fix(image-gen): force-refresh plugin providers in long-lived sessions

tools/image_generation_tool.py

@@ -927,6 +927,16 @@ def _dispatch_to_plugin_provider(prompt: str, aspect_ratio: str):
         logger.debug("image_gen plugin dispatch skipped: %s", exc)
         return None
 
+    if provider is None:
+        try:
+            # Long-lived sessions may have discovered plugins before a bundled
+            # backend was patched in or before config changed. Retry once with
+            # a forced refresh before surfacing a missing-provider error.
+            _ensure_plugins_discovered(force=True)
+            provider = get_provider(configured)
+        except Exception as exc:
+            logger.debug("image_gen plugin force-refresh skipped: %s", exc)
+
     if provider is None:
         return json.dumps({
             "success": False,