fix(llama-cpp): explain tensor count mismatch

llama.cpp reports the same tensor-count error for unsupported model layouts and damaged GGUF files. Add a focused hint so operators can update the backend or verify the model without losing the upstream diagnostic.

Assisted-by: Codex:gpt-5.6
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/cpp/llama-cpp/model_load_error_test.cpp

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: MIT
+
+#include "model_load_error.h"
+
+#include <cassert>
+#include <string>
+
+int main() {
+  const std::string issue_error =
+      "llama_model_load: error loading model: done_getting_tensors: wrong number of tensors; expected 2131, got 720; "
+      "llama_model_load_from_file_impl: failed to load model";
+  const std::string issue_result = localai::model_load_error_with_hint(issue_error);
+  assert(issue_result.compare(0, issue_error.size(), issue_error) == 0);
+  assert(issue_result.find("incompatible") != std::string::npos);
+  assert(issue_result.find("corrupt") != std::string::npos);
+
+  const std::string generic_error =
+      "wrong number of tensors; expected 42, got 17";
+  const std::string generic_result = localai::model_load_error_with_hint(generic_error);
+  assert(generic_result.compare(0, generic_error.size(), generic_error) == 0);
+  assert(generic_result.size() > generic_error.size());
+
+  const std::string unrelated_error = "failed to open GGUF file";
+  assert(localai::model_load_error_with_hint(unrelated_error) == unrelated_error);
+}