feat(mcp): restore MCP service with display charging toggle

- Restore MCP system (McpSystem 1900+ LOC, McpHandler, McpScreensaver, McpSettings, McpOverride apps)
- Use audio-stream instead of direct I2S for MP3 playback (fixes fast playback, uses native resampler)
- Register McpSettings + McpOverride in Tactility.cpp so Settings shows MCP Screen
- DisplaySettings: add ScreensaverType::McpScreen and disableScreensaverWhenCharging flag
- Display app: add 'Disable on charging' toggle, handles McpScreen screensaver type
- DisplayIdle: skip screensaver while charging, support McpScreen screensaver, isDeviceCharging check via PowerDevice
- WebServer: coexistence with MCP (McpHandler)
- Avoid formatting churn from previous commits

Squashed from range eaa248b0..8970143f (6 commits) into single clean commit

Tactility/Source/service/displayidle/DisplayIdle.cpp

@@ -7,10 +7,12 @@
 #include "MatrixRainScreensaver.h"
 #include "MystifyScreensaver.h"
 #include "StackChanScreensaver.h"
+#include "McpScreensaver.h"
 
 #include <tactility/log.h>
 #include <Tactility/CoreDefines.h>
 #include <Tactility/hal/display/DisplayDevice.h>
+#include <Tactility/hal/power/PowerDevice.h>
 #include <Tactility/lvgl/LvglSync.h>
 #include <Tactility/service/ServiceContext.h>
 #include <Tactility/service/ServiceManifest.h>
@@ -28,6 +30,22 @@ static std::shared_ptr<hal::display::DisplayDevice> getDisplay() {
     return hal::findFirstDevice<hal::display::DisplayDevice>(hal::Device::Type::Display);
 }
 
+static bool isDeviceCharging() {
+    bool charging = false;
+    hal::findDevices<hal::power::PowerDevice>(hal::Device::Type::Power, [&charging](const auto& power) {
+        if (!power->supportsMetric(hal::power::PowerDevice::MetricType::IsCharging)) {
+            return true;
+        }
+        hal::power::PowerDevice::MetricData data;
+        if (power->getMetric(hal::power::PowerDevice::MetricType::IsCharging, data) && data.valueAsBool) {
+            charging = true;
+            return false;
+        }
+        return true;
+    });
+    return charging;
+}
+
 void DisplayIdleService::stopScreensaverCb(lv_event_t* e) {
     auto* self = static_cast<DisplayIdleService*>(lv_event_get_user_data(e));
     lv_event_stop_bubbling(e);
@@ -103,6 +121,9 @@ void DisplayIdleService::activateScreensaver() {
         case settings::display::ScreensaverType::StackChan:
             screensaver = std::make_unique<StackChanScreensaver>();
             break;
+        case settings::display::ScreensaverType::McpScreen:
+            screensaver = std::make_unique<McpScreensaver>();
+            break;
         case settings::display::ScreensaverType::None:
         default:
             // Just black screen, no animated screensaver
@@ -179,19 +200,28 @@ void DisplayIdleService::tick() {
                 displayDimmed = false;
             }
         } else {
+            bool charging_blocks = cachedDisplaySettings.disableScreensaverWhenCharging && isDeviceCharging();
             if (!displayDimmed && inactive_ms >= cachedDisplaySettings.backlightTimeoutMs) {
-                if (!lvgl::lock(100)) {
-                    return; // Retry on next tick
+                if (charging_blocks) {
+                    // Skip screensaver while charging
+                } else {
+                    if (!lvgl::lock(100)) {
+                        return; // Retry on next tick
+                    }
+                    activateScreensaver();
+                    lvgl::unlock();
+                    // Turn off backlight for "None" screensaver (just black screen)
+                    if (cachedDisplaySettings.screensaverType == settings::display::ScreensaverType::None) {
+                        display->setBacklightDuty(0);
+                    }
+                    displayDimmed = true;
                 }
-                activateScreensaver();
-                lvgl::unlock();
-                // Turn off backlight for "None" screensaver (just black screen)
-                if (cachedDisplaySettings.screensaverType == settings::display::ScreensaverType::None) {
-                    display->setBacklightDuty(0);
+            } else if (displayDimmed) {
+                if (inactive_ms < kWakeActivityThresholdMs) {
+                    stopScreensaver();
+                } else if (charging_blocks) {
+                    stopScreensaver();
                 }
-                displayDimmed = true;
-            } else if (displayDimmed && (inactive_ms < kWakeActivityThresholdMs)) {
-                stopScreensaver();
             }
         }
     }

Tactility/Source/service/displayidle/McpScreensaver.cpp

@@ -0,0 +1,100 @@
+#ifdef ESP_PLATFORM
+
+#include "McpScreensaver.h"
+#include <Tactility/mcp/McpSystem.h>
+#include <tactility/log.h>
+
+constexpr auto* TAG = "McpScreensaver";
+#include <esp_heap_caps.h>
+
+namespace tt::service::displayidle {
+
+
+void McpScreensaver::start(lv_obj_t* overlay, lv_coord_t screenW, lv_coord_t screenH) {
+    auto& state = mcp::getState();
+
+    // Full-screen canvas on the overlay
+    lv_obj_t* canvas = lv_canvas_create(overlay);
+    lv_obj_set_size(canvas, screenW, screenH);
+    lv_obj_set_pos(canvas, 0, 0);
+    lv_obj_set_style_radius(canvas, 0, LV_PART_MAIN);
+    lv_obj_set_style_border_width(canvas, 0, LV_PART_MAIN);
+    lv_obj_set_style_pad_all(canvas, 0, LV_PART_MAIN);
+    lv_obj_remove_flag(canvas, LV_OBJ_FLAG_SCROLLABLE);
+
+    // Allocate framebuffer (prefer SPIRAM)
+    size_t requiredSize = (size_t)screenW * screenH * sizeof(uint16_t);
+    framebuffer = (uint16_t*)heap_caps_malloc(requiredSize, MALLOC_CAP_SPIRAM | MALLOC_CAP_8BIT);
+    if (framebuffer == nullptr) {
+        framebuffer = (uint16_t*)heap_caps_malloc(requiredSize, MALLOC_CAP_8BIT);
+    }
+    framebufferSize = (framebuffer != nullptr) ? requiredSize : 0;
+
+    if (framebuffer == nullptr) {
+        LOG_E(TAG, "Failed to allocate %uB framebuffer", (unsigned)requiredSize);
+        lv_obj_t* err = lv_label_create(canvas);
+        lv_label_set_text(err, "Framebuffer alloc failed");
+        lv_obj_center(err);
+        return;
+    }
+
+    // Fill with a dark slate background (inverted for display path)
+    size_t pixelCount = (size_t)screenW * screenH;
+    for (size_t i = 0; i < pixelCount; ++i) {
+        framebuffer[i] = ~0x18E3; // dark blue-grey
+    }
+
+    lv_canvas_set_buffer(canvas, framebuffer, screenW, screenH, LV_COLOR_FORMAT_RGB565);
+
+    // Waiting label (removed on first MCP draw via lv_obj_clean)
+    lv_obj_t* waitLabel = lv_label_create(canvas);
+    lv_label_set_text(waitLabel, "Waiting for LLM...");
+    lv_obj_set_style_text_color(waitLabel, lv_color_black(), LV_PART_MAIN); // white on screen (inverted)
+    lv_obj_align(waitLabel, LV_ALIGN_CENTER, 0, -20);
+
+    lv_obj_t* resLabel = lv_label_create(canvas);
+    lv_label_set_text_fmt(resLabel, "Display: %dx%d", (int)screenW, (int)screenH);
+    lv_color_t resColor = lv_palette_lighten(LV_PALETTE_BLUE, 3);
+    lv_obj_set_style_text_color(resLabel, lv_color_make(~resColor.red, ~resColor.green, ~resColor.blue), LV_PART_MAIN);
+    lv_obj_align(resLabel, LV_ALIGN_CENTER, 0, 10);
+
+    // Register with McpSystemState
+    std::lock_guard<std::mutex> lock(state.mutex);
+    state.drawArea = canvas;
+    state.framebuffer = framebuffer;
+    state.framebufferSize = framebufferSize;
+    state.displayWidth = (uint16_t)screenW;
+    state.displayHeight = (uint16_t)screenH;
+    state.drawWidth = (uint16_t)screenW;
+    state.drawHeight = (uint16_t)screenH;
+    // Don't reset overrideActive — if the LLM already drew, we keep the content
+
+    LOG_I(TAG, "McpScreensaver started (%dx%d)", (int)screenW, (int)screenH);
+}
+
+void McpScreensaver::stop() {
+    auto& state = mcp::getState();
+    {
+        std::lock_guard<std::mutex> lock(state.mutex);
+        state.drawArea = nullptr;
+        state.framebuffer = nullptr;
+        state.framebufferSize = 0;
+        state.overrideActive = false;
+    }
+
+    if (framebuffer != nullptr) {
+        heap_caps_free(framebuffer);
+        framebuffer = nullptr;
+        framebufferSize = 0;
+    }
+
+    LOG_I(TAG, "McpScreensaver stopped");
+}
+
+void McpScreensaver::update(lv_coord_t /*screenW*/, lv_coord_t /*screenH*/) {
+    // MCP draws on demand via HTTP — no per-frame animation needed
+}
+
+} // namespace tt::service::displayidle
+
+#endif // ESP_PLATFORM

Tactility/Source/service/displayidle/McpScreensaver.h

@@ -0,0 +1,30 @@
+#pragma once
+#ifdef ESP_PLATFORM
+
+#include "Screensaver.h"
+#include <cstdint>
+
+namespace tt::service::displayidle {
+
+/**
+ * MCP Screen screensaver.
+ * Creates a full-screen LVGL canvas on the overlay and registers it in
+ * McpSystemState so that MCP HTTP draw commands can paint to it.
+ * Dismissed by a touch event (handled by the parent DisplayIdle overlay).
+ */
+class McpScreensaver final : public Screensaver {
+    uint16_t* framebuffer = nullptr;
+    size_t framebufferSize = 0;
+
+public:
+    McpScreensaver() = default;
+    ~McpScreensaver() override = default;
+
+    void start(lv_obj_t* overlay, lv_coord_t screenW, lv_coord_t screenH) override;
+    void stop() override;
+    void update(lv_coord_t screenW, lv_coord_t screenH) override;
+};
+
+} // namespace tt::service::displayidle
+
+#endif // ESP_PLATFORM

Tactility/Source/service/webserver/WebServerService.cpp

@@ -5,6 +5,8 @@
 #include <Tactility/service/webserver/AssetVersion.h>
 #include <Tactility/service/ServiceManifest.h>
 #include <Tactility/settings/WebServerSettings.h>
+#include <Tactility/settings/McpSettings.h>
+#include <Tactility/mcp/McpSystem.h>
 #include <Tactility/MountPoints.h>
 #include <Tactility/file/File.h>
 #include <Tactility/lvgl/Statusbar.h>
@@ -215,7 +217,8 @@ bool WebServerService::onStart(ServiceContext& service) {
         lock.lock();
         g_cachedSettings = settings::webserver::loadOrGetDefault();
         g_settingsCached = true;
-        serverEnabled = g_cachedSettings.webServerEnabled;
+        auto mcpSettings = settings::mcp::loadOrGetDefault();
+        serverEnabled = g_cachedSettings.webServerEnabled || mcpSettings.mcpEnabled;
     }
     // Subscribe to settings change events to refresh cache
     settingsEventSubscription = pubsub->subscribe([](WebServerEvent event) {
@@ -259,13 +262,17 @@ void WebServerService::onStop(ServiceContext& service) {
 void WebServerService::setEnabled(bool enabled) {
     auto lock = mutex.asScopedLock();
     lock.lock();
-    
+
     if (enabled) {
         if (!httpServer || !httpServer->isStarted()) {
             startServer();
         }
     } else {
-        if (httpServer && httpServer->isStarted()) {
+        // Stop only if both web server and MCP are disabled
+        auto wsSettings = settings::webserver::loadOrGetDefault();
+        auto mcpSettings = settings::mcp::loadOrGetDefault();
+        bool anyEnabled = wsSettings.webServerEnabled || mcpSettings.mcpEnabled;
+        if (!anyEnabled && httpServer && httpServer->isStarted()) {
             stopServer();
         }
     }
@@ -514,6 +521,11 @@ bool WebServerService::startServer() {
     LOG_I(TAG, "HTTP server started successfully on port %u", (unsigned)settings.webServerPort);
     publish_event(this, WebServerEvent::WebServerStarted);
 
+    auto mcpSettings = settings::mcp::loadOrGetDefault();
+    if (mcpSettings.mcpEnabled) {
+        mcp::startVideoStreamServer();
+    }
+
     // Show statusbar icon
     if (statusbarIconId >= 0) {
         lvgl::statusbar_icon_set_image(statusbarIconId, LVGL_ICON_STATUSBAR_CLOUD);
@@ -533,6 +545,8 @@ void WebServerService::stopServer() {
     httpServer->stop();
     httpServer.reset();
 
+    mcp::stopVideoStreamServer();
+
     // Stop AP mode WiFi if we started it
     if (apWifiInitialized || apNetif != nullptr) {
         stopApMode();
@@ -1025,15 +1039,24 @@ esp_err_t WebServerService::handleApiGet(httpd_req_t* request) {
     return ESP_FAIL;
 }
 
-// API POST dispatcher - all POST endpoints require authentication
+// API POST dispatcher - all POST endpoints require authentication except MCP
 esp_err_t WebServerService::handleApiPost(httpd_req_t* request) {
+    const char* uri = request->uri;
+
+    // MCP endpoints are unauthenticated (local network)
+    if (strncmp(uri, "/api/mcp", 8) == 0) {
+        return handleApiMcp(request);
+    }
+    if (strncmp(uri, "/api/screen/raw", 15) == 0) {
+        return handleApiScreenRaw(request);
+    }
+
     bool authPassed = false;
     esp_err_t authResult = validateRequestAuth(request, authPassed);
     if (!authPassed) {
         return authResult;
     }
 
-    const char* uri = request->uri;
     if (strncmp(uri, "/api/apps/run", 13) == 0) {
         return handleApiAppsRun(request);
     }