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-runtime-lifecycle.mjs

@@ -2,6 +2,9 @@ function extensionName(config) {
   return String(config?.name ?? '').trim();
 }
 
+/** Stdio MCP extensions that must survive agent-run quiesce (page write + image gen). */
+export const PRESERVED_STDIO_EXTENSIONS = new Set(['sandbox-fs']);
+
 async function readJson(response) {
   const text = await response.text();
   if (!response.ok) {
@@ -52,6 +55,7 @@ export async function cancelSessionActiveRequest(apiFetch, sessionId, requestId)
 /**
  * Stop per-session stdio MCP children while preserving the Goose conversation.
  * Session reconciliation restores the required extensions before the next turn.
+ * Critical page tools (sandbox-fs) stay attached so the next turn is not tool-less.
  */
 export async function quiesceSessionStdioExtensions(apiFetch, sessionId) {
   const normalizedSessionId = String(sessionId ?? '').trim();
@@ -60,7 +64,9 @@ export async function quiesceSessionStdioExtensions(apiFetch, sessionId) {
   const payload = await readJson(
     await apiFetch(`/sessions/${encodeURIComponent(normalizedSessionId)}/extensions`),
   );
-  const names = sessionStdioExtensionNames(payload?.extensions);
+  const names = sessionStdioExtensionNames(payload?.extensions).filter(
+    (name) => !PRESERVED_STDIO_EXTENSIONS.has(name),
+  );
   const removed = [];
   for (const name of names) {
     await readJson(