core/archipelago/src/mesh/meshtastic.rs

@@ -180,6 +180,12 @@ impl MeshtasticDevice {
             "Failed to open serial port {} (permission denied? device busy?)",
             path
         ))?;
+        // See probe_rnode() in reticulum.rs for why: ESP32-S3 native-USB
+        // boards reset on a DTR/RTS transition, so deassert both and settle
+        // before the handshake below.
+        let _ = port.set_dtr(false);
+        let _ = port.set_rts(false);
+        tokio::time::sleep(Duration::from_millis(300)).await;
         info!(path = %path, baud = BAUD_RATE, "Opened Meshtastic serial port");
 
         Ok(Self {

core/archipelago/src/mesh/reticulum.rs

@@ -1005,6 +1005,14 @@ fn parse_hash16(hex_str: &str) -> Result<[u8; 16]> {
 async fn probe_rnode(path: &str) -> Result<()> {
     let port = serial2_tokio::SerialPort::open(path, PROBE_BAUD)
         .with_context(|| format!("Failed to open {} for Reticulum probe", path))?;
+    // ESP32-S3 native-USB boards (Heltec V3/V4 etc. — no separate USB-UART
+    // bridge chip) treat a DTR/RTS transition on open as a reset signal, the
+    // same mechanism esptool uses to force bootloader entry. Deassert both
+    // and let the board settle before writing the probe, or the reboot eats
+    // the DETECT_RESP window below.
+    let _ = port.set_dtr(false);
+    let _ = port.set_rts(false);
+    tokio::time::sleep(Duration::from_millis(300)).await;
     let probe: [u8; 13] = [
         KISS_FEND,
         KISS_CMD_DETECT,

core/archipelago/src/mesh/serial.rs

@@ -57,6 +57,12 @@ impl MeshcoreDevice {
             "Failed to open serial port {} (permission denied? device busy?)",
             path
         ))?;
+        // See probe_rnode() in reticulum.rs for why: ESP32-S3 native-USB
+        // boards reset on a DTR/RTS transition, so deassert both and settle
+        // before the handshake below.
+        let _ = port.set_dtr(false);
+        let _ = port.set_rts(false);
+        tokio::time::sleep(Duration::from_millis(300)).await;
 
         info!(path = %path, baud = BAUD_RATE, "Opened serial port");