fix(providers): detect llama.cpp context size overflow in error classifier

internal/providers/error_classify.go

@@ -170,6 +170,9 @@ func isContextOverflow(lower string) bool {
 		"request_too_large",         // Generic
 		"input is too long",         // DashScope
 		"exceed_context_size",       // Ollama native /api/chat 400
+		// llama.cpp / OpenAI-compat local servers return:
+		//   "request (N tokens) exceeds the available context size (M tokens)"
+		"context size",              // llama.cpp native /v1/chat/completions 400
 		"请求输入过长",                    // Chinese generic
 	)
 }

internal/providers/error_classify_test.go

@@ -151,6 +151,14 @@ func TestClassifyTooManyTokens(t *testing.T) {
 	}
 }
 
+func TestClassifyContextOverflowLlamaCpp(t *testing.T) {
+	classifier := NewDefaultClassifier()
+	result := classifier.Classify(nil, 400, `{"error":{"code":400,"message":"request (218678 tokens) exceeds the available context size (204800 tokens), try increasing it","type":"exceed_context_size_error","n_prompt_tokens":218678,"n_ctx":204800}}`)
+	if result.Kind != "context_overflow" {
+		t.Errorf("expected context_overflow for llama.cpp message, got %s", result.Kind)
+	}
+}
+
 func TestClassifyNetworkTimeoutError(t *testing.T) {
 	classifier := NewDefaultClassifier()
 	timeoutErr := &net.DNSError{