Pause SD queue early on M25 (MarlinFirmware#21317)

Marlin/src/gcode/host/M115.cpp

@@ -120,6 +120,9 @@ void GcodeSuite::M115() {
     // REPEAT (M808)
     cap_line(PSTR("REPEAT"), ENABLED(GCODE_REPEAT_MARKERS));
 
+    // SD_WRITE (M928, M28, M29)
+    cap_line(PSTR("SD_WRITE"), ENABLED(SDSUPPORT) && DISABLED(SDCARD_READONLY));
+
     // AUTOREPORT_SD_STATUS (M27 extension)
     cap_line(PSTR("AUTOREPORT_SD_STATUS"), ENABLED(AUTO_REPORT_SD_STATUS));
 

Marlin/src/gcode/queue.cpp

@@ -567,14 +567,20 @@ void GCodeQueue::get_serial_commands() {
       const bool is_eol = ISEOL(sd_char);
       if (is_eol || card_eof) {
 
-
         // Reset stream state, terminate the buffer, and commit a non-empty command
         if (!is_eol && sd_count) ++sd_count;          // End of file with no newline
         if (!process_line_done(sd_input_state, command.buffer, sd_count)) {
 
           // M808 L saves the sdpos of the next line. M808 loops to a new sdpos.
           TERN_(GCODE_REPEAT_MARKERS, repeat.early_parse_M808(command.buffer));
 
+          #if DISABLED(PARK_HEAD_ON_PAUSE)
+            // When M25 is non-blocking it can still suspend SD commands
+            // Otherwise the M125 handler needs to know SD printing is active
+            if (command.buffer[0] == 'M' && command.buffer[1] == '2' && command.buffer[2] == '5' && !NUMERIC(command.buffer[3]))
+              card.pauseSDPrint();
+          #endif
+
           // Put the new command into the buffer (no "ok" sent)
           ring_buffer.commit_command(true);
 

Marlin/src/gcode/sd/M24_M25.cpp

@@ -87,6 +87,10 @@ void GcodeSuite::M24() {
 
 /**
  * M25: Pause SD Print
+ *
+ * With PARK_HEAD_ON_PAUSE:
+ *   Invoke M125 to store the current position and move to the park
+ *   position. M24 will move the head back before resuming the print.
  */
 void GcodeSuite::M25() {