Unify prompt box affordance colors

[brsbl]

Human comments

What was wrong

The prompt-box footer applied semantic warning and hover colors to secondary affordances. Full Access correctly made the permission label amber, but it also made the dropdown caret amber; hovering Create thread in worktree promoted its icon to foreground. Both controls therefore stood out from the prompt box's other neutral affordances.

What changed

• Moves the permission caret to the prompt box’s text-subtle-foreground/75 chrome tier while the selected permission label retains its warning tone.
• Moves the Create thread in worktree icon to the same low-emphasis chrome tier, with the established muted hover treatment.
• Uses normal weight for the model selector so its long label and provider mark do not dominate the composer.
• Aligns the top-right collapse caret exactly with the permission caret while preserving its hit target.
• Expands the existing Control emphasis story to show Full Access and the worktree-create action together.
• Adds focused regression assertions for the color, weight, and caret-alignment contracts.
• No wire, persistence, SDK, CLI, or daemon protocol behavior changed.

How you verified

• Chrome for Testing 149.0.7827.55 rendered matched DPR 2 crops of the same Control emphasis fixture at 1440×900. Per product review, the Before image combines the target controls’ parent behavior (68a9aa715db41ede83ae66ccf72cf385aabab28c) with main’s plus/model/composer-caret styling (ec8f4ef04105c2cb5a59f7a9a9328bf2b16b39ce); After is the exact child head cb254b273da66575afcc307fefd466602650f02d.
• Before: the permission label and caret both resolved to the amber warning color; the worktree-create icon sat at the stronger muted tier.
• After: the permission label remains amber, while the permission caret, worktree-create icon, model caret, composer caret, and plus icon all resolve to the exact same text-subtle-foreground/75 color in light and dark themes.
• The same neutral equality was checked in dark theme. On the final light-theme capture, the model selector resolves to weight 400; the collapse and permission carets both render at 16px with center x=894 and the same color. Local CI-equivalent checks were not run per repository policy; GitHub CI owns test and typecheck execution.

Before — main styling for the other prompt-box controls

The plus, model caret, and composer caret use their main styling; the permission caret remains amber and the worktree-create icon remains darker.

After — child head cb254b273da66575afcc307fefd466602650f02d

The warning remains on the Full Access label; the model returns to normal weight, and the two right-edge carets align exactly.

BB-Thread-ID: thr_fdabesxhdr

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