--- a/src/mouse.c	2026-07-23 13:55:22.649216163 -0500
+++ b/src/mouse.c	2026-07-23 14:01:32.777853582 -0500
@@ -1772,6 +1772,26 @@
         break;
 
     case DEVICE_ON:
+        /*
+         * illumos/Solaris CR 6892799 fix: the VUID /dev/mouse stream
+         * (unlike a plain serial line) does not tolerate being closed
+         * and reopened across every console mode switch (X VT
+         * enter/leave toggles DEVICE_OFF/DEVICE_ON around each
+         * switch). Keep the fd + Xisb buffer alive once opened; only
+         * (re)open here on the very first DEVICE_ON, or if a prior
+         * open attempt failed. DEVICE_OFF no longer closes the fd -
+         * the real close now happens once, in DEVICE_CLOSE.
+         */
+        if (pInfo->fd != -1) {
+            /* Already open from a previous DEVICE_ON - just re-enable. */
+            xf86FlushInput(pInfo->fd);
+            xf86AddEnabledDevice(pInfo);
+            if (pMse->emulate3Buttons || pMse->emulate3ButtonsSoft) {
+                RegisterBlockAndWakeupHandlers (MouseBlockHandler,
+                                                MouseWakeupHandler,
+                                                (pointer) pInfo);
+            }
+        } else {
         pInfo->fd = xf86OpenSerial(pInfo->options);
         if (pInfo->fd == -1)
             xf86Msg(X_WARNING, "%s: cannot open input device\n", pInfo->name);
@@ -1820,6 +1840,7 @@
                 }
             }
         }
+        }
         pMse->lastButtons = 0;
         pMse->lastMappedButtons = 0;
         pMse->emulateState = 0;
@@ -1832,12 +1853,11 @@
     case DEVICE_OFF:
         if (pInfo->fd != -1) {
             xf86RemoveEnabledDevice(pInfo);
-            if (pMse->buffer) {
-                XisbFree(pMse->buffer);
-                pMse->buffer = NULL;
-            }
-            xf86CloseSerial(pInfo->fd);
-            pInfo->fd = -1;
+            /*
+             * 6892799: do NOT close/free the buffer or fd here - the
+             * VUID /dev/mouse stream must survive the mode switch.
+             * Actual teardown is deferred to DEVICE_CLOSE.
+             */
             if (pMse->emulate3Buttons || pMse->emulate3ButtonsSoft)
             {
                 RemoveBlockAndWakeupHandlers (MouseBlockHandler,
@@ -1848,6 +1868,16 @@
         device->public.on = FALSE;
         break;
     case DEVICE_CLOSE:
+        /* 6892799: the fd/buffer were kept open across DEVICE_OFF/ON
+         * cycles; do the real close here, once, at final teardown. */
+        if (pInfo->fd != -1) {
+            if (pMse->buffer) {
+                XisbFree(pMse->buffer);
+                pMse->buffer = NULL;
+            }
+            xf86CloseSerial(pInfo->fd);
+            pInfo->fd = -1;
+        }
         free(pMse->mousePriv);
         pMse->mousePriv = NULL;
         break;
@@ -3738,6 +3768,16 @@
 #define VAL_THRESHOLD 40
 
 /*
+ * SDK-drift compat fix: mouse.c relies on the X server's misc.h `sign()`
+ * macro, which the XLibre 25.1.8 SDK this port builds against no longer
+ * provides (dropped upstream). Define the historical semantics locally if
+ * it is not already defined by the SDK.
+ */
+#ifndef sign
+#define sign(x) ((x) > 0 ? 1 : ((x) < 0 ? -1 : 0))
+#endif
+
+/*
  * checkForErraticMovements() -- check if mouse 'jumps around'.
  */
 static void