Background work bar: Stop re-enables as soon as the interrupt is accepted, so it flickers and invites repeat clicks #24993

What happened

A Claude thread started a Next.js dev server in the background, and the composer showed the bar "Running: Start Next.js dev server" with a Stop button. Clicking Stop makes the button text flicker between "Stop" and "Stopping...", and the bar stays up for a few seconds before it goes away. It flickers again on every click. It looks like Stop didn't work, so I clicked it again.

Diagnosis

On web/desktop, the bar's Stop handler clears its "stopping" state as soon as the server accepts the interrupt command, not when the background task ends:

• apps/web/src/components/chat/useThreadLifecycle.tsx:392-404 (handleStopBackgroundWork) sets stoppingBackgroundWorkKey, awaits interruptThreadTurn, then clears it. The comment there says "Acceptance does not confirm termination. Allow retry while the provider finishes stopping the tasks or reports a failure."
• useThreadLifecycle.tsx:532-533 passes that state as stopDisabled / stopping, and ThreadActivityBanners.tsx:155 renders "Stopping..." vs "Stop" from it.

The accept round-trip is about 25 ms, but the provider takes about 2 s to stop. So the label shows "Stopping..." for one frame, returns to an enabled "Stop" while the task is still running, and the bar stays until the task is reported ended. Each click repeats this and sends another interrupt.

Server trace for the session (server.trace.ndjson), one burst of clicks:

01:54:56.069  ThreadCommands.interruptTurn          30 ms
01:54:56.099  ProviderTurnControlService.interrupt  2002 ms   (ClaudeAdapterV2.interruptTurn 2001 ms)
01:54:57.159  ThreadCommands.interruptTurn          25 ms
01:54:57.627  ThreadCommands.interruptTurn          25 ms
01:54:57.835  ThreadCommands.interruptTurn          21 ms
01:54:58.018  ThreadCommands.interruptTurn          26 ms
01:54:58.109-123  ProviderTurnControlService.interrupt x4, ~0.4 ms each

Five interrupt commands in about 2 s, because the button was re-enabled after each ~25 ms accept while the first ~2 s provider interrupt was still running.

Expected: the button stays "Stopping..." and disabled until the background task leaves the bar or the stop fails. Then it either disappears or re-enables with an error.

References are on main aa247c52. The two web files have no changes to this logic since 2026-10-22.

Steps to reproduce

1. In a Claude thread, ask the agent to start a long-running background command, such as npm run dev for a Next.js app.
2. After the turn ends, the composer shows "Running: Start Next.js dev server" with Stop.
3. Click Stop once. The label flashes "Stopping..." and immediately returns to "Stop" while the bar stays for a few seconds.
4. Click Stop again during that window. It flickers again and another interrupt is sent.

Version

T3 Code (Nightly) desktop 0.1.3-nightly.20261024.3630.

Environment

macOS 15.1, desktop app against its local server. Provider: Claude (claudeAgent), model claude-opus-5-5.

Impact

Minor bug. Stop does work eventually, but the UI says it didn't, which invites repeated clicks and sends extra interrupts.

Related

• fix(server): stopping a Claude turn no longer hangs without an acknowledgement #16419 fix(server): stopping a Claude turn no longer hangs without an acknowledgement (server-side stop latency, not this UI state)
• fix(web): keep background tasks visible during follow-up turns #24336 fix(web): keep background tasks visible during follow-up turns (same bar, different problem)
• fix(mobile): confirm before stopping background work from the floating capsule #24385 fix(mobile): confirm before stopping background work from the floating capsule (mobile)

Investigated and drafted by Claude Code (claude-opus-5-5) on the reporter's machine, following .github/triage/PLAYBOOK.md.