fix(billing): resolve terminal promise even if success side effects throw

A thrown error in the success-path side-effects block (dialog close,
settings show, or toast add) silently skips resolveTerminal, leaving
any caller awaiting startOperation() hanging forever. poll()'s
catch-all swallowed the exception, masking the hang.

Adds a try/finally so resolveTerminal runs unconditionally after the
success side-effects block. Adds a regression test that throws from
the second mockToastAdd call and asserts the terminal promise still
resolves to succeeded.

Found in the review of #14421.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: christian-byrne

src/platform/workspace/stores/billingOperationStore.test.ts

@@ -660,6 +660,25 @@ describe('billingOperationStore', () => {
 
       expect(mockToastRemove).toHaveBeenCalledWith(receivedToast)
     })
+
+    it('resolves the terminal promise even if a success side effect throws', async () => {
+      vi.mocked(workspaceApi.getBillingOpStatus).mockResolvedValue({
+        id: 'op-1',
+        status: 'succeeded',
+        started_at: new Date().toISOString()
+      })
+      mockToastAdd.mockImplementationOnce(() => {})
+      mockToastAdd.mockImplementationOnce(() => {
+        throw new Error('toast rendering failed')
+      })
+
+      const store = useBillingOperationStore()
+      const terminal = store.startOperation('op-1', 'topup')
+
+      await vi.advanceTimersByTimeAsync(0)
+
+      await expect(terminal).resolves.toMatchObject({ status: 'succeeded' })
+    })
   })
 
   describe('polling failure', () => {

src/platform/workspace/stores/billingOperationStore.ts

@@ -419,26 +419,28 @@ export const useBillingOperationStore = defineStore('billingOperation', () => {
       return
     }
 
-    // A subscription checkout shows its own success step in the pricing dialog,
-    // so leave it open. Top-ups have no such step: close and surface settings.
-    if (operation.type === 'topup') {
-      useDialogStore().closeDialog({ key: 'top-up-credits' })
-      useSettingsDialog().show('workspace')
-    }
+    try {
+      // A subscription checkout shows its own success step in the pricing dialog,
+      // so leave it open. Top-ups have no such step: close and surface settings.
+      if (operation.type === 'topup') {
+        useDialogStore().closeDialog({ key: 'top-up-credits' })
+        useSettingsDialog().show('workspace')
+      }
 
-    const toastStore = useToastStore()
-    const messageKey =
-      operation.type === 'subscription'
-        ? 'billingOperation.subscriptionSuccess'
-        : 'billingOperation.topupSuccess'
+      const toastStore = useToastStore()
+      const messageKey =
+        operation.type === 'subscription'
+          ? 'billingOperation.subscriptionSuccess'
+          : 'billingOperation.topupSuccess'
 
-    toastStore.add({
-      severity: 'success',
-      summary: t(messageKey),
-      life: 5000
-    })
-
-    resolveTerminal(opId)
+      toastStore.add({
+        severity: 'success',
+        summary: t(messageKey),
+        life: 5000
+      })
+    } finally {
+      resolveTerminal(opId)
+    }
   }
 
   function handleFailure(opId: string, errorMessage: string | null) {