Arduino CLI build system with HAL-based test architecture

Build and upload tool (arduino-build.sh):
- Compile, upload, and monitor via arduino-cli
- Device discovery with USB ID identification (--devices)
- Persistent reconnecting serial monitor (--watch)
- Split compile/upload workflow (--verify, --upload-only)
- First-time setup wizard (--setup)
- Comprehensive --help with troubleshooting and RedBoard specs

Testable application architecture:
- Hardware abstraction layer (lib/hal/) decouples logic from Arduino API
- Google Mock HAL for unit tests (exact call verification)
- Simulated HAL for system tests (GPIO state, virtual clock, I2C devices)
- Example I2C temperature sensor simulator (TMP102)
- Host-side test suite via CMake + Google Test (21 tests)

Example sketch:
- blink/ -- LED blink with button-controlled speed, wired through HAL

test/test_i2c_example.cpp

@@ -0,0 +1,140 @@
+#include <gtest/gtest.h>
+
+#include "hal.h"
+#include "sim_hal.h"
+
+// ============================================================================
+// Example: I2C Temperature Sensor Simulator
+//
+// Demonstrates how to mock an I2C device. This simulates a simple
+// temperature sensor at address 0x48 (like a TMP102 or LM75).
+//
+// Protocol (simplified):
+//   Write register pointer (1 byte), then read 2 bytes back.
+//   Register 0x00 = temperature (MSB:LSB, 12-bit, 0.0625 deg/LSB)
+//   Register 0x01 = config register
+// ============================================================================
+
+class TempSensorSim : public I2cDeviceSim {
+public:
+    static const uint8_t ADDR = 0x48;
+    static const uint8_t REG_TEMP   = 0x00;
+    static const uint8_t REG_CONFIG = 0x01;
+
+    TempSensorSim() : reg_pointer_(0), temp_raw_(0) {}
+
+    // Set temperature in degrees C (converted to 12-bit raw)
+    void setTemperature(float deg_c) {
+        temp_raw_ = static_cast<int16_t>(deg_c / 0.0625f);
+    }
+
+    // I2cDeviceSim interface
+    void onReceive(const uint8_t* data, size_t len) override {
+        if (len >= 1) {
+            reg_pointer_ = data[0];
+        }
+    }
+
+    size_t onRequest(uint8_t* buf, size_t max_len) override {
+        if (max_len < 2) return 0;
+
+        if (reg_pointer_ == REG_TEMP) {
+            // 12-bit left-aligned in 16 bits
+            int16_t raw = temp_raw_ << 4;
+            buf[0] = static_cast<uint8_t>((raw >> 8) & 0xFF);
+            buf[1] = static_cast<uint8_t>(raw & 0xFF);
+            return 2;
+        }
+        if (reg_pointer_ == REG_CONFIG) {
+            buf[0] = 0x60;  // default config
+            buf[1] = 0xA0;
+            return 2;
+        }
+        return 0;
+    }
+
+private:
+    uint8_t reg_pointer_;
+    int16_t temp_raw_;
+};
+
+// -----------------------------------------------------------------------
+// Helper: read temperature the way real Arduino code would
+// -----------------------------------------------------------------------
+static float readTemperature(Hal* hal, uint8_t addr) {
+    // Set register pointer to 0x00 (temperature)
+    hal->i2cBeginTransmission(addr);
+    hal->i2cWrite(TempSensorSim::REG_TEMP);
+    hal->i2cEndTransmission();
+
+    // Read 2 bytes
+    uint8_t count = hal->i2cRequestFrom(addr, 2);
+    if (count < 2) return -999.0f;
+
+    uint8_t msb = static_cast<uint8_t>(hal->i2cRead());
+    uint8_t lsb = static_cast<uint8_t>(hal->i2cRead());
+
+    // Convert 12-bit left-aligned to temperature
+    int16_t raw = (static_cast<int16_t>(msb) << 8) | lsb;
+    raw >>= 4;  // right-align the 12 bits
+    return raw * 0.0625f;
+}
+
+// ============================================================================
+// Tests
+// ============================================================================
+
+class I2cTempSensorTest : public ::testing::Test {
+protected:
+    void SetUp() override {
+        sensor_.setTemperature(25.0f);
+        sim_.attachI2cDevice(TempSensorSim::ADDR, &sensor_);
+        sim_.i2cBegin();
+    }
+
+    SimHal sim_;
+    TempSensorSim sensor_;
+};
+
+TEST_F(I2cTempSensorTest, ReadsRoomTemperature) {
+    sensor_.setTemperature(25.0f);
+    float temp = readTemperature(&sim_, TempSensorSim::ADDR);
+    EXPECT_NEAR(temp, 25.0f, 0.1f);
+}
+
+TEST_F(I2cTempSensorTest, ReadsFreezing) {
+    sensor_.setTemperature(0.0f);
+    float temp = readTemperature(&sim_, TempSensorSim::ADDR);
+    EXPECT_NEAR(temp, 0.0f, 0.1f);
+}
+
+TEST_F(I2cTempSensorTest, ReadsNegativeTemperature) {
+    sensor_.setTemperature(-10.5f);
+    float temp = readTemperature(&sim_, TempSensorSim::ADDR);
+    EXPECT_NEAR(temp, -10.5f, 0.1f);
+}
+
+TEST_F(I2cTempSensorTest, ReadsHighTemperature) {
+    sensor_.setTemperature(85.0f);
+    float temp = readTemperature(&sim_, TempSensorSim::ADDR);
+    EXPECT_NEAR(temp, 85.0f, 0.1f);
+}
+
+TEST_F(I2cTempSensorTest, UnregisteredDeviceReturnsNack) {
+    // Try to talk to a device that does not exist
+    sim_.i2cBeginTransmission(0x50);
+    sim_.i2cWrite(0x00);
+    uint8_t result = sim_.i2cEndTransmission();
+    EXPECT_NE(result, 0);  // non-zero = error
+}
+
+TEST_F(I2cTempSensorTest, TemperatureUpdatesLive) {
+    sensor_.setTemperature(20.0f);
+    float t1 = readTemperature(&sim_, TempSensorSim::ADDR);
+
+    sensor_.setTemperature(30.0f);
+    float t2 = readTemperature(&sim_, TempSensorSim::ADDR);
+
+    EXPECT_NEAR(t1, 20.0f, 0.1f);
+    EXPECT_NEAR(t2, 30.0f, 0.1f);
+}