Strip attachments from copilot messages when handling the CLI commands

Copilot sends files in the context in the following format:
```
<attachment>
file
<attachment>
user query
```

Fixes: #1061

Author: jhrozek

src/codegate/pipeline/cli/cli.py

@@ -94,6 +94,21 @@ def _get_cli_from_continue(last_user_message_str: str) -> Optional[re.Match[str]
 
     return codegate_regex.match(last_user_message_str)
 
+def _get_cli_from_copilot(last_user_message_str: str) -> Optional[re.Match[str]]:
+    """
+    Process Copilot-specific CLI command format.
+
+    Copilot sends messages in the format:
+    <attachment>file contents</attachment>codegate command
+
+    Args:
+        last_user_message_str (str): The message string from Copilot
+
+    Returns:
+        Optional[re.Match[str]]: A regex match object if command is found, None otherwise
+    """
+    cleaned_text = re.sub(r'<attachment>.*</attachment>', '', last_user_message_str, flags=re.DOTALL)
+    return codegate_regex.match(cleaned_text.strip())
 
 class CodegateCli(PipelineStep):
     """Pipeline step that handles codegate cli."""
@@ -136,6 +151,8 @@ async def process(
                 match = _get_cli_from_open_interpreter(last_user_message_str)
             elif context.client in [ClientType.CONTINUE]:
                 match = _get_cli_from_continue(last_user_message_str)
+            elif context.client in [ClientType.COPILOT]:
+                match = _get_cli_from_copilot(last_user_message_str)
             else:
                 # Check if "codegate" is the first word in the message
                 match = codegate_regex.match(last_user_message_str)