refactor: board-owned display init, zero cfg in application code

- Each board now exports DisplayDriver type and create_display() async fn
- ESP32-S3 boards share SSD1306 create_display in board/esp32s3.rs
- RAK WisBlock has its own SSD1306 create_display (different I2C type)
- Wio Tracker has SH1106 create_display (different display IC)
- Removed all cfg_if from display.rs — calls board::create_display()
- Removed display init retry logic (single attempt, return None on failure)
- ZERO board-specific #[cfg(feature)] outside board/, host/mod.rs, and hal/

firmware/src/board/esp32s3.rs

@@ -47,6 +47,34 @@ pub struct DisplayParts {
     pub mac: [u8; 6],
 }
 
+// ── Display driver ──────────────────────────────────────────────────
+
+pub type DisplayDriver = ssd1306::Ssd1306Async<
+    ssd1306::prelude::I2CInterface<DisplayI2c>,
+    ssd1306::size::DisplaySize128x64,
+    ssd1306::mode::BufferedGraphicsModeAsync<ssd1306::size::DisplaySize128x64>,
+>;
+
+/// Construct and initialize an SSD1306 display from raw I2C.
+pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+    use ssd1306::mode::DisplayConfigAsync;
+    use ssd1306::prelude::{Brightness, DisplayRotation};
+    use ssd1306::size::DisplaySize128x64;
+    use ssd1306::{I2CDisplayInterface, Ssd1306Async};
+
+    let interface = I2CDisplayInterface::new(i2c);
+    let mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
+        .into_buffered_graphics_mode();
+
+    embassy_time::Timer::after_millis(100).await;
+    if display.init().await.is_err() {
+        defmt::error!("SSD1306 display init failed");
+        return None;
+    }
+    let _ = display.set_brightness(Brightness::BRIGHTEST).await;
+    Some(display)
+}
+
 // ── Shared peripheral init helpers ──────────────────────────────────
 
 /// Construct SX1262 radio from an initialized SPI bus.

firmware/src/board/heltec_v3.rs

@@ -5,7 +5,10 @@ use super::traits::LoRaBoard;
 use crate::hal::esp32s3 as mcu;
 
 #[allow(unused_imports)] // Re-exported for other modules (display, radio, uart tasks)
-pub use super::esp32s3::{DisplayI2c, DisplayParts, RadioDriver, RadioParts, UartDriver, UartParts};
+pub use super::esp32s3::{
+    create_display, DisplayDriver, DisplayI2c, DisplayParts, RadioDriver, RadioParts, UartDriver,
+    UartParts,
+};
 
 // ── Board init ──────────────────────────────────────────────────────
 

firmware/src/board/heltec_v4.rs

@@ -5,7 +5,10 @@ use super::traits::LoRaBoard;
 use crate::hal::esp32s3 as mcu;
 
 #[allow(unused_imports)] // Re-exported for other modules (display, radio, usb tasks)
-pub use super::esp32s3::{DisplayI2c, DisplayParts, RadioDriver, RadioParts, UsbDriver, UsbParts};
+pub use super::esp32s3::{
+    create_display, DisplayDriver, DisplayI2c, DisplayParts, RadioDriver, RadioParts, UsbDriver,
+    UsbParts,
+};
 
 // ── Board implementation ────────────────────────────────────────────
 

firmware/src/board/rak_wisblock_4631.rs

@@ -21,6 +21,31 @@ pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
 pub type UsbDriver = mcu::UsbNrfDriver;
 pub type DisplayI2c = mcu::I2cBus;
 
+pub type DisplayDriver = ssd1306::Ssd1306Async<
+    ssd1306::prelude::I2CInterface<DisplayI2c>,
+    ssd1306::size::DisplaySize128x64,
+    ssd1306::mode::BufferedGraphicsModeAsync<ssd1306::size::DisplaySize128x64>,
+>;
+
+pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+    use ssd1306::mode::DisplayConfigAsync;
+    use ssd1306::prelude::{Brightness, DisplayRotation};
+    use ssd1306::size::DisplaySize128x64;
+    use ssd1306::{I2CDisplayInterface, Ssd1306Async};
+
+    let interface = I2CDisplayInterface::new(i2c);
+    let mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
+        .into_buffered_graphics_mode();
+
+    embassy_time::Timer::after_millis(100).await;
+    if display.init().await.is_err() {
+        defmt::error!("SSD1306 display init failed");
+        return None;
+    }
+    let _ = display.set_brightness(Brightness::BRIGHTEST).await;
+    Some(display)
+}
+
 // ── Peripheral bundles ──────────────────────────────────────────────
 
 pub struct RadioParts {

firmware/src/board/wio_tracker_l1.rs

@@ -21,6 +21,20 @@ pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
 pub type UsbDriver = mcu::UsbNrfDriver;
 pub type DisplayI2c = mcu::I2cBus;
 
+pub type DisplayDriver = crate::driver::sh1106::Sh1106<DisplayI2c>;
+
+pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+    let mut display = crate::driver::sh1106::Sh1106::new(i2c, 0x3D);
+
+    embassy_time::Timer::after_millis(100).await;
+    if display.init().await.is_err() {
+        defmt::error!("SH1106 display init failed");
+        return None;
+    }
+    let _ = display.set_brightness(0xFF).await;
+    Some(display)
+}
+
 // ── Peripheral bundles ──────────────────────────────────────────────
 
 pub struct RadioParts {

firmware/src/display.rs

@@ -123,52 +123,10 @@ pub async fn display_task(
         mac: &mac_str,
     };
 
-    cfg_if::cfg_if! {
-        if #[cfg(feature = "wio_tracker_l1")] {
-            let mut display = crate::driver::sh1106::Sh1106::new(parts.i2c, 0x3D);
-
-            Timer::after_millis(100).await;
-
-            if display.init().await.is_err() {
-                defmt::error!("SH1106 init failed — retrying");
-                Timer::after_millis(500).await;
-                if display.init().await.is_err() {
-                    defmt::error!("SH1106 init failed twice, giving up");
-                    return;
-                }
-            }
-            if display.set_brightness(0xFF).await.is_err() {
-                defmt::warn!("display brightness set failed");
-            }
-        } else {
-            use ssd1306::mode::DisplayConfigAsync;
-            use ssd1306::prelude::DisplayRotation;
-            use ssd1306::size::DisplaySize128x64;
-            use ssd1306::{I2CDisplayInterface, Ssd1306Async};
-
-            let interface = I2CDisplayInterface::new(parts.i2c);
-            let mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
-                .into_buffered_graphics_mode();
-
-            Timer::after_millis(100).await;
-
-            if display.init().await.is_err() {
-                defmt::error!("SSD1306 init failed — retrying");
-                Timer::after_millis(500).await;
-                if display.init().await.is_err() {
-                    defmt::error!("SSD1306 init failed twice, giving up");
-                    return;
-                }
-            }
-            if display
-                .set_brightness(ssd1306::prelude::Brightness::BRIGHTEST)
-                .await
-                .is_err()
-            {
-                defmt::warn!("display brightness set failed");
-            }
-        }
-    }
+    let Some(mut display) = crate::board::create_display(parts.i2c).await else {
+        defmt::error!("display init failed, giving up");
+        return;
+    };
 
     let mut state = DisplayState::new();
     let Some(mut receiver) = status.receiver() else {