From 33396a522aaf76d5da758666e63310e2a078894a Mon Sep 17 00:00:00 2001
From: themavik <themavik@users.noreply.github.com>
Date: Fri, 20 Feb 2026 23:52:40 -0500
Subject: [PATCH 1/2] fix(tools): provide detailed error messages in edit_file
 when old_text not found

Uses difflib to find the best match and shows a helpful diff,
making it easier to debug edit_file failures.

Co-authored-by: Cursor <cursoragent@cursor.com>
---
 nanobot/agent/tools/filesystem.py | 35 ++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/nanobot/agent/tools/filesystem.py b/nanobot/agent/tools/filesystem.py
index 419b088..d9ff265 100644
--- a/nanobot/agent/tools/filesystem.py
+++ b/nanobot/agent/tools/filesystem.py
@@ -150,7 +150,7 @@ class EditFileTool(Tool):
             content = file_path.read_text(encoding="utf-8")
 
             if old_text not in content:
-                return f"Error: old_text not found in file. Make sure it matches exactly."
+                return self._not_found_message(old_text, content, path)
 
             # Count occurrences
             count = content.count(old_text)
@@ -166,6 +166,39 @@ class EditFileTool(Tool):
         except Exception as e:
             return f"Error editing file: {str(e)}"
 
+    @staticmethod
+    def _not_found_message(old_text: str, content: str, path: str) -> str:
+        """Build a helpful error when old_text is not found."""
+        import difflib
+
+        lines = content.splitlines(keepends=True)
+        old_lines = old_text.splitlines(keepends=True)
+
+        best_ratio = 0.0
+        best_start = 0
+        window = len(old_lines)
+
+        for i in range(max(1, len(lines) - window + 1)):
+            chunk = lines[i : i + window]
+            ratio = difflib.SequenceMatcher(None, old_lines, chunk).ratio()
+            if ratio > best_ratio:
+                best_ratio = ratio
+                best_start = i
+
+        if best_ratio > 0.5:
+            best_chunk = lines[best_start : best_start + window]
+            diff = difflib.unified_diff(
+                old_lines, best_chunk,
+                fromfile="old_text (provided)", tofile=f"{path} (actual, line {best_start + 1})",
+                lineterm="",
+            )
+            diff_str = "\n".join(diff)
+            return (
+                f"Error: old_text not found in {path}.\n"
+                f"Best match ({best_ratio:.0%} similar) at line {best_start + 1}:\n{diff_str}"
+            )
+        return f"Error: old_text not found in {path}. No similar text found. Verify the file content."
+
 
 class ListDirTool(Tool):
     """Tool to list directory contents."""

From e0edb904bd337cf5a3aaf675f39627d022043377 Mon Sep 17 00:00:00 2001
From: Re-bin <xubinrencs@gmail.com>
Date: Sat, 21 Feb 2026 06:35:10 +0000
Subject: [PATCH 2/2] style(filesystem): move difflib import to top level

---
 nanobot/agent/tools/filesystem.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/nanobot/agent/tools/filesystem.py b/nanobot/agent/tools/filesystem.py
index d9ff265..e6c407e 100644
--- a/nanobot/agent/tools/filesystem.py
+++ b/nanobot/agent/tools/filesystem.py
@@ -1,5 +1,6 @@
 """File system tools: read, write, edit."""
 
+import difflib
 from pathlib import Path
 from typing import Any
 
@@ -169,8 +170,6 @@ class EditFileTool(Tool):
     @staticmethod
     def _not_found_message(old_text: str, content: str, path: str) -> str:
         """Build a helpful error when old_text is not found."""
-        import difflib
-
         lines = content.splitlines(keepends=True)
         old_lines = old_text.splitlines(keepends=True)