JP LBT: prevent forced TX during backoff, no CAD timeout in Japan mode

Dispatcher's default 4-second getCADFailMaxDuration() would trigger
forced transmission before JP LBT backoff completes (max 16s), violating
ARIB STD-T108 which prohibits TX while channel is busy.

- Add isJapanMode() virtual method to Radio base class (Dispatcher.h)
- Override getCADFailMaxDuration() in all Mesh subclasses to return
  UINT32_MAX in Japan mode — no forced TX, channel must be free
- Default non-JP behavior unchanged (4000ms)

If ambient noise exceeds -80dBm, TX is blocked indefinitely. Users can
monitor noise floor via companion app: menu (⋮) -> Tools -> Noise Floor.

Author: jirogit

examples/companion_radio/MyMesh.h

@@ -150,6 +150,10 @@ class MyMesh : public BaseChatMesh, public DataStoreHost {
 
   uint32_t calcFloodTimeoutMillisFor(uint32_t pkt_airtime_millis) const override;
   uint32_t calcDirectTimeoutMillisFor(uint32_t pkt_airtime_millis, uint8_t path_len) const override;
+  uint32_t getCADFailMaxDuration() const override {
+    if (_radio->isJapanMode()) return UINT32_MAX;  // JP LBT: no forced TX — channel must be free per ARIB STD-T108
+    return Dispatcher::getCADFailMaxDuration();
+  }
   void onSendTimeout() override;
 
   // DataStoreHost methods

examples/simple_repeater/MyMesh.h

@@ -142,6 +142,10 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
   void logTx(mesh::Packet* pkt, int len) override;
   void logTxFail(mesh::Packet* pkt, int len) override;
   int calcRxDelay(float score, uint32_t air_time) const override;
+  uint32_t getCADFailMaxDuration() const override {
+    if (_radio->isJapanMode()) return UINT32_MAX;  // JP LBT: no forced TX — channel must be free per ARIB STD-T108
+    return Dispatcher::getCADFailMaxDuration();
+  }
 
   uint32_t getRetransmitDelay(const mesh::Packet* packet) override;
   uint32_t getDirectRetransmitDelay(const mesh::Packet* packet) override;

examples/simple_room_server/MyMesh.h

@@ -130,6 +130,11 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
   void logTxFail(mesh::Packet* pkt, int len) override;
 
   int calcRxDelay(float score, uint32_t air_time) const override;
+  uint32_t getCADFailMaxDuration() const override {
+    if (_radio->isJapanMode()) return UINT32_MAX;  // JP LBT: no forced TX — channel must be free per ARIB STD-T108
+    return Dispatcher::getCADFailMaxDuration();
+  }
+
   const char* getLogDateTime() override;
   uint32_t getRetransmitDelay(const mesh::Packet* packet) override;
   uint32_t getDirectRetransmitDelay(const mesh::Packet* packet) override;

examples/simple_sensor/SensorMesh.h

@@ -116,6 +116,10 @@ class SensorMesh : public mesh::Mesh, public CommonCLICallbacks {
   float getAirtimeBudgetFactor() const override;
   bool allowPacketForward(const mesh::Packet* packet) override;
   int calcRxDelay(float score, uint32_t air_time) const override;
+  uint32_t getCADFailMaxDuration() const override {
+    if (_radio->isJapanMode()) return UINT32_MAX;  // JP LBT: no forced TX — channel must be free per ARIB STD-T108
+    return Dispatcher::getCADFailMaxDuration();
+  }
   uint32_t getRetransmitDelay(const mesh::Packet* packet) override;
   uint32_t getDirectRetransmitDelay(const mesh::Packet* packet) override;
   int getInterferenceThreshold() const override;

src/Dispatcher.h

@@ -40,6 +40,7 @@ class Radio {
 
   virtual int getMaxTextLen() const { return 10 * 16; }  // default: non-JP
   virtual int getMaxGroupTextLen() const { return 10 * 16; }  // default: non-JP
+  virtual bool isJapanMode() const { return false; }  // default: non-JP
 
   /**
    * \brief  starts the raw packet send. (no wait)