diff --git a/metagpt/actions/design_api.py b/metagpt/actions/design_api.py
index 86fa699bb..68a66d5a4 100644
--- a/metagpt/actions/design_api.py
+++ b/metagpt/actions/design_api.py
@@ -231,7 +231,7 @@ class WriteDesign(Action):
     async def _save_mermaid_file(self, data: str, pathname: Path):
         pathname.parent.mkdir(parents=True, exist_ok=True)
         await mermaid_to_file(self.config.mermaid.engine, data, pathname)
-        image_path = pathname.parent / f"{pathname.name}.png"
+        image_path = pathname.parent / f"{pathname.name}.svg"
         if image_path.exists():
             await GalleryReporter().async_report(image_path, "path")
 
diff --git a/metagpt/actions/write_prd.py b/metagpt/actions/write_prd.py
index 4b2015145..7a04520d6 100644
--- a/metagpt/actions/write_prd.py
+++ b/metagpt/actions/write_prd.py
@@ -278,7 +278,7 @@ class WritePRD(Action):
         pathname = output_filename or self.repo.workdir / COMPETITIVE_ANALYSIS_FILE_REPO / Path(prd_doc.filename).stem
         pathname.parent.mkdir(parents=True, exist_ok=True)
         await mermaid_to_file(self.config.mermaid.engine, quadrant_chart, pathname)
-        image_path = pathname.parent / f"{pathname.name}.png"
+        image_path = pathname.parent / f"{pathname.name}.svg"
         if image_path.exists():
             await GalleryReporter().async_report(image_path, "path")
 
diff --git a/metagpt/base/base_role.py b/metagpt/base/base_role.py
index 49dbcd617..2f6c9f963 100644
--- a/metagpt/base/base_role.py
+++ b/metagpt/base/base_role.py
@@ -8,7 +8,10 @@ class BaseRole:
     """Abstract base class for all roles."""
 
     name: str
-    is_idle: bool
+
+    @property
+    def is_idle(self) -> bool:
+        raise NotImplementedError
 
     @abstractmethod
     def think(self):
diff --git a/metagpt/provider/base_llm.py b/metagpt/provider/base_llm.py
index 813e77d95..75d8bfe00 100644
--- a/metagpt/provider/base_llm.py
+++ b/metagpt/provider/base_llm.py
@@ -300,7 +300,6 @@ class BaseLLM(ABC):
         if compress_type == CompressType.NO_COMPRESS:
             return messages
 
-        current_token_count = 0
         max_token = TOKEN_MAX.get(self.config.model, max_token)
         keep_token = int(max_token * threshold)
         compressed = []
@@ -318,7 +317,7 @@ class BaseLLM(ABC):
         # system_msgs = [msg for msg in messages if msg["role"] == system_msg_val]
         # user_assistant_msgs = [msg for msg in messages if msg["role"] != system_msg_val]
         compressed.extend(system_msgs)
-        current_token_count += self.count_tokens(system_msgs)
+        current_token_count = self.count_tokens(system_msgs)
 
         if compress_type in [CompressType.POST_CUT_BY_TOKEN, CompressType.POST_CUT_BY_MSG]:
             # Under keep_token constraint, keep as many latest messages as possible
diff --git a/metagpt/utils/mermaid.py b/metagpt/utils/mermaid.py
index 64996717e..008bb849d 100644
--- a/metagpt/utils/mermaid.py
+++ b/metagpt/utils/mermaid.py
@@ -38,7 +38,7 @@ async def mermaid_to_file(
     Returns:
         int: 0 if the conversion is successful, -1 if the conversion fails.
     """
-    suffixes = suffixes or ["png"]
+    suffixes = suffixes or ["svg"]
     # Write the Mermaid code to a temporary file
     config = config if config else Config.default()
     dir_name = os.path.dirname(output_file_without_suffix)