Fix progress bars not clearing on completion after React 19 upgrade

[nickwesselman]

Summary

• The Ink 6 / React 19 upgrade (Upgrade Ink to v6 and React to v19 #6831, 269f3aa6) deferred unmountInk() in ConcurrentOutput with setImmediate() to let React 19 flush batched state updates, but missed the same pattern in useAsyncAndUnmount (used by Tasks) and SingleTask
• Without the deferral, unmountInk() fires before the setState that triggers return null is flushed, so the final render still contains the LoadingBar and it is never erased from the terminal
• Wraps unmountInk() in setImmediate() in both places, matching the existing fix in ConcurrentOutput
• Fix error swallowing on sequential renderSingleTask calls: The setImmediate deferral introduced a race condition — when renderSingleTask is called sequentially, the first instance's deferred unmountInk() can fire after the second instance starts, causing the second waitUntilExit() to resolve prematurely. If the second task throws, the error is silently swallowed (the promise never settles). Fix: add onError callback to SingleTask (mirroring onComplete) so errors propagate directly rather than relying on waitUntilExit() rejection.

Repro: shopify kitchen-sink async — progress bars remain on screen after completing.

See the equivalent change in ConcurrentOutput.tsx from #6831 (269f3aa6).

Test plan

• Tasks.test.tsx — 13 tests pass
• SingleTask.test.tsx — 11 tests pass
• ui.test.ts — 16 tests pass
• Verified sequential renderSingleTask error path works (previously hung indefinitely)
• Manual: run shopify kitchen-sink async and verify progress bars clear on completion

🤖 Generated with Claude Code

[ryancbahan]

Let a note in Slack -- we should merge to fix regression, since this matches code we shipped elsewhere. but this manual management of Node event loop within a React side effect to handle mounting/unmounting feels...very cursed. I'd like us to come back to this.

[nickwesselman]

• Add shopify store bulk commands (execute, status, cancel) #7071
• Add shopify store execute command #7064
• Refactor: extract shared GraphQL execution logic #7063
• Add agent-compatible device auth with explicit CLI commands #7067
• Fix progress bars not clearing on completion after React 19 upgrade #7062 👈 (View in Graphite)
• main

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[github-actions]

Differences in type declarations

We detected differences in the type declarations generated by Typescript for this branch compared to the baseline ('main' branch). Please, review them to ensure they are backward-compatible. Here are some important things to keep in mind:

• Some seemingly private modules might be re-exported through public modules.
• If the branch is behind main you might see odd diffs, rebase main into this branch.

New type declarations

We found no new type declarations in this PR

Existing type declarations

packages/cli-kit/dist/private/node/ui/components/SingleTask.d.ts

@@ -4,8 +4,9 @@ interface SingleTaskProps<T> {
     title: TokenizedString;
     task: (updateStatus: (status: TokenizedString) => void) => Promise<T>;
     onComplete?: (result: T) => void;
+    onError?: (error: Error) => void;
     onAbort?: () => void;
     noColor?: boolean;
 }
-declare const SingleTask: <T>({ task, title, onComplete, onAbort, noColor }: SingleTaskProps<T>) => React.JSX.Element | null;
+declare const SingleTask: <T>({ task, title, onComplete, onError, onAbort, noColor }: SingleTaskProps<T>) => React.JSX.Element | null;
 export { SingleTask };
\ No newline at end of file