feat: implement Fast Apply edit_file tool

- Add EditFileTool with Fast Apply approach using full-file rewrites
- Implement LLM-powered file editing with context awareness
- Add comprehensive unit and integration tests
- Include backup functionality for safety
- Support multiple file types with proper encoding handling

Resolves #3238

Co-Authored-By: João <joao@crewai.com>

src/crewai/tools/__init__.py

@@ -1,7 +1,9 @@
 from .base_tool import BaseTool, tool, EnvVar
+from .agent_tools.edit_file_tool import EditFileTool
 
 __all__ = [
     "BaseTool",
-    "tool",
+    "tool", 
     "EnvVar",
-]
+    "EditFileTool",
+]

src/crewai/tools/agent_tools/__init__.py

@@ -1 +1,7 @@
 """Agent tools for crewAI."""
+
+from .edit_file_tool import EditFileTool
+
+__all__ = [
+    "EditFileTool"
+]

src/crewai/tools/agent_tools/edit_file_tool.py

@@ -0,0 +1,127 @@
+from crewai.tools import BaseTool
+from crewai.llm import LLM
+from typing import Type, Optional
+from pydantic import BaseModel, Field
+import os
+from pathlib import Path
+
+
+class EditFileToolInput(BaseModel):
+    """Input schema for EditFileTool."""
+    file_path: str = Field(..., description="Path to the file to edit")
+    edit_instructions: str = Field(..., description="Clear instructions for what changes to make to the file")
+    context: Optional[str] = Field(None, description="Additional context about the changes needed")
+
+
+class EditFileTool(BaseTool):
+    name: str = "edit_file"
+    description: str = (
+        "Edit files using Fast Apply model approach. Performs full-file rewrites instead of "
+        "brittle search-and-replace operations. Provide clear edit instructions and the tool "
+        "will generate an accurate, complete rewrite of the file with your changes applied."
+    )
+    args_schema: Type[BaseModel] = EditFileToolInput
+
+    def __init__(self, llm: Optional[LLM] = None, **kwargs):
+        super().__init__(**kwargs)
+        self.llm = llm or LLM(model="gpt-4o-mini", temperature=0.1)
+
+    def _run(self, file_path: str, edit_instructions: str, context: Optional[str] = None) -> str:
+        """
+        Execute file editing using Fast Apply approach.
+        
+        Args:
+            file_path: Path to the file to edit
+            edit_instructions: Instructions for what changes to make
+            context: Optional additional context
+            
+        Returns:
+            Success message with details of the edit
+        """
+        try:
+            path = Path(file_path)
+            if not path.exists():
+                return f"Error: File {file_path} does not exist"
+            
+            if not path.is_file():
+                return f"Error: {file_path} is not a file"
+            
+            try:
+                with open(path, 'r', encoding='utf-8') as f:
+                    current_content = f.read()
+            except UnicodeDecodeError:
+                return f"Error: Cannot read {file_path} - file appears to be binary or uses unsupported encoding"
+            
+            prompt = self._build_fast_apply_prompt(
+                current_content=current_content,
+                edit_instructions=edit_instructions,
+                file_path=file_path,
+                context=context
+            )
+            
+            response = self.llm.call(prompt)
+            new_content = self._extract_file_content(response)
+            
+            if new_content is None:
+                return f"Error: Failed to generate valid file content. LLM response was malformed."
+            
+            backup_path = f"{file_path}.backup"
+            with open(backup_path, 'w', encoding='utf-8') as f:
+                f.write(current_content)
+            
+            with open(path, 'w', encoding='utf-8') as f:
+                f.write(new_content)
+            
+            original_lines = len(current_content.splitlines())
+            new_lines = len(new_content.splitlines())
+            
+            return (
+                f"Successfully edited {file_path}. "
+                f"Original: {original_lines} lines, New: {new_lines} lines. "
+                f"Backup saved as {backup_path}"
+            )
+            
+        except Exception as e:
+            return f"Error editing file {file_path}: {str(e)}"
+
+    def _build_fast_apply_prompt(self, current_content: str, edit_instructions: str, 
+                                file_path: str, context: Optional[str] = None) -> str:
+        """Build the Fast Apply prompt for the LLM."""
+        file_extension = Path(file_path).suffix
+        
+        prompt = f"""You are an expert code editor implementing Fast Apply file editing. Your task is to rewrite the entire file with the requested changes applied.
+
+IMPORTANT INSTRUCTIONS:
+1. You must output the COMPLETE rewritten file content
+2. Apply the edit instructions precisely while preserving all other functionality
+3. Maintain the original file's style, formatting, and structure
+4. Do not add explanatory comments unless they were in the original
+5. Output ONLY the file content, no explanations or markdown formatting
+
+FILE TO EDIT: {file_path}
+FILE TYPE: {file_extension}
+
+CURRENT FILE CONTENT:
+```
+{current_content}
+```
+
+EDIT INSTRUCTIONS:
+{edit_instructions}"""
+
+        if context:
+            prompt += f"\n\nADDITIONAL CONTEXT:\n{context}"
+
+        prompt += "\n\nOUTPUT THE COMPLETE REWRITTEN FILE CONTENT:"
+        
+        return prompt
+
+    def _extract_file_content(self, llm_response: str) -> Optional[str]:
+        """Extract the file content from LLM response."""
+        content = llm_response.strip()
+        
+        if content.startswith('```') and content.endswith('```'):
+            lines = content.split('\n')
+            content = '\n'.join(lines[1:-1])
+        
+        return content if content else None