supervisor: keep CIRCUITPY writable after a USB bus reset

supervisor/shared/usb/usb_msc_flash.c

@@ -202,10 +202,25 @@ static fs_user_mount_t *get_vfs(int lun) {
     return NULL;
 }
 
+// Release the locks that USB MSC holds. Locks held by others (Python, workflows) are not touched.
+static void release_msc_locks(void) {
+    for (uint8_t i = 0; i < LUN_COUNT; i++) {
+        if (!locked[i]) {
+            continue;
+        }
+        fs_user_mount_t *vfs = get_vfs(i);
+        if (vfs != NULL) {
+            blockdev_unlock((supervisor_vfs_t *)vfs);
+        }
+        locked[i] = false;
+    }
+}
+
 static void _usb_msc_uneject(void) {
+    // A bus reset doesn't call tud_umount_cb(), so USB MSC may still hold its locks.
+    // Keep them: tud_msc_is_writable_cb() sees locked[] and doesn't lock again.
     for (uint8_t i = 0; i < LUN_COUNT; i++) {
         ejected[i] = false;
-        locked[i] = false;
     }
 }
 
@@ -214,14 +229,7 @@ void usb_msc_mount(void) {
 }
 
 void usb_msc_umount(void) {
-    for (uint8_t i = 0; i < LUN_COUNT; i++) {
-        fs_user_mount_t *vfs = get_vfs(i);
-        if (vfs == NULL) {
-            continue;
-        }
-        blockdev_unlock((supervisor_vfs_t *)vfs);
-        locked[i] = false;
-    }
+    release_msc_locks();
 }
 
 // Release the USB MSC lock on CIRCUITPY (LUN 0), if USB MSC holds it.
@@ -493,9 +501,13 @@ bool tud_msc_start_stop_cb(uint8_t lun, uint8_t power_condition, bool start, boo
             if (disk_ioctl(current_mount, CTRL_SYNC, NULL) != RES_OK) {
                 return false;
             } else {
-                blockdev_unlock((supervisor_vfs_t *)current_mount);
+                // Release the lock only if USB MSC holds it. Locks held by others
+                // (Python, workflows) are not touched.
+                if (locked[lun]) {
+                    blockdev_unlock((supervisor_vfs_t *)current_mount);
+                    locked[lun] = false;
+                }
                 ejected[lun] = true;
-                locked[lun] = false;
             }
         } else {
             // We can only load if it hasn't been ejected.