fix: stabilize Gemma 4 brewery generation

remove misleading turn-token output guidance from the brewery prompt
extract the last balanced JSON object before validation
keep README model setup and run instructions aligned
preserve Gemma 4 sampling defaults and local model usage

pipeline/src/data_generation/llama/generate_brewery.cpp

@@ -26,8 +26,9 @@ auto ExtractFinalJsonPayload(std::string raw_response) -> std::string {
       return text.substr(first, last - first + 1);
    };
 
-   static const std::array<std::string_view, 4> separator_tokens = {
-       "<|turn|>", "<turn|>", "<channel|>", "<|channel|>"};
+   static const std::array<std::string_view, 6> separator_tokens = {
+       "<|think|>", "<think|>",   "<|turn|>",
+       "<turn|>",   "<channel|>", "<|channel|>"};
 
    std::size_t separator_pos = std::string::npos;
    std::size_t separator_length = 0;
@@ -46,18 +47,13 @@ auto ExtractFinalJsonPayload(std::string raw_response) -> std::string {
    }
 
    const std::string_view trimmed = trim(raw_response);
-   const std::size_t first_brace = trimmed.find('{');
-   if (first_brace == std::string_view::npos) {
-      return std::string(trimmed);
+   std::string json_candidate =
+       ExtractLastJsonObjectPublic(std::string(trimmed));
+   if (!json_candidate.empty()) {
+      return ExtractLastJsonObjectPublic(std::string(trimmed));
    }
 
-   const std::size_t last_brace = trimmed.find_last_of('}');
-   if (last_brace == std::string_view::npos || last_brace < first_brace) {
-      return std::string(trimmed.substr(first_brace));
-   }
-
-   return std::string(
-       trimmed.substr(first_brace, last_brace - first_brace + 1));
+   return std::string(trimmed);
 }
 
 }  // namespace
@@ -147,9 +143,11 @@ auto LlamaGenerator::GenerateBrewery(const BreweryLocation& location,
       // limits.
       prompt =
           "Your previous response was invalid. Error: " + validation_error +
-          "\nReturn ONLY valid JSON with this exact schema: "
-          "{\"name\": \"string\", \"description\": \"string\"}."
-          "\nDo not include markdown, comments, or extra keys.";
+          "\nReturn ONLY valid JSON with exactly these keys: "
+          "{\"name\": \"<brewery name>\", "
+          "\"description\": \"<single-paragraph description>\"}."
+          "\nDo not include markdown, comments, extra keys, or literal "
+          "placeholder values.";
       prompt += "\n\n";
       prompt += retry_location;
    }

pipeline/src/data_generation/llama/helpers.cpp

@@ -263,12 +263,14 @@ static void AppendTokenPiece(const llama_vocab* vocab, llama_token token,
    output.append(buffer.data(), static_cast<std::size_t>(bytes));
 }
 
-static bool ExtractFirstJsonObject(const std::string& text,
-                                   std::string& json_out) {
+static bool ExtractLastJsonObject(const std::string& text,
+                                  std::string& json_out) {
    std::size_t start = std::string::npos;
    int depth = 0;
    bool in_string = false;
    bool escaped = false;
+   bool found = false;
+   std::string candidate;
 
    for (std::size_t i = 0; i < text.size(); ++i) {
       const char ch = text[i];
@@ -303,13 +305,27 @@ static bool ExtractFirstJsonObject(const std::string& text,
          }
          --depth;
          if (depth == 0 && start != std::string::npos) {
-            json_out = text.substr(start, i - start + 1);
-            return true;
+            candidate = text.substr(start, i - start + 1);
+            found = true;
          }
       }
    }
 
-   return false;
+   if (!found) {
+      return false;
+   }
+
+   json_out = std::move(candidate);
+   return true;
+}
+
+std::string ExtractLastJsonObjectPublic(const std::string& text) {
+   std::string extracted;
+   if (ExtractLastJsonObject(text, extracted)) {
+      return extracted;
+   }
+
+   return {};
 }
 
 static std::string ValidateBreweryJson(const std::string& raw,
@@ -371,7 +387,7 @@ static std::string ValidateBreweryJson(const std::string& raw,
    std::string validation_error;
    if (ec) {
       std::string extracted;
-      if (!ExtractFirstJsonObject(raw, extracted)) {
+      if (!ExtractLastJsonObject(raw, extracted)) {
          return "JSON parse error: " + ec.message();
       }