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() {

frontend/packages/shared/src/forms.js

@@ -20,14 +20,16 @@
 // Error handling: `asyncBtn` restores the button on any thrown error /
 // rejected promise but does NOT surface the error — callers must catch
 // and display it themselves (via `themedToast`, `alert`, a status span,
-// etc.) before the re-throw, or handle it inside `fn` without
-// re-throwing.
+// etc.) inside `fn` without re-throwing. `fn` must not let errors escape
+// unhandled: `asyncBtn` returns the `fn().finally(...)` promise so
+// callers can optionally chain `.catch` or `await`, but does not add its
+// own catch — an unhandled rejection from `fn` will propagate normally.
 export function asyncBtn(btn, fn) {
   if (btn.disabled) return; // double-click guard
   const orig = btn.innerHTML;
   btn.disabled = true;
   btn.innerHTML = '<span class="spinner">◐</span>';
-  fn().finally(() => {
+  return fn().finally(() => {
     btn.disabled = false;
     btn.innerHTML = orig;
   });