[Bug] TextArea: isLoading spinner is misaligned — should sit inside the resizable textarea (like the status icon)

[cixzhang]

Summary

In TextArea's isLoading (busy) state, the loading Spinner is misaligned — it doesn't sit inside the textarea where you'd expect it. It should appear inside the resizable textarea (e.g. anchored to a corner of the field), consistent with how the status icon is placed.

Steps to reproduce

1. Render a <TextArea isLoading /> (or a controlled TextArea whose optimisticValue !== value, which also sets busy).
2. Observe the spinner position.

Expected

Spinner appears inside the textarea's box (anchored to a corner, like the status icon), not disrupting layout.

Actual

Spinner is misaligned (see screenshot) — it renders in normal flow, not positioned within the field.

Root cause

In TextArea.tsx the spinner is rendered with no positioning styles at all:

{isBusy && <Spinner size="sm" />}

Compare the status icon right below it, which IS correctly anchored:

statusIcon: {
  position: 'absolute',
  top: spacingVars['--spacing-2'],
  insetInlineEnd: spacingVars['--spacing-2'],
  ...
}

The spinner has no equivalent absolute-positioning style, so it falls into the flow of the relative wrapper instead of sitting inside the textarea's corner.

Fix direction

Give the busy spinner the same absolute-positioning treatment as statusIcon (anchored inside the field), reusing the existing spacing tokens. Consider: (a) the spinner and status icon can both be present — ensure they don't overlap (stack or share the same corner slot with the spinner taking precedence while busy); (b) the textarea reserves end-padding for the status icon via textareaWithStatus — the busy state should reserve the same space so text doesn't flow under the spinner.

Acceptance

• Spinner is visually anchored inside the resizable textarea (corner), aligned like the status icon.
• No overlap between spinner and status icon; end-padding reserved when busy.
• Storybook story for the isLoading state; test asserting the spinner renders with the positioned class.