Add sensors Sensor interface and a verified host test setup

Sensor/SensorValue in components/sensors/include/sensor.h is modeled
on Zephyr's sensor API: a fetch()/get() split so multi-channel sensors
(e.g. BME280) pay the hardware read cost once, fixed-point SensorValue
(no float/double -- ESP32-C6 has no hardware FPU), a fine-grained
SensorChannel enum, and an optional interrupt-driven set_trigger() for
the battery-first sleep/wake design.

Adds components/sensors/test_apps/host, a self-contained ESP-IDF
project building against the `linux` target so this logic is
host-testable per AGENTS.md's testing philosophy -- verified in a
clean run against the pinned espressif/idf:v6.0.2 image (builds, 4/4
tests pass). Replaces the earlier generic top-level test/README.md
placeholder now that a real per-component pattern exists.

Also fixes .gitignore's build/managed_components patterns to match
nested paths, not just the repo root.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

components/sensors/CMakeLists.txt

@@ -1,3 +1,4 @@
 idf_component_register(
+    INCLUDE_DIRS "include"
     REQUIRES drivers
 )

components/sensors/README.md

@@ -1,3 +1,12 @@
 # sensors
 
 Turns raw `drivers` readings into typed sensor values (e.g. debounced contact state, calibrated analog readings). Knows values, not hardware. `REQUIRES drivers`.
+
+Common interface: `include/sensor.h` defines `Sensor` and `SensorValue`, deliberately modeled on Zephyr's sensor API:
+
+- **fetch()/get() split**: `fetch()` triggers one hardware read and caches it; `get(channel, out)` pulls a single channel out of that cache. Multi-channel sensors (e.g. BME280: temperature + humidity + pressure) pay the hardware cost once per `fetch()`, not once per channel.
+- **Fixed-point `SensorValue`**: `val1 + val2 * 1e-6`, no `float`/`double`. ESP32-C6 has no hardware FPU, so this avoids software-emulated floating point on every sample.
+- **Fine-grained `SensorChannel`** enum (`AmbientTemperature`, `Humidity`, `AccelX`, ...), mirroring Zephyr's `SENSOR_CHAN_*` granularity. `supports(channel)` lets `profiles` discover capabilities generically.
+- **`set_trigger()`** for interrupt-driven sensors (data-ready pin, threshold, reed switch edge), so wake-on-event is possible instead of pure polling -- matters for the battery-first sleep/wake philosophy in `AGENTS.md`. Defaults to unsupported; polling-only sensors don't override it.
+
+Every concrete sensor (reed switch, DS18B20, BME280, ...) implements `Sensor`, so `profiles` and `lua_runtime` can consume any of them uniformly.

components/sensors/include/sensor.h

@@ -0,0 +1,81 @@
+#pragma once
+
+#include <cstdint>
+
+namespace kvida {
+
+// Fine-grained channel identifiers, one per physical quantity a sensor can
+// expose -- mirrors Zephyr's SENSOR_CHAN_* granularity so a single sensor
+// (e.g. a BME280) can expose several channels from one fetch().
+enum class SensorChannel {
+    Contact,
+    Motion,
+    AmbientTemperature,
+    Humidity,
+    Pressure,
+    AccelX,
+    AccelY,
+    AccelZ,
+    Analog,
+    PulseCount,
+    Generic,
+};
+
+// Fixed-point value: actual value = val1 + val2 * 1e-6 (same convention as
+// Zephyr's struct sensor_value). ESP32-C6 has no hardware FPU, so avoiding
+// float/double here avoids paying for software-emulated floating point on
+// every sample -- relevant given the battery-first design goal.
+struct SensorValue {
+    int32_t val1;
+    int32_t val2;
+    const char* unit;
+    uint64_t timestamp_ms;
+};
+
+enum class SensorTriggerType {
+    DataReady,
+    Threshold,
+};
+
+// Plain function pointer + user_data, not std::function, to avoid heap
+// allocation for callback storage on embedded targets.
+using SensorTriggerHandler = void (*)(void* user_data);
+
+class Sensor {
+public:
+    virtual ~Sensor() = default;
+
+    virtual const char* id() const = 0;
+
+    virtual void begin() = 0;
+
+    // True if this sensor exposes the given channel. Lets `profiles`
+    // discover capabilities generically instead of hardcoding per
+    // concrete sensor.
+    virtual bool supports(SensorChannel channel) const = 0;
+
+    // Triggers a hardware read and caches the result internally. A
+    // single fetch() may populate several channels at once (e.g. one
+    // I2C transaction on a BME280 yields temperature + humidity +
+    // pressure), so multi-channel sensors only pay the hardware cost
+    // once per fetch(), not once per channel.
+    virtual bool fetch() = 0;
+
+    // Reads a previously fetched channel from the internal cache.
+    // Returns false if the sensor doesn't support the channel, or if
+    // fetch() hasn't been called yet.
+    virtual bool get(SensorChannel channel, SensorValue& out) = 0;
+
+    // Registers an interrupt-driven callback (data-ready pin, threshold
+    // crossing, edge on a reed switch, ...) for sensors that support it.
+    // Default: not supported: polling-only sensors don't override this.
+    virtual bool set_trigger(SensorTriggerType type, SensorTriggerHandler handler, void* user_data)
+    {
+        (void)type;
+        (void)handler;
+        (void)user_data;
+        return false;
+    }
+};
+
+} // namespace kvida

components/sensors/test_apps/host/CMakeLists.txt

@@ -0,0 +1,18 @@
+# Host-based unit tests for the `sensors` component, run on ESP-IDF's
+# `linux` target (no board needed). Build/run with:
+#
+#   idf.py --preview set-target linux
+#   idf.py build
+#   ./build/test_sensor_host.elf
+#
+# COMPONENTS is restricted (mirrors the pattern used by ESP-IDF's own
+# in-tree host test apps, e.g. components/cxx/test_apps/*) so the build
+# doesn't try to pull in board-only components that don't build for
+# linux.
+cmake_minimum_required(VERSION 3.16)
+
+set(EXTRA_COMPONENT_DIRS "${CMAKE_CURRENT_LIST_DIR}/../../../")
+set(COMPONENTS main sensors unity)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(test_sensor_host)

components/sensors/test_apps/host/main/CMakeLists.txt

@@ -0,0 +1,4 @@
+idf_component_register(
+    SRCS "test_sensor.cpp"
+    PRIV_REQUIRES sensors unity
+)

components/sensors/test_apps/host/main/test_sensor.cpp

@@ -0,0 +1,85 @@
+#include "sensor.h"
+#include "unity.h"
+
+using namespace kvida;
+
+namespace {
+
+// Minimal fake sensor exercising the fetch()/get() cache contract and
+// SensorValue's fixed-point convention (val1 + val2 * 1e-6).
+class FakeSensor : public Sensor {
+public:
+    const char *id() const override { return "fake0"; }
+    void begin() override {}
+
+    bool supports(SensorChannel channel) const override
+    {
+        return channel == SensorChannel::AmbientTemperature;
+    }
+
+    bool fetch() override
+    {
+        fetched_ = true;
+        return true;
+    }
+
+    bool get(SensorChannel channel, SensorValue &out) override
+    {
+        if (!fetched_ || channel != SensorChannel::AmbientTemperature) {
+            return false;
+        }
+        out = SensorValue{21, 500000, "C", 1234};
+        return true;
+    }
+
+private:
+    bool fetched_ = false;
+};
+
+double to_double(const SensorValue &v)
+{
+    return v.val1 + v.val2 * 1e-6;
+}
+
+} // namespace
+
+TEST_CASE("get fails before fetch", "[sensor]")
+{
+    FakeSensor sensor;
+    SensorValue value{};
+    TEST_ASSERT_FALSE(sensor.get(SensorChannel::AmbientTemperature, value));
+}
+
+TEST_CASE("fetch then get returns the cached value", "[sensor]")
+{
+    FakeSensor sensor;
+    sensor.begin();
+    TEST_ASSERT_TRUE(sensor.fetch());
+
+    SensorValue value{};
+    TEST_ASSERT_TRUE(sensor.get(SensorChannel::AmbientTemperature, value));
+    TEST_ASSERT_EQUAL_DOUBLE(21.5, to_double(value));
+}
+
+TEST_CASE("get fails for an unsupported channel", "[sensor]")
+{
+    FakeSensor sensor;
+    sensor.begin();
+    sensor.fetch();
+
+    SensorValue value{};
+    TEST_ASSERT_FALSE(sensor.get(SensorChannel::Humidity, value));
+}
+
+TEST_CASE("default set_trigger reports unsupported", "[sensor]")
+{
+    FakeSensor sensor;
+    TEST_ASSERT_FALSE(sensor.set_trigger(SensorTriggerType::DataReady, nullptr, nullptr));
+}
+
+extern "C" void app_main(void)
+{
+    UNITY_BEGIN();
+    unity_run_all_tests();
+    UNITY_END();
+}