fix

pkg/providers/openai_compat/provider.go

@@ -302,13 +302,20 @@ func parseResponse(body []byte) (*LLMResponse, error) {
 			name = tc.Function.Name
 			if tc.Function.Arguments != "" {
 				if err := json.Unmarshal([]byte(tc.Function.Arguments), &arguments); err != nil {
-					// JSON is malformed (likely truncated due to max_tokens). Log and signal truncation.
+					// JSON is malformed (likely truncated due to max_tokens or LLM stopping early).
+					// Try to repair it by appending closing characters.
+					if repairedArgs, repairErr := repairJSON(tc.Function.Arguments); repairErr == nil {
+						arguments = repairedArgs
+						log.Printf("openai_compat: recovered tool call arguments for %q (auto-repaired)", name)
+					} else {
+						// JSON is too malformed to repair. Log and signal truncation.
 						log.Printf("openai_compat: failed to decode tool call arguments for %q: %v", name, err)
 						truncated = true
 						continue // Skip this malformed tool call entirely
 					}
 				}
 			}
+		}
 
 		// Build ToolCall with ExtraContent for Gemini 3 thought_signature persistence
 		toolCall := ToolCall{
@@ -458,3 +465,25 @@ func asFloat(v any) (float64, bool) {
 		return 0, false
 	}
 }
+
+// repairJSON attempts to fix commonly truncated JSON objects by appending closing characters.
+func repairJSON(s string) (map[string]any, error) {
+	var result map[string]any
+
+	// Fast path: try closing suffixes for flat JSON objects
+	suffixes := []string{
+		"}",
+		"\"}",
+		"\"}}",
+		"\"}]}",
+		"]}",
+	}
+
+	for _, suffix := range suffixes {
+		if err := json.Unmarshal([]byte(s+suffix), &result); err == nil {
+			return result, nil
+		}
+	}
+
+	return nil, fmt.Errorf("failed to repair json")
+}

pkg/providers/openai_compat/provider_test.go

@@ -513,3 +513,51 @@ func TestSerializeMessages_StripsSystemParts(t *testing.T) {
 		t.Fatal("system_parts should not appear in serialized output")
 	}
 }
+
+func TestProviderChat_RepairsTruncatedToolCall(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		resp := map[string]any{
+			"choices": []map[string]any{
+				{
+					"message": map[string]any{
+						"content": "",
+						"tool_calls": []map[string]any{
+							{
+								"id":   "call_1",
+								"type": "function",
+								"function": map[string]any{
+									"name":      "read_file",
+									"arguments": "{\"path\": \"/my/file.txt\"", // missing }
+								},
+							},
+						},
+					},
+					"finish_reason": "length",
+				},
+			},
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	p := NewProvider("key", server.URL, "")
+	out, err := p.Chat(t.Context(), []Message{{Role: "user", Content: "hi"}}, nil, "gpt-4o", nil)
+	if err != nil {
+		t.Fatalf("Chat() error = %v", err)
+	}
+	if len(out.ToolCalls) != 1 {
+		t.Fatalf("len(ToolCalls) = %d, want 1", len(out.ToolCalls))
+	}
+	if out.ToolCalls[0].Name != "read_file" {
+		t.Fatalf("ToolCalls[0].Name = %q, want %q", out.ToolCalls[0].Name, "read_file")
+	}
+	if out.ToolCalls[0].Arguments["path"] != "/my/file.txt" {
+		t.Fatalf("ToolCalls[0].Arguments[path] = %v, want /my/file.txt", out.ToolCalls[0].Arguments["path"])
+	}
+	// Even though it was repaired, the finish reason should still be truncated because the LLM originally returned length or we truncated it?
+	// Actually, if finish_reason was "length", parseResponse will set finishReason to "truncated" anyway.
+	if out.FinishReason != "truncated" {
+		t.Fatalf("FinishReason = %q, want %q", out.FinishReason, "truncated")
+	}
+}