fix(sensors): make CPU temperature single-writer

inc/sp140/system_monitors.h

@@ -7,7 +7,14 @@
 void addInternalMonitors();
 void addAltimeterMonitors();
 
-// Thread-safe cached CPU temperature reading (updates max once per second)
+// Prime the CPU temperature cache during single-threaded setup.
+void primeCpuTemperatureCache();
+
+// Refresh the sensor at most once per second. ctrlSensorTask is the sole
+// runtime owner; all other tasks must use getCachedCpuTemperature().
+float refreshCpuTemperature();
+
+// Cross-core read of the last published CPU temperature; never touches tsens.
 float getCachedCpuTemperature();
 
 #endif  // INC_SP140_SYSTEM_MONITORS_H_

src/sp140/main.cpp

@@ -310,10 +310,9 @@ void throttleTask(void *pvParameters) {
 }
 
 // Lightweight task: reads controller sensors and writes to TelemetryHub at 10Hz.
-// Uses CACHED barometer/CPU values — uiTask is the sole I2C reader, and
-// getCachedCpuTemperature throttles tsens access. This avoids i2cMutex
-// contention and the "tsens: Do not configure..." error that arises when
-// multiple tasks call temperatureRead() concurrently.
+// Uses CACHED barometer/CPU values — uiTask is the sole I2C reader, and this
+// task is the sole runtime owner of tsens refresh. Other tasks only consume the
+// atomically published CPU temperature.
 void ctrlSensorTask(void *pvParameters) {
   (void)pvParameters;
   TickType_t lastWake = xTaskGetTickCount();
@@ -327,7 +326,7 @@ void ctrlSensorTask(void *pvParameters) {
     float bt = getBaroTemperature();
     float bp = getBaroPressure();
     float vs = getCachedVerticalSpeed();
-    float mt = getCachedCpuTemperature();
+    float mt = refreshCpuTemperature();
     uint16_t pr = getLastThrottleRaw();
     telemetryHubWriteController(alt, bt, bp, vs, mt, pr, now);
     vTaskDelayUntil(&lastWake, sensorTicks);

src/sp140/simple_monitor.cpp

@@ -307,6 +307,9 @@ void initSimpleMonitor() {
   addESCMonitors();
   addBMSMonitors();
   addAltimeterMonitors();
+  // Prime while setup is still single-threaded so monitor readers never see
+  // the zero-initialized cache and no runtime task races tsens initialization.
+  primeCpuTemperatureCache();
   addInternalMonitors();
   USBSerial.printf("Monitoring %d sensors\n", monitors.size());
 }

src/sp140/system_monitors.cpp

@@ -2,6 +2,7 @@
 #include "sp140/monitor_config.h"
 #include "sp140/altimeter.h"
 #include <Arduino.h>
+#include <atomic>
 
 // External references to core monitoring infrastructure
 extern std::vector<IMonitor*> monitors;
@@ -10,18 +11,28 @@ extern MultiLogger multiLogger;
 // External reference to BMP sensor status
 extern bool bmpPresent;
 
-// Cached CPU temperature to avoid "tsens: Do not configure the temp sensor when it's running!" error
-static float cachedCpuTemp = 0.0f;
+// ESP32 tsens configuration is not safe from concurrent tasks. One task owns
+// temperatureRead(); readers consume this atomic cross-core publication.
+static std::atomic<float> cachedCpuTemp{0.0f};
 static unsigned long lastCpuTempRead = 0;
 static const unsigned long CPU_TEMP_READ_INTERVAL = 1000;  // Read every 1 second
 
-float getCachedCpuTemperature() {
+void primeCpuTemperatureCache() {
+  cachedCpuTemp.store(temperatureRead(), std::memory_order_relaxed);
+  lastCpuTempRead = millis();
+}
+
+float refreshCpuTemperature() {
   unsigned long now = millis();
   if (now - lastCpuTempRead >= CPU_TEMP_READ_INTERVAL) {
-    cachedCpuTemp = temperatureRead();
+    cachedCpuTemp.store(temperatureRead(), std::memory_order_relaxed);
     lastCpuTempRead = now;
   }
-  return cachedCpuTemp;
+  return cachedCpuTemp.load(std::memory_order_relaxed);
+}
+
+float getCachedCpuTemperature() {
+  return cachedCpuTemp.load(std::memory_order_relaxed);
 }
 
 void addInternalMonitors() {