feat: Warning message when no workers are available for a task list

[YoavLev]

Problem

When starting a workflow through the web UI, users had no visibility into whether the specified task list had active workers. This could lead to workflows being started against task lists with no workers (or missing activity/decision handlers), resulting in stuck or failed workflows with no immediate feedback.

Solution

Added a debounced task list lookup that validates the entered task list name against the cluster in real-time. A warning banner is displayed when:

• The task list has no workers at all
• The task list is missing activity workers
• The task list is missing decision workers
• A loading spinner is shown in the input while the lookup is in progress, and an error caption appears if the API call fails.

Changes Made

• useDescribeTaskList hook — New hook that debounces the task list name input (300ms) and calls the describe-task-list API. Properly handles cleanup on unmount and reports a unified isLoading state that accounts for both debounce pending and fetch in-flight.
• TaskListWorkersInfo component — Renders a warning banner when the task list is missing decision handlers, activity handlers, or has no workers at all.
• workflow-action-start-form.tsx — Integrated the new hook and component into the Task List field. Added a loading spinner via endEnhancer, error state feedback, and real-time trimming of whitespace on input change. Now destructures and passes domain prop to the hook.

Examples

Loading state

Error state

Warning

[Assem-Uber]

Design comments:

• Banner is more suitable for whole form/page errors and not for a single field issue. Would recommend using styles similar to Form control caption.
• Banner (the message) should be aligned with the input
• I see that we are showing a caption if the task list request fails, can you add a screenshot for that one
• Can you add screenshot for loading state