fix(#2443): address asyncBtn review notes

- asyncBtn now returns fn().finally(...) so callers can await/chain it
- Move re-fetch calls inside try/catch in core.js and permissions.js so
  network errors from fetchAndRenderStalePerms / fetchAndRender* are
  caught instead of escaping as unhandled rejections
- clearStaleAgent returns the asyncBtn promise so the function is
  properly awaitable when a button is present
- Update asyncBtn doc comment to reflect the return-value contract

frontend/packages/dashboard/src/core.js

@@ -115,12 +115,11 @@ function renderStalePerms(root, ghosts) {
           errP.hidden = false;
           return;
         }
+        await fetchAndRenderStalePerms();
       } catch (err) {
         errP.textContent = 'failed to clear perms for ' + name + ': ' + err;
         errP.hidden = false;
-        return;
       }
-      await fetchAndRenderStalePerms();
     }));
     li.append(btn);
     ul.append(li);

frontend/packages/dashboard/src/permissions.js

@@ -337,17 +337,17 @@ async function clearStaleAgent(name, sectionRoot) {
         setSaveNote('failed to remove ' + name + ': ' + text, true);
         return;
       }
+      // Re-fetch both sections so the stale row disappears.
+      await Promise.all([fetchAndRenderCapabilities(), fetchAndRenderToolGroups()]);
     } catch (err) {
       setSaveNote('failed to remove ' + name + ': ' + err, true);
-      return;
     }
-    // Re-fetch both sections so the stale row disappears.
-    await Promise.all([fetchAndRenderCapabilities(), fetchAndRenderToolGroups()]);
   };
   // asyncBtn guards double-submit; fall through without guard when there
   // is no button (e.g. called programmatically without a DOM context).
-  if (btn) asyncBtn(btn, doDelete);
-  else await doDelete();
+  // Return the promise so callers can await clearStaleAgent() if needed.
+  if (btn) return asyncBtn(btn, doDelete);
+  await doDelete();
 }
 
 function clearSaveStatus() {