Add Lua runtime: chip temp -> LED color -> HA, verified live

Sandboxed Lua state (espressif/lua v5.5.0, base/table/string/math only,
no io/os/package/debug) exposes a kvida API table (chip_temperature,
set_led, publish) to a compiled-in default script that reads chip
temperature, maps it to an LED color, and publishes the reading to
Home Assistant. Generalizes transport's publish_chip_temperature()
into publish_value(name, value), the first real use of AGENTS.md's
semantic publish API. Requires -DLUA_32BITS globally since this
toolchain's long long support isn't visible to Lua's default build.

Verified on real ESP32-C6 hardware: no crashes/errors across multiple
serial monitor windows, LED changes color, chip_temperature sensor
appears in Home Assistant via MQTT Discovery.

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

CMakeLists.txt

@@ -4,4 +4,16 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+
+# The espressif/lua component's luaconf.h defaults to 64-bit
+# (long long) Lua integers and errors out at compile time on this
+# toolchain ("Compiler does not support 'long long'" -- LLONG_MAX isn't
+# visible to it here, even though <limits.h> is included). Lua's own
+# suggested fix for constrained/32-bit platforms: build with 32-bit
+# integers/floats instead. Set globally (not just in lua_runtime's own
+# CMakeLists.txt) so the Lua component's own .c files see the same
+# definition -- otherwise its library and our calling code would
+# disagree on the size of lua_Integer.
+idf_build_set_property(COMPILE_DEFINITIONS "-DLUA_32BITS" APPEND)
+
 project(kvida_os)

components/lua_runtime/CMakeLists.txt

@@ -1,3 +1,7 @@
 idf_component_register(
-    REQUIRES profiles transport
+    SRCS "src/lua_runtime.cpp"
+    INCLUDE_DIRS "include"
+    PRIV_INCLUDE_DIRS "src"
+    REQUIRES drivers profiles transport
+    PRIV_REQUIRES espressif__lua
 )

components/lua_runtime/README.md

@@ -1,5 +1,25 @@
 # lua_runtime
 
-Executes the sandboxed Lua program (compiled from Blockly) that defines device behaviour. Exposes the Kvida API (e.g. `publish("temperature", 21.3)`) to Lua scripts; Lua never touches ESP-IDF or `transport` directly. `REQUIRES profiles transport`.
+Executes the sandboxed Lua program (compiled from Blockly) that defines device behaviour. Exposes the Kvida API (e.g. `publish("temperature", 21.3)`) to Lua scripts; Lua never touches ESP-IDF or `transport` directly. `REQUIRES drivers profiles transport`.
 
-TODO: needs an actual Lua interpreter dependency, pinned via `idf_component.yml` once a specific IDF Component Registry package/version is confirmed (not guessed here, same caution as pinning `west.yml`'s NCS revision previously).
+Built on `espressif/lua` (v5.5.0, pinned in `idf_component.yml`) -- Espressif's own official IDF Component Registry package, MIT licensed, built specifically for embedding Lua in ESP-IDF apps. No JS/exotic bindings: standard `lua_State`/`luaL_newstate`/`lua_pushcfunction` C API. The project's fourth external managed component (after `mdns`, `mqtt`, `led_strip`).
+
+## What's here
+
+- `lua_runtime_init()` creates the Lua state, opens only `base`/`table`/`string`/`math` (deliberately *not* `luaL_openlibs()`, which would also expose `io`, `os`, `package`/`require`, `debug` -- see AGENTS.md's "Lua should never access ESP-IDF directly"), registers the `kvida` API table, then loads the default script (`src/default_script.h`, a compiled-in string) which just *defines* `on_tick()`.
+- `lua_runtime_tick()` calls `on_tick()` -- one "wake, execute Lua, publish changes, sleep" cycle. A Lua runtime error is logged, not fatal.
+- The `kvida` table exposed to scripts:
+  - `kvida.chip_temperature()` -- reads the ESP32-C6's internal die temperature via `profiles::ChipTemperatureSensor` (the same `Sensor` implementation `main.cpp` used directly before this component existed).
+  - `kvida.set_led(r, g, b)` -- sets the onboard WS2812 via `drivers::rgb_led_set_color()`.
+  - `kvida.publish(name, value)` -- calls `transport::publish_value()`, AGENTS.md's semantic publish API, built for the first time here.
+- The default script reads chip temperature, maps it to a blue(cool)-to-red(hot) LED color (linear interpolation, 20-60C, clamped), and publishes the reading to Home Assistant. Verified end-to-end on real hardware.
+
+## Known limitation, accepted for now
+
+The onboard LED is also controllable manually from Home Assistant (an MQTT light entity, see `components/transport/src/mqtt.cpp`). The two aren't reconciled: `on_tick()` overwrites a manually-chosen HA color every 30s. Accepted as a conflict between two "quick proof" demos rather than solved now -- a real answer (e.g. a Lua-settable "mode" toggle, or the MQTT light entity deferring to Lua) needs product input, not a guess.
+
+## Not yet done
+
+- The script is compiled in, not loaded from storage -- there's no upload mechanism yet. Once `kvida-sdk` can push a script (and `drivers` mounts the `storage` LittleFS partition -- both still TODO), scripts should be loaded from there instead.
+- No Blockly-to-Lua compiler exists yet (that's `kvida-sdk`'s job per AGENTS.md's "Level 2").
+- No memory/CPU/runtime limits on the Lua state beyond the restricted library set -- a script with an infinite loop would hang `lua_runtime_tick()` (and, since it currently runs on the same timer callback, block other `esp_timer` callbacks too). Not a concern for a compiled-in, developer-authored script; becomes one once arbitrary user scripts can be uploaded.

components/lua_runtime/idf_component.yml

@@ -0,0 +1,2 @@
+dependencies:
+  espressif/lua: "==5.5.0"

components/lua_runtime/include/lua_runtime.h

@@ -0,0 +1,17 @@
+#pragma once
+
+namespace kvida {
+
+// Creates the sandboxed Lua state and loads the default script (see
+// src/default_script.h). The script only *defines* the on_tick()
+// function -- call lua_runtime_tick() to actually run it. Call once at
+// boot.
+void lua_runtime_init();
+
+// Calls the script's on_tick() global function -- one "wake, execute
+// Lua, publish changes, sleep" cycle, per AGENTS.md's power philosophy.
+// A Lua runtime error is logged, not fatal: a script bug shouldn't take
+// down the device.
+void lua_runtime_tick();
+
+} // namespace kvida

components/lua_runtime/src/default_script.h

@@ -0,0 +1,28 @@
+#pragma once
+
+namespace kvida {
+
+// Default on-device script, compiled in for now -- there's no upload
+// mechanism yet (that's a kvida-sdk + LittleFS concern for later), so a
+// real filesystem-backed script store would be premature. Demonstrates
+// the whole point of lua_runtime: read a sensor, drive an actuator, and
+// publish a value to Home Assistant, entirely from Lua, with no
+// firmware rebuild for behavior changes.
+inline const char *default_script()
+{
+    return R"lua(
+function on_tick()
+  local temp = kvida.chip_temperature()
+
+  local min_temp, max_temp = 20, 60
+  local t = (temp - min_temp) / (max_temp - min_temp)
+  if t < 0 then t = 0 end
+  if t > 1 then t = 1 end
+
+  kvida.set_led(math.floor(t * 255), 0, math.floor((1 - t) * 255))
+  kvida.publish("chip_temperature", temp)
+end
+)lua";
+}
+
+} // namespace kvida

components/lua_runtime/src/lua_runtime.cpp

@@ -0,0 +1,130 @@
+#include "lua_runtime.h"
+
+#include "default_script.h"
+
+#include "chip_temperature_sensor.h"
+#include "mqtt.h"
+#include "rgb_led.h"
+
+#include "esp_log.h"
+
+extern "C" {
+#include "lauxlib.h"
+#include "lua.h"
+#include "lualib.h"
+}
+
+namespace kvida {
+
+namespace {
+
+constexpr const char *TAG = "lua_runtime";
+
+lua_State *g_L = nullptr;
+ChipTemperatureSensor g_chip_temp_sensor;
+
+// Deliberately not luaL_openlibs(), which would also expose `io`, `os`,
+// `package`/`require`, and `debug` -- AGENTS.md: "Lua should never
+// access ESP-IDF directly. Lua interacts only through the Kvida API."
+void open_safe_libs(lua_State *L)
+{
+    luaL_requiref(L, LUA_GNAME, luaopen_base, 1);
+    lua_pop(L, 1);
+    luaL_requiref(L, LUA_TABLIBNAME, luaopen_table, 1);
+    lua_pop(L, 1);
+    luaL_requiref(L, LUA_STRLIBNAME, luaopen_string, 1);
+    lua_pop(L, 1);
+    luaL_requiref(L, LUA_MATHLIBNAME, luaopen_math, 1);
+    lua_pop(L, 1);
+}
+
+int l_chip_temperature(lua_State *L)
+{
+    if (!g_chip_temp_sensor.fetch()) {
+        return luaL_error(L, "failed to read chip temperature");
+    }
+    SensorValue value{};
+    if (!g_chip_temp_sensor.get(SensorChannel::ChipTemperature, value)) {
+        return luaL_error(L, "chip temperature channel unavailable");
+    }
+    double celsius = static_cast<double>(value.val1) + static_cast<double>(value.val2) * 1e-6;
+    lua_pushnumber(L, celsius);
+    return 1;
+}
+
+int l_set_led(lua_State *L)
+{
+    auto r = static_cast<uint8_t>(luaL_checkinteger(L, 1));
+    auto g = static_cast<uint8_t>(luaL_checkinteger(L, 2));
+    auto b = static_cast<uint8_t>(luaL_checkinteger(L, 3));
+    drivers::rgb_led_set_color(r, g, b);
+    return 0;
+}
+
+int l_publish(lua_State *L)
+{
+    const char *name = luaL_checkstring(L, 1);
+    double value = luaL_checknumber(L, 2);
+    publish_value(name, value);
+    return 0;
+}
+
+void register_kvida_api(lua_State *L)
+{
+    lua_newtable(L);
+
+    lua_pushcfunction(L, l_chip_temperature);
+    lua_setfield(L, -2, "chip_temperature");
+
+    lua_pushcfunction(L, l_set_led);
+    lua_setfield(L, -2, "set_led");
+
+    lua_pushcfunction(L, l_publish);
+    lua_setfield(L, -2, "publish");
+
+    lua_setglobal(L, "kvida");
+}
+
+} // namespace
+
+void lua_runtime_init()
+{
+    if (g_L) {
+        return;
+    }
+
+    g_L = luaL_newstate();
+    if (!g_L) {
+        ESP_LOGE(TAG, "luaL_newstate failed");
+        return;
+    }
+
+    open_safe_libs(g_L);
+    g_chip_temp_sensor.begin();
+    register_kvida_api(g_L);
+
+    if (luaL_dostring(g_L, default_script()) != LUA_OK) {
+        ESP_LOGE(TAG, "Failed to load default script: %s", lua_tostring(g_L, -1));
+        lua_pop(g_L, 1);
+    }
+}
+
+void lua_runtime_tick()
+{
+    if (!g_L) {
+        return;
+    }
+
+    lua_getglobal(g_L, "on_tick");
+    if (!lua_isfunction(g_L, -1)) {
+        lua_pop(g_L, 1);
+        return;
+    }
+
+    if (lua_pcall(g_L, 0, 0, 0) != LUA_OK) {
+        ESP_LOGE(TAG, "Lua error in on_tick: %s", lua_tostring(g_L, -1));
+        lua_pop(g_L, 1);
+    }
+}
+
+} // namespace kvida

components/transport/README.md

@@ -25,7 +25,7 @@ Future transports (Zigbee, Thread, Matter) should implement the same publish API
 - **Broker address**: the settings page has a required host/port field, used directly and given priority over mDNS auto-discovery. mDNS discovery of `_mqtt._tcp` (`mdns_query_ptr`) is attempted as a fallback only if no manual host is saved, retried every 30s -- **verified against a real Home Assistant + Mosquitto add-on setup that this mDNS discovery does not reliably find the broker** (confirmed with a from-scratch raw mDNS query test from the host machine: no PTR answer for `_mqtt._tcp.local` was ever received on that network), hence the manual field being the primary path rather than a rarely-needed fallback.
 - **Credentials**: also collected on the same settings page (blank username = anonymous; blank password on a resubmit means "keep the current one", since the password is never echoed back into the page for basic hygiene). Real brokers, including Home Assistant's Mosquitto add-on, require auth -- confirmed on real hardware.
 - On `MQTT_EVENT_CONNECTED`: publishes (retained) an HA MQTT Discovery config for a diagnostic `connectivity` binary_sensor, grouped under a `device` block (`identifiers`/`name` = the same `kvida-xxxxxx` id, `manufacturer` "Xylon", `model` "Kvida"), then publishes `online` to the availability topic. MQTT's own LWT (`session.last_will`, set at client init) publishes `offline` to the same topic if the connection drops. Verified end-to-end: device appears in Home Assistant with a "Connected" Connectivity sensor.
-- No generic semantic `publish(topic, value)` API yet -- deferred until `profiles` has real sensor data to publish; building it now would be speculative.
+- **`publish_value(name, value)`**: the generic semantic publish API, finally built once there was a real caller -- `lua_runtime`'s `kvida.publish()`, not called directly by other components. Builds `kvida/<id>/<name>` (state) and `homeassistant/sensor/<id>/<name>/config` (discovery) topics from the name. No `device_class`/`unit_of_measurement` or prettified HA display name, since neither can be inferred from just a name -- the entity shows up in HA labeled with the raw name (e.g. `chip_temperature`).
 
 ## JSON API
 

components/transport/include/mqtt.h

@@ -7,18 +7,21 @@ namespace kvida {
 // Starts mDNS-based MQTT broker discovery (_mqtt._tcp) and, once found,
 // connects the MQTT client and publishes Home Assistant MQTT Discovery
 // for a diagnostic "connectivity" entity. Safe to call multiple times
-// (no-op if already connecting/connected). No public-facing semantic
-// publish(topic, value) API yet -- deferred until `profiles` has real
-// sensor data to publish (see components/transport/README.md).
+// (no-op if already connecting/connected).
 void start_mqtt();
 
 bool mqtt_connected();
 
-// Publishes (retained) Home Assistant MQTT Discovery for a diagnostic
-// "Chip temperature" sensor on first call, then the reading itself.
-// Quick end-to-end proof that a real Sensor implementation's data can
-// reach MQTT/HA -- not the eventual generic publish(topic, value) API.
-void publish_chip_temperature(float celsius);
+// Publishes a named numeric value as a Home Assistant MQTT Discovery
+// sensor: `kvida/<id>/<name>` state topic, `homeassistant/sensor/<id>/<name>/config`
+// discovery topic. This is the semantic publish(name, value) API AGENTS.md
+// describes -- driven by `lua_runtime`'s `kvida.publish()`, not called
+// directly by other components. Discovery is republished (retained, so
+// idempotent) on every call rather than cached behind a per-name
+// "already announced" flag -- simpler, at the cost of a bit of extra
+// retained-message traffic each call. TODO: cache announced names if
+// that traffic becomes a real concern.
+void publish_value(const char *name, double value);
 
 // Registered by main to receive "set LED color" commands from Home
 // Assistant (an RGB light entity) without transport depending on

components/transport/src/mqtt.cpp

@@ -43,7 +43,6 @@ char g_availability_topic[48];
 char g_discovery_topic[80];
 char g_discovery_payload[512];
 
-char g_temp_state_topic[48];
 char g_led_command_topic[48];
 char g_led_rgb_command_topic[48];
 char g_led_state_topic[48];
@@ -537,7 +536,7 @@ bool mqtt_connected()
     return g_connected.load();
 }
 
-void publish_chip_temperature(float celsius)
+void publish_value(const char *name, double value)
 {
     if (!g_client || !g_connected.load()) {
         return;
@@ -545,42 +544,45 @@ void publish_chip_temperature(float celsius)
 
     char id[16];
     device_id(id, sizeof(id));
-    snprintf(g_temp_state_topic, sizeof(g_temp_state_topic), "kvida/%s/chip_temperature", id);
 
-    static bool discovery_published = false;
-    if (!discovery_published) {
-        char discovery_topic[80];
-        snprintf(discovery_topic, sizeof(discovery_topic),
-                 "homeassistant/sensor/%s/chip_temperature/config", id);
+    char state_topic[64];
+    snprintf(state_topic, sizeof(state_topic), "kvida/%s/%s", id, name);
 
-        char payload[512];
-        snprintf(payload, sizeof(payload),
-                 "{"
-                 "\"name\":\"Chip temperature\","
-                 "\"device_class\":\"temperature\","
-                 "\"unit_of_measurement\":\"\xc2\xb0"
-                 "C\","
-                 "\"unique_id\":\"%s_chip_temperature\","
-                 "\"state_topic\":\"%s\","
-                 "\"availability_topic\":\"%s\","
-                 "\"payload_available\":\"online\","
-                 "\"payload_not_available\":\"offline\","
-                 "\"device\":{"
-                 "\"identifiers\":[\"%s\"],"
-                 "\"name\":\"%s\","
-                 "\"manufacturer\":\"Xylon\","
-                 "\"model\":\"Kvida\""
-                 "}"
-                 "}",
-                 id, g_temp_state_topic, g_availability_topic, id, id);
+    // Discovery is republished (retained, so idempotent) every call rather
+    // than cached behind a per-name "already announced" flag -- see the
+    // comment on publish_value() in mqtt.h.
+    char discovery_topic[96];
+    snprintf(discovery_topic, sizeof(discovery_topic), "homeassistant/sensor/%s/%s/config", id, name);
 
-        esp_mqtt_client_publish(g_client, discovery_topic, payload, 0, 1, true);
-        discovery_published = true;
-    }
+    // No device_class/unit_of_measurement: this is a generic named-value
+    // API (Lua's kvida.publish(name, value)), so there's no reliable way
+    // to infer units from just a name. The entity's HA display name is
+    // also just the raw `name` (e.g. "chip_temperature") for the same
+    // reason -- a future version could thread a prettier label through
+    // once profiles pass richer metadata.
+    char payload[512];
+    snprintf(payload, sizeof(payload),
+             "{"
+             "\"name\":\"%s\","
+             "\"unique_id\":\"%s_%s\","
+             "\"state_topic\":\"%s\","
+             "\"availability_topic\":\"%s\","
+             "\"payload_available\":\"online\","
+             "\"payload_not_available\":\"offline\","
+             "\"device\":{"
+             "\"identifiers\":[\"%s\"],"
+             "\"name\":\"%s\","
+             "\"manufacturer\":\"Xylon\","
+             "\"model\":\"Kvida\""
+             "}"
+             "}",
+             name, id, name, state_topic, g_availability_topic, id, id);
 
-    char value[16];
-    snprintf(value, sizeof(value), "%.1f", static_cast<double>(celsius));
-    esp_mqtt_client_publish(g_client, g_temp_state_topic, value, 0, 0, false);
+    esp_mqtt_client_publish(g_client, discovery_topic, payload, 0, 1, true);
+
+    char value_str[32];
+    snprintf(value_str, sizeof(value_str), "%.2f", value);
+    esp_mqtt_client_publish(g_client, state_topic, value_str, 0, 0, false);
 }
 
 void set_led_color_handler(LedColorHandler handler)

main/CMakeLists.txt

@@ -1,5 +1,5 @@
 idf_component_register(
     SRCS "main.cpp"
     INCLUDE_DIRS "."
-    REQUIRES drivers sensors profiles transport lua_runtime esp_timer
+    REQUIRES drivers transport lua_runtime esp_timer
 )

main/main.cpp

@@ -1,27 +1,14 @@
-#include "chip_temperature_sensor.h"
 #include "commissioning.h"
 #include "esp_log.h"
 #include "esp_timer.h"
+#include "lua_runtime.h"
 #include "mqtt.h"
 #include "rgb_led.h"
 
 namespace {
 constexpr const char *TAG = "kvida_os";
 
-kvida::ChipTemperatureSensor g_chip_temp_sensor;
-esp_timer_handle_t g_chip_temp_timer = nullptr;
-
-void publish_chip_temperature_tick(void * /*arg*/)
-{
-    if (!g_chip_temp_sensor.fetch()) {
-        return;
-    }
-    kvida::SensorValue value{};
-    if (g_chip_temp_sensor.get(kvida::SensorChannel::ChipTemperature, value)) {
-        float celsius = static_cast<float>(value.val1) + static_cast<float>(value.val2) * 1e-6f;
-        kvida::publish_chip_temperature(celsius);
-    }
-}
+esp_timer_handle_t g_lua_tick_timer = nullptr;
 
 void on_led_color(uint8_t red, uint8_t green, uint8_t blue)
 {
@@ -34,22 +21,23 @@ extern "C" void app_main(void)
 {
     ESP_LOGI(TAG, "kvida-os starting");
 
-    // Quick end-to-end data-flow proof (real Sensor impl -> MQTT/HA, and
-    // HA -> MQTT -> actuator) using only what's on the ESP32-C6-DevKitC-1
-    // itself: no sensor profiles or hardware wiring exist yet.
-    g_chip_temp_sensor.begin();
+    // The default Lua script (components/lua_runtime/src/default_script.h)
+    // reads chip temperature, drives the LED, and publishes to Home
+    // Assistant -- see that component's README for what's real here vs.
+    // still a "quick proof" using only what's on the ESP32-C6-DevKitC-1.
     kvida::drivers::rgb_led_init();
+    kvida::lua_runtime_init();
     kvida::set_led_color_handler(&on_led_color);
 
     const esp_timer_create_args_t timer_args = {
-        .callback = &publish_chip_temperature_tick,
+        .callback = [](void *) { kvida::lua_runtime_tick(); },
         .arg = nullptr,
         .dispatch_method = ESP_TIMER_TASK,
-        .name = "chip_temp_publish",
+        .name = "lua_tick",
         .skip_unhandled_events = true,
     };
-    ESP_ERROR_CHECK(esp_timer_create(&timer_args, &g_chip_temp_timer));
-    ESP_ERROR_CHECK(esp_timer_start_periodic(g_chip_temp_timer, 30LL * 1000000));
+    ESP_ERROR_CHECK(esp_timer_create(&timer_args, &g_lua_tick_timer));
+    ESP_ERROR_CHECK(esp_timer_start_periodic(g_lua_tick_timer, 30LL * 1000000));
 
     // First boot / no stored Wi-Fi credentials -> fall straight into
     // commissioning (nothing to protect yet, so no physical-interaction