1 files changed, 36 insertions, 10 deletions

diff --git a/app/backends/common.py b/app/backends/common.py
index 7974b58..20de432 100644
--- a/app/backends/common.py
+++ b/app/backends/common.py
@@ -9,6 +9,7 @@ TUI) so it can be reused without pulling curses into a non-interactive
 run.
 """
 
+import ast
 import os
 import re
 import shutil
@@ -306,25 +307,50 @@ def update_config_value(key: str, value,
     """Set ``KEY`` to VALUE in app/converter/config.py and in memory.
 
     Only the value of the named assignment changes: indentation and any
-    trailing comment are preserved. Strings render double-quoted; other
-    literals (ints, booleans) render bare. After a successful write (or
-    when the file already holds VALUE) the new value is mirrored onto the
-    imported ``converter.config`` module, so a wizard's change takes
-    effect immediately instead of only after the next process start.
-    Returns True when the file now holds VALUE, False when it could not
-    be read or written (or KEY has no line in it).
+    trailing comment are preserved. Strings render as proper Python
+    literals via ``repr`` (quoting with bare double quotes would instead
+    produce invalid syntax — or silently change the value — whenever the
+    string itself contains a quote or a backslash, corrupting
+    config.py); other literals (ints, booleans) render bare. After a
+    successful write (or when the file already holds VALUE) the new
+    value is mirrored onto the imported ``converter.config`` module, so
+    a wizard's change takes effect immediately instead of only after
+    the next process start. Returns True when the file now holds VALUE,
+    False when it could not be read or written (or KEY has no line in
+    it, or the edit would not parse).
     """
     path = Path(config_path) if config_path is not None else CONFIG_PATH
-    rendered = f'"{value}"' if isinstance(value, str) else str(value)
+    rendered = repr(value) if isinstance(value, str) else str(value)
     try:
         text = path.read_text(encoding="utf-8")
         match = re.search(
-            rf'(?m)^(\s*{re.escape(key)}\s*=\s*)("[^"]*"|\S+)(\s*(?:#.*)?)$',
+            rf'(?m)^(\s*{re.escape(key)}\s*=\s*)'
+            # Any valid Python string literal, single- or double-quoted
+            # (both spellings occur once repr() has written a value),
+            # else a bare literal token.
+            r'("[^"\\]*(?:\\.[^"\\]*)*"'
+            r"|'[^'\\]*(?:\\.[^'\\]*)*'"
+            r'|\S+)'
+            r'(\s*(?:#.*)?)$',
             text)
         if match is None:
             return False
-        if match.group(2) != rendered:
+        try:
+            # Semantic equality first: a file still holding the value in
+            # the old quoting style must not be rewritten (a no-op save
+            # stays a no-op), and the matched token may be any literal.
+            same = (match.group(2) == rendered
+                    or ast.literal_eval(match.group(2)) == value)
+        except (ValueError, SyntaxError):
+            same = match.group(2) == rendered
+        if not same:
             text = text[:match.start(2)] + rendered + text[match.end(2):]
+            try:
+                # Never write a file that fails to import: a broken
+                # config.py breaks every later process start.
+                compile(text, str(path), "exec")
+            except (SyntaxError, ValueError):
+                return False
             path.write_text(text, encoding="utf-8")
     except OSError:
         return False