fix(session): restore sandbox-fs after agent-run quiesce

Agent runs quiesced stdio MCP extensions including sandbox-fs, but reconcile
skipped re-adding missing stdio extensions and treated absent listings as OK.
Preserve sandbox-fs across quiesce and re-add other required stdio extensions
on the next reconcile so generate_image and write_file stay available.

Co-authored-by: Cursor <cursoragent@cursor.com>

session-reconcile.mjs

@@ -86,9 +86,6 @@ export function extensionsNeedingRefresh(currentExtensions, desiredExtensions) {
     if (!name) continue;
     const exists = current.some((ext) => extensionName(ext) === name);
     if (!exists) {
-      // goosed may omit active stdio MCP extensions from the session listing
-      // even though /agent/start already loaded them; do not hot-add stdio.
-      if (String(config?.type ?? '') === 'stdio') continue;
       toAdd.push(config);
     }
   }
@@ -98,7 +95,7 @@ export function extensionsNeedingRefresh(currentExtensions, desiredExtensions) {
 
 function stdioListingOmissionAllowed(currentExt, desiredConfig) {
   if (String(desiredConfig?.type ?? '') !== 'stdio') return false;
-  if (!currentExt) return true;
+  if (!currentExt) return false;
   const currentExec = extensionExecutionConfig(currentExt);
   const desiredExec = extensionExecutionConfig(desiredConfig);
   return currentExec.type === 'stdio'