fix(engine): decode every JSON escape in message content

cactus-engine/src/utils.h

@@ -568,21 +568,10 @@ inline std::string env_or_default(const char* key, const char* fallback) {
     return std::string(fallback);
 }
 
-inline std::string json_string_field(const std::string& json, const std::string& key) {
-    std::string pattern = "\"" + key + "\":";
-    size_t pos = json.find(pattern);
-    if (pos == std::string::npos) return {};
-
-    size_t i = pos + pattern.size();
-    while (i < json.size() && std::isspace(static_cast<unsigned char>(json[i]))) i++;
-    if (i >= json.size() || json[i] != '"') return {};
-    ++i;
-
-    std::string out;
-    out.reserve(128);
+inline bool read_json_string(const std::string& json, size_t& i, std::string& out) {
     while (i < json.size()) {
         char c = json[i++];
-        if (c == '"') return out;
+        if (c == '"') return true;
         if (c == '\\' && i < json.size()) {
             char e = json[i++];
             switch (e) {
@@ -628,7 +617,21 @@ inline std::string json_string_field(const std::string& json, const std::string&
         }
         out.push_back(c);
     }
-    return {};
+    return false;
+}
+
+inline std::string json_string_field(const std::string& json, const std::string& key) {
+    std::string pattern = "\"" + key + "\":";
+    size_t pos = json.find(pattern);
+    if (pos == std::string::npos) return {};
+
+    size_t i = pos + pattern.size();
+    while (i < json.size() && std::isspace(static_cast<unsigned char>(json[i]))) i++;
+    if (i >= json.size() || json[i] != '"') return {};
+    ++i;
+
+    std::string out;
+    return read_json_string(json, i, out) ? out : std::string();
 }
 
 inline std::string json_array_field(const std::string& json, const std::string& key) {
@@ -1021,27 +1024,7 @@ inline std::vector<cactus::engine::ChatMessage> parse_messages_json(const std::s
         size_t content_pos = json.find("\"content\"", role_end);
         if (content_pos != std::string::npos && content_pos < obj_end) {
             size_t content_start = json.find('"', content_pos + 9) + 1;
-            size_t content_end = content_start;
-
-            while (content_end < json.length()) {
-                content_end = json.find('"', content_end);
-                if (content_end == std::string::npos) break;
-                if (json[content_end - 1] != '\\') break;
-                content_end++;
-            }
-
-            msg.content = json.substr(content_start, content_end - content_start);
-
-            size_t escape_pos = 0;
-            while ((escape_pos = msg.content.find("\\n", escape_pos)) != std::string::npos) {
-                msg.content.replace(escape_pos, 2, "\n");
-                escape_pos += 1;
-            }
-            escape_pos = 0;
-            while ((escape_pos = msg.content.find("\\\"", escape_pos)) != std::string::npos) {
-                msg.content.replace(escape_pos, 2, "\"");
-                escape_pos += 1;
-            }
+            read_json_string(json, content_start, msg.content);
         }
 
         auto parse_path_array = [&](const char* key, std::vector<std::string>& dest,

cactus-engine/tests/test_messages_json_escapes.cpp

@@ -0,0 +1,29 @@
+#include "test_utils.h"
+#include "../src/utils.h"
+
+using cactus::ffi::parse_messages_json;
+
+bool test_content_decodes_json_escapes() {
+    std::vector<std::string> images;
+    auto messages = parse_messages_json(
+        R"([{"role":"user","content":"func main() {\n\tprint(\"C:\\temp\\new\")\n} caf\u00e9"}])", images);
+    return messages.size() == 1
+        && messages[0].content == "func main() {\n\tprint(\"C:\\temp\\new\")\n} caf\xc3\xa9";
+}
+
+bool test_content_ending_in_backslash() {
+    std::vector<std::string> images;
+    auto messages = parse_messages_json(
+        R"([{"role":"user","content":"the path is C:\\"},{"role":"assistant","content":"ok"}])", images);
+    return messages.size() == 2
+        && messages[0].content == "the path is C:\\"
+        && messages[1].role == "assistant" && messages[1].content == "ok";
+}
+
+int main() {
+    TestUtils::TestRunner runner("Message Content Escape Tests");
+    runner.run_test("content_decodes_json_escapes", test_content_decodes_json_escapes());
+    runner.run_test("content_ending_in_backslash", test_content_ending_in_backslash());
+    runner.print_summary();
+    return runner.all_passed() ? 0 : 1;
+}