Add serial reset and bootloader commands, no more BOOT+RST

Two new debug commands:
- 'X' (reset): ESP.restart() for clean reboot
- 'Z' (bootloader): sets RTC_CNTL_FORCE_DOWNLOAD_BOOT and restarts,
  putting the ESP32-S3 directly into download mode for esptool

Workflow: screenshot.py z → esptool write_flash (no BOOT+RST)

Also adds reset/bootloader subcommands to screenshot.py.

Gui.h

@@ -8,6 +8,7 @@
 #if BOARD_MODEL == BOARD_TWATCH_ULT
 
 #include <lvgl.h>
+#include "soc/rtc_cntl_reg.h"
 
 // Custom fonts: generated with lv_font_conv --no-compress from Montserrat Bold
 // IMPORTANT: must use --no-compress or set LV_USE_FONT_COMPRESSED=1 in lv_conf.h
@@ -1335,6 +1336,25 @@ static void gui_cmd_execute() {
             Serial.flush();
             break;
         }
+        case 'X': {  // Hard reset
+            Serial.write(hdr, 4);
+            Serial.println("{\"reset\":true}");
+            Serial.flush();
+            delay(100);
+            ESP.restart();
+            break;
+        }
+        case 'Z': {  // Reboot into download mode (no BOOT+RST needed)
+            Serial.write(hdr, 4);
+            Serial.println("{\"bootloader\":true}");
+            Serial.flush();
+            delay(100);
+            #if MCU_VARIANT == MCU_ESP32
+              REG_WRITE(RTC_CNTL_OPTION1_REG, RTC_CNTL_FORCE_DOWNLOAD_BOOT);
+              ESP.restart();
+            #endif
+            break;
+        }
     }
 }
 

scripts/screenshot.py

@@ -241,6 +241,20 @@ def cmd_files(s):
     print(f"Timeout ({len(buf)} bytes)")
 
 
+def cmd_simple(s, cmd_char, label):
+    """Send a command, print response, don't wait long"""
+    send_cmd(s, ord(cmd_char))
+    time.sleep(0.5)
+    data = s.read(s.in_waiting or 1)
+    if data:
+        magic = PREFIX + cmd_char.encode()
+        idx = data.find(magic)
+        if idx >= 0:
+            print(data[idx + 4:].decode('ascii', errors='replace').strip())
+            return
+    print(label)
+
+
 def cmd_log(s):
     send_cmd(s, ord('L'))
     buf = b""
@@ -295,6 +309,12 @@ def main():
     sub.add_parser("files", aliases=["f"],
                     help="List files on SD card")
 
+    sub.add_parser("reset", aliases=["x"],
+                    help="Hard reset the device")
+
+    sub.add_parser("bootloader", aliases=["z"],
+                    help="Reboot into download mode (no BOOT+RST needed)")
+
     args = parser.parse_args()
     if not args.command:
         parser.print_help()
@@ -322,6 +342,10 @@ def main():
             cmd_log(s)
         elif args.command in ("files", "f"):
             cmd_files(s)
+        elif args.command in ("reset", "x"):
+            cmd_simple(s, 'X', "Reset sent")
+        elif args.command in ("bootloader", "z"):
+            cmd_simple(s, 'Z', "Rebooting into download mode...")
     finally:
         s.close()