fix session display replay consistency

backend/api/server.py

@@ -3169,8 +3169,42 @@ def _stored_display_messages(
     stored: StoredAgentSession,
 ) -> tuple[dict[str, Any], ...]:
     if stored.display_messages:
-        return tuple(dict(message) for message in stored.display_messages)
-    return tuple(dict(message) for message in stored.messages)
+        messages = tuple(dict(message) for message in stored.display_messages)
+    else:
+        messages = tuple(dict(message) for message in stored.messages)
+    return tuple(message for message in messages if _is_visible_display_message(message))
+
+
+_INTERNAL_DISPLAY_KINDS = {
+    'compact_boundary',
+    'compact_summary',
+    'continuation_request',
+    'file_history_replay',
+    'plugin_tool_runtime',
+    'runtime_context',
+    'snipped_message',
+    'system_context',
+}
+
+
+def _is_visible_display_message(message: dict[str, Any]) -> bool:
+    if message.get('role') == 'system':
+        return False
+    metadata = message.get('metadata')
+    if isinstance(metadata, dict):
+        kind = metadata.get('kind')
+        if isinstance(kind, str) and kind in _INTERNAL_DISPLAY_KINDS:
+            return False
+    content = message.get('content')
+    if isinstance(content, str):
+        stripped = content.strip()
+        if stripped.startswith('<system-reminder>'):
+            return False
+        if message.get('role') == 'user' and stripped.startswith(
+            'This session is being continued from a previous conversation'
+        ):
+            return False
+    return True
 
 
 def _stored_session_has_incomplete_tail(stored: StoredAgentSession) -> bool:
@@ -3572,10 +3606,7 @@ def _save_in_progress_session(
             stored = load_agent_session(safe_id, directory=directory)
         except (FileNotFoundError, OSError, json.JSONDecodeError):
             return None
-        messages = list(stored.messages)
         display_messages = list(_stored_display_messages(stored))
-        if messages and _is_pending_user_message(dict(messages[-1])):
-            messages.pop()
         if display_messages and _is_pending_user_message(dict(display_messages[-1])):
             display_messages.pop()
         pending_message = {
@@ -3585,9 +3616,6 @@ def _save_in_progress_session(
             'metadata': pending_metadata,
             'message_id': f'user_pending_{int(time.time() * 1000)}',
         }
-        messages.append(
-            dict(pending_message)
-        )
         display_messages.append(dict(pending_message))
         budget_state = (
             dict(stored.budget_state)
@@ -3599,7 +3627,6 @@ def _save_in_progress_session(
             save_agent_session(
                 replace(
                     stored,
-                    messages=tuple(messages),
                     display_messages=tuple(display_messages),
                     budget_state=budget_state,
                 ),