fix: preserve original indentation character in /improve suggestions

pr_agent/tools/pr_code_suggestions.py

@@ -609,10 +609,26 @@ def dedent_code(self, relevant_file, relevant_lines_start, new_code_snippet):
                 original_initial_spaces = len(original_initial_line) - len(original_initial_line.lstrip()) # lstrip works both for spaces and tabs
                 suggested_initial_spaces = len(suggested_initial_line) - len(suggested_initial_line.lstrip())
                 delta_spaces = original_initial_spaces - suggested_initial_spaces
+                # Detect indentation character from original line
+                indent_char = '\t' if original_initial_line.startswith('\t') else ' '
                 if delta_spaces > 0:
-                    # Detect indentation character from original line
-                    indent_char = '\t' if original_initial_line.startswith('\t') else ' '
                     new_code_snippet = textwrap.indent(new_code_snippet, delta_spaces * indent_char).rstrip('\n')
+                elif delta_spaces < 0:
+                    new_code_snippet = textwrap.dedent(new_code_snippet).rstrip('\n')
+                # Normalize all lines in the suggestion to use the original's
+                # indentation character. This fixes the bug where /improve
+                # replaces tabs with spaces in Go, Makefile, and other
+                # tab-indented codebases (#1858).
+                if indent_char == '\t':
+                    new_lines = []
+                    for line in new_code_snippet.split('\n'):
+                        stripped = line.lstrip(' ')
+                        leading_spaces = len(line) - len(stripped)
+                        if leading_spaces > 0:
+                            new_lines.append('\t' * (leading_spaces // 4) + stripped)
+                        else:
+                            new_lines.append(line)
+                    new_code_snippet = '\n'.join(new_lines)
         except Exception as e:
             get_logger().error(f"Error when dedenting code snippet for file {relevant_file}, error: {e}")