message: fixed Answer header for TXT format

chatmastermind/message.py

@@ -96,7 +96,7 @@ class AILine(str):
 
     def __new__(cls: Type[AILineInst], string: str) -> AILineInst:
         if not string.startswith(cls.prefix):
-            raise TagError(f"AILine '{string}' is missing prefix '{cls.prefix}'")
+            raise MessageError(f"AILine '{string}' is missing prefix '{cls.prefix}'")
         instance = super().__new__(cls, string)
         return instance
 
@@ -116,7 +116,7 @@ class ModelLine(str):
 
     def __new__(cls: Type[ModelLineInst], string: str) -> ModelLineInst:
         if not string.startswith(cls.prefix):
-            raise TagError(f"ModelLine '{string}' is missing prefix '{cls.prefix}'")
+            raise MessageError(f"ModelLine '{string}' is missing prefix '{cls.prefix}'")
         instance = super().__new__(cls, string)
         return instance
 
@@ -133,7 +133,7 @@ class Answer(str):
     A single answer with a defined header.
     """
     tokens: int = 0  # tokens used by this answer
-    txt_header: ClassVar[str] = '=== ANSWER ==='
+    txt_header: ClassVar[str] = '==== ANSWER ===='
     yaml_key: ClassVar[str] = 'answer'
 
     def __new__(cls: Type[AnswerInst], string: str) -> AnswerInst:
@@ -355,17 +355,20 @@ class Message():
             try:
                 pos = fd.tell()
                 ai = AILine(fd.readline()).ai()
-            except TagError:
+            except MessageError:
                 fd.seek(pos)
             # ModelLine (Optional)
             try:
                 pos = fd.tell()
                 model = ModelLine(fd.readline()).model()
-            except TagError:
+            except MessageError:
                 fd.seek(pos)
             # Question and Answer
             text = fd.read().strip().split('\n')
-            question_idx = text.index(Question.txt_header) + 1
+            try:
+                question_idx = text.index(Question.txt_header) + 1
+            except ValueError:
+                raise MessageError(f"Question header '{Question.txt_header}' not found in '{file_path}'")
             try:
                 answer_idx = text.index(Answer.txt_header)
                 question = Question.from_list(text[question_idx:answer_idx])