off, -106 with the GNSS receiver in standby, -98 with it running. The
receiver's serial line isn't it (one sentence a second changes nothing),
and neither are the main loop, the CPU frequency, Wi-Fi, the screen or
the radio's own regulator, all within 1 dB.

Settings > "Pause GNSS for LoRa", off by default: the receiver waits in
standby while the radio listens or sweeps, except during a Track, and
has a Fix again about 7 s after. The GNSS App says it's paused.

11 dB remain between the antenna with GNSS quiet and the chip alone,
untouched by anything that can be switched from the firmware.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/services/radio_service.h

@@ -100,6 +100,15 @@ class RadioService : public Service {
     void setEcho(bool echo);
     void probe(Print& out);  // `lora probe`: runs on the radio task
 #ifdef RORO_DEBUG
+    // For the noise self-test (issue #20): the chip's regulator as an LDO instead of its DC-DC
+    // converter, and receive gain boosted or not. Used the next time the radio is set up.
+    void debugOptions(bool ldo, bool boostedGain) {
+        ldo_ = ldo;
+        boostedGain_ = boostedGain;
+    }
+    // The antenna switch (the Cap's expander, P0), for the reference "what the chip hears alone".
+    // From the main loop only, which owns the I2C bus.
+    void debugAntenna(bool on);
     // `lora inject`: a packet into the ring as if received, to test the App and Captures with no
     // transmitter in range. Nothing goes on air.
     void inject(const uint8_t* data, size_t len, float rssi, float snr);
@@ -132,6 +141,7 @@ class RadioService : public Service {
     Config config_;
     bool present_ = false, expander_ = false;
     float tcxo_ = 1.8f;
+    std::atomic<bool> ldo_{false}, boostedGain_{true};
     std::atomic<uint8_t> clients_{0};
     std::atomic<bool> listening_{false}, configChanged_{false}, probeWanted_{false}, echo_{false};
     std::atomic<uint32_t> seq_{0}, packets_{0}, crcErrors_{0}, radioErrors_{0}, restarts_{0};