fix(converters): preserve Codex config on no-MCP install (#564)

src/targets/codex.ts

@@ -116,12 +116,29 @@ async function readFileSafe(filePath: string): Promise<string> {
 export function mergeCodexConfig(existingContent: string, mcpToml: string | null): string | null {
   // Strip current and previous managed blocks
   let stripped = existingContent
+  let removedManagedBlock = false
   for (const [start, end] of [[MANAGED_START_MARKER, MANAGED_END_MARKER], [PREV_START_MARKER, PREV_END_MARKER]]) {
-    stripped = stripped.replace(
+    const next = stripped.replace(
       new RegExp(`${escapeForRegex(start)}[\\s\\S]*?${escapeForRegex(end)}\\n?`, "g"),
       "",
     )
+    if (next !== stripped) removedManagedBlock = true
+    stripped = next
   }
+
+  // No MCP servers to write — only remove bounded managed blocks. Do not strip
+  // unmarked legacy markers here: old Codex config files may contain user
+  // settings after "# Generated by compound-plugin", and there is no safe
+  // boundary for deleting only plugin-owned TOML.
+  if (!mcpToml) {
+    if (!existingContent) return null
+    const legacyMarkerIndex = stripped.indexOf(LEGACY_MARKER)
+    if (legacyMarkerIndex !== -1) {
+      return stripped.slice(0, legacyMarkerIndex).trimEnd()
+    }
+    return removedManagedBlock ? stripped.trimEnd() : existingContent
+  }
+
   stripped = stripped.trimEnd()
 
   // Strip from legacy markers to end of content (old formats wrote everything after the marker)
@@ -133,12 +150,6 @@ export function mergeCodexConfig(existingContent: string, mcpToml: string | null
     }
   }
 
-  // No MCP servers to write — return cleaned content, or null only if there was never a file
-  if (!mcpToml) {
-    if (!existingContent) return null
-    return cleaned
-  }
-
   const managedBlock = [
     MANAGED_START_MARKER,
     mcpToml.trim(),