feat(mcp): Add edit_file tool - native edit replacement that preserves indentation

- New edit_file(path, old_string, new_string, replace_all) function
- Reads/writes with newline='' to preserve CRLF and 1-space indentation
- Returns error if old_string not found or multiple matches without replace_all
- Added to MUTATING_TOOLS for HITL approval routing
- Added to TOOL_NAMES and dispatch function
- Added MCP_TOOL_SPECS entry for AI tool declaration
- Updated agent configs (tier2, tier3, general) with edit_file mapping

Note: tier1, tier4, explore agents don't need this (edit: deny - read-only)

src/mcp_client.py

@@ -51,6 +51,7 @@ MUTATING_TOOLS: frozenset[str] = frozenset({
  "py_update_definition",
  "py_set_signature",
  "py_set_var_declaration",
+ "edit_file",
 })
 
 # ------------------------------------------------------------------ state
@@ -315,6 +316,37 @@ def set_file_slice(path: str, start_line: int, end_line: int, new_content: str)
  except Exception as e:
   return f"ERROR updating slice in '{path}': {e}"
 
+def edit_file(path: str, old_string: str, new_string: str, replace_all: bool = False) -> str:
+ """
+ Replace exact string match in a file. Preserves indentation and line endings.
+ Drop-in replacement for native edit tool that destroys 1-space indentation.
+ """
+ p, err = _resolve_and_check(path)
+ if err:
+  return err
+ assert p is not None
+ if not p.exists():
+  return f"ERROR: file not found: {path}"
+ if not old_string:
+  return "ERROR: old_string cannot be empty"
+ try:
+  content = p.read_text(encoding="utf-8", newline="")
+  if old_string not in content:
+   return f"ERROR: old_string not found in '{path}'"
+  count = content.count(old_string)
+  if count > 1 and not replace_all:
+   return f"ERROR: Found {count} matches for old_string in '{path}'. Use replace_all=true or provide more context to make it unique."
+  if replace_all:
+   new_content = content.replace(old_string, new_string)
+   p.write_text(new_content, encoding="utf-8", newline="")
+   return f"Successfully replaced {count} occurrences in '{path}'"
+  else:
+   new_content = content.replace(old_string, new_string, 1)
+   p.write_text(new_content, encoding="utf-8", newline="")
+   return f"Successfully replaced 1 occurrence in '{path}'"
+ except Exception as e:
+  return f"ERROR editing '{path}': {e}"
+
 def _get_symbol_node(tree: ast.AST, name: str) -> Optional[ast.AST]:
  """Helper to find an AST node by name (Class, Function, or Variable). Supports dot notation."""
  parts = name.split(".")
@@ -824,7 +856,7 @@ def get_ui_performance() -> str:
   return f"ERROR: Failed to retrieve UI performance: {str(e)}"
   # ------------------------------------------------------------------ tool dispatch
 
-TOOL_NAMES: set[str] = {"read_file", "list_directory", "search_files", "get_file_summary", "py_get_skeleton", "py_get_code_outline", "py_get_definition", "get_git_diff", "web_search", "fetch_url", "get_ui_performance", "get_file_slice", "set_file_slice", "py_update_definition", "py_get_signature", "py_set_signature", "py_get_class_summary", "py_get_var_declaration", "py_set_var_declaration", "py_find_usages", "py_get_imports", "py_check_syntax", "py_get_hierarchy", "py_get_docstring", "get_tree"}
+TOOL_NAMES: set[str] = {"read_file", "list_directory", "search_files", "get_file_summary", "py_get_skeleton", "py_get_code_outline", "py_get_definition", "get_git_diff", "web_search", "fetch_url", "get_ui_performance", "get_file_slice", "set_file_slice", "edit_file", "py_update_definition", "py_get_signature", "py_set_signature", "py_get_class_summary", "py_get_var_declaration", "py_set_var_declaration", "py_find_usages", "py_get_imports", "py_check_syntax", "py_get_hierarchy", "py_get_docstring", "get_tree"}
 
 def dispatch(tool_name: str, tool_input: dict[str, Any]) -> str:
  """
@@ -868,6 +900,13 @@ def dispatch(tool_name: str, tool_input: dict[str, Any]) -> str:
    str(tool_input.get("base_rev", "HEAD")), 
    str(tool_input.get("head_rev", ""))
   )
+ if tool_name == "edit_file":
+  return edit_file(
+   path,
+   str(tool_input.get("old_string", "")),
+   str(tool_input.get("new_string", "")),
+   bool(tool_input.get("replace_all", False))
+  )
  if tool_name == "web_search":
   return web_search(str(tool_input.get("query", "")))
  if tool_name == "fetch_url":
@@ -1048,7 +1087,33 @@ MCP_TOOL_SPECS: list[dict[str, Any]] = [
      "description": "New content to insert."
     }
    },
-   "required": ["path", "start_line", "end_line", "new_content"]
+  "required": ["path", "start_line", "end_line", "new_content"]
+  }
+ },
+ {
+  "name": "edit_file",
+  "description": "Replace exact string match in a file. Preserves indentation and line endings. Drop-in replacement for native edit tool.",
+  "parameters": {
+   "type": "object",
+   "properties": {
+    "path": {
+     "type": "string",
+     "description": "Path to the file."
+    },
+    "old_string": {
+     "type": "string",
+     "description": "The text to replace."
+    },
+    "new_string": {
+     "type": "string",
+     "description": "The replacement text."
+    },
+    "replace_all": {
+     "type": "boolean",
+     "description": "Replace all occurrences. Default false."
+    }
+   },
+   "required": ["path", "old_string", "new_string"]
   }
  },
  {