Reconnect to a restarted Wayland compositor

Windows now outlive the compositor. On connection loss YASL sends
DISPLAY_LOST instead of closing every window, retries the connection on
a loop timer, rebuilds each toplevel with its title, size, state and GL
context, and sends DISPLAY_RESTORED. CPU windows keep their pixels;
GPU renderers drop Vulkan surfaces and GL objects on loss and rebuild
them on restore.

- Free the dead connection's objects on the next wait, after the
  application has released GPU objects built on them.
- Report a lost connection as an event rather than a failed wait.
- Refuse window and Vulkan surface creation while offline with the new
  YASL_ERROR_DISCONNECTED.
- Close popups, cancel drags and fail pending clipboard requests on loss.
- Print only protocol errors, not ordinary disconnects.
- Examples survive a restart; game.c rebinds its GL context.
- Add an end-to-end test that kills Weston under CPU, GL and Vulkan
  windows and requires them to recover.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

4 files changed, 7 insertions, 2 deletions

diff --git a/src/common/backend.h b/src/common/backend.h
index e3dc6de..bf6815a 100644
--- a/src/common/backend.h
+++ b/src/common/backend.h
@@ -16,6 +16,7 @@ struct yasl_private_event_state;
 struct yasl_private_display {
     const struct yasl_private_backend_ops *ops;
     void *native_handle;
+    bool offline; /* Connection lost; native handles are unusable until it is restored. */
     struct yasl_private_display_cbs callbacks;
     struct yasl_private_loop *loop;
     /* Backend's copy of yasl_private_display_spec.app_id, or NULL; for desktop services. */
diff --git a/src/common/surface.c b/src/common/surface.c
index 897b95a..9b4a8ad 100644
--- a/src/common/surface.c
+++ b/src/common/surface.c
@@ -32,13 +32,14 @@ bool yasl_public_fail(int error)
     else if (error==ENOMEM) code=YASL_ERROR_NO_MEMORY;
     else if (error==EBUSY) code=YASL_ERROR_BUSY;
     else if (error==EPERM) code=YASL_ERROR_WRONG_THREAD;
+    else if (error==ENOTCONN) code=YASL_ERROR_DISCONNECTED;
     yasl_public_set_error(code,error); errno=error; return false;
 }
 enum yasl_error yasl_get_error(const char **description)
 {
     static const char *const messages[]={"No error","Invalid argument","Unsupported operation",
         "Out of memory","Library not initialized","Operation is busy","Wrong thread",
-        "Input context expired","Native operation failed"};
+        "Input context expired","Native operation failed","Display disconnected"};
     if(description) *description=messages[last_error];
     return last_error;
 }
@@ -254,6 +255,7 @@ static bool convert_event(const struct yasl_private_event *p,yasl_event *e)
     case YASL_PRIVATE_EVENT_DISPLAY_QUIT:e->type=YASL_EVENT_QUIT;break;
     case YASL_PRIVATE_EVENT_DISPLAY_REOPEN:e->type=YASL_EVENT_REOPEN;break;
     case YASL_PRIVATE_EVENT_DISPLAY_LOST:e->type=YASL_EVENT_DISPLAY_LOST;break;
+    case YASL_PRIVATE_EVENT_DISPLAY_RESTORED:e->type=YASL_EVENT_DISPLAY_RESTORED;break;
     case YASL_PRIVATE_EVENT_REFRESH:
         if(!p->surface) return false;
         if(!refresh_ready(p->surface)) { p->surface->refresh_owed=true; return false; }
diff --git a/src/common/types.h b/src/common/types.h
index 91f8a47..40c502f 100644
--- a/src/common/types.h
+++ b/src/common/types.h
@@ -355,7 +355,8 @@ enum yasl_private_event_type {
     YASL_PRIVATE_EVENT_DISPLAY_LOST,
     YASL_PRIVATE_EVENT_PEN,
     YASL_PRIVATE_EVENT_TEXT_EDIT,
-    YASL_PRIVATE_EVENT_REFRESH, /**< No payload; display connection failed. */
+    YASL_PRIVATE_EVENT_REFRESH, /**< No payload; surface contents are needed. */
+    YASL_PRIVATE_EVENT_DISPLAY_RESTORED, /**< No payload; display reconnected after DISPLAY_LOST. */
 };
 
 /** Physical keyboard transition with optional layout labels.
diff --git a/src/common/vulkan.c b/src/common/vulkan.c
index 1bca415..62bc3a0 100644
--- a/src/common/vulkan.c
+++ b/src/common/vulkan.c
@@ -55,6 +55,7 @@ VkResult yasl_vulkan_create_surface(yasl_surface *s,VkInstance instance,const Vk
 {
     if(out)*out=VK_NULL_HANDLE;
     if(!yasl_public_surface(s,false)||!instance||!out||!get_proc){yasl_public_fail(EINVAL);return VK_ERROR_INITIALIZATION_FAILED;}
+    if(s->display->offline){yasl_public_fail(ENOTCONN);return VK_ERROR_SURFACE_LOST_KHR;}
     if(s->presenter!=YASL_PRIVATE_PRESENTER_NONE){yasl_public_fail(EBUSY);return VK_ERROR_NATIVE_WINDOW_IN_USE_KHR;}
     VkResult result=VK_ERROR_EXTENSION_NOT_PRESENT;
     switch(s->display->ops->type) {