feat: simplify tool format to TOOL:/ARGUMENTS: pattern

Replace complex OpenAI-style JSON format with simple format:

TOOL: tool_name
ARGUMENTS: {param: value}

This matches what the tool server expects and is much easier
for smaller models to generate correctly. Also add parser for
this format with priority over other formats.

src/api/routes.py

@@ -68,13 +68,18 @@ def format_messages_with_tools(messages: list, tools: Optional[list] = None) ->
         tool_instructions = """You have access to these tools:
 
 read: Read a file (filePath)
-write: Write to a file (filePath, content)
+write: Write to a file (filePath, content)  
 bash: Run a shell command (command)
 
-When you need to use a tool, respond with ONLY this JSON format:
-{"tool_calls": [{"id": "call_1", "type": "function", "function": {"name": "TOOL_NAME", "arguments": "{\\"param\\": \\"value\\"}"}}]}
+When you need to use a tool, respond with ONLY this format:
+TOOL: tool_name
+ARGUMENTS: {"param": "value"}
 
-Do not explain - just output the JSON when using tools."""
+Example:
+TOOL: read
+ARGUMENTS: {"filePath": "hello.txt"}
+
+Do not explain - just output TOOL: and ARGUMENTS: when using tools."""
         
         # Add to system message or create one
         has_system = False
@@ -264,6 +269,28 @@ def parse_tool_calls(text: str) -> tuple:
     except Exception as e:
         pass
     
+    # Try new simple format: TOOL: name\nARGUMENTS: {...}
+    tool_pattern = r'TOOL:\s*(\w+)\s*\nARGUMENTS:\s*(\{[^}]*\})'
+    tool_match = re.search(tool_pattern, text, re.IGNORECASE)
+    if tool_match:
+        tool_name = tool_match.group(1)
+        args_str = tool_match.group(2)
+        try:
+            args_dict = json.loads(args_str)
+            tool_calls = [{
+                "id": "call_1",
+                "type": "function", 
+                "function": {
+                    "name": tool_name,
+                    "arguments": json.dumps(args_dict)
+                }
+            }]
+            # Extract content before the tool call
+            content = text[:tool_match.start()].strip()
+            return content, tool_calls
+        except json.JSONDecodeError:
+            pass
+    
     # Try alternative format: look for function call patterns
     # Pattern: function_name(arg1=value1, arg2=value2)
     func_pattern = r'(\w+)\s*\(([^)]*)\)'